PDP Output Rules

It is not legal to connect anything except the radio to the 12V-2A port of the VRM, and the 12V-500mA port of the VRM doesn’t have enough current. You could perhaps use the 5V-2A output, but I would recommend against it.

Funny enough, I was picking up on a lot of people that tried to do 16 motors + limelight while CADathon judging.
It’s simply not legal by any recent set of robot rules.

Aren’t there TWO 12V 2A slots. One for the radio, the other for whatever your heart doth desire?

See R47

Nice, yes, agree

Or consider if you can use pneumatic actuators after you make a concerted effort to simplify your design.

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Well, R30 says you can use up to 2 BAG or AM 9015 motors on one controller which is great. But, you cannot use two motor controllers per PDP output, which is quite unfortunate. Really hoping to see this rule changed in future years, especially with the now widespread adoption of CAN bus.

is that new this year ?

No. That rule has always been there (at least since we switched to the OMAP radios).

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ok. in that case we have messed up in years past :man_shrugging:

No. R54 in 2019 had identical wording and picture, as did R53 in 2018, R51 in 2017, and R43 in 2016. R32 in 2016 was nearly the same, except it referenced the 5V 2A slots instead (due to the different radio requiring a 5V input instead of 12V). Prior to that… we didn’t have the VRM.

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More so, your RI missed it.

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Likely because it’s not called out on the inspection checklist. The checklist from 2019 has the line:

Robot Radio – A single OpenMesh OM5P-AN or OM5P-AC radio must be powered via a VRM +12 volt, 2 amp output. The VRM must connect to the dedicated +12 volt output on the PDP. Radio LEDs are easily visible. <R54,R55,R65>

@Al_Skierkiewicz - Possible update in wording for this line item this year?

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just out of curiosity why does that rule exist

To reduce risk and improve reliability. Despite having 8 pairs of terminals, the VRM only has 4 regulators. The two 12V-2A terminals share a regulator. If anything happens to one set of outputs (e.g. a short or overload, or even just noise) it will directly affect the other set of outputs on the same regulator. The radio is one of the most critical pieces of the robot to keep powered, and takes a long time to reboot, so this rule is really to protect teams.


Probably to protect teams. Those terminals put out a combined 2A. The radio requires 1A to operate, if you hook something else up that needs more than 1A, you’ll run into problems.

Personally, I don’t want anything at all connected to the VRM powering the radio. If we need something else, I’d sooner put a second VRM on the robot for it. Something as simple as an LED ring light shorting out can completely take out your VRM and leave you dead on the field. It’s just not worth the risk, in my opinion. The dedicated “hockey puck” converters we had in the cRio days were better from that regard - there weren’t extra terminals or wires for you to hook into!


The VRM for the radio is protected by a fuse on the PDP. If an overload on the 5V output causes that fuse to blow, the radio is guaranteed to not reset until the fuse is replaced.

[Small Squirrel] Which is why you should connect the PCM to a regular breaker slot rather to the same fuse that powers your radio. (The dedicated PCM slot is protected by the same fuse that protects the radio)[\Small Squirrel]

Especially when powering the compressor from the PCM. A PCM with nothing but low-load solenoids on it is probably ok, but if you have the open PDP slots, it’s not worth even the small risk of shorting there blowing the fuse. Doesn’t really help the OP, who plans to have as many motors as possible, though.

Where to start…?

  1. The VRM sum total output current for all outputs is 2 amps. Although the robot rules do not require the radio to be the only device connected to a VRM, I suggest that is what you do. The radio specification is a maximum load of 1.5 amps, so that is near the VRMmax current.
  2. There are two fuses on the PDP, one 20 amp that feeds the outputs for PCMs and radio VRM. The 10 amp feeds the output for the RoboRio. I highly recommend that that a PCM that feeds a compressor be connected to a main PDP output fed with a 20 amp auto reset breaker. This keeps the power for the radio as reliable as possible.
  3. There may be only one wire connected to a main output for the PDP because that is what the manufacturer has specified. The robot rules for certain conditions allows wires to be spliced in the branch. See R49.
  4. FRC is by nature an engineering challenge and choice of actuators is part of that challenge.
  5. Philso, please check your post, a blown 10 amp fuse feeding the VRM for the radio will cause the radio to fail. As others have pointed out, I highly recommend that the radio be the only load on that VRM to prevent failures and brownout of the radio.
  6. I want to remind everyone now (as I will be doing this a lot this season) that I have talked with the Limelight engineers and guarantee that the illumination is not only controllable it can be dimmed as well. Please be aware that the LEDS can produce illumination that can temporarily blind volunteers near the field. Please read R8 as it pertains to light sources.
  7. I have no reason to modify the Inspection Checklist for the radio (as quoted above) as the rules has not changed.
  8. Please read R33 carefully as to the use of the USB battery on your robot.
  9. Electrical rules for the robot in the section for the PDP i.e. branch load wiring and breaker size is included to keep the PDP in a safe window and to protect the wiring attached to the PDP from causing fires. Those rules are derived from the NEC for open frame, low voltage wiring.
  10. Custom circuits should be evaluated by your robot inspector to prevent violation of another robot rule.
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