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,
Michael "Mac" McReary
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
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.
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
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
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
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.
Lots and lots of model images --
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!
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 ;)