Are you allowed to have a small fan for a motor to be used during a match

I have heard people say they have fans for during matches but people also say they can only use fans for in between matches, so I don’t know?

You cant have a fan on your robot during a match. after your match yo ucan use a fan to cool the motors but during an match its illegal

1 Like

Just a reminder that for V5 motors, the vents are fake. They don’t vent anything, they are there to make the motors look cool not actually be cool. In fact the motor is completely encased in plastic so fans / icy spray is pretty ineffectual.

The best way to solve an overheating issue is to do some engineering / re-engineering to move the motor from an overload condition to back into the sweet spot of current vs workload.

26 Likes

Hot swap is a pretty good option if you have the funds

3 Likes

THEY’RE FAKE!?!?! My team and I have been using canned air this whole time thinking it was doing something and THE VENTS ARE FAKE!! I feel so dumb :smiling_face_with_tear:

5 Likes

I think the vents have function, although they aren’t actually used for ventilation. I have a faint memory of someone saying that the “vents” are actually used to increase surface area in order to make it more difficult for the motor to overheat, or something like that.

6 Likes

Plastic is unfortunately a very poor material for heat exchange. If the motor casing was made from metal, and had a good, snug fit against the motor itself, then the fins would serve some purpose. As they are plastic, it’s at best a negligible effect for increasing the surface area for heat exchange.

4 Likes

The rules are quite clear about this. “People say” a lot of things, some of which are true, some of which is not true. Your best bet in all situations is to go to the primary source.

For example, I could say “Fans with a blade length of 6 inches or less powered by a 9 volt battery are legal to use during matches”.

6 Likes

See this explanation from one of the VEX MEs during V5 beta program (which is in a closed channel so not visible to most forum members).

The OP is correct on this one - they’re cooling fins, not cooling vents. The internal motor makes a great heater, so we had to have a way keep it cool. The motor is mounted against the inside of the case, adjacent to the heat fins. The heat fins greatly increases the exterior surface area of the housing available for convection cooling. This really only works because the case is made from 30% glass filled nylon, which has a higher coefficient of heat transfer than most plastics.

27 Likes

If the game manual doesn’t prohibit it it is most of the time legal

The game manual prohibits any non V5 components, so unless you make a fan out of V5 parts, this would not be allowed.

8 Likes

So if you look here: The thermal conductivity of unfilled plastics | Electronics Cooling

The overall conductivity of plastic is really, really poor when compared to other materials. This table shows good conductors of heat Top 10 Thermally Conductive Materials

The difference is many orders of magnitude. Plastic, glass filled, fake fins or not is an extremely poor conductor of heat.

So I will stand on my opinion that you should do some redesign / re-engineering in cases of overheating motors. Killing the Ozone layer with fluorocarbons isn’t my preferred move.

5 Likes

Unless I see good/repeatable data, I think spraying canned air just gives the kids something to do to quell their impatience, while the motors just cool down on their own. There are only two real options: (1) design so the motors don’t overheat, or (2) use some form of the “hot swap” system.

4 Likes

This is the correct answer.

The question shouldn’t be “How do I cool my motor?”, the question should be “Why is my motor getting so hot?”

The cooling fins (not vents) do help a little in that it adds more surface area, which does play a factor. This is why heat sinks are finned. However, it’s still plastic. Even though 30% GF nylon conducts heat better than regular nylon, it’s a marginal increase (something like 10-15% at best).

Having done some cooling experiments on various FRC motors as well as the V5 motor, cooling from the outside of the case is pretty ineffective. Doesn’t matter if it’s a fan, or freeze spray. You still have to cool the housing substantially before you have any impact on the motor itself. Then after you cool the housing, you still have the wait for the housing to conduct heat away from the motor.

Even running a fan on the motor during the match produces minimal results. The amount of cool air you’re moving over the motor is doing almost nothing compared to the amount of heat created by a motor running at 10W or 11W. The most effective way to cool motors is from the inside, but there’s no legal way to do that.

You could hot swap the motor, but that isn’t solving the root of the problem. You’re just creating more warm motors that need to be cooled.

Thus, @Foster’s advice is best. Re-design/engineer the design so the motor runs at a more optimal area of the power curve. The more power you’re consuming at steady state, the more power is being converted to heat, the faster your motor will reach thermal protection. A motor running at 10W or 11W continuously will reach thermal much faster than a motor running at 5W continuously.

17 Likes

Just to build on this, the OP’s question is, therefore, is an XY Problem ( https://xyproblem.info/ ). The real problem is: when V5 motors overheat, their performance degrades, and motors running at maximum power hit this thermal point sooner than motors running at lower power. The user must define what the timeframe of expectation of “non-degraded” performance is, and what the recovery time from this state should be. Should it be “match time” (e.g. 1:45 or 2 minutes)? Should it be “practice session time” (e.g. a driver wants to practice continuously for however long a fully charged battery lasts)? Should the motors be expected to return to non-degraded performance within 2 minutes (e.g. possibly the tightest turnaround time on a back-to-back competition match)?

While, strictly, it is true that hot-swaps don’t solve the root problem, hot-swaps may allow teams to achieve the SLAs answered above. That said, there may be other benefits (e.g. faster drives, fewer overheat problems, etc.) to solving root problems (e.g. too much friction in the system, etc.) which also allows the team to achieve SLAs (either with or without hot-swapping).

As Jon suggests, another solution would be to simply limit the motors to consuming 5Watts…though this decision may have other, adverse effects on the robot.

Solving these problems is what makes engineering fun!

8 Likes

Regarding the allowable limit of motor power. Speaking in general terms, we are seeing about 50% power will allow a motor to run all match, with brief usage to 100%, without overheating.

This can depend a lot on 1) starting temp… is it still 5 degrees warmer than ambient air due to a recent run 2) ambient temp. Ambient temp can be bad… not only does the motor start warmer, it’s got warmer air surrounding it.

I’d suggest some constant load testing and temp graphing for the heating up AND cooling down with results posted for all to see.

fellas will say its an engineering problem but haven’t had motors overheat after tugging against robots for the entire duration of a match.

your robot shouldn’t drop performance from overheating during regular use, but there will always be situations in a match where you put more strain on your motors than usual. when you run into these situations, i highly recommend hot swapping your motors. during a Bo3 series this year, we doused our motors in canned air refrigerant due to the fact it would’ve been difficult to hot swap the motors in time. at the end of the match, neither robot could make it up the platform.

design your robot so that it doesn’t overheat, but when it does (and it usually will), quick swapping motors is a very good solution for the problem

4 Likes

Fans are not specifically allowed in the rulebook and would noy fall under decorstion items because its functional. Thus it is not legal.

Sure, COTS fans aren’t allowed, but what about using legal materials and a V5 motor as one?

1 Like

Sure, if you want to burn a motor from your motor allotment to cool another motor for very very marginal cooling gains, this would be legal.

15 Likes