We are planning on using an electromagnetic clutch to “freespin” a van door motor for our launching device. The only problem is the electromagnetic clutch from the vendor we are allowed to purchase through is a 24v device.
Is it legal to have a 12v to 24v converter?
If it’s just a permanent magnet motor, on 12V it will simply run at half speed and have a lower stall torque. Will this be a problem? How much of the speed and torque performance of the device do you need?
Graham.
I don’t think he is talking about a motor… I’m guessing that the electromagnet will engage or disengage a clutch separate from the van door motor. I don’t see anywhere that a converter is illegal, but just remember, the 12 volts will drop to about 7 volts sometimes, especially in pushing matches.
I don’t see purchased electromagnetic clutch assemblies listed in [R48]. Is there a ruler somewhere else that makes this legal?
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Perhaps this is this being used under the new rule which permits solenoids? If so, it must be no more than 10 watts.
Maybe, maybe not. Before investing too much effort on this, you might want GDC to clarify rule [R48]J with respect to this question.
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I agree that you should ask in the Q&A if it is legal before preceding.
What is the the force the clutch is rated to transmit? If you don’t need all of that force you may get enough force running it at 12v.
This question has come up before.
In 2005, the rules were different, and all electronic “motor[s], solenoid[s], pump[s] or other actuator[s]” were prohibited, other than the ones in the KOP. (This type of clutch is either a solenoid or other actuator.)
In 2010, the rules were more similar to 2012. In that case, the Q&A noted that if the clutch did not contain a prohibited actuator (and implicitly, did not violate any other rules), it would be allowable. In 2010, there was some unresolved discussion about whether the clutch contained a true solenoid, or merely some other type of electromagnetic actuator.
For 2012, [R48] provides a new complication, because it now says “The only motors and actuators permitted on 2012 FRC Robots include” instead of “Motors specifically permitted on 2010 FRC ROBOTS include”. This means that a new restriction on actuators has been explicitly added for this year.
Therefore, if the clutch contains a solenoid, then that solenoid must meet the specifications from the rulebook for the clutch to be legal. If the clutch does not contain an appropriate solenoid (or other thing from [R48]), it’s a prohibited actuator. (Of course, the device must also meet all other rules, particularly the ones dealing with custom circuits and power regulating devices for actuators.)
I think the rule is clear in its meaning, but not so clear in its intent. Why ban a device that was previously allowed, even as you allow solenoids for the first time in over 10 years (and possibly ever)? You might therefore want to raise it in the Q&A not for clarification, but with the intention of prompting FIRST to change the rule.
With respect to this issue, the converter is a custom circuit, and must therefore conform with [R47], which says that “[c]ustom circuits shall not directly alter the power pathways between the battery, PD Board, speed controllers, relays, motors, or other elements of the Robot control system (including the power pathways to other sensors or circuits).”
You might want to ask the Q&A whether a solenoid actuator is an other element of the robot control system, as enumerated in the rule. That will determine if your custom circuit can legally affect it.
If the clutch is utilizing a solenoid to accomplish it’s task, then R42 (power distribution), R47(custom circuits can’t alter voltage), R48J(solenoids must be 10W @ 12V), and R50E (can be hooked up to a Solenoid breakout board which is powered by 12V) combine to say that a 24V electric solenoid is specifically prohibited.
That being said, I would still go to Q&A though.
The electromagnetic clutch doesn’t operate with a solenoid, I have attached a wikipedia article about how they work.
I will follow up with the GDC Q&A forum to find out if it is legal
Issac,
The clutch you linked to specifically discusses the attraction of an armature plate by the magnetic field set up when the field coil is energized. It attracts the armature to a frictional coupling with the driver mechanism. This is exactly what an electric solenoid actuator is and therefore must conform to the solenoid rule, 10 watts @ 12 volts continuous. This is much different than an eddy current clutch where no parts move and no friction is used in the transfer of power.
There might be a distinction. I believe that in a solenoid actuator (of the conventional commercial type) the axis of the wrapped wire coil (not the wire itself) is coincident with the central axis of the armature (generally a shaft or similar). The armature moves within the central void.
In this design, it looks like the coil might be instead wrapped around a circular axis (i.e. toroidally). In that case, the armature is not moved within the centre of the coil. It wouldn’t be a solenoid (even a toroidal one, if that’s even possible), because there is no open core within the windings of the coil.
I can’t tell exactly what’s going on the diagrams, but here’s another cutaway for comparison:
[img2]http://www.scag.com/images/clutch-cutawayBIG.jpg[/img2]
Scag Power Equipment
Tristan,
You forget the test we have used for this in the past. If it is a coil and something moves when you apply current, it is considered a solenoid/electric actuator. It is strictly limited by the GDC to limit the power sources that can be used on a robot.
I didn’t forget that test…but I don’t like the way it conflates a solenoid with an electromagnetic actuator as if they’re necessarily the same thing. Here’s an example of something which is clearly an actuator, but also clearly not a solenoid:
For the first time, it looks clear that FIRST wants to regulate all electromagnetic actuators (per the rule change noted in a previous post). But in that case, why not subclassify them as motors and non-motors? Is there something special about a solenoid actuator that doesn’t apply to another kind of electromagnet that does mechanical work?
And while it’s a convenient distinction, what would FIRST’s rationale be for caring about whether a device does mechanical work or not? There’s no correlation with electric power input, and there’s no guarantee that a device not designed to do work is inherently safer than one that is.
Despite my concern with the rationale, given the rules this year, the way I think the test should work is as follows:
1 Despite its wording, [R48] appears to apply to electromagnetic actuators…if that weren’t true, there would be a rules conflict for pneumatic actuators.
Are you saying that the bell is not doing work? Is not a solenoid? How was the bell legal in 2010?
2010 Robot Rules…
<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).
The bell is:
There was no prohibition against electric actuators in 2010, except that motors other than those listed were illegal, and solenoid actuators were illegal. Think of it as a custom circuit. (It must still comply with all other rules.)
(The 2012 rules are somewhat different, as noted above.)
A solenoid is simply a coil of conductive material (Technically, there are many accidental solenoids on robots every year, but those are not actuators). The bell pictured clearly utilizes a pair of solenoids wrapped around the iron core. As stated it is an actuator. The actuation occurs as a result of current passing through said solenoids, thus, it is a solenoid actuator.
A solenoid is a particular kind of wire coil: it’s oriented such that it produces a uniform magnetic field within the core.
For sufficiently lax definitions of “uniform”, sure, we’ve got all sorts of solenoids. But then you get into perverse situations where every motor winding is a rudimentary solenoid, and thus the motor is a solenoid actuator as well as a motor. (I, for one, certainly don’t want to believe that this is what FIRST intended. It kind of flies in the face of conventional nomenclature, both for motors and solenoids.)
For the bell and the clutch, if the windings are squarishly wound around a squarish core (in cross-section), the magnetic field will likely be very non-uniform. That’s also a poor approximation of a solenoid.
Contrast this with an ordinary solenoid actuator, which does indeed contain a tightly-wound cylindrical coil of wire, designed to provide a uniform magnetic field within the core.
I don’t really see any way to judge from the rules that the level of non-uniformity found in the clutch’s magnetic field is substantially different from the non-uniformity of magnetic field produced by a motor’s windings.
Tristan,
The bell was not legal in 2010. And there is no way anyone can convince me it’s a custom circuit. The bell meets none of the criteria below that would make it allowed. And in all likelihood I would also rule it illegal under R02.
8.3.7 Motors & Actuators
<R52> Motors specifically permitted on 2010 FRC ROBOTS include:
A. All motors, actuators, and servos listed in the 2010 KOP,
B. An unlimited number of COTS servos with a maximum output torque of 55 oz-in and maximum rotational speed of 100 rpm at 6 Vdc (e.g. HITEC model HS-322HD or HS-325HB servos, as provided in the KOP),
C. An unlimited number of FIRST Tech Challenge (FTC) servos (HITEC HS-475HB servos),
D. One, two, or three additional 2½” CIM motors (part #FR801-001 and/or M4-R0062-12) in addition to those provided in the KOP. This means that up to five, and no more, 2½” CIM motors can be used on the ROBOT.
E. Identical one-to-one SPARE PARTS for motors, actuators, and servos provided in the 2010 KOP that may have failed or become damaged.
<R02> ROBOT parts shall not be made from hazardous materials, be unsafe, or cause an unsafe condition. Items specifically PROHIBITED from use on the ROBOT include (but are not limited to):
B. Speakers, sirens, air horns, or other audio devices that generate sound at a level sufficient to be a distraction or hindrance affecting the outcome of a MATCH
![http://www.scag.com/images/clutch-cutawayBIG.jpg[/img2]](http://www.scag.com/images/clutch-cutawayBIG.jpg%5B/img2%5D){kind=link}