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Discussion Starter · #1 ·
Let me start by saying that I am electrically illiterate. Basic circuits are as advanced as I get before getting confused. With that said...

We have an SCX Audi R8 LMP car that used to be one of our fastest runners. My son put it on the track yesterday and the car barely moves and sounds like the motor is bound up. I took the body off and put it back on the track. When I pulled the trigger I could see a small puff of smoke coming off the motor. I pulled the brushes out and put them back in thinking that maybe one was stuck as this car has not run in 6-8 months. That did not help. Is there something else I can try? What else can go wrong with a motor?
 

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Lee Green
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Get some contact cleaner and spray it in the motor aiming it at the comm , if this doesn't work , run the motor backwards for a minute or two before running and it will clear the motor
 

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Discussion Starter · #3 ·
Tried both suggestions (contact cleaner and running backwards). No dice. The motor just stutters a little and puffs a little smoke.
 

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I had the same problem with a SCX Audi DTM car I bought used (Probably why it was used) It was super slow and the motor would get very hot along with the smoke. Same results with the motor out of the car on my bench power supply. I tried the same things as you did but to no avail. Decided to take the motor apart because back in the 90's I raced a lot of 1/24th and worked on lot of motors. After checking out the armature for shorts and such the only thing I could figure out was it seemed like I could hear the arm scratching something when I turned it by hand in the can with no brushes. Carefully looking at the armature it looked like one of the laminations had shifted. I chucked the arm up in my lathe, took a couple of light passes to even out the stacks. Put the motor back together, ran it on the power supply and it seems to work ok now. Right now I don't have a running track to fully test the car but think it will work, if not I'll just adapt a different motor in it.
 

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Hi sjc115
Have you already checked the motor is rotating freely? (Excess friction can stop motors)
When you checked out the brushes, did you check the brushes were still long enough so the springs were still pressing on the brushes? Some types of brush holder have a slot that the spring runs in, when the spring gets to the end of the slot it cannot put any pressure on the brush, even though there is some brush left. New brushes will fix that.

Have a look at the armature. (This can be seen through the ventilation holes of many motors, if your motor hasn't got vent holes in the can, the motor will have to be dismantled) Are any wires off? Have the windings on one (or more) of the poles has turned dark? Unless you are into serious motor rebuilding, fixing either needs the armature replacing. Armatures are not often sold separately in this sector of the market, so that means a new motor is needed.

If none of those suggestions are the answer, possibly there's too much debris for the contact cleaner to clear. You could dismantle the motor, try cleaning out the debris from the slots in the commutator, and cleaning out any debris from inside the endbell.
Inspect the commutator for any wires off that weren't visible before taking the motor apart. (If it was visible through the can hole, most likely its beyond repair). If a wire has come unsloldered and there is enough wire left to solder back on the commutator tag, that's worth a go. That can be a symptom of a fault in the windings, in which case resoldering it won't do much good, but there's not much lost giving it a try.
 

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Hi, when you apply power to the car/motor does the power light on your powerbase dim and then go out all together? (not sure but I think if the light goes out the motor may be causing the track to short out) If it does then its possible you will need to replace the motor if you don't want to fix it. I have no knowledge at all of electronics, so I just give the motor a drop of oil and try to run it, if its still smoking and not working after a few attempts at running, I would replace it.

Matthew
 

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Discussion Starter · #7 ·
I did forget what might have been an important piece of info. As matthew77 said, my power base was acting like there was a short.

300SLR: I checked the brush springs and they had plenty of slot left, so I decided to take the motor apart. The wires all looked good. The area where the brushes make contact was pretty dirty, so I cleaned it up with an eraser and cleared a bunch of gunk out of the slots with a hobby knife. Then I blasted it again with contact cleaner and reassembled.

Voila! We once again have our favorite LMP car running. Thanks for all the suggestions everyone!
 

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Discussion Starter · #8 ·
Bad news. After about 20 laps or so, the problem is back. The car stutters and the powerbase goes in to 'overload' or 'short' mode and want to shut down.

Any more ideas?
 

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Hi sj115
One more idea that might work-

How about checking the brush gear alignment.
If the brushes are far enough out of line so they can both touch one comm segment at the same time, it'll produce a short circuit which sounds like what you've got. It's plausible that when the motor was reassembled the brushes displaced enough to run for a short time till they bedded in again and the problem returned.
The brushes should be worn into a curve where they meet the comm, this should be even each side. If they are wearing off centre, - if possible realign the brush holders - if that's not practical, cutting off the corners where the brush touches the comm will provide a cure till the brushes wear down again - then it'll need doing again.
 

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I would think it is the same problem still, probably a bit of carbon is still shorting between the commutator segments, try cleaning out the slots again and make sure you get all the way to the start of the slot. Fingers crossed.

If you have run it shorting too much then the smoke may be terminal breakdown of the coil wires.

Can you check resistance with a meter - there are three segments so you get three different resistance readings but they should all be close +/- 10%. Any big difference is indication of either the commutator segments shorting or the coil wires shorting.
 

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Peter Farrell
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you must be aware that all electrical appliances are runon smoke; therefore if you once let the smoke out, it is ruined and cannot work!!!!!
Alfetta
 

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Shoot, unless money is REALLY tight, patience like Solomon and time like a solitary confinement prisioner; I'd have long since given up and consigned that motor to "labour-saving" department (AKA file 13, AKA trash can), and spent 10 quid on a new one.

Ahhh Alfetta, finally someone talking truth LOL

Reminds me of an old story.
[warning, totally off-topic]

The No Smoke Power Supply

Tech: 'What's the problem?

'User: 'There is smoke coming out of the power supply.

'Tech: 'You'll need a new power supply.

'User: 'No I don't! I just need to change the startup files.

'Tech: 'Sir, the power supply is faulty. You'll need to replace it.

'User: 'No way! Someone told me that I just needed to change the startup and it will fix the problem!
All I need is for you to tell me the command.

'10 minutes later, the User is still adamant that they are right. The Tech is frustrated and fed up.

Tech: 'Sorry, Sir. We don't normally tell our customers this, but there is an undocumented DOS
command that will fix the problem.

'User: 'I knew it!

'Tech: 'Just add the line LOAD NOSMOKE.COM at the end of the CONFIG.SYS. Let me know
how it goes.

'10 minutes later. User: 'It didn't work. The power supply is still smoking.

'Tech: 'Well, what version of DOS are you using?

'User: 'MS-DOS 6.22.

'Tech: 'That's your problem there. That version of DOS didn't come with NOSMOKE. Contact
Microsoft and ask them for a patch that will give you the file. Let me know how it goes.

1 hour later.
User: 'I need a new power supply.

'Tech: 'How did you come to that conclusion?

'User: 'Well, I rang Microsoft and told him all about what you said, and he started asking questions
about the make of power supply.

'Tech: 'Then what did he say?

'User: 'He told me that my power supply isn't compatible with NOSMOKE.'
 

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I'm used sometime to phone calls of customers due to tech troubles... will make a good use of this one



Returning to topic, I've been able to restore some motor (not to the old amazing performances, but "honestly reusable"), by cleaning the spaces between the comm contacts (as said by other friends above), BUT I've then placed few drops of cyano glue between comms contact and then laid some sodium bicarbonate on the commutator.
This will become just as hard as ceramic, and when dried required the commutator to be re-trued (not that difficult with just a "Dremel-alike" tool and some thin sandpaper and abrasive paste for final finishing).
This will prevent the carbon particles from sticking in between (and motor will run again, quietly and smoothly)
For sure all this will cost more time than just throw the motor in the trash bin and get a new one, but is a matter of "personal satisfaction" to get 'em running again!

Regards
 

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Discussion Starter · #15 ·
It's running once again!

I took the motor apart and inspected the comm and brushed carefully. The brushes were worn to sharp points on both edges and the comm was noticeably worn (i.e. the area where the brushes contact the comm was noticeably smaller in diameter than where the brushes don't contact. The resistance values between sections of the comm were very close to each other (3, 3.1, 3.3). So...

I cleaned the slots in the comm very thoroughly with a hobby knife and contact cleaner. I also sanded the 'points' off of the edges of the brushes. I'm not sure which one of those things did the trick, but the car is running so my son (and I) are very happy.

Thanks again for all the help!
 

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One other thing to try before taking the motor apart is to run it under water. I've done that with a couple of motors, no problems so far. Grab a cup of water, stick the motor in it with some leads attached to your track or drivers' station, and throttle it up. Sounds like a blender making something nice to drink and most people will think you're crazy.

Blow it out afterwards with compressed air, give it some (very little) lube and run it awhile. Although, I kinda agree with Slotcrazy when you're talking about one of those motors.

Randy
 
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