Hey everyone, I am work on a sort of "Drill Press" I have recently upgraded a Servo motor to a much more powerful 35kg/cm DSPOWER (my original 11kg/cm MG966R kept braking.)
Ever since I have upgraded my new servo motor started jittering and having erratic movements by itself - I didn't even have to send a signal to it. This issue ONLY occurs when the DC motor is turned on. With it off the servo functions incredibly well.
This was not an issue with the previous servo motors (11kg/cm MG966R). I can in fact change them out and the weaker servo works just fine with the DC motor running.
I have come to believe that these more powerful DSPOWER servo motors are more vulnerable to EMI (yes I have tried 2 of these 35/kg servos with the same result).
The wiring for both the Servo and the DC motor are going through the same 5-pin Aviation Plug and the cables are tied together for the length of around 2 meters, and I would like to keep it this way if possible.
After researching EMI I have just attempted to attach 2x 0.1uf ceramic capacitors to the motor connectors:
This seemed to help, the servo no longer moves without me sending a signal to it. Buuuuutt the issue still persists, when I send a signal to the servo its movements are very back and forward until it reaches its destination. It is Certainly not acting the same as when the DC motor is off.
Any suggestions on removing the EMI? Is that the best configuration for the capacitors? Do I need more? thanks
You need to step up the killing of that DC motor electrical noise.
2 meter cables in one bundle needs to be changed. I would try twisting the 2 DC motor cables.
If the DC motor only runs in one direction a kick back diode could do a lot.
What is the driver of the DC motor?
I would put an 2 extra fly-back diodes, 1 right near the servo, and 1 before the 2nd stage PSU's.
Also i would stabilize the PSU that is powering both the Arduino and the servo. on the input side of it i would put a diode in series on Vcc in of the PSU and on GND in of the PSU and add a significant size capacitor, which because of the diodes can not drain into the DC-motor PSU.
Hey thanks for your response.
The motor only needs to run in one direction, It is capable of going in reverse by swapping around the connectors but there is no use case for this in the project. The motor actually doesn't have a driver. I have a toggle switch between the motor and its power to manually turn it off and on.
I will certainly try twisting the wires of the Motor.
Thanks,
Do you have a recommendation for the diode? I would assume it would need to handle at least the current and voltage from the motor? I see there are different types of diodes too (Schottky etc).
I have found a couple that are available near me:
schottky 3A-50v here
1N5404 3A 400V Diode SSR D0-27 here
Would either of these be suitable as fly-back diodes for my project?
I have read your suggestions on diodes and fly back diodes. I have placed them and their polarity as per your suggestion. Is this correct? I am unsure as to where the large capacitor should go (and what size)?
well i would add is as an extra input capacitor on the low-voltage PSU, but i realize now that the PSU has one already of course an extra 470uF wouldn't hurt though.
yeah, in my box i don't have to many choices, but for the 2 in-line diodes i would just grab 1N4007 's Of course 1N4001 would work, but if it's ok to use 100v diodes, then 700v ones are also ok, and those i have !
and i think i'd use one of them for the fly-back as well, probably not ideal, but should do the job. Main thing is to get rid of the noise on the line, but those bundled cables can also be an issue, maybe you could remove them for testing purposes, so they can be in- or ex-cluded as a cause.
Ok I have fixed the issue. I implemented a number of mitigation options.
I'm going to list out what I think had the most effect in reducing the issue.
I added 3x 0.1uf ceramic capacitors to the DC motor in the configuration below (10%).
I implemented all diodes suggested by Deva as per my previous diagram (0%).
I removed the ground from the Arduino's DC plug and instead used the ground pin from the Arduino board to the power (80%)
I added Shielded Cable for the DC motor and the Signal wire of the Servo Motor (5%)
I twisted the wires of the Servo Power cables (5%).
