Penalizing mecanum wheeled robots durring alliance selection.

[Kevin Sheridan]

Originally Posted by EricH

Mechanically, yes. The amount of man-hours required to build a tank drive and a mecanum drive will be very similar from a mechanical standpoint. 2 more gearboxes, possibly wheel assembly, that's probably under a typical meeting for 1-2 people.

HOWEVER, to truly calculate the time, you need to factor in programming. A tank drive can be as simple as mapping two joystick axes to two PWM (or CAN) outputs (in teleop, anyway). A mecanum drive requires three joystick axes mapped to four PWM/CAN outputs, and the outputs can all be different (in theory at least, in practice it'll more likely be two and two, but which two changes a bit...). Sure you can use the pre-done stuff and adapt it--but you are going to want to tweak it to match your system, which may or may not be more trouble than it's worth.

That extra time may be the difference between a so-so vision code or so-so automode and a good or great vision or automode.

I would even argue that mechanically there is a pretty big difference too. The tolerances are a lot tighter when machining and assembling the frame for mecanum, otherwise you could end up with only 3 wheels on the ground and a really bad drivetrain. 6WD tank is much more forgiving in regards to bad machining.

[Andrew Schreiber]

Originally Posted by Kevin Sheridan

I would even argue that mechanically there is a pretty big difference too. The tolerances are a lot tighter when machining and assembling the frame for mecanum, otherwise you could end up with only 3 wheels on the ground and a really bad drivetrain. 6WD tank is much more forgiving in regards to bad machining.

Oddly, for mecanum you want a floppy chassis. Rigidity is your enemy. It's one of those small things most teams miss when building mecanum and then get confused when they lift a corner on a mounting plate under the carpet and their bot gets all squirrelly.

But I wouldn't know this unless I've built a handful of omni directional drives (kiwi and a handful of mecanums) and fielded them. It's NOT as simple as people think.

[Max Boord]

Originally Posted by Kevin Sheridan

I would even argue that mechanically there is a pretty big difference too. The tolerances are a lot tighter when machining and assembling the frame for mecanum, otherwise you could end up with only 3 wheels on the ground and a really bad drivetrain. 6WD tank is much more forgiving in regards to bad machining.

My team has run varying degrees of "floppiness" and pretty conclusively showed a rock solid chasis with properly tuned PID loops preforms about the same or worse than a floppy frame running the default WPI holonomic code. The difference also increases as the robot goes through more and more events.

EDIT:
CG has far more of an effect than frame rigidity. Even 2 metal pneumatic tanks on one side caused strafing to deteriorate noticeably.