Linear servo motor going crazy in particular condition - How to solve it?

Good day!

I'm suffering from this issue for 3days now.

I'm currently working on with a robot which has 2 circuits of using 7.4V and 11.1V.

It also has 4 of 6V L12 linear servo motor. The motor works fine if the 11.1V circuit is turned off.

But whenever the 11.1V circuit is turning or turned on, the linear motors go crazy.

Since 2 circuits are totally separated except the ground, I assumed that

noise from the 11.1V circuit goes into the linear servo signal cable and makes the problem.

So I tried to twist the servo cable to compensate the noise, it didn't work at all.

Because of this issue I'm pretty much last these days.

Would anyone give me some help with this problem?

A complete circuit diagram and a picture of your setup would be useful plus a datasheet for your linear servo motors.

E.g. what is the 7.4V (2S Lipo battery?) source connected to? And what is the 11.1V source (3S lipo?) powering? Is there an Arduino involved? What sort? What is powering that? What else is connected to it other than 4 linear servos?

Basically there is too much information missing to offer any real answer I'm afraid.


Sorry for lack of information. So power source of both circuit is LIPO battery.

The 7.4V circuit consists of Arduino and 4 servos which are controlled by Arduino and they are directly connected to the battery.

The 11.1V circuit is composed of 2 suction motors, 6 DC motors(2 for brush, 4 for locomotion), and drivers.

I guess the current would be about 10A max.

There are also some vision cams and various sensors but I don’t think it’s related to the problem.

So the thing is if I turn on the Arduino and operate the servo without the 11.1V circuit, it works just like I expected,

But if the 11.1V circuit is turned on, the servo goes ups and downs crazy

As you can see that the servo cable at right is all tangled, I made a twisted cable but it didn’t work at all…

Here is the data sheet for the servo motors.

I'm using 'L12 6V 30mm 210:1 option-R' servo

Is everything star-grounded and isolated from the chassis? (no need to ground the chassis when using low voltage, that can increase interference issues).

Route all the high current wiring away from all sensors and logic signals. If necessary shield all sensor cables (connecting shield to ground at one end only to avoid ground loops).

Hard to see from that photo the actual servo wires, but its a good idea to run 4 wires, a pair for power and a separate pair for signal+ground. If they have 3-wire cable this could be an issue as the signal ground sees high current.

Do you have access to a 'scope for seeing what's going on?

Thx for the detailed reply!

Everything star-grounded and isolated from the chassis with plastic supporters.

It would be hard to make a significant change in moving high cables away from the signal cables

I think I will try with shielding but since I’m a mechanical engineering student,

I’m really having a hard time finding how to do it. Would there be an easy way to shield the cable?

what is ‘scope for seeing what’s going on’? I’m totally new here so I’m sorry that I know nothing.

Btw does the stable DC power source makes the signal noise too?

I thought it only happens when the power source is turning on since it makes high frequency at the moment

Thank for the reply again