Problem with brushed motor

I'm fairly new to RC, but not to electronics. I'm itching to try out a new Mini Sportster, but I'm having problems with interference (RFI). When I throttle up, the 400-series electric motor begins to "miss" intermittently. At the same time, the servos glitch. I've installed capacitors on the motor (even tried a second pair). I've tried a couple of different ESC's, receivers, transmitters. I've checked for loose connections, but still can't get rid of the glitches. If I test everything without the prop, then there are NO glitches. Maybe it's static electricity? Maybe something's flakey in the motor. I don't know.

I'm waiting for a brushless motor to arrive in the next couple of days, but if anyone has any suggestions, I'd really like to hear them. I've taken it back to the shop where I got the plane, and they're scratching their heads, too.


Michael "Mac" McReary

Reply to
Michael McReary
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Oh....its a subject all right.

I have found that the single biggest problem once you have stuck the three caps on, is routing motor wires long and near the receiver.

A few hints.

First of all, run the motor in. The brushes will spark BADLY for the first few minutes - they come out 'hollow ground' and the edges need to be worn down to actually make decent contact with the commutator. Just a few minutes with no prop on or at part throttle with the prop on is enough. Maybe a couple of packs worth.

Now make sure the three caps are on, one across the brushes, two from each brush to the case. A dry joint here will INCREASE interference.

A Schottky diode across the brushes CAN help.

Next get the ESC WELL away from the receiver, connected by short twisted wires to the motor. Route the receiver antenna WELL clear of any other wiring.

In 99% of cases this is good enough to fly.

Other things you can do are to put another capacitor across the +ve and

-ve lines of the receiver...its available on any spare servo connector, and a small cap soldered into a spare servo plug and inserted often helps a bit.

If all that fails, its time to try a different ESC or different receiver...but the only two planes that were actually unflyable, were the two that had the ESC rammed up against the receiver, once the rest of the issues had been addressed.

Reply to
The Natural Philosopher

Good advice...

Another thing to try is wrapping the ESC RX wires around a ferrite ring just before it plugs into the RX.


Reply to

And your comments were really good.

All my sealed (canned) motors are broken-in a glass of water. Just wire them to run and drop them in. The worn brush material will be seen on the water. After a minute or two running in the reverse direction I want the motor to run in, I reverse the polarity and let it run that direction for two or three minutes.

The adjustable brushed motors get two D cells connected to them and then the they go in the fridge. When the batteries are run down, the brushes are good. I will get hot if just left on the workbench.

I used to think I would fly them while breaking them in...not a good idea because of the RFI and it takes forever and with the prop the bearings/bushings are wearing and that is not what needs to seat.

And the polarity of the Schottky should be minus to the positive lead. This dumps the back-EMF as well as quietens the brush noise. This back-EMF can make the ESC mad. Many ESC have a Schottky on them. They are likely to be big enough to be seen. Some ESC manufacturer's have a Schottky on the board and still provides an extra one for the motor.

After proper break-in and with the capacitors and Schottky, I have only had one ESC that bothered any of my many receivers because of wiring placement. Still keeping the RF/DC/antenna well separated is just good thinking.

I have never needed this but that is a very clever idea! I will remember this.

Most of the sloppiness on my part has shown up when the motor came up to full power. Once under constant load, the RFI/EMI seemed to have been less.

One last comment...range testing with motor power on and throttle back. This is not a good idea because the first loss of signal can turn the motor on and with the limited signal, the RFI/EMI that is normal will appear much larger and then the throttle control at the xmitter might not have any affect on a model that has now decided to be a free flight.

It is easier to make bad mistakes with e-models than IC models. E-models are cleaner but the pilot will still bleed the same way.

Ken Lots and lots of model images --

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Reply to
Ken Cashion

OK. Lots of good suggestions. My favorite hobby shop doesn't carry the ferrite rings, but I've ordered some through eBay.

Last night, I twisted the motor wires and it seemed to help, some. The main theme I saw seemed to be to get some distance between the ESC and the Rx. I picked up an extra servo extension cable and did just that. It meant putting the Rx in the canopy, but the RFI has disappeared.

If I notice any other glitches, I'll try the diode and additional cap. But, I think it's going to be OK, now.

Thanks to everyone!


Reply to
Michael McReary

You don't eliminate interference, you just get it down to the level where its not a lot worse than anything else around - car ignitions, arc welders, cosmic radiation ;-)

If you have better than 30meters ground range with motor running and tx antenna down, fly.

MILD interference usually has the effect of the motor 'misfiring' rather than total out of control glitching.

Fly until you are either far enough away that you can't rely on seeing the model, or until this happens, and then fly closer thereafter ;)

Reply to
The Natural Philosopher

And the higher the model is, the further away you can fly. And perhaps, the further away it will land.


Reply to
Ken Cashion

What do you expect? Perfection? ;-)

Reply to
The Natural Philosopher

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