Solution for rainy condition usage of friction drive

[loopernow]

I have been lurking these forums reading about friction drives. I came across a video on YouTube by a guy who built his own rollered friction drive and he has a solution for riding in wet weather that I've never seen before, and have not seen in these forums either, so I thought I would share. It seems a more permanent and less damaging solution that the sandpaper route.

He writes in his video notes that the roller is " studded with 50 self-tapping screws" -- so it ends up with a bunch of raised knobs, like a mountain bike tire. He comments onscreen at 3:20 in the video that "this roller grips even when the tyre is wet."

Good view of the roller:
https://www.youtube.com/watch?v=6JkpryxaR8E&t=1m3s

So not something I can personally attest to but still seems like good info!

 

[crossbreak]

Interesting. Thanks for sharing. Still not much different to the Metall roller with teeth like a gearwheel. Saw ones that used helical gears recently..did not shoot a photo though. Still there is no way it wont eat your tire quickly IMOE

 

[fiddler]

I'd have to call BS on those little round headed screws having more friction than the smooth metal drum they are screwed into. They have far less effective surface area touching the wheel at any one time and friction is all about surface area and material coefficient of friction. A rubber coated drum would do the trick but at the expense of having to replace it fairly often.

 

[loopernow]

I wonder if the reason it works in wet is not the knobs but rather that he has manual control over how close the roller is to the tire. He has the whole motor/roller rig connected to a cable-and-lever attached to his handle bar so he can engage/disengage the drive.

 

[crossbreak]

I wonder if the reason it works in wet is not the knobs but rather that he has manual control over how close the roller is to the tire. He has the whole motor/roller rig connected to a cable-and-lever attached to his handle bar so he can engage/disengage the drive.

this is absolutely necessary.

Rubber did not work that bad. Still a simple chain drive works so much better.

The "Prick"
https://endless-sphere.com/forums/viewtopic.php?f=28&t=50107&start=50#p752023

Here is a rail excavator with non-helical gear roller. Not so common here.. the ones i see around here all use helical gear rollers.
Again you can see how much the suffers

 

[gogo]

I'd have to call BS on those little round headed screws having more friction than the smooth metal drum they are screwed into. They have far less effective surface area touching the wheel at any one time and friction is all about surface area and material coefficient of friction. A rubber coated drum would do the trick but at the expense of having to replace it fairly often.

Don't forget about the increased normal force on the smaller effective contact area. I'd guess the screws work because they force the water away from their contact area.

 

[loopernow]

Rubber did not work that bad. Still a simple chain drive works so much better.

The "Prick"
https://endless-sphere.com/forums/viewtopic.php?f=28&t=50107&start=50#p752023

Very cool.

I was at first going to build my own friction drive but I really do not have much experience in this area; I would prefer to pay. Perhaps the Go-E system will be available in the US soon. The Gboost system is available now & is affordable, like the Go-E. Both of these are mounted in the same place as yours was, and the Gboost has a manual lever for applying the motor to the tire. However, I cannot find any documentation for the Gboost regarding engine specifics, battery specifics, can the motor be disengaged/engaged while peddling, etc. No reviews online. I finally found an email for them so maybe they will email me back.

I have read that hub drives feel something like a very broad tire or underinflated or flat tire when pedaling without power. Extra resistance of perhaps 5-20%, I read someone saying as a purely subjective explanation. You mention a chain drive--do you mean mid-drive?

The appeal for me of the friction drive is that it is light and does not add appreciable extra resistance when pedaling without power. How does a mid-drive (if that's what you meant by chain drive) compare to a friction drive or hub drive in terms of efficiency when pedaling without power?

 

[goa604]

I'd have to call BS on those little round headed screws having more friction than the smooth metal drum they are screwed into. They have far less effective surface area touching the wheel at any one time and friction is all about surface area and material coefficient of friction. A rubber coated drum would do the trick but at the expense of having to replace it fairly often.

Oh god and i have to call BS on your science because friction has absolutely nothing to do with surface area. You got the coefficient of friction right, other factor is force exerted by each surface on the other.

 

[turbo1889]

I'd have to call BS on those little round headed screws having more friction than the smooth metal drum they are screwed into. They have far less effective surface area touching the wheel at any one time and friction is all about surface area and material coefficient of friction. A rubber coated drum would do the trick but at the expense of having to replace it fairly often.

Oh god and i have to call BS on your science because friction has absolutely nothing to do with surface area. You got the coefficient of friction right, other factor is force exerted by each surface on the other.

Yes, and No.

High school and 100 maybe 200 level college course physics and engineering is indeed calculated simply by the coefficient of friction and the force.

BUT ----- At a higher level of understanding one finds out that things are a whole lot more complicated then that simple calculation which works fairly well for most situations but truly is an oversimplification. Its kind of like Newtonian Physics vs. Relativistic Physics. Newtons simple equations work well for most applications but not for all and sometimes you have to use Relativistic Physics in some applications and even then it has been proven that isn't the whole answer and doesn't always give a perfect answer.

Contact surface area in some situations does indeed matter but not always with the same result one would expect.

 

[goa604]

I dont believe this case is an exception. It isnt even worth going this route of discussion. One thing when someone says something completely wrong and its other when we start talking about
fundamental building blocks of forces which in this case dont matter at all for end result.

 

[whatever]

many moons ago I started into ebikes with friction drive, best solution is to not use friction drive, there is no need.
My experience was rapid tyre wear, though it works, there are hub motors these days and they are relatively cheap.
I think your wasting time using friction drive.

 

[Punx0r]

I don't think a few screw heads digging into rubber is comparable to smooth rubber-on-rubber. The later is solely dependent on friction whereas the screws will transmit a significant fraction of the force by mechanical locking as the edges of the screw heads dig into the rubber (and consequently chew up the tyre over time).

I do agree that ignoring surface area when considering friction is overly-simplistic. IIRC the coefficient is often not constant, hence a tendency towards larger and larger vehicle tyres for transmitting greater force to the road surface.

 

[Hillhater]

There is a difference between friction and mechanical grip.