# I'm designing a bike to be dubbed The Green Gobblin. feedback?



## xXNightRiderXx (Jul 27, 2017)

I want to know if anyone can tell me how this suspension design would actuate, if the brake posts are aligned properly, and what changes I would need to make to it to make it work. Don't worry about the lack of bolts or cable routing, I'm working on that now that I've finished the general shape of the frame.


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## pvd (Jan 4, 2006)

It looks like you are thinking of fashion more than function. Try to imagine all of the jobs that each member has to do and help it do it's job.


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## Darth Lefty (Sep 29, 2014)

xXNightRiderXx said:


> I want to know if anyone can tell me *how this suspension design would actuate*, if the *brake posts are aligned properly*, and what changes I would need to make to it to make it work.


You should design those things _first _before you draw tubes in between them.


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## Drew Diller (Jan 4, 2010)

Well, regarding your specific questions, there's no way of knowing. You've supplied a 3D view in FreeCAD with no numbers. I don't know where the pivots are in space, I don't know where the disc caliper tabs are. Even if it were an orthographic side view, numbers would be needed.

There's an app called Linkage that could inform you about suspension behavior, but you need to give it rather specific measurements.

...Regardless of numbers, can you explain your motivations behind the head tube? Looks like the short distance between the bearings is going to chew up headsets really quick while giving wobbly front end feedback, while also being difficult to create.

Is your shock location and orientation for packaging purposes? Like you want to fit a frame bag or something like that?

First thing I'd do in your shoes is learn the specifics about disc caliper placement. This is one of those things where PVD is useful -- he's left a trail behind in the form of many drawings for this on his website.

The lack of cable routing and bolts is indeed an after thought. No one is worried about that, we're just not equipped to give any good answers with the limited info provided.

That said... just looking at the linkage pivot locations... the top bushing of the swingarm, where it pulls on the black dog link. As the rear axle moves up, that top bushing is only going to move forward, and by a small amount. It looks like the black link is meant to be pulled on, which would in turn drive the rocker arm and shock. The problem with this in your design is that the black link is not being effectively pulled on. This design as is would be sofa squishy and bottom out readily.


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## 127.0.0.1 (Nov 19, 2013)

umm, nope.

try this for a while

Free 3D CAD with Motion Simulation : AR-CAD freeCAD


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## scottzg (Sep 27, 2006)

Some thoughts

-uh, whoa.
-what material is this going to be?
-will you be able to source that head, down, and seat tube?
-why is the head tube so short? That's gonna introduce problems.
-why do you need the giant dt 'belly?' your design doesn't require it and it has downsides
-why did you go with a poorly triangulated rear triangle?
-why don't you know what the linkage will do?
-why didn't you define your linkage behaviors first, then create a linkage that hit those targets?
-why do the stays extend way past the rear dropouts?
-isn't that a lot of seat tube considering the reach and stack?
-you need to post geo numbers, your dimensions, and intended use to get good feedback on that stuff
-have you built anything before?

Looks like a cad project.


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## chazpat (Sep 23, 2006)

Is OP heading to China to show his design around and find someone to manufacturer it, ala Pink Bike?

OP, I'll go ahead and apologize for giving you a hard time, but are you really a bike mechanic? I know very little about suspension design and I've never built a frame but I've been around them enough to know… looks like you're just having fun drawing in some free CAD software.

You should be able to pivot the rear triangle around the pivot point in your software and see how that *might* translate through the link and rocker by positioning them to where the new linkage points end up. Like I said, I don't know much about this but I'm not too sure it's going to work at all.


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## xXNightRiderXx (Jul 27, 2017)

After a few edits and refinements, I'm now posting the updated version with numbers.

head angle: 68
head tube length: 4"
seat tube angle: 74
seat tube I.D: 30.8
Reach: 429.5mm
seat tube length: 18"
chainstay length: 432mm
wheelbase: 1252mm 
stack: 664.5mm
wheel diameter: 27.5
shock E2E length: 190mm
BB drop: 28.3mm









-what material is this going to be?

Three materials will be tested for the final product: Hemp composite, Al alloy, and carbon.

-will you be able to source that head, down, and seat tube?

Using composites, the sourcing for that is a non-issue. The problem comes with sourcing the downtube, as that is a complex "ace of spades" profile with the top area being its own hollow area for cable guides.

-why is the head tube so short? That's gonna introduce problems.

The original was not a final rendition, and that has been changed.
-why do you need the giant dt 'belly?' your design doesn't require it and it has downsides

I understand the risk of casing and tube deformation with the "belly." I personally like the flow it provides, and I have accepted that risk of damage, and have profiled the tube according to the stresses present.

-why did you go with a poorly triangulated rear triangle?

This is the first time I had actually managed to draw out a rear triangle, and it was a lot of work. I have since refined the rear triangle.
-why don't you know what the linkage will do?

Because I cannot afford Linkage.

-why didn't you define your linkage behaviors first, then create a linkage that hit those targets?

Same as above.

-why do the stays extend way past the rear dropouts?

It's a looks thing. I thought it would look interesting. Glad to see it worked.
-isn't that a lot of seat tube considering the reach and stack?

Yes, I admit it is. It's been since balanced out.

-you need to post geo numbers, your dimensions, and intended use to get good feedback on that stuff

Numbers are posted above, and the purpose of this is for Enduro racing.

-have you built anything before?

Solid nope on that one. I have however done enough research to understand enough about frame design to learn more as I go about it, and refine my design style based on what I have learned up to that point. Honestly, if I had done anything like this before, I wouldn't be askin for feedback on the specifics as much as the general look of the frame. Being my first actual MTB design, let alone my first 3D bike design period, I was more looking to make sure I was doing things right... I guess I wasn't, haha.


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## 127.0.0.1 (Nov 19, 2013)

edit: removed.....


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## slapheadmofo (Jun 9, 2006)

I would recommend doing a hardtail (or 10 or 20) first.


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## Fleas (Jan 19, 2006)

When your rear swingarm extends, there is nothing to stop the short link from rotating past center. If you are relying on the compression of that link to stop the swingarm from rotating downward, it will likely break or snap off the rocker link, esp. if loaded in a strange way in the case of a crash. Imagine the forces on the rear swingarm of going OTB and catching the top of the rear wheel on a rock or tree.

Am I seeing that right?

-F


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## xXNightRiderXx (Jul 27, 2017)

I'm starting on this, because if I can design this, I can design just about any mtb.

I have figured out how to use a sketch in FreeCAD to perform basic kinematics, and so I'm now optimizing for 160mm travel at the wheel.

I've had to shorten the nose on the driver link and move the lower pivot on the dog link forward, and move the axle back about an inch and a half, and that's getting me the travel I'm looking for.


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## 127.0.0.1 (Nov 19, 2013)

tip: don't go nuts finalizing the finish....build prototypes with your specific pivot locations first, but expect it to ride like ass for a lot of revisions. only put a lot of effort into a design you know will work. saves a bunch of time and stress knowing your first run is prototype and you can use unpolished hardware and whatnot


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## scottzg (Sep 27, 2006)

xXNightRiderXx said:


> After a few edits and refinements, I'm now posting the updated version with numbers.
> 
> head angle: 68
> head tube length: 4"
> ...


If you were able to model it, hard to argue with that... but i don't think this geo is possible.



xXNightRiderXx said:


> -why don't you know what the linkage will do?
> 
> Because I cannot afford Linkage.
> 
> ...


If you can't design the linkage, then you can't build a FS bike. Full stop. That said, it's just geometry. It can be calculated by hand if necessary. (fwiw that lower pivot location is gonna make that bike suuuuuuuck to pedal, and that tiny link is a heap of problems)

Project sounds very ambitious, way beyond my (modest) abilities. I'd be tempted to do a couple less ambitious projects to get my materials, methods, and design objectives locked in rather than tackling so many unknowns at once.


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## xXNightRiderXx (Jul 27, 2017)

Alright, the sketch I drew for this worked beautifully, and allowed me to move the pivots around for clearance at full compression. Unfortunately, I can't upload the file for you guys, but I hope that these screenshots provide enough information:









I've actually been fuddlin with this particular linkage design in my head for a couple years now, ever since I first saw the linkage in the Evil Calling, which the geometry of my design is inspired by.

I could probably slap the pivot right onto the BB, but that wouldn't do very much I don't think. Unfortunately, anything else would compromise a large part of the frame's geo. I am planning on using a shock with remote lockout for the climbs, so I think that will become a non-issue. I'm kinda tryin to make this frame go faster on the downhills, while not being a total PITA goin back up. I'm slow on the climbs anyways.

Final CS length is 480.2mm.

OH, almost forgot: Once this frame has been built, it will be equipped with the Trust Performance Shout. Gonna see what this setup can do.


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## scottzg (Sep 27, 2006)

spend some time reading this guy's blog. Pretty sure he has an overview of the different design elements for rear suspension there. Takes a bunch of reviews to get a sense for how it all works together.

Linkage Design

Use your browser to translate to english.


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## VegasSingleSpeed (May 5, 2005)

Low, single-pivot design, long chain-stays. You're gonna party like it's 1999.


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## 127.0.0.1 (Nov 19, 2013)

you'll be renaming the bike 'The Crotch Goblin' after the first rides


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## xXNightRiderXx (Jul 27, 2017)

Thanks scott, but BikeRadar has a better article explaining what each thing is and how it affects suspension performance. Having to work through the translation takes away from the focus i need to keep on working through the content itself. The concept of suspension is easy to understand, the nuances are the difficult part: designing for one particular aspect over another. Personally, my thoughts on it are "if it works, it works, and there's little need to change it until it stops working."

I seem to have a pretty progressive leverage ratio thanks to the use of those dog links, so I don't really NEED to look at other suspension designs on this bike. If I need pedaling performance, I could just lock the shock. Otherwise, with maybe a few reinforcements and finishing touches, I think this frame is ready to be tested.

So, with the design stuff out of the way, how does this rendition look?


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## xXNightRiderXx (Jul 27, 2017)

> you'll be renaming the bike 'The Crotch Goblin' after the first rides


HAhaha, probably! Although, it's been a while (knocking on live wood) since I've gone OTB... I slide out far more often! I also have very little issue with jumps normally, but we'll see once I have a prototype being tested.


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## Drew Diller (Jan 4, 2010)

Hold the phone... you can't afford Linkage personal license, but you can afford a Trust fork?

Perhaps you could afford SolveSpace (free) and do your own trajectory plotting. Yeah you'll have to model it twice, and that involves a new set of hotkeys, but, the wire parameter solving works similarly to a FreeCAD sketch, it's just more "alive" in SolveSpace.

Tacking on to what scottzg said about your main pivot, look at how almost every monopivot swingarm is designed on a bike (or a motorcycle). Where you have it now, the chain when pedaled hard will pull on the rear axle such that it compresses the suspension a bit. In other words, you'll be putting a portion of pedaling energy into heating up the oil in your shock damper rather than going forward. The term "center of curvature" is useful here for searches. There is a caveat that some (_some_) monopivots are designed with a wrongly designed CoC because the rear end travel is relatively short and the rider demands a specific feature such as singlespeeding without a tensioner that demands no chain growth. That's not going to fly in your case since you're building something long travel.

Can you host the FCstd file on a 3rd party site and link to it, perhaps? Normally I would not ask people to share their actual files, but it seemed like you were willing to do so while experiencing a technical barrier in the form of this vBulletin forum software on this website only allowing certain formats.


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## Drew Diller (Jan 4, 2010)

Another comment on CoC, look at where the main pivot is on the Evil you refer to. Imagine where the chain connects to the chainring on the pulling side of the chainring. See how close those contact points are? Their design will pedal well because the chain tension is nearly in line with the main pivot.

https://www.kineticbikebearings.com...f78eab33525d08d6e5fb8d27136e95/u/n/undead.jpg


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## xXNightRiderXx (Jul 27, 2017)

ALRIGHTY, I can now share my file with you guys: https://www.filehosting.org/file/details/846051/The Green Gobblin.FCStd

I thought BB drop was there not only to provide stability, but also to move the chainline more in line with the Axle-Pivot line? I could be mistaken. Drawing a line from the OD of a 28T chainring to the axle, it's a fairly straight line. However, the IC intersection is AT the axle.

I don't really see much of a way to use this type of suspension without having a low pivot behind the BB.

Oh yeah, about the Trust fork: I plan on having won a few races by the time I'm ready to have this frame built. I should have enough to cover the 8k pricing of the complete bike.


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## scottzg (Sep 27, 2006)

xXNightRiderXx said:


> Thanks scott, but BikeRadar has a better article explaining what each thing is and how it affects suspension performance. Having to work through the translation takes away from the focus i need to keep on working through the content itself. The concept of suspension is easy to understand, the nuances are the difficult part: designing for one particular aspect over another. Personally, my thoughts on it are "if it works, it works, and there's little need to change it until it stops working."
> 
> I seem to have a pretty progressive leverage ratio thanks to the use of those dog links, so I don't really NEED to look at other suspension designs on this bike. If I need pedaling performance, I could just lock the shock. Otherwise, with maybe a few reinforcements and finishing touches, I think this frame is ready to be tested.
> 
> So, with the design stuff out of the way, how does this rendition look?


Nah dude.

If you're gonna jump to the hardest possible project, you have to understand EVERY POSSIBLE CONSIDERATION, or you're wasting your time. If something doesn't behave desirably, how will you know if it's because of geo, or suspension, or shock tune, or rider preference, or materials, or engineering decisions? Or some combination thereof? You can't. Worse if by jumping in to the deep end you make something that doesn't hold up- at best you gain limited insight, at worst you randomly regain consciousness with a damaged body while on a test ride. It happens.

Bike industry specialty knowledge is weirdly accessible because of the quick product cycle and custom builders need to explain the value in a hand-tailored product. Ignoring professional insight in favor of magazine-marketing entertainment because you're impatient is... really dumb. IMO.

Your profile says you ride a beginner hardtail mtb (or at least you did recently). You have fairly significant design problems with your first couple renderings. You might be riding that dunning-kruger high.








I don't mean to discourage you at all, and look forward to seeing what you build. I just wonder if a candid self-assessment might be helpful.


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## Drew Diller (Jan 4, 2010)

xXNightRiderXx said:


> I thought BB drop was there not only to provide stability


I suppose.



xXNightRiderXx said:


> but also to move the chainline more in line with the Axle-Pivot line?


Nope!



xXNightRiderXx said:


> I don't really see much of a way to use this type of suspension without having a low pivot behind the BB.


I linked an image to example pic from Evil. It's a "pull" type dog link on a monopivot, the monopivot is high up in line with the chain.



xXNightRiderXx said:


> Oh yeah, about the Trust fork: I plan on having won a few races by the time I'm ready to have this frame built. I should have enough to cover the 8k pricing of the complete bike.


Your confidence is ... well it's something, I'll give you that.

I was able to download your FCSTD file. You appear to have a working understanding of how the Body relationships work in FreeCAD -- good start. I'm not going to be able to be quick about it because I have a lot of stuff going on right now, but I'll get back to you about where some of your measurements are off from a practical perspective.

Some starting points on working in FreeCAD - _whoa_ don't color your oejects black when designing. Can't see anything.

Mirror object function is your buddy. If you don't need to model it twice -- don't.


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## Sparticus (Dec 28, 1999)

I'm hesitant to post in this thread because I have no dog in this fight and something tells me it may be best to keep my distance. At the same time I'm attracted like a moth to a flame because I'm curious how this story will end. Well, here goes.

scottzg, I pulled your post out of context (because I don't want to stick my nose in the middle of the fray up there) just to ask a question about the D-K graph you included. Here's that graph:



scottzg said:


> Your profile says you ride a beginner hardtail mtb (or at least you did recently). You have fairly significant design problems with your first couple renderings. You might be riding that dunning-krueger high.
> View attachment 1309971


Does the graph really say "No nothing" at its origin? Can this be right? I could see it saying, "Know nothing" or "No knowledge" there. But "No nothing"? Seriously? Somehow I expect anyone possessing adequate intelligence to create such a graph to also have at least a rudimentary grasp of the lexicon. Otherwise it would seem they may be ironic victims of the very malady they're attempting to describe. In no way to I mean to imply that I think you created the graph, scottzg.

Meanwhile xXNightRiderXx, best of luck with your frame project.
=sParty


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## Drew Diller (Jan 4, 2010)

@Sparticus cue Sarah Palin (remember her???) and her whole "language is fluid" nonsense. Anyway yeah I'm betting he didn't make that image. I seem to recall the DK graph being more violent. A quick search suggests that many people have made their own interpretations of the graph.

I think the best service we could do for OP is cause him to realize that he's at the start of the curve without insulting him. Taking the DK roller coaster ride is vicious enough on its own.


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## scottzg (Sep 27, 2006)

Sparticus said:


> I'm hesitant to post in this thread because I have no dog in this fight and something tells me it may be best to keep my distance.
> 
> scottzg, I pulled your post out of context (because I don't want to stick my nose in the middle of the fray up there) just to ask a question about the D-K graph you included. Here's that graph:
> 
> Does the graph really say "No nothing" at its origin? Can this be right? I could see it saying, "Know nothing" or "No knowledge" there. But "No nothing"? Seriously? Somehow I expect anyone possessing adequate intelligence to create such a graph to also have at least a rudimentary grasp of the lexicon. Otherwise it would seem they may be ironic victims of the very malady they're attempting to describe. In no way to I mean to imply that I think you created the graph, scottzg.


hahahahaha

Nah, i did a google image search, and picked one that didn't look too shitty or condescending. Cuz that isn't my intention. Maybe that typo makes it better! Probably not.

I hope it's not necessary to have a dog, and that there isn't a fight? OP is approaching frame building with a hell of a lot more competence than i did.


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## xXNightRiderXx (Jul 27, 2017)

Thanks scott and sparticus, that means a lot.

It may be that I'm overly confident in this arrangement, so I'm going to play around with it, including changing around the shock length, experimenting with different rear triangles, etc. The end goal will be to always have the shock mounted on top of the driver link. Water bottles man! I'll just be using simple sketches to examine the action of each design.

I'm designing this frame primarily around composite materials, so that's why the headtube has so much extra material. Ideally, that would actually be hollow with a 2mm honeycomb latice. The interior will be 3D printed and then placed into the frame mold. I know it will be an expensive process, but I think it would be worth it to have that extra flare. That said, I will also be experimenting with other headtube concepts.

I also want to stay away from the DELTA system used in the Evil bikes. That's a can-o-worms I'd rather not open right now.

I'll start working on those triangle/linkage combinations.


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## chazpat (Sep 23, 2006)

Maybe they left out a comma?

No, nothing


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## Erichimedes (Jul 30, 2010)

So, all the other problems with the design aside, have you put any thought into the main pivot location? It looks like it was chosen here as a simple result of wanting a convenient place to stick it. I put this into Linkage just for fun and found that it has a chain growth of... ready for this? -7mm. If you're not familiar with chain growth, it's one of the things that helps prevent the suspension from compressing when you pedal up hill.

A lot of modern single pivots have a chain growth in the neighborhood of about 45mm, which helps them compress less (or not at all) when being pedaled up hill. Your design actually has chain shrinkage, which means you're giving the bike a mechanical advantage to compress the rear shock when you pedal.

The first time you stand into pedaling this thing you might actually fall off the back.

Do a quick google search on chain growth and pedal bob and how it relates to the pivot location of a single pivot full suspension mountain bike design.


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## slapheadmofo (Jun 9, 2006)

OP is seriously planning on winning $8k worth of prize money from his first few races to fund this project and you guys are shy about wheeling out the D-K? 

Ya'll are a whole lot nicer people than I am, that's for sure.
To a fault, I'd say.


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## xXNightRiderXx (Jul 27, 2017)

Alright, so I've sketched out another rear triangle design, modified the seat tube and the BB, and added parts to measure chain growth.
















Wheel travel per 5mm of shock travel:








I'm having an issue with getting the last 6mm of wheel travel taken up...is that very much of an issue, or am I just wasting time on it?

Also, that guy with that article that needed translating only gave me graphs I cannot read and jargon that I don't know. Literally, that article I mentioned on BikeRadar is MUCH easier to understand, gets into EVERY aspect of suspension design, and explains *what* each aspect ACTUALLY IS! All that spanish article does is say "this bike behaves like this" in garbled sentences. Nothing in there that helps with any kind of linkage design.


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## Drew Diller (Jan 4, 2010)

xXNightRiderXx, I notice your sketch lines are white. One suspicion I'm having is that you're encountering resistance from the "auto solving" portion of the sketch solver when not everything is defined? It looks like many dimensions are missing. (Or, are they part of another sketch?) I've noticed if some dimensions are missing, there is this sort of... I dunno... elastic band behavior. Like if you were trying to drag a point from 0,0 to 1,1, you would never, ever reach 1,1 no matter how close you got, unless you define it. Maybe that's not the best explanation...

Attached are what a fully constrained sketch looks like in the solver bar to the side of the viewport. I have my own color scheme for full constraints, typically a fully constrained sketch defaults to bright green lines.

Are you willing to post your most recently revised FCstd file?
Another important question, what version of FreeCAD are you using?


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## xXNightRiderXx (Jul 27, 2017)

Dont worry, all things that should be constrained have been, I just hid the least important values to declutter the image. When I get home, I'll be happy to edit this post with the .fcstd file. Ive also calculated the linkage rate at 1.7-1.1 if that helps.

http://www.filedropper.com/thegreengobblinI did make a few changes before I uploaded this, so don't take the ratio I calculated as fact...


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## Drew Diller (Jan 4, 2010)

I will worry (a bit, and worry is a strong word), your sketches have room for improvement specifically as it relates to how FreeCAD works. You're not using the non-numerical constraints -- vertical, horizontal, point-on-line, perpendicular, parallel, tangent, etc.

If you do those things, you can do things like simulate the position of the taut section of bike chain (a circle representing the chainring at the bottom bracket, another circle representing the chosen rear sprocket, connect a line that is tangent to the upper half of each circle).

The fewer things you need to call out with numbers, the better. You're always going to need to call out some things, obviously, but, you could afford to cut down on your dimension complexity by exchanging for some constraint complexity. It makes reading easier, not just for me, but for you.

The first example I could think of is those stepped travel measures where you had a measure of 2 micrometers to keep a point near a line. You want the point-on-line constraint for that type of thing.

Next thing regarding excess dimensions: what's your point of reference? The ground? The bottom bracket? The "attachment position" data can be changed for a sketch so that you can orient X,Y [0,0] at some other point in 3D space other than the default [0,0]. Then you could orient some major component at the [0,0] within the discrete sketch space using the Coincident constraint, thereby cutting down some dimensions.

I am attaching a file with some mods to the Body025 - Rear Triangle type 2 kinematics sketch. I changed how the shock attaches - it is now a "reference" dimension (it changes in response to driving dimensions such as travel). I added a "travel" datum. The taut section of virtual chain is tangent and dimensionless. I did not make any changes to influence your design decisions of the frame itself -- I'm only trying to help you learn FreeCAD, and I've never encountered another person designing a bike in FreeCAD, so I figure I might be useful here.

Attachment to follow in the next little bit.

Also, you didn't answer my question what FreeCAD version you're using. I stick to the dev branch 0.19 (currently rev 19758), it may be bleeding edge, but it is a heck of a lot more useful than 0.18 stable.


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## Drew Diller (Jan 4, 2010)

Here's the modified FCstd file link. Again -- I did NOT change your design, I cleaned it up a bit to illustrate the powers of the constraints and sketch editor that you are not yet tapping.

What follows are some screen caps from the origin of your file, through the changes I made. Things of note:

- The dimensions have names (trying to script something like Dimension0037 is super annoying, if you have a name it gets easier).
- Small elements - such as the rocker arm, and pulling link - are separated and dimensioned on their own, and then linked using the Equality constraint.
- The front and rear sprockets are given formulaic dimensions. For the rear, I'm assuming you were going for a 42T, I used this: 12.7 / (2 * sin(180 / 42)) ...the formula / expression editor is in the dimension value popup, there's a little icon in the right of the input that you click on that brings up yet another dialog into which you can enter Expressions - including references to spreadsheet values!

Tell me, what do you find easier to read? To maintain? Also are some screen caps showing the difference between dimension reference mode and driving mode.

Your starting point:








After I named and constrained everything:








Highlighting the "Travel" dimension I added:








Changing it to "reference" mode so that the rear axle can be pulled up and down animatedly with the mouse cursor.


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## Drew Diller (Jan 4, 2010)

Also, it seems to me that your total travel is about 186mm, and the shock length goes from 190.88 to 122.58 mm. Some math:

190.88 - 122.588 = 68.292 total shock stroke
186 / 68.292 = leverage ratio approx 2.72


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## Drew Diller (Jan 4, 2010)

One more thought, in the modified file I included a dimension named REFEffectiveChainStayLength.

It goes from 476.477 (at 0.1mm travel) to 504.33 mm, so the chainring to rear sprocket distance grows approx 27.8 mm. I'm still designing suspensions as a newbie, but I've read that this value is a bit high, like you might get some pedal kickback. So, you're close, but, from what I understand the location of the pivot is rather sensitive.


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## Drew Diller (Jan 4, 2010)

One more thought. That angle near the front of the swing arm where it attaches to the monopivot. That geometry in that area? Totally useless for doing triangle calculation. You want the _wires_, not the _frame member geometry_. Don't draw all the parts of the swingarm where you want to go around the tire, for now draw the straight line from the monopivot to the rear axle. That line will be more informative for when you want to start doing things like plot the leverage ratio through the active range of motion.

The frame member geometry should be a separate sketch _based_ on the driving points of the wiring sketch. If you don't separate your concerns, the sketches become heavily overloaded, and no amount of two-layer on-off business is going to make it much more sane.

Maybe this is a lot of feedback but like I said I've never been able to interact with another FreeCAD bike designer.

I hope you don't encounter any bugs considering I'm probably using a newer version of FreeCAD. It can happen. MAKE FILE COPIES. SAVE EARLY. SAVE OFTEN.


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## xXNightRiderXx (Jul 27, 2017)

Drew Diller said:


> Also, it seems to me that your total travel is about 186mm, and the shock length goes from 190.88 to 122.58 mm. Some math:
> 
> 190.88 - 122.588 = 68.292 total shock stroke
> 186 / 68.292 = leverage ratio approx 2.72


Actually, I'm goin for a 190x50 shock and 160mm travel.

I'm using FreeCAD 0.18.


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## Drew Diller (Jan 4, 2010)

Well I must reiterate then, FreeCAD 0.19 has some very useful additions, perhaps the most useful to me is the portion where elements that are not fully constrained can be highlighted. Bunch of stuff really. 

Are you familiar with Python programming language at all? If not it is fairly approachable. It's useful if you want to do things like plot the leverage ratio along its travel, or animate a suspension assembly (to make sure nothing is smacking together through travel), stuff like that.


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## xXNightRiderXx (Jul 27, 2017)

I know nothing of any programming language at all. I'm currently reading through the FreeCAD Python tutorial page to try and get something out of it, but I do want to be able to simulate terrain and how the suspension will actuate over bumps..... I suppose this is why most mtb manufacturers have a team for the design...

I have just downloaded the animation addon, so I'm gonna go play with that a bit.

After trying to use the animation bench, the report window consistently shows an error by circular dependency, so I can't use any animation tool, and I need to go back and fix something. Only problem is, I don't know how to open the DAGView window so I can FIND the circular dependency...


OK, I found it... I needed Graphviz installed. I have figured out where that dependency is...and it's in the pad of the BB001. I've deleted the pad (not the sketch) and removed dependent operations (the pocket and mirror), and I've redone them in order. Hopefully that will remove the circular dependency and allow me to use animations.


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## Drew Diller (Jan 4, 2010)

xXNightRiderXx said:


> I suppose this is why most mtb manufacturers have a team for the design...


I mean, that's why some of the other folks in here were suggesting you do a hardtail (or a dozen of them) first. What you're embarking on is a multi-disciplinary effort. You can learn all of them, but, it's gonna take a while. FS bikes are hard. Achievable, but hard.

Regarding the animation workbench, I believe there are some different ones available. The way I personally do it is to ignore the workbench entirely, and script everything. So the main thing with learning Python, its primary advantage is that you DON'T need to learn about opening and closing brackets. You _do_ need to rigidly respect indenting for logic blocks. It is vastly easier to read compared to other languages. There are some norms for writing FreeCAD specific Python, like you need to import certain packages where they assume you know what the names are. The FreeCAD python community pages are useful for this in terms of looking at examples (including examples of other scripts totally unrelated to what you're doing).

An animation script (without the workbench) could be something as simple (and I'm using pseudo-code) as:

Set datum Travel = 0.1mm
Update view
Print REFShockLength
Set datum Travel = 1.0mm
Update view
Print REFShockLength
Set datum Travel = 2.0mm
Update view
Print REFShockLength

etc

This is dumping a whole lot of new info on you really fast. Googling can sometimes find exactly what you need for FreeCAD report view errors -- but if you don't find the particular answer quickly, you won't find it at all. At least that's how my troubleshooting has gone.


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## scottzg (Sep 27, 2006)

It's weird seeing python come up in this thread. I've used python to automate about half of my job. I'm not a programmer at all, but i learned enough to let the computer do those tasks for me. I look like an overachiever but really i just feel guilty surfing mtbr all day.

I don't know anything about how python relates to frame building.


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## Drew Diller (Jan 4, 2010)

scottzg said:


> It's weird seeing python come up in this thread. I've used python to automate about half of my job. I'm not a programmer at all, but i learned enough to let the computer do those tasks for me. I look like an overachiever but really i just feel guilty surfing mtbr all day.


It's just happenstance that FreeCAD is built on python, and they expose some elements to the user -- be it through single-line-command terminal, or the ability to write long multi-instruction macros.

I mean, I could write a competitor to BikeCAD or Linkage using just FreeCAD and one hell of a python macro. I don't because I don't want to do the customer support. Just doing cost control on my end while I'm still struggling financially - I will probably end up buying those softwares one day when I am able.

The thing that really pushed me into python for FreeCAD was that I had to model something that couldn't be made with geometric primitive shapes. But, that's like, _really_ off-topic gearbox stuff. And it's pretty dumb because it ends up looking almost exactly like a primitive.

SolveSpace is also useful for wiring, and the dimensioning can be multi-layered (more than two layer limit in FreeCAD), which makes things easier to read in sections. And the animation is more intuitive in SolveSpace. It's just, SolveSpace has fewer overall features than FreeCAD with respect to complex 3D geometry.


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## Drew Diller (Jan 4, 2010)

scottzg said:


> but really i just feel guilty surfing mtbr all day


Also, and I hate to hijack this thread further with my own BS, but you _really_ struck a nerve here, hard. At least your employer is keeping you halfway engaged, yes? At my last paid position, I had saved up a bunch of money, and circumstances were such that I more or less twiddled my thumbs all day. There was NO engagement. I complained about it a lot, "is there some purpose for me being here?" I'd walk past homeless dudes on the way to the train going home. Collecting checks. Not doing work. It was contrary to every value I was raised to believe. I couldn't stand it. I felt _intense_ guilt. I felt like I was going *crazy*. Wife and I don't have children to support so I left the job and started building bikes with professional sales in mind, and I spent all my saved money at an alarming rate, even with frugality in mind. The nickel and diming is _insane_. So, don't feel too guilty. Or at least, don't let it get the better of you. There's some jerk out there somewhere working less than you and collecting a whole lot more.


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## xXNightRiderXx (Jul 27, 2017)

I feel guilty just sitting here playing games most of my time while collecting SSI-D because of my autism....sooo, i'm putting time into something a lot more productive. If this bike wins races, I can put my time into producing more, and start collecting income that way instead.

I understand why you guys say I need to work on designing hardtails first, but at the same time, I thrive on challenge, and a hardtail is just too easy for me. I mean, just look at the front triangle of my design! The downtube is a complex profile that takes rigidity and force redirection to a level I personally haven't seen in any modern bikes...just by using the structures of the arch and triptych. The BB is designed to direct mud and dust kicked up by the tire away from the spindle to preserve bearing life. IF the seat tube buckles, (which it shouldn't ever, even if the rider doesn't ride it right), it is designed to buckle towards the tire, but at the same time, the rear triangle will be pushing it forward, fighting the buckling of the tube. Even the shock mount location on the top tube is placed for ideal force redistribution through that arch. If all goes well, this bike will not break except under extreme (falling off a cliff level) forces. As I've stated before, multiple materials will be tested towards this end. I'm personally leaning more towards carbon-hemp composite though. Evidently, carbon-hemp composites couple the strengths of both materials to make a much stronger one.

I'm trying to design this bike to last a minimum of 10 years of race level riding on all terrains. If I don't design it like that NOW, when I haven't gotten even a prototype made up, then I will regret not doing so when the prototype fails. I think I'm going to fabricate a wooden model of the suspension though, just so I can test the rotations and map the wheel path manually. Getting the angles cut is going to be the primary issue with that though.... -sigh- Gotta love geometry.


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## Drew Diller (Jan 4, 2010)

xXNightRiderXx said:


> I feel guilty just sitting here playing games most of my time while collecting SSI-D because of my autism....sooo, i'm putting time into something a lot more productive. If this bike wins races, I can put my time into producing more, and start collecting income that way instead.
> 
> I understand why you guys say I need to work on designing hardtails first, but at the same time, I thrive on challenge, and a hardtail is just too easy for me. I mean, just look at the front triangle of my design! The downtube is a complex profile that takes rigidity and force redirection to a level I personally haven't seen in any modern bikes...just by using the structures of the arch and triptych. The BB is designed to direct mud and dust kicked up by the tire away from the spindle to preserve bearing life. IF the seat tube buckles, (which it shouldn't ever, even if the rider doesn't ride it right), it is designed to buckle towards the tire, but at the same time, the rear triangle will be pushing it forward, fighting the buckling of the tube. Even the shock mount location on the top tube is placed for ideal force redistribution through that arch. If all goes well, this bike will not break except under extreme (falling off a cliff level) forces. As I've stated before, multiple materials will be tested towards this end. I'm personally leaning more towards carbon-hemp composite though. Evidently, carbon-hemp composites couple the strengths of both materials to make a much stronger one.
> 
> I'm trying to design this bike to last a minimum of 10 years of race level riding on all terrains. If I don't design it like that NOW, when I haven't gotten even a prototype made up, then I will regret not doing so when the prototype fails. I think I'm going to fabricate a wooden model of the suspension though, just so I can test the rotations and map the wheel path manually. Getting the angles cut is going to be the primary issue with that though.... -sigh- Gotta love geometry.


Well there's a fair amount to unpack there as well. Don't feel guilty about collecting SSI. I know more than a few people (wrongfully) _trying_ to get onto support programs they don't need, whereas you likely need it. The funny thing about guilt is the people who _need_ to feel it most... never do. Those who generally don't need to feel it, often do (such as imposter syndrome, for example, which I've felt every day of my life with rare exception).

That said, high functioning autism is not my area of expertise. I've seen some mind boggling high quality stuff from some autistic folks who know how to channel the way their brain works, so I don't see it as a limiting factor to your long term success of this project.

However, you are showing something that has been shown by people on and off the spectrum: target fixation. Sort of a desire to be perfect on the first try. I understand the desire, but this just isn't how things work. In terms of a hardtail being "too easy" -- look, just try it. You'll be shocked at how not easy it is to something that is easy. This was referred to earlier with the Dunning Kruger graphs. We all do it.

I'm not sure I follow about the mixed-fiber hemp and carbon hybrid. What's your info on this? Far as I know, the stiffest members in a structure load first, and hemp and carbon have quite different values.

Wood is a good way to start modeling something if you lack metal working tools.

One word of caution I'd give you on your confidence in how suspension systems work after reading one bike industry journal website. You need to read something written by an engineer. Look up Tony Foale - he has a book about motorcycle chassis that applies to your goals. The physical version is prohibitively expensive for most people, but he offers a digital download that is much more budget friendly. I'll use myself as an example yet again. Some time ago I decided I was going to design a linkage front suspension fork (reasons: democratic external shock choice, low static friction, upper legs that don't move that can support sprung-mass panniers). I read some stuff about anti-dive and thought I knew what's what. I _sort of_ did, but after reading Mr Foale's book and understanding... like... part of it... I realized I needed more study. He does a very interesting job of translating curves and graphs into "what does a human _feel_ with ____ system conditions?" How do you quantify feel, etc. The reading convinced me that I should take a more conservative anti-dive scheme than I was originally planning.

Could you consider building a hardtail as like a stepping stone? A personal-state-of-tech-capacity evaluation, rather than a final product? The vast majority of people venturing into precision construction for the first time get something conspicuously _off_ about alignment. And full suspension, with its multiple links and whatnot, is all about precision alignment.

Consider the number of outfits that manufacture standalone rear suspension. It's, like, Ventana. And that's it. I think you can do this in the long run but in the short term you should make some physical pieces that you can evaluate, and eventually translate those evaluations into your long term thing.


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## Drew Diller (Jan 4, 2010)

Heyyy xXNightRiderXx, so I owe you an apology. I didn't know it's uncouth to use the term "high functioning", like a slur. *For others reading this, who, like me, don't know anything about this subject*, if I could use a SUPER short analogy based on my limited knowledge on this subject, here's the car guy version: you know how high octane doesn't produce more (_or_ less) power, but it can prevent pre-ignition under certain conditions? It's ... complicated.

At any rate I'm sorry if I had you feeling a bit less than whole with those specific remarks. As I said I think your biggest self-limitation here is your extremely high standards and ambition, which are ideals that have already been found in many an aspiring frame builder. You are not obligated to accept my apology, I didn't mean any offense, but harm is not necessarily tied to impact.


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## xXNightRiderXx (Jul 27, 2017)

Sure, just to humor you guys, I'll do one hardtail. I tell ya though, I doubt you'll find much wrong with it. Hardtail is pretty standard when it comes to design work. FS at least lets me get a lot more creative with the overall look of the bike.

Also, for the record, when someone mentions being autistic while designing a full sus frame, it's generally because they ARE high functioning. High functioning is not a slur, it is a location on the autism spectrum (which, I personally despise, because I feel it takes away from the importance of some of the more severe cases of autism).

This will be a good starting point for those interested in learning more about autism:
https://www.google.com/url?sa=t&rct...syc-20352928&usg=AOvVaw0y56tFJB5irKTvjl0zFKYE


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## xXNightRiderXx (Jul 27, 2017)

https://westernstateshemp.com/hemp-composite-vs-carbon-fiber/
View attachment 1315539


Hemp dampens vibration, so when it is used in handle bars alongside carbon, you get a strong, lightweight, comfortable handlebar. Use a carbon-hemp composite AND regular carbon in the rear triangle, you can make a bike with lateral flexibility and vertical rigidity while reducing the trail vibrations transferred into the frame. Because hemp creates car panels that make a splitting axe rebound out of a guy's hands despite the edge, it should provide excellent impact resistance when used alongside carbon in the frame, reducing the micro-fracturing caused by sharp impacts. Currently, carbon that can withstand such things is expensive. The inclusion of hemp would make it much cheaper.

I haven't read just the one article though, and I haven't even fully read the one article yet. I got to the point where it starts talking about CoC and it loses me, and I have to backtrack and figure out what the hell it's referencing, much like a lot of other engineering articles I've tried reading. As I've been working on this, and new things pop up, I search it up, find what I can about it, and study that information. If it doesn't give me what I need, I move onto the next one.


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## xXNightRiderXx (Jul 27, 2017)

Alright, I bought Linkage and plugged by bike into it, modified the links and the swingarm a bit, and relocated the rocker fix pivot.
https://www.4shared.com/folder/xhWVELQO/_online.html

I will be replicating those modifications in Freecad.

What I find most interesting are the curves that this geometry creates. I want to compare it to the Delta system by DW, but I can't find a good enough image of any Evil bikes. I'll do a bit more digging for some graphs.

Anyways, here are my graphs:











































Anyone able to say how this might perform in the real world?


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## scottzg (Sep 27, 2006)

Welcome back. Cool you got linkage!



xXNightRiderXx said:


> View attachment 1328461


Am i reading it correctly that your leverage ratio goes from 7.2:1 to 1.6:1 through its travel? That's not gonna work. You'll use half the travel by setting the bike on the ground and still not get full travel. You don't typically see a ratio that doubles through its travel. Getting the leverage curve right is REALLY important. Also you want the average to be around 3:1, or a little less.

Pedal feedback looks good. I'd like to see the antisquat. I don't know how to draw useful conclusions from the rest of the plots.

Don't take anything i say at face value. Idk what i'm talking about.

Here's evil bikes page on linkageblog. Linkage Design: Evil Bikes I don't see any reason to copy them, necessarily.


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## pvd (Jan 4, 2006)

DW/Evil Delta system is a single pivot. Done. This is the more obvious stuff.


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## slapheadmofo (Jun 9, 2006)

xXNightRiderXx said:


> If this bike wins races, I can put my time into producing more, and start collecting income that way instead.


Curious - have you done a lot of racing and been successful at it? This sounds like an wildly unrealistic scenario.

FWIW, bikes don't win races. If you're not already an very strong racer you're not going to just show up and start winning, regardless of bike. If you're planning on hiring an incredible rider to win on your bike, how do you plan to pay/sponsor/support them? How many of these homemade bikes do you realistically think you can build and sell at a profit?

Not trying to bring you down but sometimes a little reality check isn't a bad idea. :thumbsup:


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## xXNightRiderXx (Jul 27, 2017)

scottzg said:


> Welcome back. Cool you got linkage!
> 
> I don't see any reason to copy them, necessarily.


Yeah, I did. I decided it was time.

I don't want to copy the Evil Delta system, I want to compare it to my design, and see if I could improve those stats in any way. Already my chainstay is longer than theirs.

Alright, I see their curves, so I know what I need to aim for.


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## scottzg (Sep 27, 2006)

xXNightRiderXx said:


> Alright, I see their curves, so I know what I need to aim for. This design already has better pedal kickback than the Offering... I'm going to aim to keep that curve where it is with the kickback.


It probably has better pedal kickback because of totally unacceptable antisquat. You didn't include the graph, but your cad rendering showed that. You want it to be ~100% as sag, and to diminish as you move through the travel.


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## xXNightRiderXx (Jul 27, 2017)

here's that anti-squat graph you asked for.









And Anti-squat through the gear range









I may need a coil shock on this bike though....


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## scottzg (Sep 27, 2006)

That's not bad!



xXNightRiderXx said:


> I may need a coil shock on this bike though....


I've never seen anything that comes CLOSE to that progressive.


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## plummet (Jul 8, 2005)

I agree with others. This is a very ambitious build. But so what. Dream big I say. 

It looks like you are doing the due diligence to get an effective result. 

I have a couple of thoughts. 

Your virtual wheel/tyre looks very skinny and it is very close to the frame at bottom out. should model the biggest volume tyre that you will fit in there to double check. 

I'm a believer of lower linkage rates. I reckon you should aim for 2.5 to 1 leverage ratio. Lower leverage ratios give you more supple suspension as you dont have to crank up the spring rate/compression/rebound to counteract the high leverage.

68° head angle is terrible for an enduro bike. Thats 2005 spec. Slack that baby out to 64-65°


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## xXNightRiderXx (Jul 27, 2017)

plummet said:


> I agree with others. This is a very ambitious build. But so what. Dream big I say.
> 
> It looks like you are doing the due diligence to get an effective result.
> 
> ...


I have 27.5x2.4's in there.

I agree, I need to reduce the leverage ratio, but I'm finding it hard to do that while having an effective forces curve...

I'd rather keep as much agility as I can while keeping it as stable as I can, so i'd rather increase the axle offset before I decrease head angle.


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## xXNightRiderXx (Jul 27, 2017)

Alright, after taking some time to recharge, I got back at it with modifying the bike's whole suspension system to optimize leverage, target travel, and the forces curve. Having examined a basic horst link in linkage (without using the sag utility: for some reason, it keeps jacking the pressure up above 1000psi), I compared the curves to my design. It looked better in some ways than Delta, but worse in others. My design seems to be somewhere between the two with the curves. Regardless, now I need to reflect these changes I made in FreeCAD.

Now, I couldn't find ANY baseline graph for the force or shock curve, so I'm going to include those here, and maybe someone can tell me how high it needs to go.


































































Bonus: this design will allow two bottle cages inside the triangle, both on the downtube.


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## xXNightRiderXx (Jul 27, 2017)

ah hahahahah, I figured it out: I didn't have the shock dimensions properly set up in the software. After measuring my shock, subtracting about 4mm from the outside measurements, and inputting that information into the program, as well as setting the initial pressure at 160psi (my weight with kit), my shock curve and force curve now look like this:


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## xXNightRiderXx (Jul 27, 2017)

Alright folks, I've done some refining and some major adjustments, and I think i have something that will work well. I couldn't get the leverage ratio down below 3 without taking away a lot of the available travel, so I settled for smoothing it out at a lower rate. This is the result:


























































Head angle: 64 degrees
Seat tube angle: 76.7 degrees
Stack: 590.8mm
Reach: 445.1mm
Chainstay length: 427.5
BB height: 354.1mm (1.1mm drop) [sag values: 24%| 314.5mm (38.5mm drop)]
Wheelbase: 1215.9mm


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## 127.0.0.1 (Nov 19, 2013)

at some point you gotta dump the graphs and build a prototype to ride...
and expect to build another prototype with the new information

if you are cloning someone elses pivot points, you know how it will ride

if you are inventing something new, graphs won't fully reveal how it will *ride* ...maybe 70%*
*proof is the bike I have now, all these experts in linkage and kinematics ragged on it, but
when ridden hard...especially uphill...the bike rules...6 inch plush bike that stomps climbs


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## xXNightRiderXx (Jul 27, 2017)

This is something new inspired by someone else's design. I've never seen any bike with a linkage that pushes the shock vertically against the top tube, and I've searched. You do make a good point though, I need to get a prototype made. I'm working on the CAD model now, though this may prove to be significantly more difficult because of the large number of complex curves.

What is the bike you have now? You've piqued my curiosity, lol.


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## plummet (Jul 8, 2005)

My suggestion is to make the frame with a number of possible shock mounting points and with the ability to easily laser cut basic linkage plates so you can tweak the design on the fly. This is the kind of stuff the big guys do when designing new bike. Once they have tweaked after riding and trying multiple set ups they settle on the settings that are best and then build the asthetically pleasing frame with the correct dimenisons.

You too should follow this path. 

Also be prepared to need to make bike number 2 or 3 as your very first one will miss something, have some dimension wrong and you will want to change it. That is ok. Its part of research and development. 

Look at atherton bikes. That model of 3d printing lugs and gluing/bolting in tubes might be a good way to try different variations without complete rebuilds.


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## xXNightRiderXx (Jul 27, 2017)

Alright, it's been some time since I last posted and I'm reviving this thread. I've got a bunch of screenshots for you guys to be Gobblin up, so let's get on with it.








First up is the geometry of the Gobblin 160. Don't ask how I got a moving ICas with a single pivot, I don't even know, lol.








Next up is a perspective view of the cad model with emphasis on the tube profiles. The seat tube profile is just a placeholder, I'll get the actual profile modeled in soon. I've decided that this bike will be made with a mixture of hemp and carbon fiber composites. Hemp will be used in areas prone to impact and to provide compliance where it's needed. Carbon will be used in areas requiring stiffness that also aren't prone to impact. The hemp fiber will be reinforced with carbon in areas that aren't prone to impact, but still require a mix of stiffness and compliance.

Now for the graphs:









































If anyone wishes to provide feedback, do feel free. I am working on getting a prototype made of this exact bike not just to test suspension but also to test structural integrity. Every location where forces will be applied will be tested extensively. I hope that the structures I used to design this frame make an impact on durability. Since there are no sharp angles in any load-bearing location, my educated guess is that the forces will be distributed evenly throughout the frame.

I am thinking of having a few lugs printed out to bolt in a few tubes to test just the suspension, but that's going to be a little expensive. I might have better luck using tubing, solid rods, and laser-cut curved plates at the joints. This would all bolt together into a test platform.


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## slapheadmofo (Jun 9, 2006)

Nothing to do with design, but is the misspelling of goblin intentional?


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## xXNightRiderXx (Jul 27, 2017)

slapheadmofo said:


> Nothing to do with design, but is the misspelling of goblin intentional?


yes, it is. It'll gobble up all the obstacles.


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## xXNightRiderXx (Jul 27, 2017)

I just want to clarify, the forces and shock characteristics graphs are for a coil shock with a 450lb/in progressive spring at a 1.3 exponent.


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