Powering two compressors with one PCM

[IndySam]

Even simpler just wire a relay (or two) through the pressure switch and avoid a PCM altogether.

[axton900]

The issue that we are facing with the idea of just using a spike relay is the fact that the compressor class in wpilib only seems to be accepting the pcm as a parameter.
Could one of the teams who was able to use a relay share the code that they used for this situation?
Thanks in advance!

[cbale2000]

Originally Posted by axton900

The issue that we are facing with the idea of just using a spike relay is the fact that the compressor class in wpilib only seems to be accepting the pcm as a parameter.
Could one of the teams who was able to use a relay share the code that they used for this situation?
Thanks in advance!

Older default code (2014 and before) would have some basic examples, though it should be pretty easy to program yourself.

There should be a way to read the pressure sensors state from the PCM in code, and if you have that, then all you have to do is use the output of the pressure state to toggle the spike on or off. The pressure sensor is a switch that activates at ~120psi and deactivates at ~ 100-110psi, so simply using it as a Boolean to toggle the compressor state should make it operate the same as a PCM controlled compressor would.

You can query the pressure switch and compressor status from the PCM and simply mimic the state of the PCM controlled compressor with the code on the bottom half of this page: https://wpilib.screenstepslive.com/s...anual-id=13810


The second compressor, for the purposes of code, isn't a compressor, it's a Spike-controlled motor. Just make sure that the spike turns on and off at the appropriate times via the methods mentioned above.

[GeeTwo]

Originally Posted by cbale2000

The second compressor, for the purposes of code, isn't a compressor, it's a Spike-controlled motor. Just make sure that the spike turns on and off at the appropriate times via the methods mentioned above.

And don't try to put it in reverse! IIRC, we connected the black lead of our compressor directly back to the Power distribution board (through a splice), and just put the red lead to a spike output to ensure that we didn't apply reverse voltage. (I never found a rule AGAINST it.) While you can't use the other output on an FRC-legal robot (per 2016 R53, second sentence), for other projects, you can use that side to control something else, like a string of LEDs or other low-current-draw custom circuit.

[axton900]

So let me just get this clear? I just have to set the relay into forward mode in order to fill up the compressor?

[GeeTwo]

Originally Posted by axton900

So let me just get this clear? I just have to set the relay into forward mode in order to fill up the compressor?

Yes, presuming the red wire on the compressor is connected to M+ and the black wire on the compressor is connected to M- (or back to the black wire coming from the breaker panel).

[Al Skierkiewicz]

To add to the above,
One and only one compressor on an FRC robot, please.
The PCM is not intended to handle the current of two compressors so a Spike or other relay is your only choice.
The pressure switch is a 3 amp device so it is not an alternative for powering a compressor. Even the smallest compressor teams will use, has a nearly 20 amp start and nearly 10 amps run current. The large Thomas type compressors have a 27 amp start and 12 amp run current.

[simpsonboy77]

You can ignore the PCM entirely and use a Y cable to control 2 spikes. Not sure if this would be legal in 2017, depends if the PCM is required. Either way you need to have the pressure switch in somehow.

On a spike powering a compressor, you are allowed to replace the yellow single blow 20A fuse with a resettable 20A fuse. I recommend doing this as sometimes the fuse can blow from inrush current, or inductive kickback when it turns off.