What did you use for the steel part connecting to the pedals
Here are a couple of pics showing some detail.
I bought a cheap set of "combination" wrenches and cut one end off (chrome vanadium steel is tough to cut and drill; stainless would be better and more rust resistant). The 5/8" wrench sleeves over the base of the pedal shaft (note that it is removable); the 1/2" wrench replaces the cut off pedal base, fitting directly over the pedal shaft. Both work equally well. They hang off the Drive harmlessly when disconnected from the handles; with the pedals remaining in place, the Drive retains its pedaling capability.
Pins would be ideal as connectors, but I had some small stainless Nyloc nuts and screws that were hand tightened -- they worked fine.
PVC is 1/2" "schedule 40" approximately 20" long overall. Remember the pedal position is adjustable so there should be plenty of accommodation for different arm lengths. Of the two experimental handles, the simple "L" is the better -- less flexing, fewer parts. I use threaded connectors for the handles so they can rotate to the most comfortable angle (threads are wrapped with Teflon tape for smooth pivoting)
This is a third generation set-up. No doubt the concept can be further refined and better executed, but at this point it adequately demonstrates the concept and is functional but inexpensive.
If you build it, post some pictures!