New friction drive concept...

[loquin]

thought about this a week or so ago, and have been tossing it around in my head... (yeah, I know - that's NOT a good place to keep ideas!!!)

Gates and other belt manufacturers make toothed belts that are toothed on BOTH surfaces. What if you build a friction drive with a toothed drive pulley and a driven, idler pulley about 6 inches apart. Use a 2 inch wide (approximately) belt, with the tension JUST snug enough to keep the belt from coming off.

Lower the assembly down to the tire, so that the outer toothed belt surface contacts the tire. As you increase the pressure, the belt deflects some, allowing a much larger surface to be in contact with the tire surface than with a single roller. (and, the belt tension goes up, keeping the belt on the rollers, under load.) There will be less deflection of the tire, resulting in lower internal power loss. (standard friction drive drive tires essentially have double the 'rolling friction.') The system should perform better when it's wet, also. And, the pulleys should have minimal wear, so you could use lighter weight, less expensive extruded aluminum pulley stock, rather than steel.

Speed calcs would be the same as any other friction drive, but the diameter used in the calc would be the diameter at the center of the belt.

Ref the attached sketch.

Thoughts?

 

[motorbikemike45]

Seems like a great idea to me. Time for you to get to work and build one to test it out. I would do it myself but I've just finished a GEBE belt drive bike and I'm busy working the bugs out. Good luck. Let us know how it works and when you start your new business building and selling them.

 

[eastwoodo4]

i think your gonna lose to much power.the bigger surface area of the belt will create more drag than the steel drive roller being pressed into the tire.the belt will slip to unless its pressed against the tire pretty good.plus the tensoin of the belt on the pulleys is gonna cause drag to.i say no go but would love to see you prove me wrong.your probably gonna have to special order that small belt.

 

[loquin]

But, it's not the surface area that causes the drag - it's the deflection of the tire. Flexing the tire surface takes some work. If your air pressure is up, and you can press down with little deflection, the drag is less.

Where the increased surface area should help is that it would provide more 'grip' between the motor and the tire, with less downward pressure leading to less deflection.

 

[moondog]

I like it. You could use two motors. 2 electric or 2 gas or 1 gas and 1 electric motor.

Also, the pulleys would not have to be the same size. The 2 motors could have different gearing.

 

[ibdennyak]

Wow, thanks Lou. I shall have to shamelessly steal that idea from you. In Juneau Ak with its 320 days of rain, friction drive is pretty hopeless unless you run a large pneumatic tire as the drive roller. It works, but is pretty cumbersome from a size point of view. The belt idea is worth pursuing. Kind of like putting tracks on a snowmobile.

Denny

 

[spad4me]

That looks nice!

 

[Mountainman]

going to be a lot of loss of HP driving that thing
but if you have a little extra HP to wast
may just be a good unit
MM

 

[moondog]

You could put 4 motors on it. 4 electric motors. Each one with a clutch. Power up 1, 2, 3, or all four of them for max power !

 

[loquin]

The cog belts are almost as efficient as a chain in transferring power, MM, and the two extra bearings won't rob much at all... There should be a net increase in power when compared to a standard friction drive roller pressing into the tire.

While the power loss in a standard friction drive is proportional to the amount of tire deflection, the amount of torque available to push you along is proportional to the amount of surface area between tire and roller. In a standard friction drive, these two goals oppose each other. In order to reduce slippage when wet, you have to deflect the tire as much as possible, in order to increase the amount of surface area (and increase the pressure between roller and rubber, both of which act to increase static friction between tire/roller) BUT, this also increases frictional losses due to tire deflection/flexing, and resultant heat in the tire.) On the other hand, in order to reduce losses and increase performance, you reduce the tire deflection, but, this raises the possibility of roller slippage.

After a while, we get used to 'setting' the roller pressure - we press down on the drive frame and lock the drive in place. If it's going to be wet, we press down harder. If it's dry, we don't press down so much. But, learning how much pressure we need can be a learning experience, that can cost us in eaten-up tires.

I really don't have the time to work on it now, so, anyone who wants to, can use the idea. (IF you start making money with the idea though, please build one for me!!!)