RF remote control range drops while the motor runs, what causes it?
A running brushed DC motor and a switching driver generate broadband electrical noise. Once that noise raises the receiver's noise floor, the same signal level is no longer enough and the range drops. Motor current can also cause a drop in the supply voltage, which reduces the receiver's sensitivity as well.
Three separate mechanisms act at the same time:
- Radiated noise: Brush arcing and switching edges produce broadband emission; the motor cable radiates it like an antenna.
- Conducted noise: The noise is carried to the receiver over the supply line.
- Supply collapse: High motor current causes a drop in the line voltage; if the receiver sits on the same supply branch it is directly affected.
Measures to take:
- Move the antenna as far as possible from the motor cable, the driver and the contactors; place it on top of a metal mass and facing an unobstructed direction.
- Run the motor supply pair twisted, leave at least 50 mm between it and the signal cables, and cross them at 90°.
- Separate the receiver supply so that it does not share the same thin cable with the motor branch; add a supply filter or a ferrite.
- Fit a suppression capacitor or a ferrite bead at the motor terminals.
- If you use shielded cable, ground the shield at one end only, on the driver side.
- Increase the cross-section of the chassis return; a poor return path is both a voltage drop and a noise source.
Run the test separately with the motor running and stopped and compare the range; if the difference is clear, the problem is definitely noise or supply related.
Full topic: DC Motor Driver Selection Guide