Trouble with electrical noise

I am building a robotic platform that is a skid-steer drive. Each motor is 24v and loaded draws 25 amp. the motor controllers that I am using two pololu 24v23 simple motor controllers. The motor controllers are set to a pwm frequency of 21 kHz I am using serial ttl to communicate between the micro and the motor controllers. As the motors pull more current, the signal errors get worse. I also have servos and an RC receiver wired up to the micro.
when the motors are powered up the servos twitch and jump. when the motors are heavily loaded the servos do not respond at all. I have a rc switch that is plugged up to the rc and its just an rc controlled relay. again when the motors are running it will randomly turn on and off regardless off the rc signal. The rc receiver gets its power from the micro, the micro gets its power from the 12v battery. the motor controllers get their power from two 12v batteries. the servos get their power from two step down dc to dc converters (one 5v one 7v). everything shares a common ground. I have twisted and wrapped the power wires to the motor controllers with copper braid so that it would help with the emi. I did the same thing with the serial tx and ground line to the motor controller. that seem to work a little. My question is, how do i go about removing all the electrical noise.


Have you been able to see the electrical noise on an oscilloscope? What you are describing sounds consistent with a battery that cannot supply enough current. Can you see if your battery voltage is dropping when things start performing poorly?

Separately it sounds like your motors at 24V might be too powerful to use with those controllers. When you say they draw 25 A loaded, do you mean when they are stalled?

- Ryan

The batteries that I am using are two 55 amp/hr. There is only a .2 volt drop when under a load. I have not yet looked at it under a oscilloscope. I Just rewired everything so that I use 12 gauge wires and the wires in the box are less than two inches.

Are you saying there is a .2 V voltage drop when you draw 50 A from the batteries? Can you answer my question about your motors? Did rewiring it help? Do you have access to an oscilloscope?

- Ryan

The platform that I am using is an old powered wheelchair with motors that are made to run at 24v. i still have not tested it. I am wiring in a dc-dc converter to run all the control side electronics. Yes I have a very old(1987) oscilloscope that I can use. The way I was powering the control side before was (see picture). now I’m using the dc-dc converter to take the 24v to 7v to power the micro.