Electrical Board for mecanum

[robotsarecool]

How would an electrical board for a robot with a mecanum drive train be different from one with a tank drive train? Any help is appreciated, thanks!

[Ari423]

Electrically, the only difference is each motor controller needs its own PWM (you can't use PWM splitters). Other than that, the difference is in the physical wheels and the programming.

[FrankJ]

Originally Posted by Begather

Yeah you are right. It is not possible.

What is not possible?

Space wise mechanum electrical doesn't take up much more than any 4 cim drive & less than a six cim drive. Granted it may have more wires. Our mechanum electrical board sits on the belly pan. With the Vex clamp gear boxes there is probably more room than we had with last years two speed six wheel drive.

[Ari423]

Originally Posted by FrankJ

What is not possible?

Space wise mechanum electrical doesn't take up much more than any 4 cim drive & less than a six cim drive. Granted it may have more wires. Our mechanum electrical board sits on the belly pan. With the Vex clamp gear boxes there is probably more room than we had with last years two speed six wheel drive.

I think he meant it isn't possible to use PWM splitters like you might for a 4 or 6 cim tank drive. I definitely agree with you about the space requirement; our mechanum setup always takes less space than our tank drive setup (except for that one year we did 4 independently driven tank drive wheels which was a big mistake).

[GeeTwo]

The biggest change to the control board would be to reflect that the four wheels must be independently driven. As such, a minimum of four motor controllers is required. If you put encoders on your wheels, you will need four, not just two. Quadrature encoders would require eight channels on the DIO, unless you're feeding back directly to the controller (e.g. Talon SRX).

Many teams which do mecanum also like to use "field coordinates" which allows the robot to go the same direction as you push the joystick, even if the robot is sideways or backwards. This will require an analog gyroscope to use the libraries.

If you only use pneumatics for shifting, this may go away; few team shift mecanum (apart from octanum style "shifting").

[EricH]

Originally Posted by GeeTwo

The biggest change to the control board would be to reflect that the four wheels must be independently driven. As such, a minimum of four motor controllers is required.

That's not a change if you're already running a 4-motor drivetrain as many teams do, under 2015's R42. (Unless you're using "non-drivetrain" motors as drivetrain motors...)

[GeeTwo]

Originally Posted by GeeTwo

The biggest change to the control board would be to reflect that the four wheels must be independently driven. As such, a minimum of four motor controllers is required.

Originally Posted by EricH

That's not a change if you're already running a 4-motor drivetrain as many teams do, under 2015's R42. (Unless you're using "non-drivetrain" motors as drivetrain motors...)

Actually, it may be a bit of a change to the control board, as the wheels must be independently driven. If using PWM to drive your motor controllers, you must use four separate PWM ports, not two with wye cables. For the record, 3946 used two-CIM drive trains for both 2013 Ultimate Ascent (the only time we seeded top 24 at Bayou regional) and 2015 Recycle Rush (the only time we were picked for eliminations -- and we put our alliance over the top to go to CMP).

[EricH]

Originally Posted by GeeTwo

Actually, it may be a bit of a change to the control board, as the wheels must be independently driven. If using PWM to drive your motor controllers, you must use four separate PWM ports, not two with wye cables.

I'm aware of that. For the record, that's not a change to the required number of motor controllers for the drive--which is what I was addressing--unless, as in your case, you're running a non-4-motor drivetrain. (Also note that CAN is not governed by the same rules as PWM, so if that is your setup, it's purely a mechanical and programming problem.) It's simply a wire routing, which should have little to no effect on the board (given that PWMs are small, light wires and there's almost certainly one going that route anyway, even if it is on a splitter for a tank-drive setup). The effect will be on the RoboRIO: namely, you have to use two more outputs for the drive motors.


There is one other change, though, that the OP should be aware of. Due to the mechanical aspects of the drivetrain, you'll have less space in the corners than normal, but if you can keep the mechanical crew from putting stuff in between the wheels, there may be more space on the sides of the robot to play with.