Clutch system

Does anyone know if a 12v clutch is allowed on the robot?
or even 5-6v if the is one that exist.

No other electrically operated motor or actuator, than what’s called out explictly by the rules, is allowed.

So, no.

I expect he is asking about an electromagnetic clutch? of the type used on air conditioning compressors in cars. If so it would likely fall into the “electromechanical actuator” category and be illegal. Or not…

Here is the appropriate Q&A:

I don’t really think that this answers all the questions. Why? Cause my team is trying to figure out if we can use a clutch that we used in 2008 for our catapault and we’re not getting any specific answers yet.

I’m not psychic GDC, just give me a straight answer. I can’t determine if x part is legal if I don’t know what the official definition of this is.

-Tanner confused

The web page pointed to in that Q&A specifically describes an electric solenoid valve actuator. It has components that aren’t part of a generic solenoid.

The “official definition” of an electric solenoid actuator is pretty simple and reasonably obvious. A solenoid consists of an electromagnet and an armature that moves to provide a mechanical output when the electromagnet is energized.

If you tell us what “x” is, many of us will be able to tell you why it is or is not legal according to the robot rules.

This is the section that applies to your answer…
<R53> Items specifically PROHIBITED from use on the ROBOT include:
A. Electric motors and/or servos different from, or in addition to, those in the KOP, with the exception of those specifically permitted by Rule <R52>.
B. Electric solenoid actuators (note: electric solenoid actuators are NOT the same as pneumatic solenoid valves – the latter are permitted, the former are not).

If you had an electric clutch that used a moving part that was attracted by a magnetic field, then this rule would have applied in 2008 and would (should) have been deemed illegal as it is in 2010. The same language existed in the rules then as now. If you would like to PM me with the part you are considering I can give you an opinion from an inspector point of view. The definitive answer still comes from the GDC via the Q&A and has been answered.

Doesn’t the definition of “solenoid” also necessarily specify that the electromagnetic coil produces a reasonably uniform magnetic field in the centre of the coil, and that the armature is located there? (Otherwise, there would be no distinction between a run-of-the-mill electromagnet, and a solenoid.)

Considering that distinction, I’m not convinced that an electromagnetic clutch is always illegal—it would depend on what’s inside. Given this question and its response, I think the GDC is agreeing in general terms with that proposition.

If there is an armature that moves in response to the electromagnet being energized, it’s probably a solenoid and illegal. If nothing moves as a result of the electromagnet being energized, it’s probably just an electromagnet and legal.

We still haven’t seen pictures of the device in question, so it’s pretty hard to say.

An electromagnetic clutch used in an automotive air conditioning compressor has a part that moves as a result of energizing the electromagnet, so it’s probably a solenoid.

If there is some other type of electromagnetic clutch, I’d like to see it.

Just for the sake of discussion, is this electromagnetic bell a prohibited solenoid actuator? (I would say no, because its geometry is inconsistent with a solenoid.)

From Wikimedia Commons

There are clutches that use a magnetorheological fluid which changes its viscosity based on an applied magnetic field.

I would expect the GDC to rule it illegal. The geometry might be inconsistent with the typical electric solenoid actuator, but the action is close enough that I think it meets the intent of the prohibition.

There are clutches that work off of magneto-strictive (sp?) materials like Terfenol-D


After examining your 2008 bot at GA Tech at the control system demo last year, several of us spent much discussion on your clutch, and the legality thereof. We came to the conclusion that the inspectors overlooked an apparent violation. This was just our opinion, we have no line into the mysterious hive mind of the GDC.

I agree that the Q&A answers have been vague, but it looks to me like they are saying that if something moves by electromagnetism, and it’s not part of a solenoid valve, or a motor provided in the kit, then it is illegal. I realize that the movement in the clutch is very small, but if they intended to allow some movement, they would have specified a maximum. By not doing so, they specified a maximum of zero inches.

All of the above is my opinion, and has no real meaning in the greater scheme of FIRST.

This type of clutch would probably be prohibited too, as it contains a liquid.

Sorry to go a little off-topic, but are you saying an electromagnet is illegal?


The GDC answer indicates that using an electromagnet to hold something in place is permitted. Using one to move something is not. This fits well with Martin’s “zero inches” interpretation.

Thanks for helping clear a bit of it up. Though this answer by the GDC kinda affirms.

I still think that they (the GDC/FIRST) could still clear up what they mean by a electromagnetic solenoid as having none isn’t exactly clear.

Not to be like a meanie or anything, but couldn’t a motor be classified as a “electromagnetic solenoid” if it shifts the axel out/in for rotations? It’s probably a extreme case, but still…

Not trying to spark anything up, just trying to make sense of confusion.


The intent is perfectly clear to me. I don’t see the need for any more specific wording in the rules. If there were to be a strict definition of an “electric solenoid actuator” in the manual, you can be certain someone would find a device that doesn’t meet the definition but really should have. The more painstaikingly detailed the rules are, the more loopholes people will find.

Not to be like a meanie or anything, but couldn’t a motor be classified as a “electromagnetic solenoid” if it shifts the axel out/in for rotations? It’s probably a extreme case, but still…

The permitted motors are itemized and granted legal status explicitly.

I think the point they are trying to make in that answer is that you may design and build a clutch, or buy an existing clutch, provided that the actuation of the clutch uses a legal motor, servo, or pneumatic cylinder.

for example you could have two plates that move together when pushed by a cylinder (big bore, short stroke, most likely)

or two plates with slots, and a servo moves a connecting bar into the slots.

or you can use the ball-based torque clutch from an electric drill and actuate the tensioning mechanism with any of the legal actuators.

While it may seem simpler to say ‘no electromagnetic clutches’ or ‘no clutches’, the GDC is trying to limit you as little as possible by just saying ‘no mechanisms with non KOP/R71/R72/servo actuators’