Swerve Drives, Omni Wheels, X Drives, and a plea to stop trolling

[technik3k]

Great post @MyrddinEmyrs!

When selecting your drive you always have to consider Speed, Torque (that are inversely related due to the limited power Speed*Torque=Power), and the directions in which they need to be applied the most.

In the ordinary “tank drive” all your power (speed*torque) is concentrated in the forward/backward direction.

When you choose a holonomic drive over the tank drive setup you pay for the ability to instantaneously go in any direction by the added power losses to friction in the rollers and, in case of mecanums, between the wheels and the bearings on the sides.

_{Since this topic comes up regularly, I would like to quote my post from the last year:}

@technik3k

Here, this is the most important graph to understand X-Drive:

Source: AURA

If you drive forward, backward, or to the side - all four motors are providing power, the velocity is MotorRPM x sqrt(2) and pushing force is 4 x OneMotorTorque/sqrt(2).

If you drive at a diagonal, then only two motors are providing power, velocity is MotorRPM and pushing force is 2 x OneMotorTorque.

Essentially, X-Drive speed is 1.41 times faster and pushing force is 1.41 times weaker than the ordinary tank drive with the identical 4 wheels & 4 motors.

Also, here are the links to the similar topics from the previous seasons: Two motor drives? , X-Drive Speed , Extinct X-Drive?

Also, mecanum drives are very similar to the traditional holonomic x-drives in their power vs direction distribution diagram:

@technik3k

Mecanums have very similar roller material as omnis, but they lose a portion of their ground traction (force) when wheel pairs “fight” each other rather than apply all of it towards pushing force in forward direction, like 4" omnis do (read previous post).

The best you could expect from mecanums is omni_max_intrack_traction/sqrt(2), but actual force is even smaller as force vector direction gets close to diagonal, when only rollers on two wheels could generate any traction - rollers on the other two will just free roll as they are oriented perpendicular to the force vector direction.