Armature unwind - HobbyTalk
 
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post #1 of 13 (permalink) Old 05-31-2007, 01:25 PM Thread Starter
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Armature unwind

hello,
Has anyone unwound an armature? How many turns is it safe to remove? How many turns does it take to drop a few ohms? Will I need stronger magnets after I do it or are the J/L mags strong enough?
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post #2 of 13 (permalink) Old 06-05-2007, 10:06 PM
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Depends . . .

T-Jet,


Depends … on 1/32s not uncommon to "unwind 25" from the arm to heat things up.

Wire on HOs is smaller, however, same analogy should fit with them as well.

If you're brave, can also rewind whole thing, using heavier wire for rewind, less resistance of course, means more power.

In 1/32 29 to 32 gauge is common fare.

On a total rewind, you can then play with advancing the timing, and so forth, 5 degrees is nominal rule of thumb, 10 usually is max.

Sometimes, simply leave commutator as is, and rewind using heavier gauge, with fewer turns.

You'll want to count the number of turns if you unwind 25 to heat up the arm, don’t daydream, count out load.

Assuming arm is not epoxy coated.

You'll want to clean off the enamel from the wire, before soldering, assume you know this as well. Be very careful when re-soldering to the tab, make sure all is clean and wire is tinned before fastening it down.

Lastly, if you really want to mess around, try a total rewind. If you decide to do so, let me know can put together a quick and dirty means to that end.

Most don't mess with rewinds or even what you want to do. Since motors are cheap. And messing with them, usually isn't what guys want to do.

Basically not much to it. Having said that, there are a couple of things you can do to increase power of a PMDC motor.

Shim the between can and magnets with paper or use thin gauge steel or brass.

Another is to replace the magnets with stronger ones.

You can also boost power by turning up the wick.

Amps are pulled by the motor, so it will only use what it is wired to use, unless a short takes place, then you get smoke. Your set up uses most amps when breaking stiction and friction from a stop. That is the toughest thing for a motor to do, is start from stop.

Volts are pushed through the arm. For example, you could use a car battery with hundreds of amps and twelve volts and the motor will only use what the windings are set for on the arm.

Had a three battery set up once [18 volts], cars ran very cool, since no AC filtering through. But takes maintenance, they’re heavy, and so forth.

Getting chatty . . .

Cheers,

Jas
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post #3 of 13 (permalink) Old 06-05-2007, 10:23 PM
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Thinner guage+more winds = less power but more RPMs. Thus, higher top speed but less acceleration. Great for large tracks with long straights.

Thicker guage+less winds=More power but less RPMs. Thus faster acceleration but lower top speeds. Great for short, twisty tracks.

Most common HO rewind wire guages are 30 -38.
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post #4 of 13 (permalink) Old 06-06-2007, 10:48 PM Thread Starter
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Ok got the idea on rewind, but has anyone unwould an armature? I know that people have done it, it reduces the toal ohms of the arm so current will increase. I want to play but prefer not to burn it open. I was told a long time ago unwind 3 turns, seems like it is not enough to make a difference but that is where I will stark. any tips for removing the varnish on the wire?
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post #5 of 13 (permalink) Old 06-06-2007, 10:55 PM
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Quote:
Originally Posted by T-Jet Racer
Ok got the idea on rewind, but has anyone unwould an armature? I know that people have done it, it reduces the toal ohms of the arm so current will increase. I want to play but prefer not to burn it open. I was told a long time ago unwind 3 turns, seems like it is not enough to make a difference but that is where I will stark. any tips for removing the varnish on the wire?
Ok, If you're looking to use the same wire then, going by what I know, you have the same power but less RPMs.

I see no advantage in that.

As for removing varnish, try nail polish remover.
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post #6 of 13 (permalink) Old 06-09-2007, 01:28 PM
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T-Jet,

As mentioned ... you will need to unwind at least 25 turns off most arms to notice anything. Three turns is a won't do anything measurably.

As for burning up, arms pull amps they need, no more. Stiction & friction is the toughest go for a PMDC motor, from start up. This is when resistance is greatest mechanically and electrically.

Volts are pushed through motors. One reason why tracks are 100% volts, needing a controller to let loose the volts. You could have a 200 amps power supply and the motor will only use what it wound for.

Stronger magnets will help any motor, regardless of windings. One of weaker links in most common PMDC motors are the magnets. Try shimming them, reducing gap between arm and magnets. This helps out a lot. In fact you can literally hear the difference when running up the motor after shimming. As said, use either paper of thin metal to do so. Cheap and easy power boost.

Amps are applied against the ohms resistance in the windings. Motors only draw amps they were wound for as said previously.

Think of RPMs as horsepower, and amps as torque. Not exactly true empirically, but suffices for this discussion.

Removing varnish is a matter of drawing end of wire through Exacto knife. Lay the wire on a piece of cardboard, or hard paper stock. Lay Exacto knife on top against about 1/4 inch of end of wire. Slowly draw the end of wire against the knife and cardboard. If you're comfortable with this version, can draw the wire through your thumb and index finger.

Either way, the varnish comes off fairly easily.

Just don't put too much pressure on the wire, else might cut or kink it.

Rewinds are easy, select wire gauge two, maybe three gauges below the one being replaced, and wind away. Because gauge is bigger, your count will always be smaller. Not enough room to describe in detail on how to wire an arm.

Meaning post would be long and nobody likes long posts, and mine are long to begin with . . .

Cheers,
Jas
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post #7 of 13 (permalink) Old 06-09-2007, 02:56 PM
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You may want to get in touch with mtyoder. He did a screamin tjet and monster for me. Does all his arms by hand and I think I talked to him about removing wire.
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post #8 of 13 (permalink) Old 06-09-2007, 04:40 PM
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arms

I think everyone just about covered everything. Great job.
I wind arms also and it would take a great deal to explain how winding is done. I do drag to road arms. If you are going to do a mild road arm use 36 or 38 gauge wire to start winding. As for removing varn. I use sand paper.
220 wet/dry. Place wire end between paper and pull easy. removes it easily. The exacto trick is a great one also.
Remember when winding do not kink or twist a bend in wire. If you do..Start over.
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post #9 of 13 (permalink) Old 06-09-2007, 06:43 PM Thread Starter
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yea bends no good, heat up and burn open
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post #10 of 13 (permalink) Old 08-27-2007, 09:33 PM
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This Is Not For The Faint Of Heart!!!!!!!!!!!
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post #11 of 13 (permalink) Old 08-28-2007, 08:03 PM
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Quote:
Originally Posted by mtyoder
This Is Not For The Faint Of Heart!!!!!!!!!!!

Yeah, but you do it anyway. I can tell when you have by just looking at you. You have little bald spots on you head from pulling out your hair.

I unwound an accelerator arm once or twice. I counted the turns and made them equal on each lam. Easier way is to measure the length.

It was a faster performer but I had excessive heat issues.

I'm thinking I took 30 turns off each lam. Randy.
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post #12 of 13 (permalink) Old 08-30-2007, 09:07 PM
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Bald spots on my arms from pulling off windings! Ha!
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post #13 of 13 (permalink) Old 09-03-2007, 12:42 PM
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Anyone have a good source for wire?????

Ive had a fair amount of success winding arms.I just cant find a decent source for the wire to do it with.

Mike
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