[CBJ]

JM are you 100% about the swing link as the only option? I did not feel any flex on my Orange 222 I would go so far to call it very stiff. Also a soft rear will not be fixed with a swing link if the softness comes from the swing arm itself as suggested above?

 

[Jm_]

JM are you 100% about the swing link as the only option? I did not feel any flex on my Orange 222 I would go so far to call it very stiff. Also a soft rear will not be fixed with a swing link if the softness comes from the swing arm itself as suggested above?

No, that's not what I said. I said that the biggest difference in stiffness would come from incorperating a swing link. Using larger tubes, pivots, braces, etc, can help, and using all of them may get you somewhere, but the most bang for the buck is a swinglink. Have you ridden a foes or as-x to compare? In my experience they make most every other similer design seem flexy, even when you think you had a pretty stiff bike.

The swing link does the most to keep the members from moving relative to each other.

 

[Tame Ape]

yakkity yak...

To lend background re/ my experiences with my Heckler. I could cause light flex between the swingarm and the seattube with my finders alone. I always wanted a way to stiffen this part up as you can feel it move in corners akin to a weak sidewall.
Also, you could use the swinglink a la ASK and modify the spring rate to your liking.

 

[CBJ]

No flex like that on the Orange but I have unfortunately not tried any bike with the swing link but no doubt it seems like a good idea also to put some stress of the shock.

 

[Jm_]

To lend background re/ my experiences with my Heckler. I could cause light flex between the swingarm and the seattube with my finders alone. I always wanted a way to stiffen this part up as you can feel it move in corners akin to a weak sidewall.
Also, you could use the swinglink a la ASK and modify the spring rate to your liking.

yakkity yak...

don't talk back

 

[Tame Ape]

No flex like that on the Orange but I have unfortunately not tried any bike with the swing link but no doubt it seems like a good idea also to put some stress of the shock.

try to flex the top of the swingarm by putting your fingers between the Seat stay and the seat tube and pushing out... Even with the crappy finger location to push with, you still have some decent leverage above the pivot, maybe 8inches?

 

[Tame Ape]

don't talk back

thats right, 'cause if you did, I'd have to shake what my momma gave me. And YOU DON'T WANT NONE OF THAT!

 

[Superdeft]

A swing link seems like a good idea, but it needs to be made carefully for a single pivot. If the paths don't match up, something will rip right off under compression.

 

[Jm_]

thats right, 'cause if you did, I'd have to shake what my momma gave me. And YOU DON'T WANT NONE OF THAT!

Nor do I want the months of therapy that it would cause me to undergo

 

[zedro]

No, that's not what I said. I said that the biggest difference in stiffness would come from incorperating a swing link. Using larger tubes, pivots, braces, etc, can help, and using all of them may get you somewhere, but the most bang for the buck is a swinglink. Have you ridden a foes or as-x to compare? In my experience they make most every other similer design seem flexy, even when you think you had a pretty stiff bike.

The swing link does the most to keep the members from moving relative to each other.

really? have you done engineering case studies, or is this from anecdotal evidence?

ever heard of the weakest link in the chain? it may not mean squat to further reinforce the fore section if most of the flex is being produced aft (and not having that tire mid-brace is key before anything else). Good bikes arent designed using blanket generalisations.

 

[Sherpa]

really? have you done engineering case studies, or is this from anecdotal evidence?

ever heard of the weakest link in the chain? it may not mean squat to further reinforce the fore section if most of the flex is being produced aft (and not having that tire mid-brace is key before anything else). Good bikes arent designed using blanket generalisations.

Ohhhhhhhhhhhhhh Zedro just called out Jm. It's on........ :evil:

 

[Jm_]

ever heard of the weakest link in the chain? it may not mean squat to further reinforce the fore section if most of the flex is being produced aft (and not having that tire mid-brace is key before anything else). .

The brace will help, but because it is aft of the main pivot the entire rear section will be able to "move" as one unit, even with the brace, and try to "twist" the post that is connected to the main pivot.

 

[dcamp29]

how long did that take you? im in mechanical engineering at cu and am wanting to build a bike(a lot more complex than that though) and am wondering if its even worth it to start. also how much $$ did you spend on metal?

 

[buildyourown]

how long did that take you? im in mechanical engineering at cu and am wanting to build a bike(a lot more complex than that though) and am wondering if its even worth it to start. also how much $$ did you spend on metal?

Seems there are a lot of people interested in building frames. To anyone interested, go for it. But start with a HT. A novice with some metal working experience can build a frame in less than 80 hours. A HT can be built for less than $100. Don't even try a FS unless you know what you're doing. Most likely, your first frame will be wall art. Mine is.

 

[zedro]

The brace will help, but because it is aft of the main pivot the entire rear section will be able to "move" as one unit, even with the brace, and try to "twist" the post that is connected to the main pivot.

still theres no use engineering a front linkage if the swingarm is still spindly. The point being, you cant stiffen a noodle by reinforcing the shock. If theres that much twisting at the front end, then main pivot area should be re-designed. Get the swingarm upto spec first, then add the gravy-link; otherwise the link will just be a poor band-aid.

 

[Jm_]

still theres no use engineering a front linkage if the swingarm is still spindly. The point being, you cant stiffen a noodle by reinforcing the shock.

Yes, I agree that the brace behind the pivot is critical.

 

[CreeP]

well my first instinct is to put a 10º bow with a 2ft radius in the 'uprights' and bring the drive side 'chainstay' down 1" and the non drive 'chainstay' to just above the pivot. And oversize all that stuff by about 15%. I'm not huge on the idea of a brace as it really can't be a very pretty solution, connecting a square's corners is always inelegant.

Very cool bike.

 

[krustydude]

Why don't you just rivet a brace from the flux capacitor to bearing CPU and back to the spoke zerk.

 

[krustydude]

Seriously though, sweet looking frame. I'm not an engineer or anything but the swing link seems to make the most sense.

 

[Spitfired]

Here's the update:
The swingarm is now two separate pieces. I call it RTT (Reactive Tire Tracking).
So, I have the RTT for 2 days while it sits in my car.
Friday, 18 hours of machineshop day, I'm going to weld a square around the four stays right up near the tire - as close as I can get within reason.
Between the two uprights will be a nice big bolt on aluminum plate (With HEAVY machined into it) which will connect the uprights for about as much surface area as they can without interference. This way, the rear end will be as solid as it can be, and with the removable inner plate I can still get the thing off of the bike.
Take a look at the Dark Cycles swingarm - the braced rear will resemble that I presume. Personally, I think it looks pretty allright.

Why does it flex? Well, the rectangular tubing is not 'designed' to accomodate the torsion in that area - Aluminum bikes (bullit for example) have nice big machined aluminum jobbies holding it all together. With steel, that's just not going to happen. The weight penalty would be redonkulous. So, for the next one, I'm going to look into oval tubing for those uprights, or just tubes if I can do it right (they'll get big and stuff will start hitting quickly). That seems to be one of the issues.

Swing link - I'm working on a design. Depending on how these changes effect things, I might run with it.

This cost me somthing like $200 to build. I bought the material for my next two frame designs, used what I needed for this one, and still have the other bike's left over. The shock I had lying around, and I milled everything the old fashion way - Sharp lathes and knee mills.

I concur with Buildyourown. I started with my XC hardtail and it turned out great. Next I tackled a linkage based downhill bike. It works, but not all that well. I'm going to clearcoat it and make some more wall art to go along with my tree-crushed rocky mountain frame.

Also, don't rush. That's probably why I keep running into problems.

 

[draco]

yo G. i was thinking about the brace thing like we discussed. I forgot to mention that you need TWO tabs... you need to bolt the brace in place from front and back... not just 1 set of tabs... two, that the piece can fit in. like slide into maybe.

 

[CreeP]

that might be tricky.

 

[DHS]

just copy santa cruz exactly....but out of steel ofcourse

so when do i get to take it for a ride.
dammit

 

[Spitfired]

If I copied an aluminum bike out of steel, it would be really heavy.
C'mon stevie. You know better.

You can ride it at some point. haha, that's the best I got. Let me know when the thursday rides are happening (weather permitting etc) and I'll try to bring it out for a night.

 

[zedro]

If I copied an aluminum bike out of steel, it would be really heavy.
C'mon stevie. You know better.

You can ride it at some point. haha, that's the best I got. Let me know when the thursday rides are happening (weather permitting etc) and I'll try to bring it out for a night.

didnt you know, anything single pivot is a blatant SC rip-off, they invented it

 

[Spitfired]

Yeah, I know.

But fortunately, I invented the hardtail.

 

[lovebunny]

not makin the feb races eh g? guess whose hittin the 4x on that rig this year...