Hi, I am currently working on a project with 4 servos and 4 DC motors controlled separately.
170RPM Motor:
HS-785HB Servo:
The only problem I am now encountering is that when the DC motor spins, the nearby servo rotates in a single direction as well.
This only happens when DC motor turns in one direction, and the servo stops spinning when I take the DC motor wire away from the servo(and returns to its original position). When I put the DC motor wire near the servo again, it starts to spin in continuous direction again.
It seemed like a high frequency AC noise was occurring on the DC motor wire when the motor is spinning.
I concluded that the EMI(Electromagnetic Interference) is the main problem, and changed the DC motor wire into a shielded wire(2C). However, I am still observing the same spinning servo.
Are there any ways to shield the servo as well? I was searching on the internet but I couldn't find the proper noise filter for the servo. The servo wire is twisted which should prevent EMI by itself, but since the wire itself isn't working, I'm trying to find a way to add a filter that can catch EMI coming from the DC wire
(Because of the project structure, the DC motor wire and the servo wire has to go through the same hole.)
I attached the 0.1uf nonpolar capacitor on the motor, used ferrite core on servo wires, and used shielded wire for the DC motor.
I just don't understand why the servo has noise when the DC motor is spinning on only one direction
tk1221:
I just don't understand why the servo has noise when the DC motor is spinning on only one direction
Brushed motors often make more electrical noise when turning in one direction. It can depend on how the brushes are positioned on the commutator and how they wear in.
If you need more noise suppression try 3 ceramic 0.1 uF capacitors on each motor, one across the two terminals and one from each terminal to the case. NOTE: "ceramic" is important, using any old capacitor may not work nearly as well.
Most brushed motors are deliberately designed to be somewhat directional because the full-speed efficiency is
distinctly higher if the brushes are advanced (just like timing advance in a petrol engine). In a DC motor
the inductance of the armature windings delays the maximum current point, advnacing the brushes
compensates. However the price paid is that the reverse direction is less efficient (higher current, lower max speed).
Often brushes are mounted at a small offset or angle - this can affect friction and smoothness of running
to favour the forwards direction.
The asymmetry is usually small enough to not be noticed unless you measure the performance. I'm sure
I've seen motors with the brushes mounted on an adjustable plate that can be turned to set the advance
angle.
I attached three 0.1uf ceramic capacitors to each of the motors and coiled a ferrite core to the servo wire.
Thankfully, It worked perfectly!
I never thought of attaching three capacitors, since I always used to attach only one for each motors.
There are no EMI found at all, and my project works perfectly.
However, I think the capacitors did all the job. The ferrite cores attached on the servo wires didn't seem very effective.
Anyways, Thanks for the help!
I finally fixed the problem that stressed me for weeks!
tk1221:
I attached three 0.1uf ceramic capacitors to each of the motors and coiled a ferrite core to the servo wire.
Thankfully, It worked perfectly!
I never thought of attaching three capacitors, since I always used to attach only one for each motors.
There are no EMI found at all, and my project works perfectly.
However, I think the capacitors did all the job. The ferrite cores attached on the servo wires didn't seem very effective.
Anyways, Thanks for the help!
I finally fixed the problem that stressed me for weeks!
There are ferrite cores and then there are ferrite cores. There are many mixes of material in the ferrite to produce a high impedance at a small, specific range of frequencies. If you don't know the frequencies of the interfering noise, then you just have to try different mixes until you find the right one.