Drivetrain First Thoughts?

[Lil' Lavery]

Originally Posted by Ether

What do you mean by the word "inefficient" in this context?

By the very nature of the wheels, you're transmitting some of the force supplied by your motors into vectors other than your desired direction of travel. Because of the angeled rollers, you don't get 100% of the power of your motors at any given time (aside of rotating in place).

[Alan Anderson]

Originally Posted by Lil' Lavery

By the very nature of the wheels, you're transmitting some of the force supplied by your motors into vectors other than your desired direction of travel.

This is where someone will claim that those elseways-directed force vectors don't actually result in a loss of power because there's no motion in the undesired direction. That someone will be wrong, because the field surface is not perfectly rigid and does move sideways when the mecanum wheel tries to drive forward.

[Kevin Sevcik]

Originally Posted by Alan Anderson

This is where someone will claim that those elseways-directed force vectors don't actually result in a loss of power because there's no motion in the undesired direction. That someone will be wrong, because the field surface is not perfectly rigid and does move sideways when the mecanum wheel tries to drive forward.

So you mean "normal" wheels aren't 100% efficient either because the field surface shifts backwards when the wheel drives forwards, right? I'm not sure that makes much of a difference between the two wheels.

Do we even have a definition for "efficiency" in this case aside from the arbitrary demand that all force vectors should be pointed in the direction of travel because we think that's efficient? In that case, I'll point out that mecanums are vastly more efficient at turning than a 6WD, and thus are obviously superior by my idiosyncratic definition of efficiency.

[JosephBurns35]

i was considering omni drive but thought of the loss of power our team has done 4 wheel with rear omni's the last 3 years other than lunacy and have had a decent amount of success. but i was wondering how hard it would be to line up to the pegs with a non articulated arm.

[Ether]

Originally Posted by Kevin Sevcik

So you mean "normal" wheels aren't 100% efficient either because the field surface shifts backwards when the wheel drives forwards, right?

Yes, indeed it does. But it can probably be safely ignored for the purposes of FRC robotics.

In the case of mecanum wheels whose rollers have axial free play, the problem is exacerbated by the axial motion of the rollers. As each roller comes into contact with the carpet, it is forcibly pushed along its axle until the free play is taken up. As it does so, there will be some rotation. When the roller leaves contact with the floor, gravity and vibration re-open the gap. High quality (expensive) mecanum wheels with well-designed bearings in the rollers suffer less from this phenomenon.