I'm working on a design for a prototype... and I've come up with a design solution (in my head)... but now I'm trying to figure out how to build it. Essentially the device I'm thinking of designing would have a string connected to a motor which would reel (or retract) the string (probably 2 or 3 inches) and then let the string back out (I think the force on the string will automatically pull it back out...assuming the motor is free and allows the string to be pulled out). This cycle would need to loop over and over about 25-30 times per minute. I'm relatively knowledgeable about different motors types and mechanism designs... but I'm wondering if anyone would have any suggestions about a motor or mech design which might achieve what I'm looking for. Ideally, the motor doesn't need to have an incredibly strong pull force... but may need to induce a force of about a 0.45kg (roughly 1lb)... and size, power, and noise might be a factor. Would a DC (small RC motor like FA-130 type) be appropriate? Or is there some other motor which would be appropriate for this application? What about driving the motor? Is there something that I should look at which would allow me to retract the string and then let it back out about 30rpm? Any advice would be greatly appreciate. Thanks in advance.
A servo is the obvious answer with an arm of suitable length cycling up and down. The torque requirement is about 50 oz/in, easily met. Long term endurance might be an issue with plastic-geared hobby servos, but metal gears are still reasonably priced. At least a servo is an easy way to test your idea.
If you use a simple DC motor then you need a gearbox running at 30 RPM. You also need some sort of arm/cam arrangement. If you can meet the mechanical requirements easily the motor is not very critical. Geared down to 30 RPM, any small decent motor(not a 2$ cheap toy motor) can handle it.
You need the Arduino for the servo, but why does the dc motor need anything more than a switch? Speed control?
I'd give the servo a try first. It has the gearbox and mechanics built in.
Thanks joe. After I posted... it dawned on me that a servo would be a good solution (glad I came to the same conclusion as you). I'm going to try with that first as I think it will have the torque and speed that I'm looking for. Thanks for the answer. Best, Andy