Tim, The center axle idea of your's sounds cool.
I don't understand driving the rear axle instead of the front? Is it so that you have ready chain adjusters? With a sprocket I don't think the track is going to care front or back and I think there is advantage to the shorter run.
Unless you aren't using a sprocket but relying on friction and driving both the front and back tires. This really wouldn't remove chain windup. And you no long have limp home mode; I don't know how important that one is but it has been mentioned.
This ^ is what I'm picturing, it may not eliminate chain windup, but will reduce it significantly
So, last night I gave it a little more thought. The slop in the sprocket/belt cog interface (the 2 foot problem) makes stopping on a slope exciting, changing fwd/rev a little clunky, AND it will affect turning response time. I suppose I could learn to live with the first two but suspect I would really hate the last one. I think we need to design this so that the sprocket fully captures the belt (track) cogs.
Good Point
I also got to thinking about tire guides. If I put the sprocket front and back with the back still an idler then I don't need tire guides since the track is fully captured. This would create two problems. In my original design I used the tire pressure of the back tire to adjust track tension. This new design needs something else that could be a little more tricky. Worse, this new design requires the front and back sprocket to be synchronized which requires choosing a cog/sprocket pitch dependent on exact axle spacing. This means you could not make a tracking system somewhat generically usable across varying machine axle spacing.
If the back Sprocket is on an Idler, would it not "Self Synchronize" with the track?
So far I'm sticking with one sprocket and tire guides.
And about the sprocket build. Generically I've described this as a trapped tire. Okay, what I see is a tire on a dual beadlock wheel. It is important that the sprocket ends up diameter stable and, from playing with air pressure and my tires, what I have isn't anywhere close to diameter stable. So I added belting external to the tire to accomplish this. It may be that there is a tire that is already diameter stable in the air pressure/suspension range that we need. If there is then we could bolt the sprocket cogs right to the tire, add an internal protective surface, and use a tube or balls for air.
If we must rely on the sleeve for diameter stability we can still bolt this to the tire at one point to combat the tire from spinning inside the sleeve and use the same tube/ball air system.
And one more thing...
RD mentioned spinning the tire as a safe point of failure. I go to thinking about this too. Let's imagine that the track becomes totally immovable and that the engine has the grunt and that everything is break proof. What would happen? I imagine that the torque will twist the tire until the diameter shrinks enough that the sprocket pulls out of the track and skips a cog. Probably loud and scary.
A big detent torque limiter. We could maybe incorporate this but I think with the machines we are talking about that the CVT will check out and you will squeal a belt, also a torque limiter.
Originally Posted by JohnF
Tim, The center axle idea of your's sounds cool.
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