Could I use a DC motor and a Relay to rotate a cylinder 90 degrees clockwise then instantly -90 degrees counter-clockwise? Axial load about 0.05 lbs. Frequency ~ 20 Rev/Sec (1 Rev = back and forth)
Not likely. The time would be 50mSec per cycle. Relays generally require more time than that (~100mSec) just to pull-in. Plus the time to start, reverse, and stop the motor.
There may be a better way. What are you attempting to do?
if u wanna use dc motors so i suggest u to change the relays and use transistors as (TIP 31 C ) its pull in time by nano sec..
also need some optical limet switchs (optical faster respons than the normal mechanical one...