# Single Sided Swingarm DH Prototype



## sirknumskullgt (Apr 10, 2008)

Hey everyone. I posted up here in a different thread about carbon wrapping the rear triangle on my single side swingarm prototype but decided not to and now the results are in and pictures posted. This is a rough mock up of the frame with the linkage and custom axles mounted up. its about a week from hitting the trail right now.

Cant get pictures to post up here.

Tons of pictures on my website. http://www.nobsbikes.com/capstone_design_bike


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## RoyDean (Jul 2, 2007)

Hey dude... having been a student and also having built 4130 chromoly structures as one, let me congratulate you on the work. Having said that, be EXTREMELY careful with this bike frame. Everyone wants to think that their engineering and fabrication techniques are acceptable, but you don't want to be riding a first attempt (in both engineering and fabrication) off of "20 foot drops" as you suggested on your website. I don't want to get into a full on critique of your prototype, because it's already been discussed a million times... just be careful.


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## sirknumskullgt (Apr 10, 2008)

RoyDean said:


> Hey dude... having been a student and also having built 4130 chromoly structures as one, let me congratulate you on the work. Having said that, be EXTREMELY careful with this bike frame. Everyone wants to think that their engineering and fabrication techniques are acceptable, but you don't want to be riding a first attempt (in both engineering and fabrication) off of "20 foot drops" as you suggested on your website. I don't want to get into a full on critique of your prototype, because it's already been discussed a million times... just be careful.


duely noted. But I dont know how soon i'll be riding this off the first 20 foot drop I come across. Ima work my way up to that slowly but I gotta see what it can take. Someone does and I'll be damned if I'll let someone else take my glory mwahaha.

Anyways that was my other proto i took off that 20 footer. I trust those bikes to take anything but I was going for a weight savings and complexity here that does not cater to big hits.

Its certainly nowhere near my first attempt at either engineering or fabrication. Its just the first time I probably took it way too far over the edge.... so to speak.


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## Thylacine (Feb 29, 2004)

Nice job, and a gutsy one, too.

You say though:

_"Once I completed the solid models and ran stress and fatigue analysis on it, I realized that it was not only viable but very functional."_

I think it's important not to get ahead of yourself here. Have you done a _real_ FEA on that swingarm? My 16 years as an Industrial Designer is saying it won't even last a single ride. You mention the Ducati and BMW single siders....yours looks nothing like theirs. Is there a reason for abandoning all the prior art?


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## garymtb (Apr 1, 2009)

Nice Job Brian....Dad
Hey Thylacine it's a Capstone project for his ME degree at NU not really ment for production.
Called your bluff on fluffy bunnies dying....nice bikes like the paint, lost on the son...color blind.


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## yoyoma (Mar 13, 2004)

First off, that is an impressive project. As an engineer that does alot of FEA, I have to say this. FEA is really only as useful as how well you know your loads. Even then, accuracy is iffy. It took me about 4 years in the field before I really felt like I knew what I was doing with FEA and there is still lots I don't know. Its easy to get a pretty picture, but difficult to get a good meaningful result that you are confident in. The loads on a DH bike where the rider weighs 3-5 times as much as the machine are super hard to predict. Do LOTS of testing... And analysis doesn't take into account sketchy welds (no offence).


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## popoff (Dec 4, 2007)

that's a significant amount of work for a senior design project, congratulations for picking up some useful skills as well as building something instead of just making some cad models. 

one thing that stands out as a glaring possible point of failure are the miter joints on the swingarm. hopefully you put a plate in those joints to support the tube cross section. another neat feature of plating miter joints is that you can make shte plates slightly oversized and use them as the filler for the joint. that's also a good place for some gussets as you can fit them.

are the parallel tubes webbed together in the top view? in picture 37 it looks like they are open. you could gain loads of strength and stiffness by adding some thin sheet to box that section. 

you can bend some welding rod in the shape of your swing arm and twist it to see how the shape will flex. add some layers of masking tape to box the shape. that will tell you more in 2 minutes than an fea will until you have loads of experience reading fea's and correlating the results to real structures. welded structures are not trivial to analyze with fea. 

good luck with it.


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## Hack On Wheels (Apr 29, 2006)

"I went on to design a quick release style rear axle assembly which utilizes a stock front 20mm rim."

I'm not sure what the rim has to do with this though, do you mean hub/wheel? Interesting concept, how are you planning to mount the gearhub? For a concept like that, I would have honestly just gone with a well placed single pivot. Hope it works out for you though, let us know how it goes!


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## sirknumskullgt (Apr 10, 2008)

Thylacine said:


> Nice job, and a gutsy one, too.
> 
> You say though:
> 
> ...


Well you can refer to the quote you presented from me when I said I ran stress and fatigue analysis on IT, I was in fact referring to the whole bike, including the single sided swingarm in question. And yes it will last a hell of a lot more than a portion of one ride. At double the bottom out load, which i determined from the program Linkage, the rear swingarm deflects a measly 1.5 mm and that is with a cantilevered bearing load like it would see in real life. I know its not actually real life, I know that anything can happen but that says a lot about the stiffness of it. Also from fatigue I determined that at double the bottom out load it last 10000 cycles with a safety factor of over 3. So what do you make of that? Im a little wet behind the ears at 22 but I know a thing or two about design too.

I use Cosmos 09 also so its not like im doing it out by hand here. I mean whatd you think I meant when I said I _did _the analysis? That I actually didnt and was praying over it every night?

Also the ducati and beemer designs are nothing more than art to me in terms of my manufacturing capabilities. If you look at BMW's its this huge hydroformed beautiful one piece deal. I have tubing and a TIG welder. So I designed it using the material available and made it strong enough through rigorous refinement and structural analysis. Ive been working on this design quite literally daily since September of last year in my spare time. Just started building this one in early March.

Still, it doesnt mean it cant break the first time I hop on it, but dont drop me your industrial engineer resume and say its gonna break before it hits the ground. Youve gotta admit that's a pretty definitive observation to make when you havent seen anything more than a picture. I dont care if you have double masters in mechanical engineering or if youre freakin DW. In fact i would love nothing more than to hear his most critical opinion on it.


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## sirknumskullgt (Apr 10, 2008)

popoff said:


> that's a significant amount of work for a senior design project, congratulations for picking up some useful skills as well as building something instead of just making some cad models.
> 
> one thing that stands out as a glaring possible point of failure are the miter joints on the swingarm. hopefully you put a plate in those joints to support the tube cross section. another neat feature of plating miter joints is that you can make shte plates slightly oversized and use them as the filler for the joint. that's also a good place for some gussets as you can fit them.
> 
> ...


Yeah it sure has been an undertaking so far making this bike from the design and fabrication. Its at least 2 steps over the bikes Ive already made and those werent all that simple either. They have taken all the abuse ive thrown at em though so I want to believe that this one can do it too.

On the sheet metal gusseting thing, I have it designed in the solid model with all that on it because I could see it deflecting a lot when the top tubes pinched together and the bottom ones spread.

Cosmos is a beautiful thing, you can actually animate the deflections of the part as the load is applied and magnify it so you know where problem areas arise. Plus its just part of SolidWorks so your models are already ready to put into the analysis. You input material properties and fatigue SN curves so it should be a good representation just as long as you make it exactly like you modeled it. You can even analyze the entire bike together with all the hardware and bearings so its just like the real deal as it can be in a virtual perfect world.

Even though I am in fact colorblind (thanks Dad) its cool to see the pretty pretty pictures flexing and changing colors in the high stress areas. Seeing that I knew I had to put something in there and will be gusseting the entire length of the top and bottom. I will definitely put some slots along it to lighten it up a little as its excess to use a complete sheet. Just havent done that part yet. You know, details.

I think I will do the same for the dropout part of it too. Its actually 3 plates welded together and I am a bit worried about the weld on it just cause its 3/8 plate. I dont usually weld stuff that thick together. I hear you should heat treat pieces that are thicker than 1/4 and inch to relieve stresses. Then again its just a prototype and it just has to not break when Im riding the stairs into the presentation.

Still there is definitely merit in using the welding rod. It effectively shows the same thing. I mean youre really just looking at the geometry of it and how it deforms more than anything anyways. Its all just planes and lines and nodes in the end. Makes you actually appreciate all the stuff you have to do out the long way on paper sometimes.

I was going to leave the burrs and a little extra overlapping just like you said though so that I dont have to use more filler rod. I try to do that on areas where theres alot of weld like that. I do it for my pivot dropouts usually at least and tried it on some of the head tube gussets. Its a nice trick. Kinda makes it look like its laser welded on too.


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## sirknumskullgt (Apr 10, 2008)

Hack On Wheels said:


> "I went on to design a quick release style rear axle assembly which utilizes a stock front 20mm rim."
> 
> I'm not sure what the rim has to do with this though, do you mean hub/wheel? Interesting concept, how are you planning to mount the gearhub? For a concept like that, I would have honestly just gone with a well placed single pivot. Hope it works out for you though, let us know how it goes!


Hah gahhh with the quotes. I need to proof read my stuff. Yeah I meant 20mm front wheel or hub. It just has a big enough body and sealed bearings that I could press out and maximize the size of the rear axle. Its a custom 30mm axle. You can see in the pics how it slides onto it.

Im going to weld some tabs onto the front triangle about 5 inches up the down tube from the bottom bracket and make an adjustable dropout out of aluminum that bolts into the tabs. That way I can adjust chain tension to the crank and rear axle. I also have to mount up a chain tensioner that I have to make so that the chain goes over the bottom bracket and down under the swingarm. The chainline blows on this thing. Theres a lot of swingarm all on one side so its hard to route a chain around it. I think I have it licked though.

Yah I knew in the beginning it would be better to just do the swingarm concept or the suspension/ gearbox concept but then I though why not all of it. I cant wait to try out the new suspension configuration. I have really high hopes for its performance. Ive learned a lot from my first three frames and think this is the best way to go.

Maybe I can get a copy of the presentation. Theyre taping it on HD supposedly.


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## RoyDean (Jul 2, 2007)

sirknumskullgt said:


> Also from fatigue I determined that at double the bottom out load it last 10000 cycles with a safety factor of over 3. So what do you make of that? Im a little wet behind the ears at 22 but I know a thing or two about design too.


Just remember that hand calculations and FEA assume PERFECT interfaces between fabricated joints. As a beginner welder (which you, or whoever welded the prototype shown in your pictures, obviously is), your welds are nowhere near a perfect interface. In fact, NO WELDER, not even the best in the world, could make a joint that perfectly matches the structural models used in FEA analysis.

I say this as someone who was in your shoes 11 years ago (only I was building Formula SAE cars, not bicycles, but all the same knowledge applies), and since then have continued to use the same tools (fea, welding, machining, etc.). So I "know a thing or two about design too", and am not so wet behind the ears. Be careful. Engineers, like statiticians and bankers, can make the numbers come out to be whatever they want. The secret to being a GOOD engineer is to know when you can trust them.


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## JOURNEYC6 (Jun 7, 2008)

I like your bikes, I'm tired of the same designs look-a-likes, we need innovation.


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## yoyoma (Mar 13, 2004)

sirknumskullgt said:


> Cosmos is a beautiful thing, you can actually animate the deflections of the part as the load is applied and magnify it so you know where problem areas arise. Plus its just part of SolidWorks so your models are already ready to put into the analysis.


I don't mean to dwell on this, but I wouldn't recommend just throwing your solid CAD model into cosmos. Are you using solid elements for the tubing? If so, remember that you should have 2 elements through the thickness of the tube. Shell elements are really the way to go in cases where your diameter-to-thickness ratio is greater than 10....For thin wall tubes, cosmos solid elements tend to be artificially stiff since they don't have rotational degrees of freedom. Sorry if you already know all this (I sure as hell didn't know all that when I was in school), I just thought I should say it. 
Basically, I rarely am able to just use CAD model geometry to do FEA. Maybe if the part is simple and shaped like a brick. I usually re-model using simplified geometry or model using surfaces for a shell model. 
Also, are you sure that your analysis converged so that it isn't mesh dependent?


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## ScaryJerry (Jan 12, 2004)

Dude, f!ck everyone talking about FEA and loads and analysis! That thing is bulletproof!

Compare that swingarm to a Cannondale Lefty... I think it looks plenty strong!


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## Thylacine (Feb 29, 2004)

You skirted answering my question.

There is single sided swingarms in other applications and you have ignored prior art with your design. It's not a materials issue either because you can adapt designs between material types, and you can also emulate designs using tubing to substitute what would in prior art be hydroformed.

You've ignored this. Why?

I also hate to break this to you, but as you will discover once you get over that early 20 something know-it-all phase that we all go through, once you've actually made and broken a few dozen bikes like the rest of us, you will get a better appreciation for how pesky reality gets in the way for 'virtual' reality.

I will tell you right now, that your frame WILL snap in one downhill run from any rider who is at the top of their game, and it will break at those unsupported butt welds on the swingarm.

Also, a split downtube has absolutely no torsional rigidity. You may think it's cool because you can keep the CG low, but every bike ever made with a downtube configuration like that breaks. Colnago Bi-Titan is the classic example, and using streamline tubing won't make any difference. Your 'gussetting' creates a multitude of mini stress risers along these two tubes, and the head tube gusset hits the downtubes at a 45 degree angle also creating a big stress riser. If the swingarm doesn't go first, that's the second place it will go.

Now, you can take my comments with whatever grain of salt you like, but it's the height of arrogance if you think you can call something 'functional' despite the fact that this is your first prototype and you haven't even ridden it yet.

There isn't a single bike company in existence that has EVER made a frame in Solidworks or whatever and gone "Yep, functional, perfect. Let's make 1000 of them", and you're acting like you'd be the first. This is a dangerous attitude and forgive me for being devil's advocate, but I don't want you to learn the hard way.

I also at the same time don't want to take away from what you've done. This is a monumental task and what you've come up with is very impressive in a lot of ways. I'm a huge fan of single sided structures and I always take a perv at a BMW motorbike whenever I see one simply because it really is a thing of beauty.


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## sirknumskullgt (Apr 10, 2008)

Well what part of their design should I even use? Its just not the same thing. I dont want a single pivot I want to use the suspension designs ive been developing. Therefore a new swingarm design is needed. I went through a million iterations of this design before I landed on this one. How would you do it if you were going to? its a very complicated problem. 

Also Im not saying its done for developments sake, its just the very first prototype of it. I had to build it at some point didnt I. This one may break but who cares? Whats the loss? You can only do so much analysis before you have to make it and see if it works which is where Im at now. Im not looking to sell or make more than a half dozen of these things, I just want to make a single sided full suspension mountain bike. 

The swingarm is due for more gusseting also. I know the butt joints are not ideal which is why im going to gusset the corners around it and the seat and chain stays (if you could still call them that). 

Just have some faith man. Its not my first rodeo and it wont be my last.


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## sirknumskullgt (Apr 10, 2008)

yoyoma said:


> I don't mean to dwell on this, but I wouldn't recommend just throwing your solid CAD model into cosmos. Are you using solid elements for the tubing? If so, remember that you should have 2 elements through the thickness of the tube. Shell elements are really the way to go in cases where your diameter-to-thickness ratio is greater than 10....For thin wall tubes, cosmos solid elements tend to be artificially stiff since they don't have rotational degrees of freedom. Sorry if you already know all this (I sure as hell didn't know all that when I was in school), I just thought I should say it.
> Basically, I rarely am able to just use CAD model geometry to do FEA. Maybe if the part is simple and shaped like a brick. I usually re-model using simplified geometry or model using surfaces for a shell model.
> Also, are you sure that your analysis converged so that it isn't mesh dependent?


See now this guy knows how to make someone feel like they dont know what theyre doing. In a good way though.

I didnt realize this was not a good convention to use just throwing the models right in. I figured it was how it was supposed to work.

Would having a greater number of elements than two running through be better or worse?

Now that you mention the thing about the tube thickness to diameter I do remember them saying something about that in my FEA class and how you need to use a specific method.

Im pretty sure that I had used a solid and not a shell for the analysis.

Why is it that having it mesh dependent not ideal? I would think it converges the result in when it actually runs the analysis but I cant be sure if that was a particular setting I missed. Can you elaborate more on this please?

I guess this is why ansys has you still select specific points on the model instead of just using the solid mesh. I always thought cosmos was just a shortcut to doing that instead of a more general kind of analysis.


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## Thylacine (Feb 29, 2004)

sirknumskullgt said:


> Well what part of their design should I even use? Its just not the same thing. I dont want a single pivot I want to use the suspension designs ive been developing. Therefore a new swingarm design is needed. I went through a million iterations of this design before I landed on this one. How would you do it if you were going to? its a very complicated problem.


I didn't say you should use their design, I just said prior art is there to be referenced. It's the first part of the design process, hopefully you've been taught that. You wouldn't have had to go through so many iterations if you'd done more prior art analysis and research and discovery. You didn't do enough of that.



sirknumskullgt said:


> Also Im not saying its done for developments sake, its just the very first prototype of it. I had to build it at some point didnt I. This one may break but who cares? Whats the loss? You can only do so much analysis before you have to make it and see if it works which is where Im at now. Im not looking to sell or make more than a half dozen of these things, I just want to make a single sided full suspension mountain bike.


If it breaks and you wind up in hospital, then you'll care. There are some basic tennants of fabrication you're ignoring - that's the loss. Can't solve that 'in virtua'.



sirknumskullgt said:


> The swingarm is due for more gusseting also. I know the butt joints are not ideal which is why im going to gusset the corners around it and the seat and chain stays (if you could still call them that).


Just don't do them like the 'gussets' on the front half. I still don't understand why you didn't make a trussed swingarm from round or box section tubing. That swingarm you've done defies logic let alone physics.

Fark, I hope you're taking notes because this is the cheapest design class you're ever going to take!


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## sirknumskullgt (Apr 10, 2008)

I dont see whats wrong with coming at the problem from my own perspective and doing it how I think. Whats the point in using whats already there when you can make something thats all your own. I thought thats what the whole custom frame building thing was about. I use engineering to make my stuff work but it doesnt mean I have to adhere to the process as linearly as I was taught. We are all trying to make something different and unique right? This is my angle at this problem. 

The streamline tubing is stronger than any size of tubing that you could find to make an adequate structure for this rear triangle. Its better than both a rectangular or circular structure in the axis that the force is being applied and it fits tight together to allow clearance for the big tires and for the cranks. If they offered a .375 x 1 inch box tubing of chromoly somewhere then maybe I would use that, but until I find that source I use the streamline tubing. 

Ive found great success with cutting and bending this tubing to make contours like you see on this prototype. It seems to hold up very well to huge drops and jumps that I continually subject them to. 

I'll be honest, on all the prototypes before this one I did absolutely no analysis on them in any way. I just used logic and my experience with metal working and came up with something that works. Ive had no cracks in my shoddy welds or in any frame members thus far and Ive been on these bikes for over a year now.

The reason I really went through it all on this one was because I dropped my wall thicknesses on my tubings to .035" from .049" to save some weight. The weight savings is very apparent but I cant wait to see what this frame will actually take when the time comes. Its going to be very easy going at first to be sure but I want to put it through some paces. 

Being in boston without a car it might just end up being stair gaps and the like. Over easter weekend I will hit up the local trail scene for some shuttle runs and see how it goes. I'll be sure to document the events thoroughly to show what this thing can really do. 

yeah and if I wind up in the hospital then you can say you told me so but until then Im going big and never going home. Someones gotta take this hog over the limit and I'll be the one to do it.

I do appreciate the thing about the design defying logic though. Thats what Im going for here.


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## yoyoma (Mar 13, 2004)

sirknumskullgt said:


> Would having a greater number of elements than two running through be better or worse?
> 
> Now that you mention the thing about the tube thickness to diameter I do remember them saying something about that in my FEA class and how you need to use a specific method.
> 
> ...


Its a little confusing, but what I mean by convergance, is not the FEA program solving to get the result you got in one analysis.... The general procedure to ensure that you are getting a correct solution is to apply finer and finer meshes (more and more elements) to your part until you keep getting the same results. Until you get to that point, you don't know if your analysis has converged. If it hasn't reached that point yet, your solution is mesh dependent, and your results could be way off. 
Regarding shells, you would definitely remember if you used them. For some reason in Cosmos 2009 (I think its called Simulation, now) you have to remodel your part with surfaces and use those to convert to shell elements. This isn;t really that hard, you just do "offset surface" on all the faces of your solid model that you want represented by shells, then delete the solid bodies.
Anyway, still a very cool project, but definitely take the good advice from the experienced builders and designers here on design and fabrication...


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## sirknumskullgt (Apr 10, 2008)

yoyoma said:


> Its a little confusing, but what I mean by convergance, is not the FEA program solving to get the result you got in one analysis.... The general procedure to ensure that you are getting a correct solution is to apply finer and finer meshes (more and more elements) to your part until you keep getting the same results. Until you get to that point, you don't know if your analysis has converged. If it hasn't reached that point yet, your solution is mesh dependent, and your results could be way off.
> Regarding shells, you would definitely remember if you used them. For some reason in Cosmos 2009 (I think its called Simulation, now) you have to remodel your part with surfaces and use those to convert to shell elements. This isn;t really that hard, you just do "offset surface" on all the faces of your solid model that you want represented by shells, then delete the solid bodies.
> Anyway, still a very cool project, but definitely take the good advice from the experienced builders and designers here on design and fabrication...


Okay but if you apply a finer and finer mesh, like I did, then isnt it still dependent on the mesh? I have it as fine as I can possibly get and with as many nodes as the processor can handle without crashing. If I wanted to wait 36 hours for the analysis to come out then I would but the computers in the lab arent that open.

It all comes down to how my welding and mitering came out anyways. I feel very confident in my welds on this particular rig and am looking very forward to the first drop I take it off.


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## dbohemian (Mar 25, 2007)

I am really looking forward to your testing of this frame. Please tell us what it does, good or bad.

I see both sides of this discussion. I believe we discussed that in a prior thread. Everybody needs to learn and the only way to do that is by experiment. School won't do it. FEA won't do it. Making things, testing them does it.

About once a year I get some engineering team over here from the U of Arizona with some new bike,trike,car like contraption. Almost universally they have been really terrible. I think the last one I said would make it 100 miles. It went like 50 before failiure they would have bet me their first born I was wrong, but as I said before, they are not going to learn that without failing.

Your design is really interesting. My comment is that really good design and engineering is something that has been simplified and optimized. I do think that your design is going to work a while but it just seems overly complex and with too many joints for potential failure. 

Look forward to your updates.

Dave B
Bohemian


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## Walt (Jan 23, 2004)

*I'm with Dave on this one*

This is far and away the best "engineering student" thread we've ever had. This is a real piece of serious engineering (I wouldn't know CAD software from minesweeper, of course, so I can only stare at the pretty pictures) that the creator *went out and built*.

Freaking cool!

That said, I also predict that the shoddy welding and insane number of joints throughout the frame will cause it to fall apart. I hope I'm wrong. SirNumbSkull - wear your helmet!

If this was being built, say, by me, for a customer, I think everyone would be justifiably outraged. But if the builder is the one riding it, we all have to respect that he's putting his money where his mouth is. The proof is in the pudding, and I for one hope that it rides well and never breaks.

Keep us updated!

-Walt



dbohemian said:


> I am really looking forward to your testing of this frame. Please tell us what it does, good or bad.
> 
> I see both sides of this discussion. I believe we discussed that in a prior thread. Everybody needs to learn and the only way to do that is by experiment. School won't do it. FEA won't do it. Making things, testing them does it.
> 
> ...


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## w8up4me (Jul 23, 2007)

dbohemian said:


> I am really looking forward to your testing of this frame. Please tell us what it does, good or bad.
> 
> I see both sides of this discussion. I believe we discussed that in a prior thread. Everybody needs to learn and the only way to do that is by experiment. School won't do it. FEA won't do it. Making things, testing them does it.
> 
> ...


I admire the spirit and enthusiasm going into this project, but I'll add my two-cents-worth. The limitations of FEA are never more apparent than when one stands next to a failed frame alongside the design engineer who did the FEA. As a witness to this event many times over, I've come to realize FEA will tell you _where_ your "hot-spots" will be, but extrapolating this into _when_ it will fail is the step that leads many into that embarrassing situation where virtual predictions fail to live up to actual reality.

That said, it shouldn't surprise you to know I'm an advocate of real-life testing. However, I get the chills when folks go direct to human-experimentation and skip over mechanical testing where the consequences of failure don't include ambulances and big medical bills.

If you have the fabrication facilities to make that frame, then you should also have the means to put together a simple test to see if your frame can actually handle the loads you expect. Do a validation of your FEA studies by actually loading the frame and measuring displacements at various points to compare with the FEA results. If your understanding is correct and your FEA is based on proper loads and constraints, then there should be a strong correlation between reality and simulation.

If you really want to get a reality-gutcheck, then subject your frame to destructive testing in a controlled environment. (It's not as difficult as you might think.) If you want to silence critics, then there's nothing like hard numbers to back up your claims.

Gary Yokota
ex-SCB test-lab guy


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## Gregg K (Jan 12, 2004)

OK, I wasn't going to chime in, but now I see I have to.

First I want to say that my senior project was so lame in comparison to what you are biting off. Good for you.

Second, I've had a single sided swing arm in my head for years. I have a project that hopefully some day I will be able to bring to fruition. I'm too embarrassed to mention it here. All I will say is "chainless". And your post has actually given me an idea. So thank you.

And third, I had a conversation with my dad the other day about how much I've forgotten in the way of stress analysis. He is now 85, and was a senior managing engineer for Applied Materials, among other companies. Here is what he had to say-

...Additionally, no matter how trained you are in using the available math tools, I learned years ago that even to begin to use these tools, you always have to make so many simplifying assumptions about a good number of the parameters involved that the credibility of the calculations is questionable. I used to tell my guys that "one test is worth a thousand opinions". I can't imagine committing to the type of wire used in the Golden Gate bridge without having tested it thoroughly for several crucial qualities.


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## sirknumskullgt (Apr 10, 2008)

Hah I think all FEA is good for on a bike is so that when you hear a crack, you know where to look. Today we actually had the bike up on wheels and were compressing the suspension to see how it held up. Even with the bottom link in two pieces still not welded together and without the gusseting the rear end does not flex one bit. I will still add the gusseting nevertheless but the apparent stiffness of the structure is very encouraging. I was actually standing on the swingarm on the ground once or twice and it fealt like a rock. I have really high hopes for the performance on this bike. The suspension feels incredible too. Exactly what I was looking for. All is left is routing the chainline. That will be done tomorrow. I expect to ride it by saturday. 

Has anyone on here had to extend a bottom bracket for clearance? Im attempting to do that with the shimano bottom bracket that I have. I couldnt find a bb wide enough so I cut the spindle in two and have made a shaft that presses into both pieces which will all get welded. I think it will work for the purposes of proving the concept of the bike. It does sketch me out a bit however. Would be cool if it works. 

Any takers?


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## dbohemian (Mar 25, 2007)

sirknumskullgt said:


> Hah Im attempting to do that with the shimano bottom bracket that I have. I couldnt find a bb wide enough so I cut the spindle in two and have made a shaft that presses into both pieces which will all get welded. I think it will work for the purposes of proving the concept of the bike. It does sketch me out a bit however. Would be cool if it works.
> 
> Any takers?


Phil wood makes some odd sizes. They also make sizes to order.

Dave B


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## Feldybikes (Feb 17, 2004)

Thylacine said:


> Also, a split downtube has absolutely no torsional rigidity. You may think it's cool because you can keep the CG low, but every bike ever made with a downtube configuration like that breaks. Colnago Bi-Titan is the classic example, and using streamline tubing won't make any difference.....


OT and quite anecdotal, my AMP B2 had a double DT and that didn't break. Maybe that's 'cause the TT broke first (through the gusset, I might add). 



Walt said:


> we all have to respect that he's putting his money where his mouth is.


...Or his mouth where his stem is.

Sorry, sirknumskull, that's just a joke (and possibly a low blow). I really do think it's cool you're doing all this and it's quite an ambitious project. I don't know if you're using the correct software package, though. If the internets have taught us anything, it's that MSPaint is the proper FS design program.


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## unterhausen (Sep 28, 2008)

dbohemian said:


> About once a year I get some engineering team over here from the U of Arizona with some new bike,trike,car like contraption. Almost universally they have been really terrible. I think the last one I said would make it 100 miles. It went like 50 before failiure


I see the same thing every year too. The subject of this post was the first interesting thing I've seen bike-wise out of a student effort in the last 15 years of watching. The pinnacle for me was when Penn State held a gravity powered car competition. The English majors won, the Mechanical Engineering car broke in half after 20 feet. They have a product dissection class here where they take apart bicycles and analyze why they were built the way they were built. I keep hoping they'll start taking something else apart. I'd rather they didn't try to learn something from the bike-like-objects they keep getting from the dumpster.


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## Feldybikes (Feb 17, 2004)

sirknumskullgt said:


> Has anyone on here had to extend a bottom bracket for clearance? Im attempting to do that with the shimano bottom bracket that I have. I couldnt find a bb wide enough so I cut the spindle in two and have made a shaft that presses into both pieces which will all get welded. I think it will work for the purposes of proving the concept of the bike. It does sketch me out a bit however. Would be cool if it works.
> 
> Any takers?


Didn't notice this question before...You can get older Shimano square taper BB's in up to 127 mm wide. I found this out when I built a DH bike in college and neglected to account for crankarm clearance at the swingarm. I've got a couple in my basement along with square taper cranks.


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## rd3 (Mar 18, 2006)

Very neat project. 
Have you checked out the Millyard downhill bike? It also uses a single sided swingarm, but with a nexus gearbox.


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## rd3 (Mar 18, 2006)




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## p.doering (Aug 1, 2008)

Very neat. Thanks for sharing!

Both this and the Millyard/John Parker machine are visionary works of high-concept bike art.



It's much safer and easier to let someone else do the big creative work and just nitpick their efforts, than embark on such a feat yourself, isn't it...


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## nice-nice (Apr 25, 2008)

awesome work, efficiency is key


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## crux (Jan 10, 2004)

Very cool stuff.


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## esilvassy (Jul 25, 2006)

sirknumskullgt
so any updates? I see a few more assembled pics on your site.
just wondering how it is progressing


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## sirknumskullgt (Apr 10, 2008)

i still dont have the chain on it because i just wanted the suspension and rear end to be workable for the presentation yesterday but I want to get that on this week if possible. 

Our presentation went better than it ever could have in my mind. I rode the bike down the stairs in the presentation room and in the tight space at the bottom whipped the back end around right in front of the judges. Best entrance ever. 

Still even though everyone was all about the bike and its ingenuity and all that, the prize went to the bionic ankle group with their step motor integration and programming wherewithall. I mean Im pretty sure it was a mechanical engineering design project but whatever. Politics. 

The bike is great though. Suspension performs exactly like I had anticipated which is nice because I finally have my leverage rate theory nailed down on paper and in real life. the rear end feels totally fine under loading. Gotta get the chain on so I can do some real trail tests. Its all looking pretty solid so far though.


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## sirknumskullgt (Apr 10, 2008)

http://www.facebook.com/home.php#/video/video.php?v=634760063599

Ok so Im sure everyone on here would get a kick out of this. This is me riding the frame down the stairs into the presentation.

Enjoy


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## sirknumskullgt (Apr 10, 2008)

sorry I guess its set to private, but I'll get the file from him directly and post it up somewhere.


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## sirknumskullgt (Apr 10, 2008)

Ok this one works.

http://www.pinkbike.com/video/71479/


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## Vlad (Feb 7, 2004)

Very cool.


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## RoyDean (Jul 2, 2007)

sirknumskullgt said:


> I mean Im pretty sure it was a mechanical engineering design project but whatever. Politics


Welcome to real life, dude.


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## sirknumskullgt (Apr 10, 2008)

Feldybikes said:


> OT and quite anecdotal, my AMP B2 had a double DT and that didn't break. Maybe that's 'cause the TT broke first (through the gusset, I might add).
> 
> ...Or his mouth where his stem is.
> 
> Sorry, sirknumskull, that's just a joke (and possibly a low blow). I really do think it's cool you're doing all this and it's quite an ambitious project. I don't know if you're using the correct software package, though. If the internets have taught us anything, it's that MSPaint is the proper FS design program.


Haha no that was well crafted. Once is enough for me with that. Thats why Ive got the full face.

You know youre right about the software, all you need to be a suspension engineer seems to be an internet connection and a few moments of thought. pfft.


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## Live Wire (Aug 27, 2007)

sirknumskullgt said:


> Ok this one works.
> 
> http://www.pinkbike.com/video/71479/


Nice!


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## mobile chernobyl (Apr 12, 2006)

Very cool. 

A conventional design will never draw criticism... 

I'm working on something similar but with an onboard geared hub and brake, and using the IC path from a short link 4 bar to imitate a single pivot, I've been able to get sub 1mm chain growth sofar so it's looking promising. 

It's always cool to see someone set out and make something they design. I hope to do something in the area of CVT's for bikes for my senior project kinda like what Lahr did.


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## gibbed (May 7, 2007)

RoyDean said:


> Just remember that hand calculations and FEA assume PERFECT interfaces between fabricated joints. As a beginner welder (which you, or whoever welded the prototype shown in your pictures, obviously is), your welds are nowhere near a perfect interface. In fact, NO WELDER, not even the best in the world, could make a joint that perfectly matches the structural models used in FEA analysis.


That is spot on. At my job, I work with people who do FEA on locomotive underframes. When the underframes are tested, they never have the same stiffness as the FEA model. As the FEA model is refined, it will get closer and closer to approaching the test results, but will always be stronger.


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## PTW (Jul 15, 2006)

Good job im impressed...few questions tho
What happend with the "internal shifting hub" idea?? Looks like you've gone with a simple idler instead.
Also why has the swingarm swapped sides? This has put your drive on the opposite side to normal meaning youl need leftside drive cranks(profile among others makes them) unless you like continiously picking your pedals up off the ground.

Not knocking your achievement at all tho...but im with Thylacine. Please becarefull, theres some things in the fab of that frame which are quite/very dodgy.
Remember any critique thats in this thread is only there to help/advise you, and comes from people with years or decades of experiance.


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## sirknumskullgt (Apr 10, 2008)

The internal hub idea is still on I just changed around the configuration on it for a few reasons. The width of the actual hub with axle and shifter thing made it way to wide to be mounted where it was on the seat tube. Also I couldnt get it low enough so that the chainstretch was an appropriate amount. The chain was shrinking too much and I didnt think the chain tensioner could keep up with it. 

Now the hub will be mounted on the bottom side of the downtubes which puts its 3 pound weight lower on the frame. I made a custom bb spindle out of an old one thats now about 150mm wide so that the cranks would clear the rear end as well as the hub. Now theres an idler pulley on the top virtual pivot link fixed pivot that the chain runs over before it goes back to the rear hub. This makes it so the chain stretches 2mm before it shrinks 6 which is much more manageable. 

The rear end is now a lefty instead of a righty because it seemed easier when I was designing it to fit the chains one on each side. Now there is one chain going from the driveside crank to the freewheel on the hub body, then a chainring mounted to the non drive side of the hub on the spoke holes that has a chain going around the idler pulley, to the rear sprocket back between the chain and seat stays of the rear end, to a derailleur cage for tension and finally back around the otherside of the hub. The way I see it theres less clutter on both sides of the bike and it works nicely with attaching to the hub. 

This seemed like the best solution to a tricky custom drivetrain on a nearly impossible frame build. Next time around I'll try and make it simpler so you all dont have to express so much concern for my well being or sanity. It was never supposed to be something you saw everyday and thought, "yeah that looks like a totally reasonable design" its supposed to make you question it. Im mearly here to provide the method behind the madness.


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## dbohemian (Mar 25, 2007)

Have you been able to ride it yet? Not just that quick entry into your classroom. Inquiring minds want to know.


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## fongtyr (Jan 18, 2007)

Really enjoy reading this educational thread. sirknumskullgt: sweet project and brilliant effort, it's good to see your passion and belief in your work; criticisms' often hard to take, for any of us, but never hurts to listen and glean what you want. There's something to be said about the young, open, unjaded mind capable of out-of-box, unhindered thinking; just as much can be said for those who've been 'round the block with real world experience and wisdom. You won't go wrong by continuing to believe in yourself (confidence) and respecting the words of the wise (humility). Good luck!

Some friends and I have developed a prototype of a 3-wheeled human-powered vehicle which we know to have significant potential but we're already modeling (SolidWorks/Inventor) a ver.2 to address some of the feedback/concerns we've received from people that have ridden it. Seeing that some of you on this thread are professional/expert mechanical engineers (RoyDean, Thylacine, yoyoma, dbohemian, w8up4me, gibbed...to name a few) I was wondering if any of you would be willing to provide some input and validation of our design and FEA, or refer us to someone of similar calibre who is based in the San Francisco Bay Area? Don't mean to hijack this thread so if appropriate please shoot me a private reply or email me at [email protected]. Thanks much in advance!


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## HungarianBarbarian (Jul 24, 2008)

Thylacine said:


> Fark, I hope you're taking notes because this is the cheapest design class you're ever going to take!


What a joke, you're ripping on this kid for only done his analysis on computer but on your website when I click on frames you only have cartoons of your frames. WTF? Are you really a framebuilder or did I just swallow the hook?


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## sirknumskullgt (Apr 10, 2008)

HungarianBarbarian said:


> What a joke, you're ripping on this kid for only done his analysis on computer but on your website when I click on frames you only have cartoons of your frames. WTF? Are you really a framebuilder or did I just swallow the hook?


First off, thank you. Secondly though I dont know what you mean by only cartoons on the site. The only cartoons are on the future design section. For example http://www.nobsbikes.com/capstone_design_bike has all the single arm bike pictures on it. You should navigate the tabs at the top of the page.


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## HungarianBarbarian (Jul 24, 2008)

I was talking about Thylacine's site actually. When you click on frames on his website it shows a cartoon mockup of each frame design he offers. I thought it was funny how he was talking down to you about how you abandoned prior artwork when you had explained that it was a design project you were doing because you wanted something different.


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## RoyDean (Jul 2, 2007)

there are plenty of pictures of Thylacine's bikes on his website....


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## Francis Buxton (Apr 2, 2004)

For the record, he's not a mechanical engineer. He's an industrial designer.


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## fongtyr (Jan 18, 2007)

Francis Buxton said:


> For the record, he's not a mechanical engineer. He's an industrial designer.


So whom amongst you are pro mechanical engineers with bike product development experience?


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## D.F.L. (Jan 3, 2004)

fongtyr said:


> So whom amongst you are pro mechanical engineers with bike product development experience?


Few builders have any mechanical engineering experience.

Sadly, a lot of mechanical engineers know little about mechanics and structure. I'm not sure how this is the case, but many times, it is. Having knowledge is important, but being able to apply it is critical.

Industrial designers can make fine bike designers, provided they use their problem-solving and lateral-thinking techniques.

It ain't (exactly) rocket science.

(from a cruddy ol' Industrial Design major who did have a great course in structural theory(from the guy who designed the frisbee and the Gossamer Condor)...)


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## compositepro (Jun 21, 2007)

i thought it was an interesting take on something ,sometimes its just worth doing to learn or simply beacause you can


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## shiggy (Dec 19, 1998)

compositepro said:


> ...or simply beacause you can


My favorite reason!


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## vk45de (Feb 1, 2009)

rd3 said:


>


That marz ruins the whole lefty look. I woulda gone with a Lefty.


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## smdubovsky (Apr 27, 2007)

vk45de said:


> That marz ruins the whole lefty look. I woulda gone with a Lefty.


As soon as you find him a 180mm(?) lefty Im sure he'll get right on that


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## sirknumskullgt (Apr 10, 2008)

smdubovsky said:


> As soon as you find him a 180mm(?) lefty Im sure he'll get right on that


nah man im all over makin a short travel version with a lefty. the southpaw will be born. Designs are done. Just need some materials.


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## ironzep (Dec 9, 2006)

Just read the thread, really cool design. Have you gotten out on a proper ride yet?


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