Mecanum Differential Drive

[Oblarg]

Originally Posted by MichaelBick

The only team that I have heard of using shifters for better acceleration is 33. Everybody else uses their second speed as a "pushing speed". 16fps has clear advantages. If you have a higher top speed then you can get to your destination faster. They way we got around the acceleration problem was by adding more motors(something you have already done). Also, our low gear is traction limited(if it wasn't teams like 254 with 6 CIMs would blow their main every time they hit another robot)

This is true.

Locking mecanums does not improve forward traction. To improve forward traction on a mecanum you would have to change the roller material.

This is false; if you draw a free-body diagram for the rollers in contact with a ground on a Mecanum drive train, you'll see that the effective coefficient of friction compared to a traction wheel of the same material is reduced by sqrt(2)/2, because the friction force on each roller acts parallel to its axis. That is to say, if you apply the same force in the forward/backward direction to a mecanum drive and a traction drive, the induced friction force on the rollers needed to keep the robot stationary is greater on the mecanum drive by a factor of sqrt(2), since the friction force from each roller is pointing at a 45-degree angle (it must, to keep the rollers on opposite sides from spinning).

Also, planetaries are extremely heavy(especially ones big/strong enough for drive). For all the weight of the planetary, you might as well put in another shifter(which would also be easier to fabricate because you could put it COTS).

This doesn't even start to mention the fact that you are removing all the benefits of mecanum. Mecanums are easy and relatively light. With this, you are making it heavy and extremely hard to manufacture. You might as well run a swerve.

This is dead-on. Large increases in weight and complexity must yield large benefits to be justified. For the amount of added weight/complexity in this design, there are a number of other proven designs with much greater added benefits.