Build of Recumbent with RS 35cc

[Lee_K]

I have built recumbent bikes before, but this is my first try at any bike with a motor. I have already spent a lot of time reading here and designing, so I will start with my design intent. It will have 20 inch wheels, it needs to freewheel easily with motor off, not too recumbent riding position so I can look around better while riding. Since I have been holding back on starting the build, I have taken time to make an accurate 3D CAD model. I have just started the actual build and will post photos soon.

[Happy Valley]

Looks interesting, I'd be intrigued to know more as the project develops. Good choice on engines.

[Lee_K]

I started with the swing arm because I had the material on hand, it is made from 3/4 by .035 tube. Its simple miter cuts. I made a template from scrap plywood with cuts made on miter saw to get the angles.


The swing arm bracket is made from 1.5 by .035 tube with large washes as end caps. The drop-outs are made from 3/16 flat steel.


Next up is the frame.

[Happy Valley]

Excellent Lee!. Great to see a project of this scope taking shape and being documented again, been a while and reminds me of the old days here.

Curious, what type or series tubing you'll be using and what weld process to join them?

[Lee_K]

Happy, thanks for taking an interest. All tubing is Chrome-molly (4130) with .035 wall thickness. I am using a small mig welder. I will have the frame roughed out real soon, then it will start to look like it might amount to something.

[Lee_K]

I use a lot of miter joints because I can't make bends without collapsing the tube. I don't like that look, so I am giving bending another try. This is 1.25 by .035 tube. I held my torch in one hand and pulled down with the other. I Heated the outside bend zone bright red while bending. I got just enough bend before the tube started to collapse. Good enough for me.
I bent the tube over a 20 inch rim so the rim flanges supported the rim partly up the sides of the tube.


I Made an accurate drawing of frame on tile board, then hot melt glued tubes in place for tack welding. I avoided the need to bend tubes by placing various brackets at transition points.

[Lee_K]

The frame is tacked together and ready for full welds. Also, this is a fork from a bike I don't use anymore. I will be cutting the steer tube off and welding in a new one for this project.

[LR Jerry]

Have you tried heating the pipe and using a conduit bender? Also I suggest using mirrors to increase your viewing area.

[Lee_K]

LR, I have have tried bending 3/4 thin wall tube with conduit bender, but this thin wall high strength tube will still collapse. In this case I was bending 1.25 thin wall tube, I feel lucky to get the small bend with just a little bit of collapsing. What do you mean by using mirrors

[Lee_K]

This shows how the the wheels are aligned to set up for welding the swing arm bracket to the frame. The Wheels are clamped between two lengths of 1-in square tube, then I used strings to pull each wheel perpendicular to the table. After getting the wheels straight, I welded the swing arm bracket.


A rear view shows that the swing arm is offset. I Built the wheel using a hefty BMX rim and a Sturmey-Archer drum brake hub. I did not dish the spoke lacing, I centered the rim with spoke flanges not the center of the hub. This moves the cassette to the outside more than on a normal bike and will line up with my jackshaft.