So Am I reading the rules correctly? According to R27 fans need to be less than 10 watts I assume that is each - correct? Can’t find a rule on how many of those 10 Watt fans you can use? 10, 20, 30, 50… with proper flow direction/amplification contraption to alter the course of flying energy cells?

IDK if its feasible - just musing on a sunday evening here

Looks like they are excempt from motor controllers so you probably could hook them in parallel and turn them on with a relay

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Why not just stick some fan blades on a CIM?

Ignoring efficiency, you would need 33 of the maximum legal 10 watt fans to match the power output of 1 CIM.

I spent about 10 minutes trying to find a fan that fits the 12 volt 10 watt rating, but I couldn’t. Even if you could get one, I expect the cost per fan to be over $5 at an absolute minimum. (prices for similar COTS options in similar quantities were over $10). At $5.01 per fan, you would have to spend about $170 on fans. For a CIM fan you would easily spend less than that, even including the cost of 3d printing a fan blade and buying a motor controller.

Actually I was thinking of using 4 cims in a planetary arrangement and drive a turbofan. The reason for the above is that ther rules state 10 Watts maximum for a fan but no max number of fans. If I stick fan blades on a Cim and run it at lets say 30 amps with lots of fan blades that would be 360 Watts. If I go with the theoretical Cim max we are talking more than a KW (blow all the fuses first) Even if you run it at its basic without fan blades it almost draws 2A which is 24 Watts so even a fan with a Cim without fan blades would be illegal hence take a ton of legal fans???

Motors are preceded by breakers, not fuses.

The rule means that CIMs are allowed alongside fans that are 10 watts max. It does not mean that if you use another actuator (ie a CIM) to build a custom fan that you would have to limit it to 10 watts. Using a CIM to build a 337 watt* fan is perfectly legal.

* The maximum output power of a CIM is 337 watts, not more than 1 KW, per this page:

Ok was calculating off stall current. But as it may be I am pretty sure the rule would be interpreted as the fan being more than 10 watts if you put blades on a cim with or without a 10 wat fan mounted to it. Probably a question for the Q & A

I will tell you right now that you are wrong as to the interpretation.

In the same way that three 1/4 inch sheets of plywood glued together are not equivalent to 3/4" PLYWOOD, a CIM with some fan blades mounted to it is not a FAN per these rules. There may be other reasons why a massive CIM-powered fan is not legal (*cough* R8), but it certainly isnt due to rule R27.

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If that is the case, why do they bother limiting fan power?

The intent for limiting fan power is so that people don’t buy giant fans and use them to power gearboxes and the like. Basically, a COTS fan with an unapproved motor should be so low-powered that it won’t reasonably be used to replace any legal motor. FIRST wants to limit the usage of fans to be primarily (or entirely) for cooling. Even as recently as 2019 fans were only legal if they were included in FIRST Choice, the KOP, as parts of motor controllers, or as parts of COTS computing devices.

2020 rules:

2019 rules:

2015 to 2018 rules: word for word the same as 2019 apart from any listed years (only 2015 has a listed year).

2014 rules:

2013 rules: word for word the same as 2014 apart from the listed year.

2012 rules:

2011 rules:

2010 and 2009 rules weren’t as clear and concise, but they were clear enough to understand that the allowed fans came in the KOP or on a Victor motor controller, but they only seem to prohibit other fans using the modern frc definition of what a Motor or an Actuator is. I wasn’t around in those years, but if someone can weigh in on the definition of Motor and Actuators from back then, it would be appreciated.

In 2008 and 2007, they didn’t mention fans at all beyond saying that “muffin fans” could be connected with 28 gauge wire, so I assume all “muffin fans” were legal.

There is no 2006 manual on the FIRST website for archived game documentation, and the manuals provided prior to that only include game/competition rules and no sections for robot rules.


So question is can imount some blades on a cim and blow your energy cells off course legally

If that is the way the rules are regulated this year, then I am going to declare that every other team is using fans as wheels and have them all disqualified.


I disagree. A fan by definition is a device to do nothing else but move air. That is why those “things” hanging from an airplane wing are turbo-fans and not wheels. If you design a device to move yourself through air then its a propeller. A round thing to move you along a more or less flat surface is a wheel. All those turn and have a power source. So what would you call it if I mount blades to a motor (CIM, NEO whatever) and put a shroud/contraption on it to improve and direct its air output and move/blow lots of air in a certain direction?

Years ago I saw some robots who had a large fan (CIM powered) with a guiding tube that blew that years projectiles off course and was used as a defensive device - quite successfully I have been doing this for 10 years I don’t remember what year and task it was and what the rules were that years.

So If you would classify a CIM with blades a fan than I think it would be illegal as its over 10 watts if you can call it an IDK what that does not call it a fan it might be legal - what would you call it and how would you believe its legal? Probably a ruling should be made on that

You are welcome to attach anything you want to a CIM motor and use it on your robot, as long as it does not violate any of the other rules. R8 was mentioned, and an uncovered fan blade, especially one large enough to effect flying balls and spin up to 6000ish RPM, would be unsafe. If you encased it in such a way that fingers are not at risk etc. then build yourself a CIM powered fan and try blowing balls off course. Sure, why not? If it suits your desired strategy for the game and meets the goals of your team then it’ll be a good use of your precious resources of time, materials, money, and people.

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I have also seen CIM powered fans on robots over the years. In 2009 they were used to attempt to increase normal force on to that stupid floor. 2013 some teams used them to blow the Frisbees off course. They might have also been used in 2016but I don’t recall seeing any.

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You can try, but experience shows it didn’t work with frisbees. So it isn’t very likely to work here.


It was brought up at the meeting as a possible defence strategy. The question was legality and yes it would be enclosed. For aerodynamics alone it would look closer to a jet engine (turbofan) than a fan you have inside your computer or other electronics. Question would be as to how much air one could move with a cim

Good to know - well we have another meeting today and we will start putting the drive train together.

There are very efficient air moving fans on the market I think, tornado fans or some such? Just like with linear actuators, you are welcome to take the motor out of a cots model and replace it with a CIM.

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I do agree with Doug though. I did see fans in past years, but I have never seen one that was effective at frc. If you want to knock a ball off course, probably best to hit the robot that’s shooting it, or stop them from getting to their protected shooting position. In fact my OPINION is that it is a bad idea, but you do you.

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Yeah maybe. Main question was as to the legality. Now the team will have to decide as to if this has any priorities. Personally I would like to see everything else finished first and if there is plenty time we can try the fan

I like the hitting part too. So I will report its probably legal - but will advise against it. In my estimation - have not done any serious design it would take at least 4 CIMS to theoretically move enough air - best case to make a noticable effect. Maybe that could be an off season project plus one would have to make a “wall of air” probably not that easy on something the size of a robot. Then if you run it for any length of time it would be quite a drain on your battery. Plus weight and 4 motor controllers - question if you got enough slots on the PDP plus cost of it all. Does not look too good if you take a closer look. And then how would you best use the power of 4 CIMS (as you need that many to move enough air) maybe a planetary arrangement where either the sun or ring becomes the fan etc etc. Probably not something that could be done in the time frame at hand

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