How to improve my friction drive situation?

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yoyoman
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How to improve my friction drive situation?

Post by yoyoman » Aug 29, 2017 6:12 pm

My used commuter booster is set up, but it's not working reliably. I’ve adjusted it so that the motor is 1mm from the wheel. The motor does engage the wheel, but it won’t stay engaged.

I’m looking for advice to improving my situation.

1) I have the CB clamped on a dowel screwed into the kickstand plate. Would there be any benefit to lowering the motor 1cm on the dowel?
2) Would a smaller, lighter motor help?
3) The prior owner’s grip tape has come off, so now I’m running with just the can. How do I clean off the adhesive gunk? I doubt it’s helping.
4) Would grip tape, ie low grit sandpaper help here?
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MadRhino
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Re: How to improve my friction drive situation?

Post by MadRhino » Aug 29, 2017 7:51 pm

I don't believe it would work with friction on the motor can alone. The grip tape is a must IMO. The distance from the wheel doesn't need to be very close, it is the pressure on the tire after it is engaged that matters. If fitting the bracket further away from the tire does make a better engagement pressure, sure you have all the advantages to do it.
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fechter
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Re: How to improve my friction drive situation?

Post by fechter » Aug 29, 2017 8:48 pm

I think you want the pivot to be further away from the wheel so the motor torque will increase the pressure.
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Chalo
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Re: How to improve my friction drive situation?

Post by Chalo » Aug 29, 2017 8:55 pm

fechter wrote:I think you want the pivot to be further away from the wheel so the motor torque will increase the pressure.
This. You don't have enough mechanical advantage when the roller makes contact, the way it's set up now.
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spinningmagnets
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Re: How to improve my friction drive situation?

Post by spinningmagnets » Aug 29, 2017 9:14 pm

To get maximum traction, you have to incorporate some way for the motor to dig-in at full power, in a position where the pivot center and the axle center are in-line with the driven wheel axle.

Don't concern your self with the un-powered position. The wheel rolling will fling it downwards and it will hang away from the wheel, and the distance is not very relevant.

On start-up, the spin-torque will cause the motor to flip up, and the spinning motor-shell will touch the tread. Since the motor-shell is spinning faster than the tread, the motor will pull itself up higher, and deeper into the tread.

Try this: Straighten the motor with your hand (unpowered) until it is in-line with the pivot and wheel-axle. It looks like you will need to move the frame attachment farther forward as much as possible. There should be some type of "stop" in the mount so the highest that the motor swingarm can reach is the in-line position (it should never rise above the inline position). Press the extended drive into the tread until it is at the proper depth of pressure (onto the tread). Lock it into place, and test.

yoyoman
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Re: How to improve my friction drive situation?

Post by yoyoman » Aug 29, 2017 9:53 pm

Thanks everyone for the responses so far. Using the CB clamp mount, I have had to get creative on this folding bike. My dowel is screwed in at an angle away from center since a vertical dowel didn't have enough space for installation. If I lower the clamp mount 1 cm will increase the pivot room a little bit.

As far as moving everything forward, I won't be able to do that with the dowel. I will have to get a coworker to 3d print something that will let me bolt the CB mount to the kickstand plate.

For now, I guess I will try to increase the angle of the dowel away from center to increase the pivot space.

I may have to give up on this and see if Kepler has new longer swing arms.

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Re: How to improve my friction drive situation?

Post by tiny_n_terrible » Aug 30, 2017 11:34 am

I have tried friction drive on ICE motorized bicycles. You need a grippy smooth center tire.
Grip tape or powdered abrasive glued on to the driving wheel. Perfectly dry roadway .Large forces pushing the drive roller into the driven wheel.The more power you try to use the more the drive wheel acts like a grinder.
I NEVER was satisfied with any friction drive implementation.

A dd hub or chain driven setup for me.

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fechter
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Re: How to improve my friction drive situation?

Post by fechter » Aug 30, 2017 1:29 pm

Can you flip the dowel clamp over so the pivot is in front of the dowel?
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Re: How to improve my friction drive situation?

Post by yoyoman » Aug 30, 2017 7:36 pm

fechter wrote:Can you flip the dowel clamp over so the pivot is in front of the dowel?
The clamp is pretty chunky. If I flipped it, it would hit the chainring on the other side, plus I don't think it'd clear the seat tube.

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Re: How to improve my friction drive situation?

Post by MadRhino » Aug 30, 2017 8:37 pm

Fit a spacing bracket to mount it under the seat tube. Alternatively, you could cut the seat tube to let you mount the unit far enough from the wheel.
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Re: How to improve my friction drive situation?

Post by Hillhater » Aug 30, 2017 9:18 pm

yoyoman wrote:.
I may have to give up on this and see if Kepler has new longer swing arms.
Have you contacted Kepler ? He has set up guidelines for these units.
I suspect longer swing arms would not be the way to go !
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fechter
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Re: How to improve my friction drive situation?

Post by fechter » Aug 30, 2017 9:23 pm

yoyoman wrote:
fechter wrote:Can you flip the dowel clamp over so the pivot is in front of the dowel?
The clamp is pretty chunky. If I flipped it, it would hit the chainring on the other side, plus I don't think it'd clear the seat tube.
I was thinking more like disassemble it at the pivot and flip the clamp over so the motor bracket stays on the same side. I can see the seat tube still being an issue. You need to get the pivot closer to the seat tube. Not having a complete picture of the clamp doesn't help. Maybe drill the hole through the dowel way off center so it's further forward.

Another idea would be to take out the dowel, flip the clamp 90 degrees and drill a hole through it for a bolt that goes to the kickstand mount and bolt it directly.
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Re: How to improve my friction drive situation?

Post by yoyoman » Aug 30, 2017 10:18 pm

I started a thread earlier when I was looking for mounting advice, https://endless-sphere.com/forums/viewt ... =3&t=89691. You'll see lots of photos there.

I bought a nut/bolt and was thinking of just using a giant washer to span the size of the clamp's hole. I tabled that for a quickee test of the dowel method.

Right now, I'm wondering about an L type bracket that I can bolt thru the kickstand plate. The right half of the clamp would be screwed into the hanging L. I think that would allow me to have the mount as far back as possible. I am worried that the L won't be able to handle the weight of the motor. Drilling a hole thru the clamp that also goes thru the to the kickstand plate would solve the hanging weight issue, but the shaft goes thru the clamp, so that cuts down on my hole position options.

Heh, thinking more about throwing down money for Kepler's mount ..

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fechter
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Re: How to improve my friction drive situation?

Post by fechter » Aug 31, 2017 11:47 am

The other pictures were helpful. The clamp looks like it's made of Delrin. If you found a chunk of Delrin (or similar material) about that size, you could make a new piece to replace the clamp that had holes in the right places including the pivot shaft. A new hole in the kick stand bracket might help too.
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yoyoman
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Re: How to improve my friction drive situation?

Post by yoyoman » Aug 31, 2017 2:51 pm

Due to the chunkiness of the CB clamp mount, I'm limited in positions since I have to contend with the chainring. I don't want to mess around with how the shaft and everything is mounted in the righthand mount. I might, however, consider making a thinner left side mount since that doesn't involve messing with the shaft, screws, etc.

I guess I'll also work on v3 of my 3d printed mount. V3 will remove the rectangular hole above the "dowel". The top piece will also be thicker and extend more to the right to allow pushing the mount position to the left. I'm also going to increase the gap between the horizontal pieces to allow for a larger bolt head.
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yoyoman
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Re: How to improve my friction drive situation?

Post by yoyoman » Apr 13, 2018 2:49 am

I scrapped the 3d print idea and went back to just bolting the commuter booster (CB) mount to the kickstand plate. To get clearance from an annoying lip on the plate, I used a destroyed 3d print as a spacer. The soft plastic is definitely not a forever solution.

I didn't realize how much smaller the 50mm motor is before I bought it. It helps a little in terms of putting more distance between the pivot and the wheel, and it's SO MUCH lighter too! To center the motor, for now I'm testing with some 1/2" spacers. These too need to be replaced with something more solid. I left about a 1mm gap between the motor and the wheel.

I temporarily jammed the battery, ESC, brain box, etc into a small bag that sits at the base of the seatpost.

Overall, for now it's still somewhat stealthy, and not too bad at 26.8lb. My alternate solution folding bike, a single speed Dahon Boardwalk, certainly weighs more than that without the e-bike extras.

No load on the stand, everything seems to do ok. Sometimes it doesn't catch the wheel right away, but it didn't seem to take long before it did when using the one click + hold setting. The two click + hold setting seemed to bite right away. All the tests will change with a load and also when I reconfigure the brain box for my 20" wheel vs the current 700mm wheel setting.

It's too late for a road test, so I'll try it out this weekend.
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SlowCo
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Re: How to improve my friction drive situation?

Post by SlowCo » Apr 13, 2018 3:15 am

The geometry of your pivot point, motor and contact to the tire are still wrong. The pivot has to move forward so the motor can "climb" the tire better. See the posts from Chalo and SpinningMagnets under your first post.

yoyoman
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Re: How to improve my friction drive situation?

Post by yoyoman » Apr 13, 2018 4:11 am

It's definitely not the optimal solution yet, but I wanted to see how a 13mm smaller motor would work out. Without creating a new mount system, I wanted to to see my limitations. Right now, the CB seat post mount is almost as far back as it can go without hitting the chainring. For whatever distance I push things back, I will have to also drop it an equal amount to clear the chainring.

Losing more than a pound by going to a smaller motor also helps in getting the initial bite to take place.

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spinningmagnets
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Re: How to improve my friction drive situation?

Post by spinningmagnets » Apr 13, 2018 4:41 am

You might want to consider designing some type of cargo rack above the rear tire, and then mounting the motor underneath it. Doing that might provide more options, since you are very limited by trying to squeeze the assembly into that particular location...

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