pic: 2605 Mecanum Drive

[Ether]

Originally Posted by holygrail

We usually gear for around a 15 to 17 fps free speed but then we use code to tone it down a bit so that when you push the joystick forward you only get 50 to 70% of the full speed. We have a turbo button on the joystick that the driver has to push for full speed. Works well.

Physics Quiz:

Imagine you have 2 robots which are identical in every way, except that Robot A is geared for 8 fps, and Robot B is geared for 16fps but has the voltage limited to 50%.

Describe the performance differences between the 2 robots: acceleration, motor heating, battery drainage, pushing force, fine control of slow maneuvers, etc.

[Twins Inc.]

Originally Posted by Ether

Physics Quiz:

Imagine you have 2 robots which are identical in every way, except that Robot A is geared for 8 fps, and Robot B is geared for 16fps but has the voltage limited to 50%.

Describe the performance differences between the 2 robots: acceleration, motor heating, battery drainage, pushing force, fine control of slow maneuvers, etc.

I imagine that the bot with the higher gear ratio, bot A, (or lower fps) would have more control and less acceleration than B. But also more heating, and power consumption because of more motor use/rpm. Or am I mixing things?

[Ether]

Originally Posted by Twins Inc.

I imagine that the bot with the higher gear ratio, bot A, (or lower fps) would have more control and less acceleration than B. But also more heating, and power consumption because of more motor use/rpm. Or am I mixing things?

Thanks for starting the discussion. I'm going to withhold comment for a while and let others discuss.

[Culvan Van Li]

Originally Posted by Ether

Physics Quiz:

Imagine you have 2 robots which are identical in every way, except that Robot A is geared for 8 fps, and Robot B is geared for 16fps but has the voltage limited to 50%.

Describe the performance differences between the 2 robots: acceleration, motor heating, battery drainage, pushing force, fine control of slow maneuvers, etc.

1) Acceleration for Robot B will theoretically be slower. It isn't as bad as you might expect because Meccanum wheels have a lower coefficient of friction than traction wheels, so some of the extra torque is lost to slipping.
2) Motor heating will depend on a large number of variables. In general terms 70.7% voltage will reduce current to 70.7% as well, resulting in only 50% of the power and heat. However the actual answer has more dependencies. If the lower amount of gearing is accomplished by removing a stage of gearing then there will be a ~9% increase in power available. The specifics of where you are on the torque curve may also make a difference.
3) Motor Heating is going to be dominated by the power consumption as listed in the previous answer.
4) Battery Drainage will also be determined by power consumption.
5) Pushing force for a meccanum robot is determined primarily by the coefficient of friction of the wheels. You lose 29.3% right of the bat because of the way the rollers work and the rollers don't have that much traction either. If you chose a meccanum drivetrain you made the choice to go around opponents, not through them.
6) Fine control of slow maneuvers is a matter of driver skill. We've found that very few students naturally think in meccanum driving terms. Even those who do, have trouble with the fine control. That's why we added the half speed mode. Like so many other things this is a trade-off we have chosen. We want to be able to cover a lot of field when we need to and we want to have reasonable control when we need it. We probably would have more control if we geared straight for the lower speed, but then we won't have the higher top end speed. The trade off works for us.