Converting 12v to 24v

[Johnny_5]

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?

[Oldbikerider]

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.

[Cecil]

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.

[Ether]

Originally Posted by Johnny_5

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?

I don't see purchased electromagnetic clutch assemblies listed in [R48]. Is there a ruler somewhere else that makes this legal?

[Jim Wilks]

Perhaps this is this being used under the new rule which permits solenoids? If so, it must be no more than 10 watts.

[Ether]

Originally Posted by jgw

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.

[Mr V]

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.

[Tristan Lall]

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.

[Tristan Lall]

Originally Posted by Johnny_5

Is it legal to have a 12v to 24v converter?

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.

[FRCTEAM1847]

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.

[Johnny_5]

The electromagnetic clutch doesn't operate with a solenoid, I have attached a wikipedia article about how they work.

http://en.wikipedia.org/wiki/Electromagnetic_clutch

I will follow up with the GDC Q&A forum to find out if it is legal

[Al Skierkiewicz]

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.

[Tristan Lall]

Originally Posted by Al Skierkiewicz

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:

Scag Power Equipment

[Al Skierkiewicz]

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.

[Tristan Lall]

Originally Posted by Al Skierkiewicz

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:

Originally Posted by Tristan Lall

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

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:

• Is the device electromagnetic and an actuator? If (and only if) so, [R48] applies.¹
• Does it contain a motor? Then see [R48A-I, K-L].
• Does it contain a solenoid? Then see [R48J].
• For electromagnetic actuators not otherwise mentioned, there is no specific permission (required because these are "[t]he only motors and actuators permitted"), thus they are illegal.

Following that logic, the electromagnetic bell (not a solenoid) above was legal in 2010, but is illegal in 2012. Similarly, an electromagnetic clutch which is not a solenoid is illegal this year (but would have been legal in some previous years). An electromagnetic clutch which is a solenoid is legal this year, provided it conforms to the solenoid rule.

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.