Motor speed sensing with the Jaguar motor controller?

[mminutto]

Can anyone tell me if there is a way to detect the actual speed of a motor being controlled by the new Jaguar motor controllers? The documentation on the Jaguar site indicates that this will not be available for use for this year's competition but may be available in the future, but I also saw a function in Labview, something like GetMotorSpeed, that seems to indicate otherwise. Not sure which to believe.

Thanks,

Mike

[Vikesrock]

The FRC Programming Guide found here has information about the functions of the WPILib VIs.

The GetSpeed VI outputs the -1.0 to 1.0 scaled value of the PWM output being fed to the Jaguar. This would be the equivalent to getting the 0 to 255 value of the PWM output in the old control system. This value is not necessarily directly related to the motor speed as there are other factors such as the load on the motor and motor's torque/speed curve.

[BradFerg]

Digging into the LabVIEW code, it appears that the Set Speed and Get Speed VIs just end up setting and retrieving the PWM output value (0..255) by way of a speed value (-1..1). By default, the VIs assume the motor's speed is linear from 0 to 255. If it isn't linear, you can specify your own VI to do the transformation.

So, there is no speed feedback from the Jaguar at this time. It is possible that speed will be available over the CAN bus in the future, but I don't know.

[RyanCahoon]

The Jaguars have the capability to report the amount of electric current being drawn by the motors (but this does not give you direct information about the actual speed of the motors) over their CAN bus interface; this interface is illegal for FRC this year. If you want to know the motor speed, try using the US Digital encoders included in the KoP. These have an API in LabVIEW that will automatically track speed, as well as distance traveled and direction of movement if both sides of the quadrature encoder are wired. The encoders get connected to two digital inputs on the Sidecar: Wire the Brown, Red, and Blue wires to the Ground (black), +5 (red), and Signal (white/yellow) wires of one PWM cable, respectively, and the Yellow wire to the Signal wire of a second PWM cable.

--Ryan

[JohnLocke]

Originally Posted by RyanCahoon

The Jaguars have the capability to report the amount of electric current being drawn by the motors (but this does not give you direct information about the actual speed of the motors) over their CAN bus interface; this interface is illegal for FRC this year.

Which rule states that we can't get use the Jaguars interface? I am under the impression you are able to use it...

[jgannon]

Originally Posted by JohnLocke

Which rule states that we can't get use the Jaguars interface? I am under the impression you are able to use it...

That would be <R62-A>.

Originally Posted by R62-A

Support for the CAN bus port on the Jaguar speed controllers is prohibited for this competition, and the port is not to be used. Nothing shall be connected to the CAN bus port. It is recommended that the port be protected with a piece of tape to prevent debris from entering the port.