Rule R13c - Tipping Point

Hello all,

Our team has wired up 5v led strips to work with the vex v5 system. The leds are being run by the motor controllers for 393 motors, with led cabling soldered to the output wires, and the neutral spliced into one of the 3 wire ends. Would this be considered to be Modification of the vex electronics during competition? Is this legal?

Here is R13c for reference:
“VEX electronics may not be used as non-functional decorations”

This is the diagram we used:

First look at rule <\R6b>:

b. Electronics from the VEX Cortex control system are not permitted. This includes the VEXnet Joystick, VEXnet Partner Joystick, VEX ARM® Cortex-based Microcontroller, VEXnet Key 1.0 and 2.0, 2-Wire Motor 393, and any other electronic components which are not compatible with the VEX V5 system

If it is connected to the V5 Brain or V5 Battery, should be illegal during inspection, there is no caveat for non-function election in VRC this year.

You should ask the Official Q&A this question as I am going to assume people will leverage past seasons’ Q&A which do not carry over to current season.


I think this topic is much more vague than you think. If you modify the motor controller 29 from its intended purpose and form, would VEX still consider the component to be a VEX part?

Would someone perceive this modification to provide an unfair advantage? What does the team benefit from this hack? I feel like a simple GDC QnA question can help clarify this, as sometimes the GDC is known to make rule exceptions.


e. Internal power sources (e.g. for a small blinking light) are permitted, provided that no other rules are violated and this source only provides power to the non-functional decoration (e.g. does not directly or indirectly influence any functional portions of the Robot).


No Wi-Fi. The Vision Sensor must have its wireless transmitting functionality disabled.

If I’m not mistaken, your lighting strip doesn’t need to be powered by the V5 cortex at all. A strip with a small battery pack should be legal, and although the rule book states no WiFi may be used, I would recommend staying away from any form of wireless communication, so just make sure your lighting strip has a built in controller, not a remote.

(Sorry if the quotes don’t work, I don’t know how to format things)


It depends - if you plug something into the brain that is explicitly prohibited (such as cortex parts including 393 motor controllers, then it could be a problem.

Best for them to ask on Q&A to be sure.


I have used a USB Battery bank previously, however when connected to the cortex its programmable and only requires one power source.

It is a 393 controller, but not being used as a vex part. It sounds like if it were at a regional comp, the inspector would pass it. Ill ask the Q&A just to be sure.

No worries - I am expecting teams wanting to be ready for Worlds with their awesome robots.

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well verdict is no:


So, Would a external battery be fine?

Yes, external battery is allowed, only to power decorations.

if the LED system is not connected electrically to the V5 system in anyway AND you are not using VEX electronics - it is a different question that is being asked inthe Q&A.

I will write this up later when I get home but I believe that this ruling is incorrect and incredibly inconsistent with the wording of the game manual.


I don’t see how this is a requirement for LED strips to be legal, on the contrary it has been legal to power nonfunctional decorations off of the brain or cortex for a long time, long before separate battery packs were made legal.


The GDC ruling states that

Per R13-c and R6-b, no, this would not be legal.

The text of R6-b is as follows

Electronics from the VEX Cortex control system are not permitted. This includes the VEXnet
Joystick, VEXnet Partner Joystick, VEX ARM® Cortex-based Microcontroller, VEXnet Key 1.0 and
2.0, 2-Wire Motor 393, and any other electronic components which are not compatible with the VEX
V5 system

The MC29 is a “cortex” part, but it is notably NOT listed in R6-b, nor does it meet the criteria for items disallowed that are not in the list (“other electronic components which are not compatible with the VEX
V5 system”). The MC29 is fully compatible with the V5 Brain, as advertised by VEX.

3-Wire ports can also serve as a PWM motor port for driving the older servos and Motor Controller 29’s.

R6-b only makes cortex electronics that are not compatible with the V5 brain illegal, therefore R6-b is not relevant when discussing MC29s.

The second portion of the ruling was in regards to R13-c. R13-c states that

VEX electronics may not be used as non-functional decorations

I have a few rebuttals to this one. First off, the MC29’s in question are heavily modified, which has previously meant that the electronic device no longer meets the definition of “VEX electronics”.

The second rebuttal to this point is as follows. By this logic, a non-VEX brand, otherwise identical electronic component modified and used in the exact same way would be legal, but since the MC29 has the VEX logo on it, it is illegal. This logical conclusion is, as it turns out, quite illogical, and I would therefore be inclined to invoke G3. For those that do not recall G3, it reads:

Use common sense. When reading and applying the various rules in this document, please
remember that common sense always applies in the VEX Robotics Competition.

Disallowing a component simply because of the VEX branding betrays all common sense. This nonsensical conclusion could therefore be ameliorated with the understanding that yes, in fact, modified MC29s are legal for decorative use.

The final rebuttal that I have to the GDC’s application of R13-c is one of definition. The rule very specifically applies to non-functional decorations. Per the text of R13, a non-functional decoration is something that

[does] not affect Robot performance in any significant way or affect the outcome of the Match

Consider the following: a Team with a robot that manipulates a ring using internal mechanisms to accomplish an arbitrary goal. The mechanisms in question obscure the state of the mechanism from the view of Drive Team Members, however the robot has sensors onboard that can determine the state of the ring mechanism. There are LED strips under the robot that are, by some method, controllable from the V5 Brain. The Team has programmed the LED lights to illuminate a certain color depending on the state of the ring mechanism. This visual feedback allows the Drive Team to more efficiently maneuver the robot, allowing them to win games that would have otherwise been lost.

A few things stand out here. First of all, one would be inclined to think “Hey! That’s not a non-functional decoration! That’s against the rules!”, and they would almost be right. This 100% does violate the criteria for non-functional decoration, which if we recall requires that a decoration “not affect Robot performance in any significant way”, which this definitely does. Where our hypothetical skeptic would be mistaken is in declaring this against the rules. In all previous years, yes, this would have been very illegal. In fact, I asked a Q&A on this last year. LED light strip usage : Robot Events. However, this year there was a small corollary added onto R13 which states that

Decorations which provide visual feedback to Drive Team Members (e.g. decorative lighting) are
permitted, provided that they do not violate any other rules and serve no other function (e.g. structural support).

R13-g very clearly allows for the lighting setup described in the above example, yet said example by no means meets the criteria for “non-functional decoration”. I would call such an apparatus “functional decoration”, or simply, “decoration” (as the corollary does).

R13-c again, if we recall, prohibits the use of VEX electronics for “non-functional decorations”. LED lights, as we’ve established, are not non-functional, therefore R13-c is completely irrelevant when considering them.

Q&A 942, which supposedly prohibits the use of MC29s for decorative lighting purposes, does so by invoking two rules which are both unquestionably inapposite for the question at hand. And, since a post on this forum is never complete without a GIF, I will conclude my argument in the only way that feels right.



Nice, but should have provided brief for the Q&A :slight_smile:
Now can you do an analysis of TP meeting the 5pt bonus for time stamping in bound notebook ?


Very well thought out and presented. However, my rebuttal is that if the MC29 Motor Controllers are legal VEX parts then R21 applies.

No modifications to electronic components are allowed.** Motors (including the internal PTC or Smart Motor firmware), microcontrollers (including V5 Robot Brain firmware), extension cords, sensors, controllers, battery packs, reservoirs, solenoids, pneumatic cylinders, and any other electrical component or pneumatics component of the VEX platform may NOT be altered from their original state in ANY way.


It’s not an electronic component though. It’s being used as a functional decoration. Notice how every single item in that list is NOT a decoration.

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No, R21 doesn’t apply. R21 is applicable to parts used for the robot’s control system. Decoration is covered by R13, not R21.

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