BoeBot - add capacitor to smooth power draw of servos

John Kauffman

I vaguely recall reading somewhere that a capacitor parallel to the servos would smooth the power draw.
Perhaps it was in Gunther's SX book, I'm not sure.
Does anyone have experience with this? If it works, can you provide specifics, including cap size and description of circuit or schematic?

Thanks

Mike Green

Assuming you're running the servos off of Vin (the 6V battery), a capacitor won't "smooth out the power draw" since the batteries will provide a stable source of power for the servos and most batteries have more than sufficient peak current capability to handle servo motors. Even though servos can draw 1A or more when they're just starting to move or are near stalling because of the mechanical load, AA alkalines or NiMH rechargables can easily handle 2A to 3A peak current for short periods of time. Servos (and other motors) can generate some electrical noise. This is normally filtered by the BoeBot's power supply which has the voltage regulator and capacitors on the output side of the regulator.

You can add capacitors across the servo's power leads, but the values needed would depend on what you're trying to solve. Typically you'd have some kind of electrolytic capacitor, perhaps 470uF or 1000uF to act as a power reserve for surges. You'd also have a 0.1uF ceramic capacitor to filter out high frequency noise.

John Kauffman

Thanks. Mike. To confirm:
Probably not important, but might help.
1000 uF electrolytic with NEG side connected to black lead of servo, other cap leg to red lead of servo
0.1 uF ceramic cap connected in parallel to above, polarity doesn't matter.