Rule R21 Clarification... please help.... Why do V5 smart motors not have vents?

I have a question about the rules for VRC Tipping Point this year. I am aware of rule R21, which states that, ¨No modifications to electronic components are allowed.¨ The question I have is this:

Does this rule account for modifying the plastic shell of the motor? My team has agreed many times that the plastic shell of the motor has extremely inefficient heat transfer, as there are no vents or heat sinks in the motor or motor casing. These little motors can create a lot of heat, and without proper heat transfer they overheat and stall out, causing many problems for my team. We are sure that our team is not alone in this struggle, and we are trying our best to solve it. Thank you for your time.


R21 states pretty clearly:

Motors […] of the VEX platform may NOT be altered from their original state in ANY

Point C also goes further:

I’m pretty sure that the rule is very clear about this.


I would recommend being some keyboard cleaner or any other cool air spray. Spraying in between rounds will stop your motors from overheating. it that doesn’t solve it try adding less load to the motors.


It almost seems like you may be pushing these little motors outside of their comfort zones. Yes, these motors are capable of outputting a consistent power of 11W. But just because you can do something, does that mean you should?

Check out these articles to learn a bit more about these motors.

After you’ve read those articles and you might understand a bit more about the 11W Smart Motor, consider the following.

The image below is a standard DC motor performance curve. As you can see max output power is further along the graph than max efficiency. When running at max efficiency, the motor will create the least amount of waste heat. But at max efficiency you aren’t getting the most power! That’s a bummer! So let’s crank it up to max power output. Notice how much less efficient a motor is at max output power?

Now let’s compare to an 11W Smart Motor performance curve I found. The engineers and programmers that designed this motor pulled off some voodoo to make using these motors easier for the masses. They basically made you have to worry about less! But unfortunately, here on Earth, we are limited by the laws of physics. So even though stall current and stall torque start off the same, they will eventually drop off. So they let you worry about less but you still have things to worry about.

You might want to try running your motors a bit more effeciently if you are trying to solve the overheating issue. You might want to ask yourself, “Do we really need this motor to run at max power?”
Or, you might just have to accept that if you want to push it to the limit, you’re going to create excess heat.

Just as a side note, this is not an issue with the V5 motors. This is an issue with every single electric motor in existence. No amount of ventilation or heat sinks will ever make a motor run the exact same all the way across it’s performance curve.


Yes it is illegal unless specifically specified in the rulebook as @trontech569 showed

This is a GIANT PURPLE CLUE jumping up and down in front of you. If you look at the DC motor chart and the VEX V5 motor chart you can see there is a sweet spot at about 40-60% of the RPM of the motor. The programming team at VEX has worked on the controller programming so you don’t get to the bad end of the curve where stall currents become a factor.

Note that there are a number of different cartridges available and a pretty decent range of gears. (12, 24,36,48,60,72,84) that let you create the best gearing for your application. It makes me pretty sad when I see everything is direct drive, I know that in most cases it’s not the best case setup.

It’s a shame to get this deep into the season without really understanding what the gear choices are.


yes we do
but in all honesty, if it’s not a drive or lift motor it probably doesn’t need to be full power
and even those don’t need full speed all the time

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/sigh … so with all the disclaimers (not a drive, not a lift) not needing to be full power, what would be? A shooter? Same heat problem, maybe worse since it will run non stop the entire match. Claw motor? Full power to open, close, hold? Full power for 1/3 of a revolution?

Help me out here.

We have no direct drive on our robot. All gearing has been designed for efficiency while still trying to maintain the needed torque and speed for the application.

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Of course, every motor has these issues. The problem that I don’t understand about V5 smart motors is that they don’t have ventilation or heat sinks AT ALL. I have taken apart motors to swap gear cartridges, and have discovered that the motor casing is completely enclosed. At first we thought that the ridges on the sides were vents, but upon further investigation they are sealed. We often use Dust Off or electronic air dusters to try and cool our motors off, and we mistakenly thought that the air was flowing through the “vents” on the sides of the motor and cooling it off. Why is there no ventilation on these motors?

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Full power is for auton and what you listed
Plus full power is nice


A better option than cold spray may be quick swap, where your motors are attached with zip ties and you can easily swap the warm ones out for cool ones. See here:


alternatively, you can tip a can of computer duster upside down and spray it, it will cool down motors instantly. a bit pricey for long time use, though

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Another point to be aware of is that VEX has government regulations to comply with.

See this post from Art_Dutra_IV discussing some of their design constraints when they were designing the motors.

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Motor heating depends on load, so lessen the load.

This does not mean regearing. This means really picking apart what a load is.

Are you stopping/starting a rotating mechanism a lot? Shave weight from it. Sand parts down if needed… particularly on the outer radius where polar moment of inertia is most affected.

Address friction aggressively.

Add soft start/stop to your code… less spike on amps that way.

Drop rpms 5%. You won’t notice a difference, but the motor will.

See how your target rpm compares against actual… if it’s less, then you are overloaded and MUST address that. Write code that does data logging during a run. Then see what the data says.


To be fair, those articles can be incorrect and even contradictory, so I would forgive a student for misunderstanding how the V5 motor works after reading them. For example:

Users can adjust the motor’s PID values to tune a motor’s performance for more advanced mechanical systems.

This is not really possible in VEXCode, and the starting values for these constants were never released by vex anyways, so it’s not possible to tune the PID controller on the motor.

the motor will perform the same every time, regardless of the battery’s charge or the motor’s temperature.

If the motor reaches its temperature limit, performance is automatically reduced to ensure no damage occurs.

These statements are contradictory, even on pretty basic behavior of the V5 motor, being that current is limited when the motor’s temperature reaches certain thresholds.

Free speed is software-limited by the motor’s processor to keep consistent performance motor-to-motor

Free speed is not limited by the motor’s processor. See below.

Raw control still has the same rpm limits

PWM control does not have RPM limits. To be clear, I’m not complaining about this (I prefer it this way), but it’s just another inconsistency these articles have with reality.


I have my own V5 motors for playing with at home outside of VEX applications. Would it be worth my time to cut vents into my motor casings?

You can do what ever you want, but you’ll find that gearing the motor to stay in the sweet spot for power vs current is your best bet.

There isn’t any clearance between the motor and the pseudo vents, so you’ll need to take it apart before you start cutting into it.

Take pictures of what you do! At one time I had a V5 that I cut in 1/2 to show the inside, but it sprouted feet and walked after a demo.