Split Thread: Design limitation of 16 PDP channels

I don’t see why we would need this controller to solve that problem. I’d love for FIRST to allow multiple controllers per PDP slot; all they need to do is snap their fingers. The snap-action breaker and battery are still the bottleneck, so the “one controller per slot” doesn’t even have the right to exist anymore, unless they’re trying to limit DoFs. (but then they wouldn’t approve this dual-motor controller, so moot point)

Split thread edit: This was originally in response to this reply


having a motor limit is an interesting restriction to the design process. I’m not sure why you would want to throw this rule out. 16 motors seems to be more than enough to do any FRC job.

Knowing how Woodie designed his class with various restrictions (only able to use the parts included in the kit that you were handed at the beginning of the semester, limited time to complete the project, etc.), I can see similar restrictions in FRC. Motor count is one of those. Restricting the number of motor controllers forces teams to make trade-offs. For example, choosing to use a swerve drivetrain with 8 motors (leaving only 8 other motor controllers for other things) is a tradeoff against a less motor-intensive drivebase leaving more motors available for other actions.

These are the kind of trade-offs that FRC forces teams to make which is part of the learning and part of the challenge.

I expect that FIRST will keep some sort of motor controller count restriction. I could see them increasing it over the current count, but overall, I think the GDC has a list of constraints they want to put in place for the teams to design within to make the challenge more challenging and motor controller count / PDP slot count is one of those constraints.


There is a control system refresh coming and I have a feeling that with it, we will see a positive change.


I want to see more use of servos/relays. They are relatively underused. Same goes for some of the communication interfaces.


I expect to see changes to both negative and positive.


What about ground?


That seems like a very current joke.


Agree to disagree.


One I charge you with potentially amping up.


I think the main reason for this is to keep inspection straightforward. I’d much rather have them authorize a larger or supplemental power distribution system than allow multiple controllers per slot.

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16 slots really isn’t that many, especially for swerve drive teams.
Take this year for example:
8 motors for swerve
2 motors for shooter
2+ motors for end game deploy/climb
1 motor for intake
1 motor for hopper/spindexer
1 motor for indexing
1 motor for turret
1 motor for adjustable hood.

That’s 17 motors right there. And you don’t have a PDP slot for limelight or a color wheel motor.

Robowranglers seem to regularly bump up against the PDP slot limit.


So what you are telling me is that if you use 8 motors to drive around, you might be limited in other areas? Sounds like a design trade off to me.


I completely understand that there are design trade-offs. We climbed with one motor this year and only had a 4 motor drivetrain. I only made an example of how quickly you can run out of motors (based heavily on 148’s Revolver) to address the idea that “16 motors seems to be more than enough.” If a robot aims to do most or all aspects of the game fairly well*, 16 motors becomes a very limiting factor. I believe Revolver wasn’t able to retract it’s intake due to that.

*I realize that most teams aren’t able to or shouldn’t shoot for this. “A jack of all trades is a master of none.” But there are teams that do accomplish this and the limit is very real for them.

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To do or to do well? We had 14 motors and used all our PDP slots this year and that was with a standard 4 motor WCD, (and not doing the color wheel). So now way we could have done swerve this year with it’s 4 additional motors (+ PDP slots).

2 intake (spin, raise/lower)
1 hopper agitator/indexer
1 elevator
1 turret
3 shooter (for enough power)
2 climber (raise, winch)

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A dual-motor speed controller would already bypass that limit, so if FIRST goes that route, effectively doubling the independently-controlled motor limit, they may as well allow multiple controllers per PDP slot.


I’d like to echo this sentiment. My team chose to run swerve this year, we definitely felt the crunch of not having enough PDP slots, and we definitely relied on our pneumatics, but we were able to pull it off:

  • 8 Swerve
  • 1 Intake
  • 2 Indexer
  • 1 Climber
  • 1 Color Wheel
  • 2 Shooter
  • 1 Limelight

I’d say that a blue banner as alliance captains is a decent metric of how well we were able to pull it off, albeit maybe not the best one, but decent enough.

I mean there have always been teams that seem to do the game tasks well with the 16 PDP slot limit.


folks can always do better with more, but in most situations resources are limited. in FRC they are artificially limited. I will say it again because history has proven this right. 16 slots seems to be enough to play any FRC game well.


Personally I’d be estatic if the pdp had 3slots for the vrm, pcm and Rio and then 20 spots for motors, LL and whatever else. Also get rid of those fuses…


But putting some of your most critical components under less protection than the things they control is all part of the fun!