How to make a tight no slip friction drive contact

[Boyntonstu]

After my 50 grit roller:

Wore my mountain tire nubs off when attempting to jump onto the tire:

I decided to force the roller against the tire.

I used a simple trick.

I deflated the tire a bit and shoved the tire against the roller.

Pumped it up and no slippage.

My intention is to ride pedal assist and if the battery goes dead, I will move the wheel away from the roller the make for easy pedaling.

 

[spinningmagnets]

I had my best luck using a beach cruiser tire with a relatively flat tread, and a fairly squared off profile.

 

[Boyntonstu]

I had my best luck using a beach cruiser tire with a relatively flat tread, and a fairly squared off profile.

My failed jumper test sanded in the flat profile.

What I would like is quick rear mount hardware for the 20" mountain bike tires in order to easily disengage the roller without tools.

I would also like a slightly larger chain ring and fewer teeth in the rear for 16-17 pedal capability. 15 is my comfort zone.

I used contact cement and epoxy, thanks to you.

It is really holding up well.

 

[Hillhater]

Most friction designs employ a torque related variable load for the roller to tire , rather than a fixed roller .
you should not expect a friction drive to work reliably ( or efficiently) on a lumpy threaded MTB tyre....that is a very extreme application of Friction Drive.

 

[Boyntonstu]

Most friction designs employ a torque related variable load for the roller to tire , rather than a fixed roller .
you should not expect a friction drive to work reliably ( or efficiently) on a lumpy threaded MTB tyre....that is a very extreme application of Friction Drive.

This 1.5 hp friction drive on my Honda bike does not slip and it does not wear the lumpy MTB tire.

[youtube]mvrOu4hw8f0[/youtube]

 

[Hillhater]

Different roller surface
Centrifugal clutch
Excessive roller pressure
..and how efficient do you think that is ?.
Why mess with MTB tyres when you are not going off road ?

 

[Chalo]

Knobbies and friction roller drives don't go together. If you really need knobbies (most people don't, even most who think they do), then you really need another kind of drive.

 

[tomjasz]

I had my best luck using a beach cruiser tire with a relatively flat tread, and a fairly squared off profile.

Do you still ride that bike. I remain fascinated by friction drives.

 

[Boyntonstu]

Different roller surface Agree, steel vs sandpaper
Centrifugal clutch - Needed for gas, not necessary with electric.
Excessive roller pressure - What is excessive? I tightened it until it would not slip. There is no obvious depression.
..and how efficient do you think that is ?. Very. I have used this method for six years with the same tire. On gas it gets 150 mpg.
Why mess with MTB tyres when you are not going off road ? Because the pink bike cost $12.50 at the Thrift Store.

 

[Boyntonstu]

I had my best luck using a beach cruiser tire with a relatively flat tread, and a fairly squared off profile.

Do you still ride that bike. I remain fascinated by friction drives.

Me too!

There are many successful friction drive builds out there.

One advantage is the drive will give the same speed for any size wheel,

No gearing required and its extra weight and drive loss.

 

[spinningmagnets]

Do you still ride that bike. I remain fascinated by friction drives

The link to my friction drive is in my sig. I havent ridden it in several years. Its funny about FDs, they are less loaded on a larger diameter wheel, where a hubmotor is less loaded on a smaller diameter wheel (leverage?). I built it the way I did to show it is doable with just a hacksaw, a vice , and a cordless drill. The design I settled on was from EVTodd.

To the OP, since the shaft is loaded from the side, the shaft is likely to break some day. I believe that the motor shaft (whether you use the motor shell as the roller, or a separate roller) needs to be suppoorted on both ends.

 

[Boyntonstu]

Do you still ride that bike. I remain fascinated by friction drives

The link to my friction drive is in my sig. I havent ridden it in several years. Its funny about FDs, they are less loaded on a larger diameter wheel, where a hubmotor is less loaded on a smaller diameter wheel (leverage?). I built it the way I did to show it is doable with just a hacksaw, a vice , and a cordless drill. The design I settled on was from EVTodd.

To the OP, since the shaft is loaded from the side, the shaft is likely to break some day. I believe that the motor shaft (whether you use the motor shell as the roller, or a separate roller) needs to be suppoorted on both ends.

If that were the case, bench grinders would frequently fail.

With respect to breakage, the shear strength of a 1/4" bolt:

Capability in shear = 75,000 lbs / in2 x .0491 in2 = 3683 lbs

Is my 2 bearing motor ever going to see more than a ton of shear?

I build it cheap and lightweight and fix it i it bends or breaks.

 

[Hillhater]

Bench grinders are purpose designed with large shafts and bearings widely spaced to withstand the relatively light radial loads.
RC motors are not designed with radial loading in mind, only axial loads from prop thrust.
Any axial load on the shaft acts as a cyclic fatigue stress due to the rotation.
Shear loading only happens if the motor is stationary.

 

[Boyntonstu]

Bench grinders are purpose designed with large shafts and bearings widely spaced to withstand the relatively light radial loads.
RC motors are not designed with radial loading in mind, only axial loads from prop thrust.
Any axial load on the shaft acts as a cyclic fatigue stress due to the rotation.
Shear loading only happens if the motor is stationary.

Have you ever seen or heard of a bent outrunner motor shaft used as a friction drive?

A piece of steel does not know how it is to be used,

If the application force is orders of magnitude below its minimum breaking point, the rotating shaft does not feel a thing.

And if you got 50,000 miles out of it, it would not be as costly to replace as the costs in building a double bearing drive.

 

[Hillhater]

Bent shafts,?...no...not what I was suggesting
But shafts that have failed from fatigue, yes !
If an out runner is mounted using the stator end only, any side loading will generate a bending moment on the shaft which can cause stress risers at imperfections in the shaft ( circlip groves have been typical)
Motor rotation converts those into stress reversals and hence potential fatigue failures .
I doesn't need a high level of stress when combined with rotation and constant high frequency reversals .
Further agrivated by the quality of steel and machining on some of those motors
The problem is eliminated if you support the shaft at both ends.

 

[Boyntonstu]

Bent shafts,?...no...not what I was suggesting
But shafts that have failed from fatigue, yes !
If an out runner is mounted using the stator end only, any side loading will generate a bending moment on the shaft which can cause stress risers at imperfections in the shaft ( circling groves have been typical)
Motor rotation converts those into stress reversals and hence potential fatigue failures .
I doesn't need a high level of stress when combined with rotation and constant high frequency reversals .
Further agrivated by the quality of steel and machining on some of those motors
The problem is eliminated if you support the shaft at both ends.

constant high frequency reversals .

What type of shafts, size, and load have failed from fatigue?

"constant high frequency reversals" In my build the motor always rotates in one direction.

http://www.maintenancetechnology.com/2012/07/failure-analysis-of-machine-shafts/

 

[Hillhater]

"constant high frequency reversals" In my build the motor always rotates in one direction.

http://www.maintenancetechnology.com/2012/07/failure-analysis-of-machine-shafts/

....I think you need to read up on this a bit more.
A good start would be your own link

Fatigue failures
Fatigue is caused by cyclical stresses, and the forces that cause fatigue failures are substantially less than those that would cause plastic deformation.....

 

[Boyntonstu]

"constant high frequency reversals" In my build the motor always rotates in one direction.

http://www.maintenancetechnology.com/2012/07/failure-analysis-of-machine-shafts/

....I think you need to read up on this a bit more.
A good start would be your own link

Fatigue failures
Fatigue is caused by cyclical stresses, and the forces that cause fatigue failures are substantially less than those that would cause plastic deformation.....

All of this theory is good. The article mentions shafts failing at 200 HP.

A rotating 1.25" torque arm pressed with less than 10 pounds force against a rubber tire and under 3 hp, I am not too concerned.

I assume that there are at least 100 outrunner friction bikes operating out there, several for a few years.

I follow several forums and Youtube videos. When one of them fails, I will post it here. I would like to see if any fails due to fatigue.