Motor Wiring Support
Contents
Summary
When using electric motors, one of the most important things to consider is motor noise. We sell several DC motors for our ATR and Vectoring Robot kits. With these motors we recommend you get a motor wiring kit too. The motor wiring kit provides protection and helps knock down the majority of the noise the motors put out. There are a lot of schools of thought on how to control the noise, Below is what we have found to be the best practice for motor noise suppression.
Capacitor Filters
A capacitor is a voltage storage device. They are frequently used to reduce noise by smoothing out voltage waveforms. The sizing of the capacitors isn't entirely critical in this specific application. We've found that anything greater than 1uF doesn't produce much of a difference in motor performance. The suggested places to employ capacitor filters are:
- Across the motor terminals. Take one or two non-polarity sensitive capacitors and bridge the two motor terminals.
- Motor terminals to motor housing. Scratch off a spot between the two motor terminals on the housing of the motor. Then solder a capacitor from this location to each motor terminal.
- Motor Controller. If you are building your own motor controller, be sure that there is a filter capacitor on the motor outputs. If you are using an off-the-shelf motor controller a sufficient filter capacitor circuit will already be implemented and an additional filter circuit is unneeded and will not produce a noticeable difference.
Shielded Cable
Whenever you are connecting to noisy devices or if you need to run cable near noisy devices, it is always recommended to use a shielded cable. Shielded cables help reduce the amount of noise absorbed over the cable run.
Ferrite Beads
Ferrite beads are often used in electronics to reduce electromagnetic interference (EMI). Long conductive cables can act as antennas and produce radio frequency energy and the addition of a ferrite bead to this antenna greatly helps to break the EMI field produced by the cable. When using ferrite beads on cables it is recommended to use the minimum sized heat shrink that will fit around.
- Around each motor input. When using a shielded cable to connect to a motor you will need to expose a couple inches of each cable in order to interface with the motor. A combination of heat shrink and a ferrite bead will help reduce the amount of noise that leaks into your cable from the motor.
- Around the main cable. Attaching a ferrite bead to the main cable will act as a second barrier to reduce noise.
Check for ground loops
What we measure as voltage is the electrical potential difference between two points, normally with one being ground. Having multiple paths to ground will create noise due to the existence of multiple reference points.
Don't run lines parallel
Shielded cable is best as discussed above. Also its important to try to keep signal lines and power lines separated and try to run them perpendicular. Twisting positive and negative power lines together is also a good practice to keep noise down (connecting the wires to the end of an electric drill is a good trick to twist the wires quickly and get a good tight twist.
Wiring Multiple Motors
When wiring multiple motors to a single motor controller channel always be sure to run your wires from each motor terminal directly to the output of your motor controller. Multiple motors can be run in parallel to the motor controller. ie a 6WD robot with 6 motors will have the 3 left motors run in parallel to once side of the motor controller, the 3 right motors would be run in parallel to the other side of motor controller. Sometimes when running multiple motors in parallel, the capacitors may cause errors with the motor controller, in which case try to remove capacitors from one motor at a time until the motor controller stops erroring.
Isolate Power Supplies
Having separate sources of power for your motors and the rest of your electronics will isolate your electronics and minimize the effect of motor noise.
Connection to an IG52 or a Motor with Encoder
When making connections with our larger IG-52 motors, or our motors with encoders, the motor terminals themselves are not accessible. For these motors it is NOT necessary to attach a capacitor across the motor leads.
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Connection to a Motor Controller
For most wheeled robot applications, it's desirable to have more than two motors. To minimize motor noise it is advised to run individual shielded cable from each motor to your motor controller. For example, if you have two motors per side, the positive (red) motor wires on the left will both go into terminal M1A while the positive motor wires on the right side of the robot will go into M2A. Please see the Electrical Schematics for more detailed description.