A
Alaskavan
Guest
How about just using a cone-shaped roller, have the motor mounted at the appropriate angle?
Dare I say a plausable multiple roller drive for friction mount...
- Thread starter bigkat650
- Start date
sparky
Active Member
That was my original idea. But something still seems fishy about that, too. Seems like there will always be "uneven wear" as long as the roller isn't flat.
sparky
Active Member
Soo... my guess is that with a cone-shaped roller attached to an engine that is angled appropriately, you could possibly get the wear to be even across the tire.
However, I see two problems with that....
(1) The roller itself could potentially be worn down unevenly, which could be problematic if there isn't some kinda tension or compression thingy holding the roller against the tire.
(2) The biggest problem is that you can't slide the roller without sliding the whole engine. With Loquin's idea, the engine stays in place... but with the cone-shaped roller, the engine itself would have to move in order to shift "gears".
However, I see two problems with that....
(1) The roller itself could potentially be worn down unevenly, which could be problematic if there isn't some kinda tension or compression thingy holding the roller against the tire.
(2) The biggest problem is that you can't slide the roller without sliding the whole engine. With Loquin's idea, the engine stays in place... but with the cone-shaped roller, the engine itself would have to move in order to shift "gears".
A
Alaskavan
Guest
The cone shaped roller could be on a splined shaft with a mechanism like that used in a Torque-A-Verter to push the cone out on the shaft. Unfortunately, I have to agree with loquin, that it would wear the tire unevenly due to the differing cross sections of the cone. IMO, the rocker/2 roller idea is probly the most practical - so far.
loquin
Well-Known Member
With such low power, the splined shaft approach could probably be just one spline - a keyway. This would certainly make building it simpler.
While a cone-shape roller could slide along a splined shaft, it still would cause excessive tire wear and have very poor efficiency. The issue isn't that the surface of the cone isn't flat on the tire, as you could tilt the whole cone. The issue is that the diameter of the cone varies as you move from the 'point' to the base. This means that the speed that the cone would try to move the bike is different, from one point to another. So, if you had one inch of cone roller in contact with the tire, the wider cross section portion of the cone would be trying to move the tire faster than the thinner portion of the cone. Which would lead to extreme tire wear.
You know, rather than jumping though engineering hoops to set up dual rollers, it might make more sense to look at applying a Comet 340 CVT to the problem, and use a single 1.5 inch roller. You would end up with, effectively, a 3/4 to 1.5 inch roller, and everything in between.
Although the efficiency would be somewhat less (95% max) than with 2 separate rollers, coupled to the engine via a timing belt, you would end up with a continuous range of torque, rather than low and hi.
While a cone-shape roller could slide along a splined shaft, it still would cause excessive tire wear and have very poor efficiency. The issue isn't that the surface of the cone isn't flat on the tire, as you could tilt the whole cone. The issue is that the diameter of the cone varies as you move from the 'point' to the base. This means that the speed that the cone would try to move the bike is different, from one point to another. So, if you had one inch of cone roller in contact with the tire, the wider cross section portion of the cone would be trying to move the tire faster than the thinner portion of the cone. Which would lead to extreme tire wear.
You know, rather than jumping though engineering hoops to set up dual rollers, it might make more sense to look at applying a Comet 340 CVT to the problem, and use a single 1.5 inch roller. You would end up with, effectively, a 3/4 to 1.5 inch roller, and everything in between.
Although the efficiency would be somewhat less (95% max) than with 2 separate rollers, coupled to the engine via a timing belt, you would end up with a continuous range of torque, rather than low and hi.
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sparky
Active Member
I figured there was still a problem with that idea, and you nailed it.
Have I ever told you that you're my hero, Loquin? You are!!
How'd you come up with a 95% max efficiency for the CVT? Because it's belt-driven??
loquin
Well-Known Member
No - I emailed the engineering department at Comet, describing the potential use of a Comet 340 on a bike with a 2HP motor. I emphasized that, due to the limited hp available, efficiency would be critical. In the reply, their engineer said that the 340 was about 95% efficient, with a new belt. As the belt wears, the efficiency gradually drops - and he says that the you should NOT get too low a ratio on the gearing, as this will lead to premature belt wear. (Apparently, the belt will be spending too much time in the high ratio state, which causes the belt to wear faster.) So, maybe a 1.25 or 1.375 inch roller should be used, rather than a 1.5 inch one.sparky said:
So, for hill climbing, you could be at full RPM but in the 12 MPH range, and 28-30 MPH at full RPM at the top end.
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