Motor Controller Amt per Motor?

[ksafin]

Hi,

A lot of our motors are used in sets of two in a gearbox;

Do we have to have a motor controller for each motor despite them being in the same gearbox, or can we use one controller to control both motors in the same gearbox?

[Mk.32]

Each motor needs it's own motor controller, even though if they are on the same gearbox.

[Ether]

Do we have to have a motor controller for each motor despite them being in the same gearbox, or can we use one controller to control both motors in the same gearbox?

[R46]

Get a copy of this document:
http://frc-manual.usfirst.org/viewItem/57

It is searchable. You can find authoritative answers quickly.

[ksafin]

In that case,
We were planning to use the banebots Cim-u-lator gearbox with two RS 775 motors, to simulate a CIM motor.

Do we need two per gearbox, or should one adequately simulate a CIM motor?
Because that would reduce the number of motor controllers we need to purchase substantially.

Thanks

[Ether]

Do we need two per gearbox, or should one adequately simulate a CIM motor?

I assume when you say "RS775" you mean the 775-18, and not the 775-12, correct?

It depends on what you're going to use it for.

The CIM's peak power is 337 watts.

The 775-18's is only 271.

For the same power output, the 775-18 will burn up much faster than the CIM.

[cgmv123]

Each motor needs it's own motor controller, even though if they are on the same gearbox.

You can split the PWM output from the sidecar/input to the speed controller into 2 controllers. That way it's almost impossible to destroy the motors/gearbox by spinning one motor one way and one motor the other way.

[mikets]

You can split the PWM output from the sidecar/input to the speed controller into 2 controllers. That way it's almost impossible to destroy the motors/gearbox by spinning one motor one way and one motor the other way.
What if you are not using PWM but the Jaguar CAN bus? I assume we will just program the same value to both motors and it will work? We haven't done two motors in the same gear-box before so we don't know what to expect in terms of programming. The concern was that code can only program one motor at a time (issuing CAN command to the Jaguar). So one motor will start a little earlier than the other one. So there is a short period that one motor would carry the whole load + turning the second motor at the same time. Probably not too much to worry but just like to hear your opinions on this.

[Ether]

What if you are not using PWM but the Jaguar CAN bus? I assume we will just program the same value to both motors and it will work? We haven't done two motors in the same gear-box before so we don't know what to expect in terms of programming. The concern was that code can only program one motor at a time (issuing CAN command to the Jaguar). So one motor will start a little earlier than the other one. So there is a short period that one motor would carry the whole load + turning the second motor at the same time. Probably not too much to worry but just like to hear your opinions on this.

http://www.chiefdelphi.com/forums/showpost.php?p=1101358&postcount=3

[mikets]

Thanks for link, Ether. We are not worrying about the encoder though because we will be mounting just one encoder on the shooter wheel axle. Coincidentally, we did plan on using the cRIO to do PID because we couldn't get the Jaguar built-in speed control to be stable enough. We ended up integrating the WPILib PID controller and get a pretty stable speed controller. We are running the Jaguars in PercentVbus mode. So once the cRIO PID control reads the speed from the Jaguar, it will compute the output power in Percentage units and program the two Jaguars with this value. My worry was the time difference between programming the two Jaguars may put a slight stress on the earlier Jaguar.

[Joe Ross]

What if you are not using PWM but the Jaguar CAN bus? I assume we will just program the same value to both motors and it will work? We haven't done two motors in the same gear-box before so we don't know what to expect in terms of programming. The concern was that code can only program one motor at a time (issuing CAN command to the Jaguar). So one motor will start a little earlier than the other one. So there is a short period that one motor would carry the whole load + turning the second motor at the same time. Probably not too much to worry but just like to hear your opinions on this.

If you just want to use %VBus mode or voltage mode, the jaguars have a sync feature. You send the output to each jaguar individually, and define a sync group. Then you send the update sync group command, which tells each jaguar to output the previous command at the same time.

I haven't looked at how it's implemented in C++ or Java, but it's pretty easy in LabVIEW.

[mikets]

If you just want to use %VBus mode or voltage mode, the jaguars have a sync feature. You send the output to each jaguar individually, and define a sync group. Then you send the update sync group command, which tells each jaguar to output the previous command at the same time.

If you want to use one of the closed loop controls, see Ether's link.
Ah that's what I suspected. I saw the SyncGroup parameter and didn't know what it's for. Now it make sense. Is there more detail documentation on using SyncGroup? I might have missed it.

[mikets]

Never mind, the WPILib APIs seem very self explanatory. When calling Set() for each Jaguar, the second optional parameter defines a "SyncGroup" (I suppose any non-zero number works). Then call UpdateSyncGroup with the non-zero SyncGroup number that I defined.

[ratdude747]

For CAN, the way I have always done it in labview is to set the inputs of the two motor set .vi blocks to the same output. I have never had issues doing it that way.

I am sure it could be done in java or c++... the easiest way, at least for me, would be to have the motor speed be set as a variable and let the two jaguars reference that same variable.