SMC04 with feedback very noisy

Hello, I have SMC04 with MAXON DC brush 12V 5W REF110121, working with potentiometer 5KOhm feedback over motor axis.
I have signal noise at frequencies over 5KHz measured on oscilloscope, when motor is working even when it has reach final position, but it is dancing around it.
The noise is in dc signal and I can hear a terrible beep continuosly.
Distance from SMC04 to motor is 20 cm.
I have tried to filter Motor+/Motor- with inductances, and I reduce a little the noise but not sufficient.
I supose I must use shielded cable with separated cables for both signals (motor and potentiometer).
What can I do?
Anybody knows other solutions?


What do you mean by “The noise is in DC signal”? You can reduce the noise from the motor leads by twisting them together. You can also filter the feedback line a bit with a capacitor. When you get the oscillation around the target point, do you have much of a load on the motor? Audible sound at 5 kHz is normal (when the motor is straining against a load) since that is the PWM frequency.

- Jan


Motor hasn´t load when it is on target point.
Sometimes we have noise in dc signal 5KHz (10 peak volts over 0-5VDC) and when green led is fixed the noise ends.
Which is the range of ACCELLIMIT? because it does not appear on manual.


I’m still not clear on which “dc signal” you are talking about. Do you mean the regulated 5V line, or the analog feedback line? You certainly shouldn’t be seeing 10 V noise on either of those lines; how are you measuring it? Where you connect your oscilloscope probes can make a big difference in what you see.

The ACCELLIMIT can be 0-127. With 0, there is no limit; otherwise, larger values mean the PWM duty cycle can be increased more quickly.

- Jan

Hello, sorry about the confusion created by me because I haven’t expressed correctly.
We return to begin.

The feedback and reference potentiometers are of 5K, they are fed from the own SMC04, and are located next to this.

We see with the oscilloscope its signal and it is perfectly stable.

When we change the reference potentiometer the motor moves (only with the load to move the feedback potentiometer) and the motor stops when position is reached. While it is turning we hear a continuous beep.
When motor stops, some times the beep disappears and in other times not.

When connect the oscilloscope between cables of the motor, it is observed that when there isn´t beep the signal is totally flat (without PWM tips).
However, when I listen the beep, appear tips of little width of 5 Khz.
The green LED remains fixed.
With other models of motor the sound is not heard neither in stopped nor march.

Actual parameters of SMC04 are:

- kronotec

What you are describing is normal behavior for the motor controller. The 5 kHz signal you are seeing on the motor leads is not noise but rather the PWM drive of the motor. Depending on the mechanical properties of your system and your PID parameters, you won’t always get the error to exactly 0. If the error is 1, it’s only a 0.1% error in the position, but the power to the motor will still be nonzero. If the drive signal is small, it won’t be strong enough to get the motor going but it will still make the motor vibrate and make the sound you are hearing.

For the given motor you are using, there is nothing you can do to make the motor quiet when it is running since the 5 kHz PWM frequency is fixed. You might be able to improve the performance of the PID by tuning the parameters, but if the green LED is coming on, it means that the error is within 3, so it might be difficult to get much better.

- Jan

I forgot to add that if the audible noise is a big factor for you, we can make a custom version of the motor controller with a 20 kHz PWM rate that would take the frequency out of the audible range. Please contact us if you would be interested in such a product.

- Jan