Additional field coils around motors

[ConKbot of Doom]

I know everyone always wants more power form their motors, and that we aren't supposed to open them up to mess with them, but if you were to wind additional coils around the motor, could you increase the field strength legally?

I was thinking something along the lines of a series wound or shunt wound coil at first, but those are for AC electric motors, and only go in one direction.

However, if you were to have the field coil on its own speed controller, you could vary the strength of the field for when you need it.

This would be considered a custom circuit, so reading R52 from 2005
Inputs to custom circuits may be connected to the following sources:
Branch Circuit breaker outputs
Speed Controller or Relay module outputs
PWM or Relay outputs on the Robot Controller
Switches, Potentiometers, the outputs from Accelerometers, Sensors, and other additional electronics allowed

So it would be legal to have the inputs of this circuit (the power inputs) connected to a Victor, at least as how I see it.
So it would be setup so that once you hit full power on the motors, you start powering up the field coils around the motor to increase the strength of the motors.

Granted it wouldn't be that easy to wind the coil so that it's field matched that of the CIM, and there already is so much power available, and current draw is allready pretty high. Would it be legal, and beneficial to make a setup like this? Maybe as a big red button for when your in a shoving match or something.

[sanddrag]

What about just putting a steel band around it like the fisher price motor has?

[Jack Jones]

Take another look at <R31> - What part of "So that every robot’s maximum power level is the same," don't you understand?

[ConKbot of Doom]

Take another look at <R31> - What part of "So that every robot’s maximum power level is the same," don't you understand?

Yes it says that, but looking at it in context it says after that "the motors in the kit may not be modified except as follows" and the purpose of this would be to do that without modifying the motors.

Sanddrag- Yeah it would be pretty easy to do that, but whats the fun in doing something that you know is going to work allready :p I'm not going to be actually trying this on anything, just thinking about it.

[Mike Betts]

Jon,

I believe that any such an attempt would be violating the spirit and intent of the rules.

Years ago, Woodie and Dean asked us not to be lawyers. I would echo that sentiment.

Regards,

Mike

[KenWittlief]

The motors can only draw their power (energy) from the victors

and you cannot build your own motors

adding additional coils to the motors is an interesting idea, but those coils would be dissapating energy into the motors (magnetic energy), which is not coming from the victors - so it violates the rules

you could come up with all sorts of creative ways to increase the power of your drive train, making a steam engine for example - but no matter how you convert stored energy into mechanical energy a motor is still a motor - if its supplying more power to the drivetrain, its a motor, and its against the rules.

[Tristan Lall]

I disagree with Jack that it violates <R31> as written, however, it clearly violates the spirit of that rule, for whatever that's worth when it comes time for the inspector to make a ruling. Part of the problem is that circuits are defined in the rules in electrical terms ("as long as the electrical system is not modified", etc.), rather than (more comprehensively) in electromagnetic terms. What we really ought to see from FIRST is a clear indication of what modifications to the motor's magnetic circuit (which includes the ferrous metal case of the motor) are permissible. This would also instantly clarify the legality of 190's lathed-down CIM housings. Personally, I'd like to see something like "additional magnets, ferrous metals, or field coils (whether separately excited, or energized by the motor's magnetic field) are not to be placed within 0.25 in of the outer diameter of any motor, if their presence would cause a significant change in motor output", along with "modifications to the motor housing are permitted, provided that they do not cause a significant change in motor output or compromise the structural integrity or safety of the motor".

Returning to the original proposal, it seems to violate <R53>, which requires that custom circuits may not "[d]irectly affect any output devices on the robot, such as by providing power directly to a motor", though I suppose that a question could be raised as to whether "directly" includes magnetic fields, or merely refers to electrical conduction.

I don't think that this circuit exactly conforms to the intended applications listed in <R52>, but because the rules do not state "if it's not included, it's not allowed", we can only note that it doesn't conform to the stated intent. (Perhaps "may" should become "may only" in the second sentence of that rule.) Also, the sense of the term "outputs" looks like it means electrical outputs (judging by context), and therefore wouldn't cover the magnetic field.

[KenWittlief]

...we aren't supposed to open them up to mess with them,

here is where your thinking is slightly offtrack - we are not allowed to modify the motors to enhance their performace, whether you open them or not

but if you were to wind additional coils around the motor, could you increase the field strength legally?


if you add field coils to a motor, with the intention of altering its torque and speed characteristics, how can you say the motor has not been modified?

from Daves post in the motor bias thread:

In 2005, Rule <R31> stated the following:

<R31> So that every robot’s maximum power level is the same, the motors in the kit may not be modified except as follows:

• It is acceptable to modify the mounting brackets and/or other structural parts of the motors (output shaft, housing, etc.) as long as the electrical system is not modified and the integral mechanical system of the moving parts (bearings, bushings, worm gear output stages, etc.) is not changed or removed. ...

[Tristan Lall]

here is where your thinking is slightly offtrack - we are not allowed to modify the motors to enhance their performace, whether you open them or not



if you add field coils to a motor, with the intention of altering its torque and speed characteristics, how can you say the motor has not been modified?The sense of the word "modification" from <R31> seems to be referring to physical changes only. ("The intent is to allow teams to modify mounting tabs and the like, not to gain a weight reduction by potentially compromising the structural integrity of any motor.") We know, obviously, that they want to limit robots to a certain power output level, but they have only described physical changes to the motor that might cause this level to be exceeded. They don't actually mention entirely new components that exist outside of the intact motor.

Also, to preempt this question, I don't think that the external coils constitute a distinct additional (i.e. illegal) motor. They don't posess a rotor (unless the CIM is part of an assembly, which is a perverse way of looking at it, given that motors are typically considered to be components), so how can they be a motor? (No mention of linear induction motors, please; they're not relevant—but they do have the equivalent of a rotor.)

Now, one thing that I didn't address before: safety. By increasing the power output, you're also increasing the heat generated by the motor. Since we assume that the motor is designed for its rated power, and no more (even if there is a margin of safety, we're not privy to how big it is, and can't convieniently calculate it), it would be fair to assume that adding extra power could cause thermal damage to the motor. The increased risk of smoke and fire would likely be a fair reason to disallow it, unless, of course, the team using it could prove that it was safe (which would be challenging, I think).

[jrocket567]

OK, so I can see how this could possibly be illegal according to the FIRST rules.
So to satisfy my curiosity, would this actually increase the power of the motor? Electricity and I usually do not get along, but this sounds like a cool off-season project.

[EricH]

Not only do you have the above mentioned issues, but you have to insulate the wires or whatever else you use. That will also affect the motor, plus you get inspectors wanting to verify that yes,that is a CIM in there, plus the CIM may be counted as part of a motor assembly, so you get hit on making your own motor. I don't think it's worth the effort, because by the time you get through th inspection process and everything else, it'll be Friday afternoon... A better option for more power might be to just have another motor that engages only when you want it to. If you really want to get an answer to whether winding more coils around the motor is legal, talk to Q&A. Oh, and all this leaves out the possibility that this whole thing might not work.

[Dave.Norton]

I know everyone always wants more power form their motors, and that we aren't supposed to open them up to mess with them, but if you were to wind additional coils around the motor, could you increase the field strength legally?

The difficultly is the case is already the field return path and by and large any externally applied flux is going to be shunted around by the case without bothering with the rotor. Somehow you would need to get the additional flux into the internal flux circuit, but I can't think of a why to do that without violating the letter of the rules (let alone the spirit :) ).

[gburlison]

What about just putting a steel band around it like the fisher price motor has?
So, if we fabricated a motor mount out of a steel band that wrapped around the CIM, the motor might have a slightly higher power output?

[sanddrag]

So, if we fabricated a motor mount out of a steel band that wrapped around the CIM, the motor might have a slightly higher power output?In a post I'm too lazy to search for right now Joe Johnson said something to the effect of "if you can pick up a large paperclip with a motor, chances are the motor could benefit from an external flux yoke" (I think that's what it is called) "Torque can be increased up to 20% in some cases"

And you'll notice the FP motor has one of these doo-dads and apparantly it serves a very important purpose.

So, I haven't tried it, and I haven't yet learned about magnetic flux and whatnot (I think about 3 weeks away from learning about that in Physics) but it sounds logical and I'd definitely be willing to try it. Does anyone know if you can pick up a paperclip with a CIM?

[KenWittlief]

the effect of increasing the strength of the field is twofold:

1. you will have more torque for a given voltage
2. your top speed will be lower

the reason for #2 is the stronger field will generate a larger counter-EMF, the back voltage that determines the motor top speed.

[Al Skierkiewicz]

Dave is the closest thus far, the motors already have a magnetic structure designed in. Trying to add to that will likely not result in an increase in performance. However, under another rule, solenoids are not allowed. See also the robot allowed parts flowchart.

[Jack Jones]

Dave is the closest thus far, the motors already have a magnetic structure designed in. Trying to add to that will likely not result in an increase in performance. However, under another rule, solenoids are not allowed. See also the robot allowed parts flowchart.

True. But it's not the result, but more the intent that bothers me.

[Al Skierkiewicz]

True. But it's not the result, but more the intent that bothers me.
??

[Tristan Lall]

??I believe that Jack is concerned about the collective state of mind of a team that encourages them to bend the rule in this manner.

I'm not sure that it's unhealthy to try to push the limits, to exploit loopholes and to generally make life a mess for the inspectors and rule-makers. It's occasionally a little frustrating for those officials, but ultimately, it's mostly harmless. If the inspector or rule-maker says "no", it's final, no matter how much effort you put into it; by bending the rules, you take the risk you will find yourself in that situation. (Now, I should point out that decisions to live on the cutting edge should be undertaken with the consent of the team as a whole. If it's a small group within the team that risks the team's success on a dubiously legal enterprise, which is eventually rejected at a competition, all hell might rightly break loose in that team's pit; just leave the inspectors out of it.)

[Al Skierkiewicz]

I think that is important to note that winning teams have won without bending the rules. GP allows you to go ask, investigate and take pictures. Learn from others when you have the chance.

[Dave.Norton]

[QUOTE=Tristan Lall]I'm not sure that it's unhealthy to try to push the limits, to exploit loopholes and to generally make life a mess for the inspectors and rule-makers.QUOTE]

Agreed. Limits are imposed by both man and nature. Understanding those limits and attempting to push past them is the basis of creativity. Railing against them is unproductive, which is to say lets have fun with the ideas.

[KenWittlief]

accepting the limits of nature? Im not too sure about this

many times it wasnt nature, it was our understanding that was flawed.

Several years ago 2.8k modems were the best you could get, because Nyquist said that is the fastest that data can be transmitted on a phoneline with a 3,000 Hz bandwidth

but now we have 56k modems, on those phonelines with the same 3kHz bandwidth

nature folded on that one and gave in. Sometimes it pays to keep railing :^)

also, sometimes when you sit and ponder ways to cheat, you come up with a good idea that is not cheating - unrestricted brainstorming!

[Dave.Norton]

[QUOTE=KenWittlief]accepting the limits of nature? Im not too sure about this many times it wasnt nature, it was our understanding that was flawed.
QUOTE]

You misunderstand, what I said was complaining about the rule is unproductive. Railing: "to revile or scold in harsh, insolent , or abusive language" (from Merriam-Webster). What I was suggesting is that "out of the box" thinking is valued, and would like to encourage it.

[greencactus3]

even if ignoring legality and spirit, i htink cooling the motor would be a much better way to 'boost' performance. a simple way we used and was effective (for our OCCRA robot) 2 years ago was to have tubes connecting the exhaust ports from the pneumatic cylinders to blow into the motor endbell. (we used our cylinders almost continuously that year and fans are not legal in occra or we didnt have any available... dont remmebr which) but as a concept it worked well. but then again from last year we learned how to make a more efficient drivetrain with much less friction and got a more 'easy on the controls' driver and havent burned a single motor since. :D

[Gdeaver]

This thread points out the Tim Allen mentality as applied to robotics. More power. However, with with the reality of the ever increasing cost of energy, the wise conservation and application of power makes more sense. A KOP trans with dual cims has a considerable amount of power. The use of this power in design and strategy will probably yield better results than trying to add more power.

[ConKbot of Doom]

I'm not really interested in trying this, just wondeing how other people saw it, glad I could stir up more than one point of view. Personally, with as common as 4 and 6 motor drive trains are now, I thing that transmission development is probably the next big area that can be developed, even more so than it is.

last year there was talk of robots killing batteries in a single match... Something like this wouldnt help matters much, but its fun to think about.

[KenWittlief]

well, no... actually motors with super magnets would be lighter and smaller for the same amount of torque or HP output

and a motor with a smaller armature will have less internal (rotational) inertia, which means it will accelerate faster and have a better response curve, allowing it to be used with tighter PID control loops.

Using a better motor gives you several benefits => advantages. Only problem so far is that FIRST understands this completely, and they have kept motor modification and substition off the table of options.

But that doesnt mean we cant talk about it :^)

BTW, controlling a motors field strength, buy using field coils instead of permanant magnets is a better way to control the motors speed and torque. With a strong field the motor will run slow and have lots of torque. With a weak field the motor will run faster, but have less torque.

[Al Skierkiewicz]

last year there was talk of robots killing batteries in a single match... Something like this wouldnt help matters much, but its fun to think about.

This has been an issue since the beginning of time. Some teams are proud of it and some teams recognize the liability. You won't find many one match robots in finals.

[KenWittlief]

I second what Al said. With the total current limits imposed on the robot (by the rules and the main breaker) and with the 12V battery a bot can pull approx 2HP from the battery continuously

that is a LOT of power! A healthy 18 yr old male can put out about 1/3 HP continuously for 2 minutes, therefore the power available to your bot is the same as having six young men exherting themselves to their full capacity.

If your bot is expending that much power for the entire 2 minute match then something is seriously wrong with the design of the machine. Most of that energy would have to be fighting against itself, not other robots. For example: tank steering with 6 rubber tires or tank treads, that takes full power just to turn, compaired to a bot with 6 omniwheels, that can spin around as easily as it can move forwards or backwards.