Good materials for maximum friction?

[akio123008]

I don't even know where the hell to post this, quite possibly on some other forum entirely, but I only have an account here, so here we go.

 

I have a home made electric bike that uses a friction based drive system. It's a BLDC motor placed over the front wheel, which drives the wheel directly by rolling on it. On the outside of the motor it's important to use a material that provides good traction on the tyre, to prevent slipping. On the other hand, materials that have too much traction, tend to ruin the tyre too quickly.

 

For instance, I've tried neoprene, which has OK traction and goes easy on the tyre (no visible wear after 500km easily), but at higher power levels and in wet conditions, it completely loses grip on the tyre.

Right now I'm using sanding cloth (the kind of stuff you put on a belt sander) which has extremely good traction, even in the wet, but just eats up the tyre. On this set of tyres, I've done about 2000km, and the rear tyre shows basically no wear, whereas the front tyre has lost about 1.5mm already.

 

So basically, I'm looking for suggestions on what sort of materials may strike a better balance between tyre wear and traction. Any idea is welcome!

 

[Kilrah]

Tread from another tire?

[akio123008]

14 minutes ago, Kilrah said:

Tread from another tire?

I've tried some kinds of rubber before but actual tread from a tyre might be grippier. Also the fact that it's got profile on it may help a lot shedding water in wet conditions so it could be a win. Maybe I could even get an RC car tyre that fits round the motor perfectly. 

[LWM723]

Skateboard tires?

[akio123008]

2 hours ago, LWM723 said:

Skateboard tires?

That's a good idea too, although many of them appear to be oversized for my motor, which is has a diameter of about 70mm.

[Lafy]

Can you press the motor against the wheel with more tension? A bike trainer typically has a steel or aluminum shaft that grips the tire with very high pressure letting the tire provide all the traction. You could also consider rotating the motor 90 degrees and clamping down on the braking surface

[Kadzo]

Any polyurethane rubber should work, so you can order a custom alu wheel and buy suitable polyurethane rubber to place over it.

[akio123008]

4 hours ago, Lafy said:

Can you press the motor against the wheel with more tension?

Maybe sligthly more, but not much. I use a spring to push the motor on the wheel, because it allows me to disengage the motor from the wheel by operating a brake lever on the handlebars. (sort of a clutch mechanism). I don't want to sacrifice this ability for various reasons, so bolting down the motor isn't really an option, although I could probably find a tighter spring. 

 

4 hours ago, Lafy said:

You could also consider rotating the motor 90 degrees and clamping down on the braking surface

This is difficult as the wheel doesn't have a good braking surface, because it uses disc brakes. It also isn't very efficient because due to the curvature of the wheel you'd effectively be slipping all the time. Although it may not be that bad on bigger wheels, my wheels aren't that big (26 inch) so that wouldn't be ideal.

 

3 hours ago, Kadzo said:

Any polyurethane rubber should work, so you can order a custom alu wheel and buy suitable polyurethane rubber to place over it.

This is in line with the other things I've heard, (another tyre, skateboard tyre) rubber does seem like a good idea, but I do think it needs some kind of profile to work in wet conditions. I've tried neoprene before which worked pretty well in dry weather but in the wet it just completely sucked. Perhaps if the neoprene wouldn't have been smooth but had ridges in it, it would have worked.

 

I think I'm going to give it a shot with some inner tube rubber I have laying around, and manually cut some profile in to see how it does in the wet, before I go out and buy a miniature tyre.

 

I also fortunately don't need a roller, the motor itself is the roller, I just need something to cover it with. 

[Kadzo]

24 minutes ago, akio123008 said:

I also fortunately don't need a roller, the motor itself is the roller, I just need something to cover it with. 

Do you have any pictures of at least a model so i can see maybe i can figure something out after i see it.

[akio123008]

This is an image of the current version with the sand cloth. It has the best grip yet, but consumes the tyre (this image is from a year ago when the tyre was still new)

[Kadzo]

 

33 minutes ago, akio123008 said:

 

This is an image of the current version with the sand cloth. It has the best grip yet, but consumes the tyre (this image is from a year ago when the tyre was still new)

Is the roller removable? if it is and it should be for maintenance you can send to a company that does polyurethane castings, we use similar stuff in my plant (but we work with steel). 

Poly rubber should't be slippery when wet silicone on the other hand will. In this case yea you will have excellent traction but its sand paper made to sand down stuff. 

 

[akio123008]

39 minutes ago, Kadzo said:

Is the roller removable? if it is and it should be for maintenance you can send to a company that does polyurethane castings

It is removable, sending it to a company for custom treatment may be a bit expensive for this project though. I'd prefer something I can apply myself.  

 

41 minutes ago, Kadzo said:

In this case yea you will have excellent traction but its sand paper made to sand down stuff. 

It works like a charm haha, but the tyre wear is problematic indeed. You can manage the slipping by carefully adjusting throttle and minimise wear, but constantly managing the throttle to save the tyre ruins the fun riding the thing. 

[Kadzo]

14 minutes ago, akio123008 said:

It is removable, sending it to a company for custom treatment may be a bit expensive for this project though. I'd prefer something I can apply myself.  

 

Actually you might be surprised, here it costs usually around 10-15 EUR + shipping per wheel. So i suggest you ask around that is the norm in the industries.

 

16 minutes ago, akio123008 said:

It works like a charm haha, but the tyre wear is problematic indeed. You can manage the slipping by carefully adjusting throttle and minimise wear, but constantly managing the throttle to save the tyre ruins the fun riding the thing. 

Ah yea, if there is no fun in the ride why the hassle   

[W-L]

On 4/5/2021 at 6:38 AM, akio123008 said:

This is an image of the current version with the sand cloth. It has the best grip yet, but consumes the tyre (this image is from a year ago when the tyre was still new)

That photo helps, try using something like SBR rubber it's relatively good for wear resistance and when applied with a flexible contact cement adhesive should hold up decently well. For an application like that you will want the drive roller to be spring loaded to allow it some play when the tire flexes and changes shape under load and at speed. Ideally if you can get something like a molded rubber roller that has a thick wall that would work well. You should be able to source stuff like this at an plastics/rubber supplier. 

https://www.mcmaster.com/rollers/abrasion-resistant-rollers/

https://www.mcmaster.com/rollers/abrasion-resistant-drive-rollers/

 

Abrasion Resistant Rubber:

https://www.mcmaster.com/rubber/abrasion-resistant-polyurethane-rubber-sheets-bars-and-strips/

https://www.mcmaster.com/rubber/economical-abrasion-resistant-sbr-rubber-sheets-and-strips/

 

[akio123008]

20 minutes ago, W-L said:

For an application like that you will want the drive roller to be spring loaded

That whole assembly is actually spring loaded, the spring is behind the white terminal block clamped on the cable in the image.

 

Since most suggestions in this thread came down to (several types of) rubber, I replaced the sanding cloth with some rubber cut from an inner tube, to give it a test. It's working surprisingly well. Even though I haven't done enough testing to know what the wear's like, a first look after 50km or so revealed no wear at all on both the tyre and the roller.

 

The specific types of rubber and even fully assembled products (tyre) you guys suggested may work even better than the inner tube, so I might give those a go too at some point, but I have to say the inner tube is doing really well, so I think I'll be using that for the time being.

 

[W-L]

15 hours ago, akio123008 said:

That whole assembly is actually spring loaded, the spring is behind the white terminal block clamped on the cable in the image.

 

Since most suggestions in this thread came down to (several types of) rubber, I replaced the sanding cloth with some rubber cut from an inner tube, to give it a test. It's working surprisingly well. Even though I haven't done enough testing to know what the wear's like, a first look after 50km or so revealed no wear at all on both the tyre and the roller.

 

The specific types of rubber and even fully assembled products (tyre) you guys suggested may work even better than the inner tube, so I might give those a go too at some point, but I have to say the inner tube is doing really well, so I think I'll be using that for the time being.

 

Hey if it lasts for more than a season of riding and all you need to do is cut up some more inner tube to refresh it then it may be more affordable than getting a premade wheel or more specialized material in that case. Just needs a bit of seasonal maintenance is all  

[artuc]

Is there not a better drive method where you could have say a belt and pulley/cog and chain straight to the wheel ?

 

 

[akio123008]

4 hours ago, artuc said:

Is there not a better drive method where you could have say a belt and pulley/cog and chain straight to the wheel ?

Technically there is but the options are limited;

The tail isn't wide enough for a Tom Stanton style belt-drive or chain drive system and I don't have a gearbox aggressive enough for a mid-drive system, so that rules out rear-wheel drive or mid drive.

 

What remains is front wheel drive then, I actually used to have chain drive system to a sprocket on the front wheel, but after the chain running off a few times, I decided to stop using that system, as I realised any kind of belt/chain whatever next to your front wheel is basically a recipe for disaster. If it ever runs off at speed you get thrown over the bars.

 

Only other option would be to buy hub motors, but that's boring, I may as well buy an off the shelf ebike then.