I want to make a low thrust linear actuator with a cheap continuous rc servo motor and then control it with a microcontroller. The thing is, I want to find out what the minimum degrees is that a motor can move but it seems to be something that is not documented. I can see the pulse range that you can control the motor with but I also have no idea how a pulse length relates to a given output. Is there some place that I can find some documentation?
PS I am sort of wanting the FS5106R motor at the moment.
Best Answer
The servo you mention is a continuous rotation servo, which is really a bit of a hack - an aftermarket modification now being done for you at the factory or distributor.
These devices do not have a closed positioning loop - to the extent that they have proportional control at all, it's of speed or torque. These are made by taking a normal servo design, and disconnecting the feedback potentiometer from the output shaft (or even substituting fixed resistors), so the internal positioning loop is opened and you get to control the apparent loop error by commanding a position different than the one it's feedback input is "stuck" at.
I've not used this particular model, but those I have used had very poor control - there was very little input range between full-on in one direction and full-on in the other. It's too bad someone doesn't make one with a closed velocity loop, though that would require a different motor technology or a rotation detection scheme (incremental optical encoder? electronically commutated brushless motor?)