Tom, I looked closely at the welds you put on the bushings and cross tube. I'd have no fear getting on that bike. Well done!
Pete
Thanks Pete, but you only saw the easy parts. It's one thing to weld in a ferrule that is a close fit with no filler rod required while it is clamped in a vise and I'm sitting on a stool resting my arm on the vise. It's quite another to do the vertical welds I needed to do while the swingarm was clamped to the jig that the bike was sitting on to prevent it from warping. My vertical welding skills still need some improvement.
Hey Tom
You have been busy--- nearly ready for '18
Just my 2c worth
cheers Bones
Yes, almost ready, but aren't we always almost ready. I'm thinking that 2" of travel is enough as well, but I'm worried that the quality of the shock may be questionable, as I can't feel any sort of dampening. As you can see below, I got a local machine shop to make me some shafts from cold rolled and ream out my bronze bushings. I also remade the "links" that connect the link shaft to the link so there is almost no slack. When the mechanical advantage of the rear movement to the link shaft movement is 7 to 1, a small amount of clearance, say .010" on each end, get multiplied into .140" movement at the rear. So without proper dampening, the first 1/8" or so is just going to vibrate.
Koncrete,
Now that you have kinks in the swingarms, it might be a good idea to think about just how rigid the arrangement will be when subjected to the chain load and tractive load. It won’t take much flexibility in the rear end to make for an anxious ride.
You might want to scab on a half-piece of tube gusset on the outside where the kink goes narrow if there is room--anything will help. Also, a piece across from arm to arm in front of the tire would be beneficial.
Might tension up the chain and then spread the two runs and see what happens. That would test the stiffness of the pivot arrangement too, which is kind of narrow.
You probably don’t want the rear end to change direction whenever you shift...
Thanks for that observation. It's been a long time since I've done of those kinds of calculations, but I've included another drawing here that shows the chain pull, the offset, the cross section of the tubing, and my calculations. They're not exact, but the 19,000 psi stress caused by the chain pull is more than it will see, as the chain pull is actually about an inch to the right of the left arm so some of the load will actually be shared by the right arm. Also, the connections of the rear axle form a rigid moment connection, so I think that also spreads the load. In any case, the maximum bending moment occurs at the kink in the arm which is just where it is hardest to reinforce. I would be happy if you would check my calcs.
Correction on my drawing - -chain pull would be closer to 1100 lbsf, so stress would be significantly less, based on 50 ft-lbs torque, 1.86 primary ratio, 2 to 1 transmission ratio, and 21 tooth front drive sprocket.
Hi Tom looking great! Could you form the swing arm rail out of one piece instead of welding 3 pieces per side?
Alp,
That may be possible, but I had to bump out that arm in a very short distance to avoid having to change my footpeg location and avoid the rear tire. Besides that, I didn't have the tools to bend rectangular tubing, but I did have a chopsaw and a welder.
Tom