Anyone Tried Friction Drive Motors?

[tomtom123]

I was just checking out some bicycle gas engine videos and came upon this thing called friction drive? There are kits out there like the Dax driction drive that uses gas engines and some other ones that uses eletric motor like the Rubbee ($1,000+). IMO, Friction drives seems kind of stupid. for one, the cost does not seem much lower than ebike kits or regular chinese gas engine kits. For gas powered friction drive , you need to get the friction drive kit and the engine, which is pointless since you can just get a cheap gas engine that runs through sprockets and crankset. ALSO, They seem to frock up your tires FAST. Seems not worth it to me but i'm just wondering if anyone tried it before and their opinions on it. Though i have to say in terms of engineering, the Rubbee is very impressive, it's a nice and sleek all in one package , but for $1K+ and the limited power it has, it's not worth it.

 

[EVTodd]

Your best bet is to do a search for friction drive. LOTS of information on here about them.

Rubbee is crazy overpriced for what it is. I also wouldn't call it a great engineering feat. They did a good job making it pretty but I don't see anything great other than that.

Friction drive can be a nice cheap and lightweight assist on a bike. I built one for myself based on an outrunner motor for $330 back in 2009. It does around 28-30 mph on 36 volts and climbs hills very well.

I've used it as my main work transportation for quite a while and have thousands of miles on it.

Tire wear issues are exaggerated and if done correctly it's really not an issue.

Only real drawback to friction drive is that they suck in the wet.

I couldn't be happier with mine. I keep thinking about switching to something else like mid drive but I don't see the point quite yet although the Bafangs might be an option once prices come down to earth.

 

[tomtom123]

Your best bet is to do a search for friction drive. LOTS of information on here about them.

Rubbee is crazy overpriced for what it is. I also wouldn't call it a great engineering feat. They did a good job making it pretty but I don't see anything great other than that.

Friction drive can be a nice cheap and lightweight assist on a bike. I built one for myself based on an outrunner motor for $330 back in 2009. It does around 28-30 mph on 36 volts and climbs hills very well.

I've used it as my main work transportation for quite a while and have thousands of miles on it.

Tire wear issues are exaggerated and if done correctly it's really not an issue.

Only real drawback to friction drive is that they suck in the wet.

I couldn't be happier with mine. I keep thinking about switching to something else like mid drive but I don't see the point quite yet although the Bafangs might be an option once prices come down to earth.

What Type of Drive roller you use? any links to it? i've seen some some rubber like ones but many i've seen use metal with rough surfaces, no way those metal ones don't wear the tire....

 

[spinningmagnets]

Here's the friction drive index thread:

http://endless-sphere.com/forums/viewtopic.php?f=28&t=14403

 

[EVTodd]

What Type of Drive roller you use? any links to it? i've seen some some rubber like ones but many i've seen use metal with rough surfaces, no way those metal ones don't wear the tire....

I use a case hardened, kurled steel roller. Think about it for a second. If it's not slipping why would it wear the tire any faster than the road does?

Most of the friction drives people have done here, including mine, use some kind of variable pressure system. Most swing on to the tire. My motor mount automatically sides further into the tire increasing pressure as you accelerate or go up a steep hill virtually eliminating slippage which is what would cause tire wear.

I've only replaced my tires once since 2009 and that was front and back.

If you look at the Tidalforce link in my signature you'll see pictures of my setup.

 

[Hillhater]

IMO, Friction drives seems kind of stupid. ...
Seems not worth it to me but i'm just wondering if anyone tried it before and their opinions on it. .

A smarter guy might have tried a quick search and a little reading before posting up a thread like this. !
A simple quick search using "Friction Drive" pulls up over 6000 initial results.
Its like walking into a bar and yelling out "Has anyone tried drinking beer" ... !

 

[tomtom123]

What Type of Drive roller you use? any links to it? i've seen some some rubber like ones but many i've seen use metal with rough surfaces, no way those metal ones don't wear the tire....

I use a case hardened, kurled steel roller. Think about it for a second. If it's not slipping why would it wear the tire any faster than the road does?

Most of the friction drives people have done here, including mine, use some kind of variable pressure system. Most swing on to the tire. My motor mount automatically sides further into the tire increasing pressure as you accelerate or go up a steep hill virtually eliminating slippage which is what would cause tire wear.

I've only replaced my tires once since 2009 and that was front and back.

If you look at the Tidalforce link in my signature you'll see pictures of my setup.

Hey i got one more question since you've already made a friction motor, it's faster to ask rather than search and read the many pages online just for this one answer. I noticed that when the motor is not running, it's not in contact with the wheel, thus not adding friction and allowing you to pedal easily with the motor off. But when the motor turns on, the arm moves near the wheel. What causes the arm to move near the wheel when engaged and away from the wheel when disengaged? does the torque of the motor moving cause the arm to move in that direction and is there a spring mechanism to help with the movement?

thanks, that was my last question....reallly... :lol:

 

[Spicerack]

Have a look at adrian_sm and his setup: http://www.commuterbooster.com/

 

[adrian_sm]

Read this link for how my design works.
http://www.commuterbooster.com/how-does-it-work

My take on friction drives in general (but based on my design):

The good:
- they are great in dry weather
- at modest power levels <1000w they do not cause any additional wear to your tires (smooth surface contacting tire)
- they are very light weight
- they have no additional drag when not in use
- they can be installed without replacing any of the high quality components on your bike

The bad:
- for them to work in the wet you typically need a rough contact surface with the tire, which will create additional tire wear
- they are limited in how well the can work in the wet
- they are noisier than a hub motor
- they are more exposed to the elements, so will not be as maintenance free as a hub motor
- they don't suit all bikes types, due to physically how they attach
- they don't like knobbly tires
- they can get in the way of mud guards

 

[spinningmagnets]

What causes the arm to move near the wheel when engaged

If you pick up a high-powered drill and pull the trigger on all the way suddenly, you will feel the drill try to "twist" in your hand. That effect provides the initial push to swing the motor outwards. Once the spinning motor touches the tire, it's rotation pulls it deeper onto the tread for as long as it's powered.

Once it is de-energized, the forward motion of the tire and a small spring on the mount will pull the motor up and away from the tire so they are not touching. It is an ingenious system. Keplers and Adrians drives are the smallest and lightest drives possible to attach to a bike. They are proven to work. They are most often added to a light road bike, and that is a perfect match for it.

If you skimmed through the index thread, you will see that Todd developed a drive where the roller is separate from the motor. I copied his drive because I felt that his design provided the most design options for experimentation, and I am very happy with the results. The roller does touch the tire, but it freewheels on one-way clutch bearings. In theory, there is some added drag (when the motor is off), but I honestly can't feel the difference when pedaling...with or without the drive on the bike.

I had been using a round-profile of tire with a soft compound (seen in the pic below). It experienced more rapid wear and slippage at high-power than I felt was acceptable. Todd suggested I switch to a square profile tire with a harder compound of rubber, such as a beach-cruiser tire. This tripled the roller contact with the tread. I have no more slippage and the tire has not worn out so far in the two years I have had it.

The smaller one-inch diameter roller using 36V (driven by a 63mm diameter motor) will climb the steepest hill around here without getting too hot.

 

[MadRhino]

The good:
- they are great in dry weather
- at modest power levels <1000w they do not cause any additional wear to your tires (smooth surface contacting tire)
- they are very light weight
- they have no additional drag when not in use
- they can be installed without replacing any of the high quality components on your bike

I would add two of the most important advantages of a friction drive:

- It is very light weight
- It can be swapped to any other bike in a very short time

Friction drive has so many advantages, it deserves some further development.

 

[spinningmagnets]

The key element that tipped the balance enough for me to actually make one was...the fact that when coupled with a 'lever style' seat-post clamp, I don't need any tools to pop the seat and the drive/controller/battery off, and carry it into the house for charging. At the time I was living on the third story of an apartment/flat, and the bike had to be locked up outside.

Unplug throttle-wire, unlatch seat-post clamp, lift and carry. Cargo-rack and battery not shown in the pic below, but I believe it shows my point.

 

[tomtom123]

What causes the arm to move near the wheel when engaged

If you pick up a high-powered drill and pull the trigger on all the way suddenly, you will feel the drill try to "twist" in your hand. That effect provides the initial push to swing the motor outwards. Once the spinning motor touches the tire, it's rotation pulls it deeper onto the tread for as long as it's powered.

Once it is de-energized, the forward motion of the tire and a small spring on the mount will pull the motor up and away from the tire so they are not touching. It is an ingenious system. Keplers and Adrians drives are the smallest and lightest drives possible to attach to a bike. They are proven to work. They are most often added to a light road bike, and that is a perfect match for it.

Thanks for the explanation, yea it's pretty smart . I'll probably make one since it's cheap and just for the hell of it. Only expensive part is getting the machines and tools and since i live in an NYC apartment with no garage, might be a little harder to set up a working environment.

 

[Chalo]

I use a case hardened, kurled steel roller. Think about it for a second. If it's not slipping why would it wear the tire any faster than the road does?

Because the road doesn't have a <1" radius.

Time has already proven that friction rollers eat tires. Implement them well and the wear rate can be tolerable, but at best it's a lot faster than normal.

One of the improvements the Rubbee appears to bring to the game is a deep-grooved roller made out of an elastomeric material. By widening the contact area and letting the roller's elasticity help reconcile shearing movements against the tire, it might substantially reduce tire wear. Or it might just transfer that wear to an expensive roller wheel. We'll see.

 

[EVTodd]

I use a case hardened, kurled steel roller. Think about it for a second. If it's not slipping why would it wear the tire any faster than the road does?

Because the road doesn't have a <1" radius.

Time has already proven that friction rollers eat tires. Implement them well and the wear rate can be tolerable, but at best it's a lot faster than normal.

One of the improvements the Rubbee appears to bring to the game is a deep-grooved roller made out of an elastomeric material. By widening the contact area and letting the roller's elasticity help reconcile shearing movements against the tire, it might substantially reduce tire wear. Or it might just transfer that wear to an expensive roller wheel. We'll see.

Lol. Well, I'm not going to argue about it (read the friction drive threads since you obviously don't understand) but I must have a magical bike (and tires, and roller) because that's not what I've found at all. I think you're basing your "facts" on friction drives that don't use variable pressure.

You should buy a rubbee with it's "special" urethane roller for $1000 and report back with your findings. I'd like to see rubbee running the same voltage I am and see if that high-tech roller doesn't slip since it doesn't appear to have variable pressure.

 

[tomtom123]

I use a case hardened, kurled steel roller. Think about it for a second. If it's not slipping why would it wear the tire any faster than the road does?

Because the road doesn't have a <1" radius.

Time has already proven that friction rollers eat tires. Implement them well and the wear rate can be tolerable, but at best it's a lot faster than normal.

One of the improvements the Rubbee appears to bring to the game is a deep-grooved roller made out of an elastomeric material. By widening the contact area and letting the roller's elasticity help reconcile shearing movements against the tire, it might substantially reduce tire wear. Or it might just transfer that wear to an expensive roller wheel. We'll see.

Lol. Well, I'm not going to argue about it (read the friction drive threads since you obviously don't understand) but I must have a magical bike (and tires, and roller) because that's not what I've found at all. I think you're basing your "facts" on friction drives that don't use variable pressure.

You should buy a rubbee with it's "special" urethane roller for $1000 and report back with your findings. I'd like to see rubbee running the same voltage I am and see if that high-tech roller doesn't slip since it doesn't appear to have variable pressure.

They use a PU concave roller, you can get some at ALibaba and test it out

 

[EVTodd]

They use a PU concave roller, you can get some at ALibaba and test it out

I suppose.

Really though, this discussion has taken place so many times. I need to stop getting sucked into it every time! lol

Just be sure to do a bunch of reading. There are some great friction drive designs here on the sphere. Decide which style would work best for you and have fun with it. Just don't let all the negative nannies here tell you friction drive doesn't work. Over the years there have been a lot of crap designs that probably do wear tires out and that's why friction drive gets such a bad rap.

 

[adrian_sm]

Just don't let all the negative nannies here tell you friction drive doesn't work. Over the years there have been a lot of crap designs that probably do wear tires out and that's why friction drive gets such a bad rap.

Totally agree.

Time has already proven that friction rollers eat tires. Implement them well and the wear rate can be tolerable, but at best it's a lot faster than normal.

BULLSHIT. In fact quite the opposite. Time has proven that the wear rate of a well designed friction drive is so minimal it is no longer an issue. This is based on various designs and 10,000's kms of testing.

Please don't state your out dated opinions as fact. It confuses the topic.