Hi, I am building a hexapod robot with 18 MG996R servos and am trying to select a buck converter for the project. I'm planning to power the robot with two 3S LiPo batteries, one battery for three legs (9 servos). I first tested the robot with a bench supply at 11.6V (close to the nominal voltage of a 3S LiPo) and wired the supply to a 5A-rated buck converter. The converter was outputting 6V to the servo driver (PCA9685) and powering three servos for the test. When I powered the robot, the power supply’s short circuit alarm shut it off.
I'm assuming there was an initial voltage spike because the servos have a stall current of 2.5A. I added two 2200µF capacitors in parallel at the output of the converter to try to absorb the spikes, but it didn’t help. However, when I powered the servo driver directly from the supply, there were no problems.
Is the buck converter the issue? Thanks.
Thanks for the responses, If I used two 20A converters one converter for 9 servos 2.5*9 = 22.5A would it be enough given all nine should not be moving at the same time?
The only way to stop servos from moving is to use the servo.detach() function call, then reattach them when they should start moving again.
Otherwise, if the power supply voltage drops, the attached servos may see that voltage drop as a false movement signal and you will end up with a twitching mass of junk.
If you want your project to work, ALWAYS generously overrate the power supply. It is impossible to stress this point enough.
Alternatives include heavy duty 6V NiMH RC battery packs and run servos directly from those, or buy 7.4V servos and run them directly from heavy duty 2S LiPO packs.
Do your research and if you have questions, identify and post links to the actual products you are considering (after carefully reading the product specifications, of course).