Yet another friction drive

Hi Guys,

I have been testing this home made friction drive to see if it could replace a hub for as an assist for commuting. Inspiration came from the friction drives here in the ES; I have put my own design changes to suit some goals. First, instead of using knurled roller and one way bearings, this one uses a live, smooth roller. The roller turns when the motor turns and no one way bearing.
The roller can auto-engage like some of the designs here, but I would rather manually engage or disengage as I don't use it all the time. Still like to pedal.

Each of the arm has a skateboard bearing to relieve stress on the motor bearings. So far, the roller/motor is holding after a few hundred miles.

Performance is acceptable--it feels like a 400 watt hub; first, it can accelerate from a dead stop without blowing anything, 22 mph/35 kph max. The motor is 53 mm/35 mm long, 235kv driving the 1.125" roller. Battery is 8AH 6S lipo and ESC is 80Amp max. This one is not stealthy as it is noisy at top speed. However, at 17-18 mph it is ok.

The design is symmetrical so it can accept 2 motors but I am pretty satisfied with the performance of one motor.




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I like that the roller is fully supported at both ends with bearings, that will take a lot of stress off of the motor. I would recommend a 63mm motor, but if this one is working for you, no sweat. The fact that the roller is a smaller diameter than the motor helps.

I would HIGHLY recommend adding one 50V low-ESR capacitor to the power input of the ESC, cheap insurance.

Nice design, and beautifully executed!

Question: Understand the 'auto-engage' (I have a friction drive from Adrian, love it)... but how do you manually engage this setup?

I've wondered about using some kind of trigger (like old Raleigh 3-speed shifter) as an on / off for friction drives.
Interested in how you are approaching that.

If I'm understanding you correctly then you are also turning the motor when off throttle. Be careful with that, from what I understand some esc's don't like the backfeed of current into them.

How do you like that controller? I was thinking about picking up that same esc for a spare but haven't found the programming interface for it yet.

Nice work btw!

footloose said:

Nice design, and beautifully executed!

Question: Understand the 'auto-engage' (I have a friction drive from Adrian, love it)... but how do you manually engage this setup?

I've wondered about using some kind of trigger (like old Raleigh 3-speed shifter) as an on / off for friction drives.
Interested in how you are approaching that.

Click to expand...

Hi footlose,

Engagement is done by pushing the arms back until it contacts the tire. Once engaged, it does not come off until I push it back forward again to disengage. The spring there serves to
keep the roller from dragging when not engaged.

I think crossbreak had a design where he re-used the front shifter to engage/disengage his friction drive. I thought that was a neat design and same thing can be implemented here.

EVTodd said:

If I'm understanding you correctly then you are also turning the motor when off throttle. Be careful with that, from what I understand some esc's don't like the backfeed of current into them.

How do you like that controller? I was thinking about picking up that same esc for a spare but haven't found the programming interface for it yet.

Nice work btw!

Click to expand...

Hi EVTodd,

Yes it is correct; when throttle is off, then drive will turn with the tire and therefore the motor is a generator. I worried about this; but after 6 months of riding this design, I have not
blown an ESC yet. Perhaps I am lucky. However, I don't ride it without throttle input when engaged/asssiting; I'd disengage it when I don't want assist.

I am thinking maybe a smarter control would improve reliability by sensing the phase current and act accordingly by diverting the motor current to charge the battery via switches/Fets in the case when motor is acting as a generator.

If you figure out how to divert the current that would be great. I have a couple of friction drive ideas that I would like to try without the clutch bearing. That kind of device would be very handy.

I will say though, that the hv85 esc that I use doesn't seem to mind the current either. My last one lasted 4 years and thousands of miles before I killed it and my drive spins the motor from time to time. Maybe it's only a few esc's that don't like it.

Do you know how many volts your esc can handle? I thought I knew which one it was but looking at it closer I'm not sure. What model is it? Since I'm on my spare hv85 I need to find another for a backup. It would be nice to find something a little cheaper that still works.

Hi EVTodd,

The ESC I am using is the Turnigy AE-80A. It is capable up to 6s lipo only. See below spec from Hobby King:


Output: Continuous 80A, burst 95A up to 10 seconds.
Input Voltage: 2-6 cells lithium battery or 5-18 cells NIMH battery.
BEC: Linear 4A @ 5V

I like the 6s lipo format and corresponding ESCs at 6s. These are numerous and cheap so I can play with them more... The HV ESCs are nice but more expensive.

lcyclist said:

Hi EVTodd,

The ESC I am using is the Turnigy AE-80A. It is capable up to 6s lipo only. See below spec from Hobby King:


Output: Continuous 80A, burst 95A up to 10 seconds.
Input Voltage: 2-6 cells lithium battery or 5-18 cells NIMH battery.
BEC: Linear 4A @ 5V

I like the 6s lipo format and corresponding ESCs at 6s. These are numerous and cheap so I can play with them more... The HV ESCs are nice but more expensive.

Click to expand...

Gotcha. Yeah, I'm looking for an HV version.

I also like the 6s lipo bricks. They are perfect for us. We use one or two on the gf's bike or double the voltage and use 4 on my bike if I want something a little lighter (and a few more volts) than the fatpacks I normally run.'

Btw... Do you have a picture of your entire bike? Looks like a dj frame. They are great for friction drive builds. The ones that are a couple of years old have geometry similar to a dh bike with a hard tail.