The friction wheel I first created was inspired by the bike powered blender instructables from the following link: https://www.instructables.com/id/STTOO5AFGWRG4LN/
or search "How to create a smoothie making human powered bike blender for less than $25"
1. I got two wooden 1.5 inch wheels from Michael's
2. I drilled a hole throught each of them
3. Pound two tee nuts into the wheels
4. I threaded them onto the all thread shaft I had made. and glued them together with wood glue
5. With some rubber from a broken bike inner tube I pulled a piece over each wheel and overlapped them coming from each side. If you can get the tube over both it is ideal.
This is the friction wheel I used. It worked ok, but because the wheels were not perfectly aligned since I drilled the holes through them myself, they didn't put even pressure onto the bike wheel and therefore caused uneven pressure on the shaft and a net loss of energy so this an area where improvement can definitely be made. Ideally the friction wheel woule be flat all around and strong enough to stay even along the bike wheel throughout pedalling.
So like a metal cylinder with like grittiness to it like a file that would be the friction against your bike wheel.