Hi all,
Didn't find anything that specificlly addressed this but I'm a noob so what do I know.
I'm using a servo in a project which requires a change in position every few minutes over a 12-20 hour period. There is insignificant load on the servo during movement and even less once it has reached the desired position. From my reading of servo.cpp it looks like servo.writeMicroseconds() strobes the servo signal line at a given frequency until you tell it to do something else. I see no good reason to keep using power to position a servo when there is nothing to cause it to move. Just a guess, but i'm thinking these hobby servos (Futaba 3003) are designed to be run for short periods. I could see where it might get hot just sitting there jumping back and forth to stay in the same place. Seems I can turn off the control signal with servo.detach(). BUT, I don,t see a good way to turn off the power without putting a relay in there. So here's the question does anyone know if:
If I turn off the servo control signal and leave the power on can I drop the current draw into the "don't care" range ?
Is there there any reason to believe that stray EMI might cause the servo to move while detached ? (The environment is about as quiet as it gets but the Arduino itself is right there with clock lines and such)
) If I turn off the servo control signal and leave the power on can I drop the current draw into the "don't care" range ?
No, servo behavior of being powered on but with no valid signal pulse is a undefined state for a servo, and how it reacts can vary with specific servo brand/model/unit. There will not be much difference is current consumption anyway if there is indeed no mechanical load variation once the servo has reached it's desired position.
2) Is there there any reason to believe that stray EMI might cause the servo to move while detached ? (The environment is about as quiet as it gets but the Arduino itself is right there with clock lines and such)
Again there in no defined behavior for a servo to have power on but no control signal. While you might be able to successfully detach a servo (and later reattach at some time) without any undesired effect, it's just not going to return any benefit that I can see? Now switching off Vcc voltage to the servo and keeping the control signal at a LOW value will save current, it's probably in the 10 ma or less 'idle' current consumption of a non moving servo.
retrolefty
Thanks for the replay. I suspected that I might be designing a solution without a problem. Guess I try it out and see if the motor gets hot or anything stupid like that. Thanks again
If the load on the servo is small enough so that it will stay in position without power then you can use the Arduino to switch off the power to the servo using a relay. The Arduino itself can't provide enough power for a servo or a relay so you need to use the Arduino to control a cheap transistor that controls the relay. You may be able to use a bigger transistor to control the servo power directly without a relay.
I believe most analog servos will stop trying to position themselves when they stop getting a signal. Digital servos will hold their last received position until they get a new one.
mmmalmberg:
I believe most analog servos will stop trying to position themselves when they stop getting a signal. Digital servos will hold their last received position until they get a new one.
Again servos are not designed for operation of being powered up but with no control signal, it's just not a defined mode that servo manufactures design for any specific response on the loss of control signal.
mmmalmberg:
I believe most analog servos will stop trying to position themselves when they stop getting a signal. Digital servos will hold their last received position until they get a new one.
Again servos are not designed for operation of being powered up but with no control signal, it's just not a defined mode that servo manufactures design for any specific response on the loss of control signal.
Some of my servos move to an end position when they are powered up if there is no control signal. I think some of the others don't move. Disconnecting the power is necessary to guarantee they won't move (assuming the load is small enough).