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Nov 27, 2021, 05:25 PM
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beazld's Avatar
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motor shielding question


I am in the middle of a build and getting wiring and servos laid out and I am getting servo interference from a brushed motor.
This is the motor in question.
https://www.servocity.com/127-rpm-mini-econ-gear-motor/
My question is how can I shield the servo wires or is there some way to suppress the interference at the motor?
I'm not an expert in electrickery but isn't there some capacitor, resistor or diode that you can solder across the motor leads to suppress the signal?
Any help greatly appreciated.
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Nov 27, 2021, 05:34 PM
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pmackenzie's Avatar
Quote:
Originally Posted by beazld
I am in the middle of a build and getting wiring and servos laid out and I am getting servo interference from a brushed motor.
This is the motor in question.
https://www.servocity.com/127-rpm-mini-econ-gear-motor/
My question is how can I shield the servo wires or is there some way to suppress the interference at the motor?
I'm not an expert in electrickery but isn't there some capacitor, resistor or diode that you can solder across the motor leads to suppress the signal?
Any help greatly appreciated.
Three capacitors work best, one between each lead and one from each lead to the motor case.
IIRC, 0.047uF ceramic was pretty common.

I will dig a bit and see if I can find a thread....

What radio are you using that is affected by motor noise? 2.4 should be fairly immune.
Nov 27, 2021, 05:40 PM
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pmackenzie's Avatar
Two cap example, 473 = .047



The diode is there to prevent damage to the ESC.

https://www.rcgroups.com/forums/show...r#post20664891
Nov 27, 2021, 06:15 PM
Registered User
I have a few hundred of the capacitors if you need 3


Don
Nov 27, 2021, 06:30 PM
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beazld's Avatar
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I’m using 2.4 Spektrum DX18 tx and I’m trying a Hobby King orange 6 channel rx for the first time. If I move the servo away from the motor the interference goes away. The way things are laid out the servo wires have to pass by the motor to get to the Rx. I found these in my stuff. Do you think they will work?
I’m running a 3 cell lipo and 2 motors and 2 ESC’s. I only have interference on one motor but it affects both servos.
Thanks
Nov 27, 2021, 06:43 PM
If it flies, I can crash it.
rocketsled666's Avatar
Quote:
I only have interference on one motor but it affects both servos.
That motor is noisy. Are you running that motor in reverse compared to the one that doesn't cause the servos to jitter? If so, that may be why. Brushes have a preferred direction, CW and CCW motors are built differently. Run in reverse, brushed motors can be much noisier.

You can't use the Zener or the Electrolytic (the cylindrical cap) in this application. You can use the two brown disc shaped capacitors. I'm not sure it matters how you hook them up, but I'd probably connect them in parallel across the motor leads. They're small parts, so they won't have big capacitance. Putting them in parallel adds them together, capacitance-wise.

Also, it might help if you made the motor leads in to a "twisted pair", a-la the way white and red are twisted around each other in a Candy Cane. Twist 'em really tight and when they "relax" they should stay twisted. Just make sure you're not pulling on the motor lead when you do the twist.
Nov 27, 2021, 07:25 PM
Registered User
The motor pictured has three (3) disc capacitors already on the motor one on each pole o case and the third one under the Electrolytic cap, which there is really no need for.

If you are still getting interference, I would check how close you are placing the speed control to the receiver and also if your antenna location is high enough in the hull for all radios, including 2.4 ghz radios. If you are using a crystal controlled radio, check and make sure that you9r antenna is not running next to any of the power leads or next to the motor or ESC.

Another trick you can try is to run a grounding wire from the motor to the stuffing box to establish an earth ground when the model is running in the water. This is done by soldering a wire from the case of the motor to the stuffing box.
Nov 27, 2021, 07:29 PM
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pmackenzie's Avatar
Try the two 103 caps, one from each lead to the case.
Nov 27, 2021, 07:30 PM
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pmackenzie's Avatar
Quote:
Originally Posted by frankg
The motor pictured has three (3) disc capacitors already on the motor one on each pole o case and the third one under the Electrolytic cap, which there is really no need for.
I missed the one hiding under the free wheeling diode
Nov 27, 2021, 08:31 PM
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beazld's Avatar
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Quote:
Originally Posted by pmackenzie
Try the two 103 caps, one from each lead to the case.
Iíll try adding them tomorrow and let you guys know what happens. I am running one motor in forward and one reverse. I get the interference on the one running backwards. Iíll also try twisting the motor leads too. Iíll post pics of the project when itís a little closer to finished. Letís just say itís a little different than your run of the mill RC boat.
Nov 27, 2021, 09:10 PM
20M northeast of Hell Mi
liljimmy's Avatar
If you are in to close of proximity and indoors from transmitter to receiver it maybe the cause of glitches
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Nov 27, 2021, 09:19 PM
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coriolan's Avatar
Quote:
Originally Posted by beazld
Iím using 2.4 Spektrum DX18 tx and Iím trying a Hobby King orange 6 channel rx for the first time. If I move the servo away from the motor the interference goes away. The way things are laid out the servo wires have to pass by the motor to get to the Rx. I found these in my stuff. Do you think they will work?
Iím running a 3 cell lipo and 2 motors and 2 ESCís. I only have interference on one motor but it affects both servos.
Thanks
The HobbyKing Orange receivers are just about the worse Spektrum compatible Rx in circulation, did you try it with a different brand Rx?
Nov 27, 2021, 10:25 PM
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beazld's Avatar
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Quote:
Originally Posted by coriolan
The HobbyKing Orange receivers are just about the worse Spektrum compatible Rx in circulation, did you try it with a different brand Rx?
No, not on this model. Itís the first orange Rx Iíve had. I wouldnít trust one in an aircraft that I cared about. I figured I'd try it in a boat first. Iíll give that a try too. Thanks.
Nov 28, 2021, 04:32 AM
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Quote:
Originally Posted by pmackenzie View Post
Two cap example, 473 = .047



The diode is there to prevent damage to the ESC.

https://www.rcgroups.com/forums/show...r#post20664891
~If intending to use reverse, DO NOT USE THE DIODE. In a forward only setup, it does a great job of soaking up the reverse voltage back-EMF spikes and stopping them being presented to the ESC output. In reverse, it provides a short circuit that will break either the ESC or the diode.
Three capacitors as found in a "suppression kit" will do the job. In practice I have always found that just one across the motor terminals does the job and avoids the trouble of soldering to the can while avoiding any problems that arise when one of the side capacitors fails. Within quite broad limits, the actual vale of the capacitor is not critical, but it does need to be a type that has good performance at passing high frequency AC.
This is very effective on older 27MHz and similar radios. Since the motor can't produce 2G4 interference, the problem is elsewhere - either the servo leads are picking up the signal and allowing that to mess with the servo electronics, , or the signal picked up by the leads is being fed into the output stage of the radio which then acts as an old-time crystal set, resolving the noise and using the output stage to mis-operate the servo. The interfering signal can be blocked from the servo lead by using a ferrite toroid -
https://www.amazon.co.uk/sourcing-ma...A%2CB07G6T8CXD Google will find others.

Just pass the servo lead through it two or three times. The only critical thing is to get rings whose inside diameter is large enough to pass the plug through.
If you've ever noticed a lump in a lead for anything electronic (I'm looking at the lead for a USB headset at the moment), that is what is going on inside.

Another afterthought - some motors simply produce too much interference to ever benefit from suppression, usually older ones that were either badly produced or designed, or ex-good ones that have passed their use-by date. Some motors mess with the basic voltage supply to the extent that control of everything that relies on a stable 5 volt supply is affected.
Last edited by mfr02; Nov 28, 2021 at 05:12 AM.
Nov 28, 2021, 07:39 AM
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beazld's Avatar
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Quote:
Originally Posted by mfr02
~If intending to use reverse, DO NOT USE THE DIODE. In a forward only setup, it does a great job of soaking up the reverse voltage back-EMF spikes and stopping them being presented to the ESC output. In reverse, it provides a short circuit that will break either the ESC or the diode.
Three capacitors as found in a "suppression kit" will do the job. In practice I have always found that just one across the motor terminals does the job and avoids the trouble of soldering to the can while avoiding any problems that arise when one of the side capacitors fails. Within quite broad limits, the actual vale of the capacitor is not critical, but it does need to be a type that has good performance at passing high frequency AC.
This is very effective on older 27MHz and similar radios. Since the motor can't produce 2G4 interference, the problem is elsewhere - either the servo leads are picking up the signal and allowing that to mess with the servo electronics, , or the signal picked up by the leads is being fed into the output stage of the radio which then acts as an old-time crystal set, resolving the noise and using the output stage to mis-operate the servo. The interfering signal can be blocked from the servo lead by using a ferrite toroid -
https://www.amazon.co.uk/sourcing-ma...A%2CB07G6T8CXD Google will find others.

Just pass the servo lead through it two or three times. The only critical thing is to get rings whose inside diameter is large enough to pass the plug through.
If you've ever noticed a lump in a lead for anything electronic (I'm looking at the lead for a USB headset at the moment), that is what is going on inside.

Another afterthought - some motors simply produce too much interference to ever benefit from suppression, usually older ones that were either badly produced or designed, or ex-good ones that have passed their use-by date. Some motors mess with the basic voltage supply to the extent that control of everything that relies on a stable 5 volt supply is affected.
Thanks mfr02, I think you are right about the servo leads picking up the signal as when I move the servo and wires away from the motor the problem goes away. Iíll see about some torroids if the caps donít work.


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