can motors be modified

[ronnie_82]

i'm with a first year team and wondering if motors can be modified? what are some situations your team may ran into your first year?thanks ronnie_82

[rbayer]

By modify, do you mean taking them apart and rewinding, etc? FIRST generally says no to modifying anything involving electricity or pneumatics, but I haven't ever heard this issue addressed specifically, so maybe it's OK.

[ronnie_82]

Thanks for that information. I will look into it further

[Adam Y.]

No. You can't rewire them at least as far as I can tell.:)

[ChrisH]

In previous years motor modifications have been specifically prohibited. The output shaft of the motor assembly may be modified.

To give an example: We used to get "window" motors. These motors had a worm gear built into the case that then turned still another gear that was the output. It would be legal to modify the output gear by putting a hole in it or otherwise changing it so it could be adapted to drive whatever you were trying to drive.

But changes to the worm gear or the motor itself were not permitted.

As a general rule we modify the motors, including the output shafts, as little as possible. That way if we fry one during a competition we can replace it more easily. It can be really hard to put a keyway into a the shaft of a new motor in the Pits at a Regional. If you absolutely must modify a motor, always buy a spare and modify that one too in the same way, and check to make sure it works as intended. Doing so will save much embarasment at the very least.

Besides the stuff you have spares for never breaks

[Adam Y.]

Wooohoo I answered a question correctly:).

[Bduggan04]

I'm pretty sure you can cut holes in the front of the housing for cooling. I've seen teams that have done it, and I'm pretty sure there are no rules against it.

[ChrisH]

Originally posted by Bduggan04
I'm pretty sure you can cut holes in the front of the housing for cooling. I've seen teams that have done it, and I'm pretty sure there are no rules against it.

As a "strict constructionist" I would say that was indeed a violation of the rules. Unless there was a specific mention of this modification in the documentation, and I don't recall any off hand.

The thermal capacity of the motors is one of the constraints we have to live with. It is however, perfectly legal to use fancy aluminum extrusions for a heatsink and incorporate them into your mount.

Just because somebody got away with it doesn't mean was legal.

[Andy A.]

Taken from the 2002 manul:

M17. 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.
• The gearboxes for the Fisher-Price, Drill, and Globe motors are not considered
“integral” and may be separated from the motors. FIRST will not provide
replacement for parts that fail due to modification.

The way I read it, it is legal to drill holes in the motor. However, I think that the extra cooling it might provide is offset by the chance of damaging the motor, either while drilling or when crap gets in it. Stick with heatsinks to avoid any problems. They look cooler anyways.

Also, be aware that these are 2002 rules, and are subject to change in Janurary.

-Andy A.

[Bduggan04]

While heat sinks are a good idea, the metal band around the drill motor makes them less effective. However, the band is necessary for the motor to be most efficient. It's best to reduce the load on the motors, or use an electrical system to monitor the current load and prevent back driving. Either way it reduces the heat of the motor and the likeliness to trip the breaker.

[Al Skierkiewicz]

How were you able to modify the cases to get more air flow without having metal shavings caught down inside the magnet structure?

[AJ Quick]

How would they check?

What is stopping someone from putting a better motor in the drill motor's casing? ;)

[Bill Gold]

Originally posted by AJ Quick
How would they check?

What is stopping someone from putting a better motor in the drill motor's casing? ;)
Pride. Honesty. Wanting to abide by the rules to try to keep a fair playing field. Those reasons, and I'm sure many more, are what stops people from using illegal motors (model and/or quantity).

[Ken Leung]

Originally posted by AJ Quick
How would they check?

What is stopping someone from putting a better motor in the drill motor's casing? ;)

Nothing at all, except something call "gracious professionalism". ;).

If you are absolutely certain you want to do something against the rules that will give you unfair advantages over other teams, there's no way for FIRST to stop you.

If you happen to win the competition because of that unfair advantage, would you really be proud when you know you cheated others out of a fair chance to compete for the champion? If so, then I would say you learned absolutely nothing valuable from this competition.

But of course you won't be doing that, right? ;)

[Bduggan04]

Originally posted by Al Skierkiewicz
How were you able to modify the cases to get more air flow without having metal shavings caught down inside the magnet structure?

Like I said earlier, I only saw it done. I'm not sure how you could do it, possibly disassembling the case from the rest of the motor and then machining it. Maybe they used another magnet to lift the shavings away from it, I'm not really sure. Previous year's motors might have been used as practice.

[Matt Reiland]

Originally posted by AJ Quick
How would they check?

What is stopping someone from putting a better motor in the drill motor's casing? ;)

This is just a quick message to all teams this year, passing inspection with illegal parts will be MUCH harder than in the past as they have asked the engineers to start doing tech inspections at events their team is not participating in. So please, don't use illegal motors or violate rules without a VERY good explanation. Telling the inspector that the van door motor is a fisher price won't fly this up coming season and saying you didn't know it wasn't legal won't work either. (Although we could have used 10 BOSCH motors last year and know one would have known, our inspector didn't even know the difference between the different motors)

Know the rules, and follow the rules, if you have a question or something that is in the gray area, get an official ruling from FIRST, first before using it. At an event is the wrong time to be pleading your case for something you think should be legal even though it isn't.

B.T.W. Myself & Brian Musser will be tech inspecting at the Western MI reigonal.

[Bduggan04]

That's a really good idea. At some of the regionals we'd get judges that were extremely unfamiliar with the control system and the kit of parts. I hope they zero their scales well too, at least to where they're all the same reading.

[Al Skierkiewicz]

There has always been some heated discussion as to the use of modified parts and trying to slip things in past the inspectors. I personally find that part of the fun and learning in this project is keeping to the rules as close as possible. For one it stimulates creativity to come up with a solution that fits the rules and it serves to level the playing field.(one of my personal favorites. I love when rookie teams, teams with limited resources and volunteers, or teams with no engineering backup can make it to the finals and perform.) It also gives us a yardstick to judge each other's design against.
As I have said many times, I would like the inspectors to perform some basic electrical checks as well. A simple ohmmeter check from both battery terminals to various chassis points, insulated battery terminals, good battery mounting, etc. I have seen inspectors reject a robot for sharp edges but never looked at exposed high current wiring.
Happy Holidays All Only 14 days to kickoff.

[AJ Quick]

That's a good idea.

Sorry for my past comment, I'm a rookie, and wasn't aware of inspections and things like that. Don't expect our team to cheat like that. (Or anyway).

[Al Skierkiewicz]

Hey AJ,
Ya gotta ask to learn. Besides we like all the MN teams, we have relatives in Minnetonka!

[Mark Hamilton]

Modifying the motors is a no-no, but you can modify the gearboxes. We always opened up the drill moto gearboxes and locked the little high/low gizmo in place. Speaking of Moto mountings, I remember us getting a certificate for putting up a model of our right angle motor mounts on the sharing first site. Whatever happened to that site, I can't find any url or reference to it anywhere.

[AJ Quick]

Originally posted by Al Skierkiewicz
Hey AJ,
Ya gotta ask to learn. Besides we like all the MN teams, we have relatives in Minnetonka!

Heh, we are the only Minnesota team. ;) We're the state champions!

[Aaron Lussier]

With all this talk of heat sinks I though I should mention what 151 is doing this year. We took some of last years drill( assuming they will be the same thing this year), and put the motor on a lathe and slowly made the back of the motor perfectly round we then made a heat sink to fit perfectly. then just above the heat sink we attached small muffin fans for extra cooling. We will not be using this motor on this years robot nor will we use the heat sink, (we have strict rules on using anything made outside the six weeks) We have read the rules carefully and belive that this is well with in the rules.

[Bduggan04]

Originally posted by The wheelman
With all this talk of heat sinks I though I should mention what 151 is doing this year. We took some of last years drill( assuming they will be the same thing this year), and put the motor on a lathe and slowly made the back of the motor perfectly round we then made a heat sink to fit perfectly. then just above the heat sink we attached small muffin fans for extra cooling. We will not be using this motor on this years robot nor will we use the heat sink, (we have strict rules on using anything made outside the six weeks) We have read the rules carefully and belive that this is well with in the rules.

I'm afraid I'm not sure what you mean by making the back of the motor perfectly round. What do you mean by back of the motor, the rear face or the circumference on the rear end of the motor? Also, how wide did you make the heatsink and how is it attached?

[Aaron Lussier]

Originally posted by Bduggan04
I'm afraid I'm not sure what you mean by making the back of the motor perfectly round. What do you mean by back of the motor, the rear face or the circumference on the rear end of the motor? Also, how wide did you make the heatsink and how is it attached?

What I meant was the rear circumference of the motor, sorry for not explaining it better, the heatsink is about half an inch wide and we attaced it with small hardware and some small dowels that somehow attached to the motor,<---- I'll check on that and get back to you with a picture.

[Matt Reiland]

For any of the new teams:

Assuming the rules stay similar to last year regarding extruded aluminum, these worked fantastic and are ultra-light they fit the FP & Drills from last year

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXTG84&P=7

And, they look extremely cool

[sanddrag]

Originally posted by Matt Reiland
For any of the new teams:

Assuming the rules stay similar to last year regarding extruded aluminum, these worked fantastic and are ultra-light they fit the FP & Drills from last year

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXTG84&P=7

And, they look extremely cool

About the heatsinks, could someone please tell me how they were legal last year. Which part of the Additional Hardware List did they fall under?

[Nate Smith]

Originally posted by sanddrag
About the heatsinks, could someone please tell me how they were legal last year. Which part of the Additional Hardware List did they fall under?

I'm pretty sure it was under the "extruded aluminum, 2"x3" cross section"

[ChrisH]

Originally posted by Nate Smith
I'm pretty sure it was under the "extruded aluminum, 2"x3" cross section"

Nate is correct. Nothing in the rules said anything about it having to be a "standard" cross-section. The extrusion just had to fit into a 2"x3" hole. You could have even used a solid 2x3 if it was extruded, and you could afford the weight.

[Pengiun Joe]

I have a related question about motor modification. It doesn't involve FIRST, but I have a motor at home in an air compressor that I'm trying to get more power out of. With my limited knowledge of motors, it would seem to me that I could rap some extra copper wire around the coils, and this would do the trick. But that's an educated guess with my again, limited knowledge of motors.

[sanddrag]

Originally posted by Pengiun Joe
I have a related question about motor modification. It doesn't involve FIRST, but I have a motor at home in an air compressor that I'm trying to get more power out of. With my limited knowledge of motors, it would seem to me that I could rap some extra copper wire around the coils, and this would do the trick. But that's an educated guess with my again, limited knowledge of motors.

I've never done this but I know for a fact that motor armatures are precisely and tightly wound. I don't belive your method would do the trick. Someone correct me if I'm wrong but the armature coils are soldered in and just rapping around some more wire would do more harm than good. For now, I would just clean out the motor with a good electronic-safe solvent and oil all the bearings/bushings.

[Bduggan04]

Originally posted by sanddrag
I've never done this but I know for a fact that motor armatures are precisely and tightly wound. I don't belive your method would do the trick. Someone correct me if I'm wrong but the armature coils are soldered in and just rapping around some more wire would do more harm than good. For now, I would just clean out the motor with a good electronic-safe solvent and oil all the bearings/bushings.

I'm pretty sure you're correct. Motor armatures are very carefully wound and wrapping more wire around it would probably decrease the power. To change how much power the motor has by changing the armature you have to re-wrap the coils with a more conductive wire. Also, I think the wire has to have a special coating for insulation.

[jrgrim12]

Yes the wire used inside of motors is specially insulated with varnish. If this is nicked in anyway it can short out and burn up the motor. I would assume that you have an AC motor on your air compresser at home. One you plug into a wall outlet. These do not have armatures inside they have rotors. The motor is wound in different phases and in specific spots around the stator. It is possible to wind more wire inside the stator but you would have to know exactly how the motor was wound to begin with and what the wire would do to the motor. And more than likely you don't have the wire to wind with anyway. Plus there won't be any room to add wire. They don't have any extra room inside motors.

What kindda problems are you having that you need more power for your compressor? I work for a motor manufacture. I might be able to help with your problem.

[Pengiun Joe]

Originally posted by jrgrim12
Yes the wire used inside of motors is specially insulated with varnish. If this is nicked in anyway it can short out and burn up the motor. I would assume that you have an AC motor on your air compresser at home. One you plug into a wall outlet. These do not have armatures inside they have rotors. The motor is wound in different phases and in specific spots around the stator. It is possible to wind more wire inside the stator but you would have to know exactly how the motor was wound to begin with and what the wire would do to the motor. And more than likely you don't have the wire to wind with anyway. Plus there won't be any room to add wire. They don't have any extra room inside motors.

What kindda problems are you having that you need more power for your compressor? I work for a motor manufacture. I might be able to help with your problem.

Well it's an old compressor (I snagged it off of ebay for like, $30). I want to get 25-30 psi out of it, but right now am barely getting 20.

[jrgrim12]

if you know that HP, max rmp, amps, volts, etc and look up a new on the internet. They may not be that expensive you also may find one at an auction. If it's really old the bearings may be shot. You can try freeing the up. If you can take the motor apart and clean it that may help.
Does the motor stall?? If it does then I would say it is the motor if it doesn't then you may need to look at the piston or snap valves and make sure they aren't bad.

[Al Skierkiewicz]

Joe,
There are a few problems to address...
The motor was already carefully wound at the factory and unless something has gone wrong with it since there is not a lot you can do to increase the output power. By changing the windings (adding wire)you affect a variety of other variables like balance, heat dissipation, etc. If it is an AC motor (as stated above) then you will change the load the motor presents to the line (electric company) or in the case of a capacitor motor will affect the current and phase supplied to the motor windings, generally reducing power not increasing it.
If the compressor was originally designed for higher pressure there is often a mechanical reason for the poor performance. Usually these are faulty piston or rings, leaking gaskets and fittings or bad over pressure regulator. If the compressor is getting up to 20 PSI and shutting off, then the limit switch may be adjusted for a lower pressure.
In general for our robots, the specifications given for each of the motors allows mechanical designers to use each motor with predictable results. The engineers may choose to run the motor at points on the curve that may not be the most efficient but optimize one factor at the sacrifice of others. That is one of the nice things about this competition is that your hands are not completely tied by the rules.
Hope this helps...

[Neill]

It is possible the rewind motors, but is NOT ALLOWED. HIGHLY ILLEGAL and it is not is the spirit of gracious professionalism.

Just as a acedemic exercise: I knew a machinist that helped his son race RC cars. With the correct winding equipment and KNOWLEDGE, the motor can be rewound with SILVER wire. Expensive compared to copper. The result? The real resistance of the motor goes down because silver is more conductive than copper. The motor will also operate cooler due to less I2R losses.

Just and interesting tid-bit for future years.

[Al Skierkiewicz]

I agree that the resistance would go down, but by an imperceptible amount. Silver wire of the same guage has about 94% the resistance of copper. A motor winding of copper at 10 ohms would be reduced to 9.4 ohms in silver. For our purposes (ignoring the other factors that affect motor current) Ohm's law suggests 12volts/10 ohms=1.2A and 12 volts/9.4 ohms=1.27 amps. When you throw in the other factors there still isn't sufficient evidence that would warrant the change. Yes there is an increase in winding current which results in an increase in magnetic field, but if the magnet structure was already optimum, increasing the electric field does not result in higher power. The increase in motor current also produces changes in power dissipation. Again ignoring other factors Ohm's Law for power shows 1.27 amps^2 x 9.4 ohms=15.16126 watts and 1.2 amps^2 x 10 ohms=14.4 watts so there is an increase in temperature due to the higher current.
And yes there are a lot of other factors to consider in the scheme of things.
In the case of our new drill motor the change in wire would result in a stall current of 138 amps vs. 129 amps and 1657 watts vs. 1548 watts dissipated at stall.