[Madison]

Kevin A wrote:

Would the spiral clutches wear out? It seams like repeated slippage and heavy spring tension wouldn't do them good.

I have no way of answering that, unfortunately. I'm hoping that I can have a set made and tested once I'm happy with the overall design. Admittedly, I'm really poor at choosing the right material for a job, so I'm not even going to venture a guess as to the best one for this application. In the drawings, the parts are shown as delrin -- mostly because of its low coefficient of friction. I'm unsure of the wear it'd see or if it'd have a significant effect. If the wear, even if it were bad, was consistent and even, the clutch should still work -- a bit like car brakes.

Sanddrag wrote:

I don't understand how the drill can power the robot in one direction until a certain speed and then the Chiaphua will take over propelling the robot in the same direction at a higher rate of speed.

In physics, one of the first things you learn about is relative motion. I'm not sure if you've taken physics, so I'll briefly explain.

If you're standing beside a railroad track, not moving, and a train goes by at 50 mph -- well, it looks like the train is passing at 50 mph, right?
Now, if you're in another train, heading in the opposite direction of the first, but also at 50 mph -- well, then that first train looks like it's traveling at 100 mph.
Think of things the opposite way as well. If you're on a train that's running parallel to the first at 50 mph, it appears as if the other train isn't moving at all. If the first train speed up to 60 mph, it would appear to us as if it's going 10 mph. See?

Imagine both sides of the clutch are now spinning at 300 RPM. It appears as if they're not moving. Speed one side up to 1000 RPM and then it appears as if it's spinning 700 RPM when your frame of reference is moving at 300. I'm not sure if this is helping.

The real point is that "relative clockwise" motion never requires the motors to spin clockwise. It just requires that the left end spin faster than the right end such that the clutch slips. After a certain point, you could actually turn the drill off altogether.

generalbrando wrote:

Has this been used on a bot before?

To my knowledge, no. My knowledge of things FIRST is fairly limited, though, as I've only been around for 6 years. If someone knows of a robot that's used something similar, please let me know. I would like to see their implementation. I know mine needs improvement.

George wrote:

M: What happens when you want to go backwards or turn? Would the clutch slip? Would you do this using only the CIM? Would the latter cause you to trip breakers?

Without adding more complication, going in reverse would rely solely on the CIM motors. The error I mentioned in my first post, in fact, had to do with this very item. I need to double and triple check my gearing to make sure it doesn't strain the system too much while going in reverse. It is possible to make a design that uses both motors in forward and reverse, but it adds an additional level of complexity that may or may not be worth the hassle. In short, it'd involved two clutches and a shifting dog.

Turning is an interesting issue, I think, and something I'm still investigating. It seems that the gearboxes would behave very differently depending on how the robot turned. If it were to steer like a car, the gearboxes, together, could be used as a "differential" and the speed differences between the motors do not seem like they'd pose any real problem -- much like many robots. With a zero turning radius, however, things get a little stickier. For that, one side is going in reverse -- using the Chiaphua motor -- while the other goes forward using whichever motor is most appropriate for the speed at which it's turning. It may be that there's an easy solution, a programming solution, or that a zero turning radius is impossible to achieve. Again, I'm just not sure.

Frank wrote:

What about a differential? Except a backwards one. Say, take a standard diff, two output shafts (the axle) and one input shaft (or gear, from the engine/transmission)

Except here, you power one of the output shafts with the drill, and the other with the chip.
...
with this, you could get power from both motors, each going at their respective optimal speed . . . no need to use two motors only to use one at a time, you know?

The differential idea, as I mentioned above, is Tytus' kingdom.

I agree that there are better solutions if you want to couple two motors together and run them all the time. You'll get more power at a given speed that way. Most of those solutions rely on averages -- as does the differential. This solution does not.
This design is explicitly for maintaining separation of your motors and taking advantage of the unique characteristics of each. The additional performance range possible via this solution means that your robot could simultaneously have the ability to output more torque and more speed than any other robot -- especially middle-of-the-road, average robots using a two motor drivetrain.

Again, thank you everyone for taking the time to read through that very long post and ask questions. You're raising issues that I haven't thought of yet or don't have satisfactory answers to and I really appreciate that. I understand that the design in its first iteration isn't close to perfect and so I'm seeking your feedback so I (and others) can make improvements before testing and using it -- if it's worth using at all.