Hi Kepler,
I have gone and made my own friction drive bracket since I got bored waiting for yours to be available and I also discovered on closer inspection that my bicycle would not fit your mount after all, as the BB locking ring has insufficient thread to mount 2.5mm of your device behind it, the BB shells do not protrude out of the BB far enough, it would be a PIA to cut down or replace the bb unit with one that would fit the bracket.
So I attacked a piece of 6mm thick 50x50mm alloy angle section with a hacksaw and drill press to make a mount that clamps to the lower rear chainstays ( mine are large rectangular section alloy frame so a simple clamp mount is perfect . my crude device mounts a 6354 against the tire with about 2 mm clearance, similar geometry to yours and a gravity spring made from a piece of coat hanger wire, I sort of copied your idea but the pivot is a steel door hinge as they are easy to mount, strong and fairly rigid with little play and easy to replace if worn out. , the stop for the range of motion limit is a crude pair of hooks on the ends of my gravity spring that catch each other at full extension The other springs I tried were long curley types and gave excessive bounce as they had a fairly constant rate the short action variable rate of a stiff wire spring is ideal as there is less motor bounce on bumps. I have a couple of extra friction dampers in the system in the form of 2 zipties that rub against the end of the spring they stop most of the jiggling. They seem strong enough so far and survive the repeated drop test ( while holding the handle bar drop the back wheel on the ground from about ½ m) my simulation of curb drops and bunnyhops. I went for a long ride today with the motor mounted to see if it would moveabout or break its primitive stops but it seems tight and the drop test is more extreme than any riding I would normally do .
I have come up with a working solution, Im still soldering all the wires together, a hall thumb throttle, vesc , 440 w/h lipo (20ah 6s), battery mounting to down tube water bottle mounting in a special alloy sheet and corflute board container and vesc in the bottom of the triangle with very short wires to battery and motor. I got vesc to work with bldc tool on my linux computer and it all works but have yet to hook up the motor and throttle and finish programming the vesc. Im waiting on a proper alloy case from poland for the vesc, for now its in a cheap food box with clip on lid … ill put up some photos soon, thanks for the inspiration. I never would have built such a simple device so quickly if you hadn’t done it first or found the vesc.
I had a couple of questions about your setup
do you allow the motor to bite into the tyre as much as it wants to ? or allow only a certain amount of pressure by limiting movement with the stop ?
My setup is presently able to compress the tyre about 5mm when its against its stop , I figure I relax the tyre bite at the desired maximum power level until it starts to slip to find the optimal bite/efficiency
I should with luck finish it in the next few days
I also have the drone pancake motor to experiment with now, an 8318 with 48 poles and 100kv, it turns real slow with heaps of torque thinking of simple single speed left side drive using 219h cart chain and sprokets with custom clutched freewheel on the back wheel to allow freewheel and regen at some later date …. hairbraned ideas abound
photos to come if your interested