Drive systems ideas

[Cyberphil]

Originally Posted by team3329

what about the mechanum wheels? how well do those fit into the eqn?

If you use a chain drive or a belt drive, or even geared drive with mecanum wheels, you are taking away the advantage, that is strafing. To strafe, the wheels in parallel (assuming the wheels are aligned correctly) turn in the opposite direction. When you mount mecanum wheels with a chain and sprocket, belt and pulley, or gear drive setup, the parallel wheels cannot rotate in opposite directions.

So, if you are planning to create a mecanum DT in which the parallel wheels are chained or belted, you should probably use a regular center drop plaction wheel setup.

I hope this helps!

[EricH]

Originally Posted by Cyberphil

If you use a chain drive or a belt drive, or even geared drive with mecanum wheels, you are taking away the advantage, that is strafing. To strafe, the wheels in parallel (assuming the wheels are aligned correctly) turn in the opposite direction. When you mount mecanum wheels with a chain and sprocket, belt and pulley, or gear drive setup, the parallel wheels cannot rotate in opposite directions.

Not necessarily. The key is 4 independent motors. Chain routing can run 1 motor/gearbox to 1 wheel, which is exactly what you'd be doing with a mecanum drive.

[Ether]

Originally Posted by EricH

Not necessarily. The key is 4 independent motors. Chain routing can run 1 motor/gearbox to 1 wheel, which is exactly what you'd be doing with a mecanum drive.

I saw at least one 2010 mecanum bot with exactly that setup.

[team3329]

We were definitely looking into mechanum for the strafing ability. So the key is 4 independent motors huh? If thats the case we have a problem. We have 4 Jags and all show that they are working with their light. however, one of them is giving the signal that it is working but it doesn't turn the motor. The others turn the motor, but extremely slowly. The battery is fully charged, so that's not the problem. is there too little power going to each one? Is there something we are over looking?

[Ether]

Originally Posted by team3329

We were definitely looking into mechanum for the strafing ability. So the key is 4 independent motors huh? If thats the case we have a problem. We have 4 Jags and all show that they are working with their light. however, one of them is giving the signal that it is working but it doesn't turn the motor. The others turn the motor, but extremely slowly. The battery is fully charged, so that's not the problem. is there too little power going to each one? Is there something we are over looking?

Look at the Dashboard. Does it indicate that your software is indeed giving a full throttle PWM command ?

[EricH]

Originally Posted by team3329

We were definitely looking into mechanum for the strafing ability. So the key is 4 independent motors huh? If thats the case we have a problem. We have 4 Jags and all show that they are working with their light. however, one of them is giving the signal that it is working but it doesn't turn the motor. The others turn the motor, but extremely slowly. The battery is fully charged, so that's not the problem. is there too little power going to each one? Is there something we are over looking?

I'm not sure about the Jags, so I'll leave that to the experts. But I'd check connections if you haven't already, and see if you can get some voltage readings on the inputs/outputs.

The key to mecanums is independently powering each wheel. Quick controls explanation follows; coding it is left as an exercise for the team.
--Front/back: all wheels forward/reverse
--Strafe (side/side): Front wheels forward, back wheels reverse/front backward, back forward, depending which way you're going
--Diagonal: Wheels not on diagonal powered the same way (Annoying physics here).
--Anything in between: various combinations of the above.
--Turning: Same as a 2WD, 4WD, 6WD, etc... It behaves like a 4WD when turning, though it doesn't bounce as much as a "sticky" 4WD does.

Oh, and the other thing about mecanums: you want their footprint to look like an O, but when the wheels are viewed from the top, they'll look like an X. This is normal.

Ether has posted a whitepaper on the physics behind mecanum drive at http://www.chiefdelphi.com/media/papers/2390

[team3329]

Ok. I'll take a look at that sometime in the next few days. Ether: No, I believe we are getting just over 1/2 PWM on each, including the one that isn't working right. Would we need to change the sensitivity on the analog output relative to the joystick?

[Ether]

Originally Posted by team3329

Ether: No, I believe we are getting just over 1/2 PWM on each, including the one that isn't working right. Would we need to change the sensitivity on the analog output relative to the joystick?

What programming language are you using? Can you post your code?

[Cyberphil]

Originally Posted by EricH

Not necessarily. The key is 4 independent motors. Chain routing can run 1 motor/gearbox to 1 wheel, which is exactly what you'd be doing with a mecanum drive.

By this, I meant one independent motor/gearbox driving 2 parallel wheels. I knew what I was talking about, I just did not convey it specific enough.

[EricH]

Originally Posted by Cyberphil

By this, I meant one independent motor/gearbox driving 2 parallel wheels. I knew what I was talking about, I just did not convey it specific enough.

You mean something like the Nonadrive, but with mecanums instead of omnis?

Nonadrive: Really good drive system, but you darn well better know what you're getting into about 3 years before you even think about trying it.