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jonboy1

loss of power - worn motor?

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Hey - I wonder if one of you clever chaps can help me out please?

A couple of weeks ago I gave my boomerang a quick run around the garden and I noticed that after a minute or so the power dropped off quite dramatically. Everything worked fine, it's just there was much less motive force!

I swapped the battery over to another car and that worked absolutely fine, so I think I can rule out the lipo as being an issue. The ESC is a Quicrun 1060 with a Flysky receiver - exactly the same set up in the other car.

I was wondering if it could be an issue with the motor, which is a Dynatech 01R that I've not really looked at. Is this a typical worn brushed motor problem? Brushes or commutator need refurbing?

Many thanks

 

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Had exactly the same with my Bear Hawk on the beach a few weeks ago running an old Yokomo 17 turn motor.  Was running along just fine, suddenly slowed right down, in the end wouldn't even turn the wheels.

If the battery is powering another car and the ESC isn't going into low-power cut-off, you can probably rule out a battery problem.  I'm not sure if the 1060 shows any lights if it's in low-power mode.

Have you tried the car since then?  Is it still slow?  I think the 1060 has a thermal cut-off, so if it gets hot it might shut off.  However it should be fine once it's cooled down, so if it's still slow it's probably not that.

Have you checked the motor connectors?  If they're not properly connected they can get hot and burn out.  If they haven't completely melted, a quick clean-up and reassemble should fix that.  It's worth a check before stripping down the motor.

Finally - onto the motor, which seems like the most likely culprit but also the most complex to check, which is why I asked about the others first:

Does the motor spin freely with the wheels off the ground?  If you put the car on a stand and run it, is the motor laboured or not running smoothly?  Can you see sparks or arcing where the brushes touch the comm?  When my Yokomo was giving me problems it would only turn over very slowly when on a stand, and there were lots of orange sparks around the comm.

You can probably remove the brushes with the motor on the car, so that might be the next step.  The Dynatech has an unconventional brush / spring assembly (at least compared to the rebuildable motors I have) but should be easy enough to pop off the springs and check the comm.  It should be shiny and clean, but if it's blackened with carbon deposits it will want cleaning.  You might get away with some cleaning solution like IPA on a contraband cotton swap, or you might have to pull the motor apart to get to the comm.  If you do this, be careful to note the position of all the shims and washers so you can reassemble it properly.  Be careful they don't wall off when you pull the comm out - it will want to jump onto a magnet as soon as the rotor is free of the nose bearing.

If the comm is unevenly worn then ideally you'll want to have it reground, personally I've had good results doing a light polish with fine wet-or-dry (1500 or similar).  I normally do this on either cheap motors or older ones that will be dead if not fixed, it's up to you if you want to try this on something special like an 01r.

Brushes - I'm not sure what new / unworn brushes look like on your motor, but if yours are worn they'll want replacing.  I'm not sure how easy they are to find.  However if they are blackened you can clean them up with some IPA and give them another try.

While you're in there, give everything a thorough clean (compressed air gets rid of carbon dust but protect your eyes and lungs), put a dab of light oil on the bearings before reassembly - dust can get into the bearings during disassembly and soak up the film that's hopefully still there since it left the factory, then the motor can start squealing when you put it back together.  A bit of oil should catch any dust, when you push the rotor through it will come out in the oil so you can wipe it away and hopefully leaves a nice film behind to support the rotor.

Hopefully this will get some more life out of your motor :) 

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Thanks very much Mr. Ax - really appreciate your help. :) 

I gave it another quick run and the same thing seems to happen - good performance for a little bit - then goes very slow. I lifted it off the ground and powered it up and it didn't seem laboured or like there was a mechanical resistance anywhere.

Motor connectors look fine. I'll take the motor out and run it on the bench where I can see it better and check for sparks, but I couldn't see any with it on the car, but it is quite hidden, so not saying no.

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Have you tried disabling the low-voltage cut-off on the ESC?

I've encountered this issue before when the battery voltage drops momentarily under load which in turn freaks out the ESC thinking the battery is running low.

If this fixes the issue, lower the cut-off voltage so it runs properly but still has the safety factor of not over discharging your LiPo. Or run a separate cut-off or alarm.

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As for your description, it could really be the brushes and commutator. 

How long has the motor been with you? Check the brushes first. If they're worn out, replace them (if you have new spare). If you know how to disassemble the end-bell from the can to see if the commutator needs lathing to, do it as well.

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Had this too after playing the whole day in sand with my buggy/stadium truck. Spotted two problems: brushes dirty were they touch the commutator and brushes worn. The first one solved with brake cleaner (whole motor) and scubbing the dirt of the brush. Second means new brushes.

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It sounds more like a thermal shutdown (except it's not shutting down entirely).  Maybe you could try another ESC?  

Cleaning a brushed motor won't hurt.  It's easy. Just dunk the whole motor in a cup of water (use a disposable cup) and run it at 5v or so for about 5-10 minutes.  It's going to slush around and clean everything.  Let it dry and lubricate the bushings.  

 

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thanks for all the tips guys - really appreciate them. 

So, over the past few days when I've been able to grab a few minutes here and there I removed the motor and stripped it down. The brushes and commutator were a little bit sooty, but not what I'd call worn. I could still see the little V grooves in the back edge of the brushes so they have plenty of meat left on them (plus with the prices of Dynatech brushes being what they are they won't be getting changed!) but I gave everything a good clean anyhow and put it all back together. That done, I powered it up on the bench (just with an old MSC and battery) and ran it for about 5 minutes and there was no change in the performance of the motor at all. I've refitted it to the car but haven't had time to give that a run again to see if there's still an issue, which, as you guys all seem to be pointing towards, may well still be there and lie with the ESC.

So, this leads to another question - I've got through 3 Quikrun 1060's in next to no time (two smoked on start up, this one looks dodgy - not all on this car though) - am I doing something very wrong or is the quality of them a bit questionable? All were bought from either Modelsport or Hobbyking, so they shouldn't have been dodgy. Is there a good alternative?

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On 6/14/2021 at 6:00 AM, jonboy1 said:

I've got through 3 Quikrun 1060's in next to no time

That is surprising. Usually that's because of high-load on the motor. 

1) Are you using 3S?   

2) Is the gear ratio excessively high? 

3) Have you mounted heavy or large diameter tires? 

4) Are the gears and wheels freely rotating?  

 

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