Friction Drive Plan (a new twist)

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John in CR

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I finally decided how to put my 2 wheelchair motors to good use. I also have 2 EV Warrior friction drives that have some kind of one way freewheel bearing. I need to fabricate a 3.4" diameter friction wheel that will get me right at 10mph per 1000rpm.

Here's the twist: I'll slide both EV Warrior friction wheels into the new larger friction wheel. This will give me the ability to use either or both motors at the same time. If one is idle, it's shaft will freewheel inside the bearing. This should give me plenty of hill climbing torque and acceleration, along with good cruising efficiency in a weight balanced drivetrain that is easy to transfer to any bike. While the extra motor does add an extra 7lbs and I will need 2 controllers and throttles, I think it will give me a very reliable and quiet rig with plenty of oomph.

I don't have a clue as to how much friction drive tension to use, so I want to make that easily adjustable. Then I can run it at the lowest friction I can without slippage, and tighten it up if necessary for the conditions (wet roads, etc.). Also, I believe that being able to alternate which 24v motor is in use that I'll be able to over-volt them to 36v without concern about durability.

From what I've been able to find through searches here in the forum, I'm surprised friction drives aren't more common. The typical issues brought up regarding tire wear and slippage when wet are contrary to what is said by those who have used friction drives for years. Instead it seems to be an efficient and quiet drive system. I love the simplicity and lack of chains and gears. If I make the drive wheel removable and make a few different diameters, then I can even easily test different gearing ratios.

This will be a test bed for a dual RC motor rig using a similar easy setup with cheap lightweight yet powerful motors. I think the larger diameter drive wheel will be a benefit. I know friction drive is old school, but if anyone sees anything that I'm not considering, I'm all ears.

John
 
Yes, friction drive has been used successfully for years. Simplicity is one of the main strong points. Forget about using it in wet weather though.

It may help if the pivot for the motor assembly is located in such a way that increasing load results in increasing roller pressure. The amount of pressure is critical to proper operation. Some kind of fine adjustment is generally needed.

Many systems have a mechanism to lift the drive wheel when you want freewheeling.

The inertia of the motor when you go over bumps can cause changes in roller pressure.

The best drive roller material seems to be something that resembles a grinding wheel or sandpaper. Knurled metal is generally too smooth.

It might be possible to use a conical drive roller and vary the effective diameter on the fly. This would be like a CVT and allow downshifting for hills.
 
My impression is that FD's get crudded-up... any squirrel guts you run over go onto your drive.

:(
 
TylerDurden said:
My impression is that FD's get crudded-up... any squirrel guts you run over go onto your drive.
:(
Click to expand...

Getting crudded up is the only thing stopping me from going searching for 3-3.5" diameter actual grinding wheels to make the drive wheel. I'm going to try metal first and cut the raised diamond pattern the same as on the EV Warrior roller. It doesn't seem like it would, slip wet or not with the right pressure. Too bad they're less than 1.5" diameter, but they may be perfect for 10k+ rpm RC motors. I'm going to adapt the 24v 50a/side wheelchair controller for the initial try. It has a very soft start, which should help eliminate slipping. If it works well and goes fast enough, then I'll need to figure out how to convert the joy stick to dual forward only thumb throttles.

Now that I think about it, the real issue with a friction drive and high speed may be heat.
 
RC motor Rim Drive.

Wish I could draw this, you'll just have to use your imagination:

A larger version of a brake caliper on the front fork. On one arm (where the rubber brake block would be) there is a rubber wheel driven by an RC motor. On the other arm (where the rubber brake block would be) there is another RC motor, or more likely an idler wheel just to balance the force from the other side of the rim. As you apply the "brake" the motor engages on the rim (and/or is powered up) thus driving it. You thus have a clutch (gradual application of power). You also have a very big down-gearing suitable for RC motor speeds.

Discuss.
 
Miles said:
http://www.youtube.com/watch?v=Qxh_cMrIyVI :lol:
Click to expand...

Yes, Miles, I saw that some while ago, thanks, but it's a "rubber rubber" and I'm suggesting a "rim rubber". The difference is I don't quickly wear out my expensive tires(shit sorry tyres). I wear out a replaceable rubber ring that contacts the rim. It's maybe more like a disc that clamps between two metal discs. Those RC motors have a clamp for a propeller. Just bolt 2 metal discs in there with a rubber disc clamped in between to contact the rim. Dig?

Whadyathink?
 
I don't think a rim drive will be very effective. There would be far greater friction because the drive wheel spins on a fixed axis and is only in contact with the rim at the proper angle along a finite line. Something's gotta stretch at every other point of contact resulting in noise, heat, and wear.
 
John in CR said:
I don't think a rim drive will be very effective. There would be far greater friction because the drive wheel spins on a fixed axis and is only in contact with the rim at the proper angle along a finite line. Something's gotta stretch at every other point of contact resulting in noise, heat, and wear.
Click to expand...

Not sure I understand you. (wish I could draw it). The RC motor's spindle is parallel to the front forks; the rubber wheel on that spindle is perpendicular to the rim at all points in the wheels rotation. Why do you say it's "only in contact with the rim at the proper angle along a finite line"?
Sorry, if I'm being thick :roll:
 
Paul,

Any point on the rim is moving in an arc and not in the same plane as any point on the drive wheel. Driving the wheel directly enables you to have both axles parallel, so the circular motion occurs in the same plane. Direct wheel drive is like traveling straight ahead, and rim drive is like turning 100% of the time. With such a small diameter wheel turning all the time, I think the difference would be significant.
 
Interesting! What about 2 motors contacting the rim on opposite sides, each with a friction wheel? Clamp the rim between the rollers. use one way clutches on each.
otherDoc
 
I thought that's what we were talking about, oDoc....
paultrafalgar said:
On one arm (where the rubber brake block would be) there is a rubber wheel driven by an RC motor. On the other arm (where the rubber brake block would be) there is another RC motor, or more likely an idler wheel just to balance the force from the other side of the rim.
Click to expand...


I think that was the system used in the ill-fated EV Warrior. Also, there's a french bike that uses this system - can't find the reference, at the moment....
 
rim drive sounds intresting, but how true would the wheel have to be? Most wheels wobble a little, especialy under load and cornering. how much tollerance would you be able to build into a rim drive?

Could you build it on some kind of sliding carrage that would let the drive wheels float side to side with the wheel?
 
Oops! U guys are way ahead of me! :oops: The carriage could ge spring loaded to keep it on the wheel durind wobble!
otherDoc
 
Or really wild and crazy!
http://www.osmoswheel.com/pages/avantages.asp?lang=en
otherDoc
 
Looks like 8000 euro for those bikes, Miles, but the principle apparently works!
otherDoc
 
Well, maybe spokes are a good idea! :) But 3 motors in a triangular frame with capture rollers inside a rimless wheel........?
otherDoc
otherDoc
 
Hey! If man were meant to ride on one wheel, we would all be circus acrobats! Nah! 2 wheels, please!
otherDoc
 
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