Anyone know if electromagnets have been allowed in the past?
If so, how could they be used on an FRC robot? Just hooked up the same way as a motor?
Thanks in advance!
Sincerely,
Clueless Rookie Coach
To my mind they are a type of actuator. So they are governed by R33. R33 has a chart if what is allowed. Outside of what is on R33, nope.
R33 lists:
Electrical solenoid actuators, no greater than 1 in. (nominal) stroke and rated
electrical input power no greater than 10 watts (W) continuous duty at 12 volts
(VDC)
Would that include these electromagnets that are listed as a solenoid and meet the 10W power requirement, such as these:
https://www.amazon.com/dp/B01NASKR8D/ref=cm_sw_r_cp_apa_Xz9uAb8CRQDP3
I don’t actually know if that particular one meets the 10W requirement, but let’s assume it does for now. Do you think it would be allowed under R33?
Unfortunately that is a hard one to answer. The only people that can answer definitively is the Q&A Say less than 10 W? OK. Defined as a COTS solenoid? OK. Does it has less than 1in travel? Q&A will likely throw it back on the LRI. (They like to answer questions about the rules, not specific devices). If I was asking Q&A, I would focus on the stroke issue rather than asking about a specific device.
If you can find a local LRI (Lead robot inspector) They could at least answer how they would view it. As a RI (robot inspector) I would run this by the LRI so we would be consistent for the event at least
That’s a victim of poor translation, obviously. There’s some leeway for deferring to a manufacturer’s naming of an item, but when it’s clearly wrong like that, then no. Actual solenoids have a steel rod that pulls in and out, thus the nominal stroke restriction. If that showed up at my desk, the first thing I’d ask is what the data sheet says the stroke on it is. And then it’d fail to pass since it doesn’t have a nominal stroke.
Forgive my ignorance. I just saw that nearly all of the electromagnets listed for sell on Amazon have Solenoid in the title. The definition of solenoid I found just said they were a coil of wire which act as a magnet when carrying electrical current. Frank, first said that he considered an electromagnet an actuator. So if it is indeed classified as an actuator, and is a solenoid. Then it fits the definition listed in R33.
As for the stroke restriction. If it has no stroke, then the stroke is zero, right. 0>1.
That’s just my thought process…which is probably wrong. I guess I will wait for the Q&A to open, unless anyone else has any experience or knowledge on the subject.
Oops, meant 0<1.
This is a question best asked in the official FIRST Q&A that will open on Wednesday.
My personal (unofficial) reading of the rules would conclude that electromagnets would fall under the “CUSTOM CIRCUITS” line in table 8-2/Rule R36. It would then have to comply with rules R47, R51, R58, and R62.
An electromagnet is part of a solenoid, but not all electromagnets are solenoids. My $0.02
Yeah, I plan to ask once they open. Just figured I would see if anyone already knew the answer from previous experience.
My personal (unofficial) reading of the rules would conclude that electromagnets would fall under the “CUSTOM CIRCUITS” line in table 8-2/Rule R36. It would then have to comply with rules R47, R51, R58, and R62.
I think it comes down to if it is considered an actuator or a custom circuit. So let’s look at what an actuator is. According to wikipedia:
An actuator is a component of a machine that is responsible for moving or controlling a mechanism or system, for example by actuating (opening or closing) a valve; in simple terms, it is a “mover”.
Based on that, I would say an electromagnet fits the definition of an actuator.
An electromagnet is part of a solenoid, but not all electromagnets are solenoids. My $0.02
According to the Wikipedia article on solenoids:
A solenoid is a coil wound into a tightly packed helix.
It goes on to say:
A solenoid is a type of electromagnet when the purpose is to generate a controlled magnetic field .If the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.
Meanwhile, the Wikipedia article on electromagnets says:
Electromagnets usually consist of insulated wire wound into a coil.
Which is a solenoid, by definition.
To my understanding, that means that while not all solenoids are electromagnetic, they can be. Also, electromagnets are basically just a solenoid creating an electromagnetic field when current is passing through them.
But we will see what the GDC has to say about it later this week.
Thanks again!
I like your two cents, Sean.
However, if I were allowed to include CUSTOM CIRCUITS that use coils to produce magnetic fields* in an assembly that also features a few permanent magnets, I could build a brushless motor. It was made clear to me quite a few years ago that the GDC did not intend to allow that.
We’re probably safer inspecting electromagnets as ACTUATORS. The one linked in the OP lacks specifications for electric power (or current draw at 12V), and for stroke length. So I’m with Brandon – it’s not legal.
*Call them solenoids, inductors, electromagnets, or stator windings – your choice.
I found a source for similar electromagnets that give more specifications.
http://www.magnetechcorp.com/round.html
Most of the 12V magnets on this site are under 10W. However, I’m not sure what the stroke length would be considered, since they don’t actually have a stroke. But would think a stroke length of zero would meet the criteria of being less than 1.
At the least, the stroke length would be the distance moved by whatever the magnet is attracting. So it’d only be 0 if the other half never moved. If it’s less than an inch, you could argue it’s legal, or buy an actual solenoid and skip the argument.
Again, I’m new to all of this, so forgive my ignorance, but does a “actual solenoid” produce any magnetic pull or is it basically a tiny linear actuator?
If it does not have any magnetic pull, then it wouldn’t really accomplish what we have in mind.
Brandon
Do you have an actual application for an electromagnet in mind? Have you estimated the force you need to perform the functions you have in mind? Have you calculated if a legal (under 10 Watt) electromagnet can provide sufficient force to perform the functions you have in mind? Have you considered other types of actuators that can perform the same function?
With a quick search, I was able to find a formula for calculating the force exerted by an electromagnet based on parameters such as the current, the area of the core, the number of turns of wire and the magnetic constant of the core material. I think this is the force right at the end of the magnet. The force would fall off as the cube of the distance from the end of the electromagnet. This means the configuration of the magnetic circuit is critical.
While relays, solenoids and motors all contain electromagnets, the magnetic circuit in these devices are all highly optimized by the component manufacturer. The gap between the coils and the core in them and the other parts they interact with are always kept very small.
Using an electromagnet can be a great learning experience. It might be a lot wiser to do this learning between competition seasons.
Do you have an actual application for an electromagnet in mind? Have you estimated the force you need to perform the functions you have in mind? Have you calculated if a legal (under 10 Watt) electromagnet can provide sufficient force to perform the functions you have in mind? Have you considered other types of actuators that can perform the same function?
Yes, we have an application in mind. We have not estimated the force required, but it will not be much. It would basically be holding a part of the robot in place and then releasing it when needed. The part would likely be less than a pound. An electromagnet is only one type of actuator we are considering. I’m just wondering of the legality of it before we move any further with it. I havr found several electromagnets that exert over 100lbs of force all drawing less than 10W of current. I provided a link a couple of posts up showing several of those.
With a quick search, I was able to find a formula for calculating the force exerted by an electromagnet based on parameters such as the current, the area of the core, the number of turns of wire and the magnetic constant of the core material. I think this is the force right at the end of the magnet. The force would fall off as the cube of the distance from the end of the electromagnet. This means the configuration of the magnetic circuit is critical.
That’s mostly unessecary, I believe, since all of the ones I have looked at have the force exerted listed in its description.
While relays, solenoids and motors all contain electromagnets, the magnetic circuit in these devices are all highly optimized by the component manufacturer. The gap between the coils and the core in them and the other parts they interact with are always kept very small.
That’s what I was thinking. The other poster suggested we use a regular solenoid actuator, but that wouldn’t really work for this application.
Using an electromagnet can be a great learning experience. It might be a lot wiser to do this learning between competition seasons.
Thanks for the suggestion. I feel like we have a good enough grasp on how they work, just need to figure out of they are legal.
I’d just like to chime in here to point out that, technically, a solenoid is merely a coil of wire. Colloquially, it’s often used to refer to actuators that have a ferrous rod inside the solenoid to provide a push or pull motion, but that’s synecdoche. FIRST got it right in R33 by specifying “Electrical solenoid actuators” (emphasis mine), but they seem to have gotten lazy and just referred to “solenoids” in other places.
Regardless, it’s a question for Q&A.
Good point. I think it may come down to if an electromagnet meets the GDC’s definition of an actuator.
Regardless, it’s a question for Q&A.
Agreed. I’ll ask on Wednesday.
Last year we considered using one of the round one from mcmaster carr to control the gear…
We successfully confirmed with a Lead Robot Inspector and he recommended that we bring the data sheet if we were to use… unfortunately, it was just not strong enough…
Good to hear.
Just to clarify. The LRI said it was legal?
I’m curious, how much weight were you trying to hold with?
We used electromagnets in 2016 and 2014 for our pneumatic catapult. It held the catapult long enough to pre-load the cylinders. Here’s some video: https://www.youtube.com/watch?v=Hb5zcQ8Fp6c
You can kind of see it in the video (the cylinder attached at the top of the frame) and it pretty much looks like this: https://goo.gl/ybyzmi
I believe the last one was connected with a Spark. I’m not sure about the specs completely, but probably similar to above. Also, I don’t know what the rules it had to comply with. We did pass at least 5 inspections with them and the rules haven’t changed that significantly in this area.