Can drive motor affect steering servo?

[WhiteWolf McBride]

I agree with the 'choke' idea, aka, a ferrite core.

You often see then on monitor power cables and the like, its that bulge in the data cord. You can get clip-on two-part ones, or simple ring-shaped ones, but feeding a servo cable to wrap it around the ring a few times may be hard. You may also want to run the power feeds to the drive motor thru a core as well... 2 or three wraps of the power line minimum.

Bit I agree, its probably a electrical/magnetic feedback issue. With a separate battery supply, there is less direct path for the feedback in the wiring. Thats why it spikes when the RPM is cranked.

WhiteWolf