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Servo Motor Interference


Paul McDonald

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I have a Hornby analogue controller providing 0-12V DC to the track on my layout. I also have a completely separate circuit (with a separate 12V DC transformer from the mains) that controls a set of servo motors which I'm using to operate points and signals. Both circuits work fine individually but when I operate a train and have the servo circuit turned on, the servo motors jitter.

 

I'm assuming that this is some kind of interference as the wires to the servos pass directly under the track (this can't be avoided).  Do I need to add some kind of suppressor somewhere, and if so where?

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We had a similar experience at our club where we'd run track feeds and the wiring for some train detection circuits through the same holes in the baseboard supports. The part of the layout concerned is switchable between DC and DCC operation. All worked fine until we started running DCC stock whereupon the ICs in the train detector circuits kept blowing. It probably doesn't help that we are also using a single "common" return. We've since fitted diodes in the 12v supply lines to the detector circuits and the problem has gone away.

 

Is there a physical separation between your two circuits?

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You probably need to twist your servo wires to try and eliminate induced currents being picked up from the parallel wiring.

 

Modern 'digital' servos have anti-jitter circuitry built in to them and using these might help. The latest TowerPro SG92R servos (with a paper QC label stuck on the outside) appear to be of this type and they are not expensive.

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We had a similar experience at our club where we'd run track feeds and the wiring for some train detection circuits through the same holes in the baseboard supports. The part of the layout concerned is switchable between DC and DCC operation. All worked fine until we started running DCC stock whereupon the ICs in the train detector circuits kept blowing. It probably doesn't help that we are also using a single "common" return. We've since fitted diodes in the 12v supply lines to the detector circuits and the problem has gone away.Is there a physical separation between your two circuits?

yes, the servo wires are below board and power to the tracks is above board. The board is approximately 10mm thick.
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