Help selecting a motor

Help & Support Robot Parts
1

Hello,

I have been tasked with selecting a motor for a project. Actually, we need more than one but I am not sure what the quantity is. We basically are looking for a servo motor to control with Arduino. I assume it will use the servo class that comes with the library. That is not a strict requirement though. Actually, we will be running it from the servo class in Matlab. We will be using a servo motor shield to isolate the current demand.

The motor will be turning a wheel that is about 6" across and has 6 lenses in it. Each lens is about the size of a lens in a pair of glasses and weighs about the same. The wheel itself will probably be a fairly light aluminum. The wheel will be sideways like a car tire. The wheel should be mounted pretty close to the motor. The wheel should be reasonably well balanced.

So we are looking for a motor that can be on its side and handle the weight of the wheel. the wheel either needs to turn about 330 degrees or all the way around. Either should be fine. I just need to learn to program a continuous motor for the latter. I am looking at the RB-Hit-30 but do not know if that is the best choice and I am looking for a recommendation from you. Ideally it will be pretty quiet once it reaches its target location. There is no speed requirement. If anything, don’t spin the wheel too fast.

Actually, I guess I should be explicit. I need to be able to turn the motor so it stops at whichever lens I require.
Thanks,
Dave Beane

2

RB-Hit-30 is limited to 180 degrees of motion, as are almost all RC servos.
Many smart servo motors can rotate up to 320 degrees, sometimes allowing for full 360 degree positioning:
robotshop.com/en/smart-servo-motors.html
A smart servo motor would likely be your best option, but it needs serial commands and does not operate using a normal RC servo signal / shield / library.

Another option is a power gearbox:
Ex: robotshop.com/en/servocity-3 … RB-Sct-823
This would ensure the wheel is well balanced, you can use normal RC servo signals and still get 330 degrees of absolute positioning.

3

Coleman,

Thank you for your response. Since I have been asked to try to make this work from a servo board (which means servo commands), the power gearbox sounds like a workable solution. A friend of mine also just suggested that a winch servo might fill my needs since I don’t need high resolution in each step. Any thoughts about the HS-785HB winch servo motor (RB-Hit-53)?

Dave Beane

4

That’s effectively the servo used in the gearbox. It rotates 3.5 turns, so like you said, the accuracy is lower.

5

OK. Thanks for the advise. I think I understand better now. It actually is that servo but the gear ratio is 3.8/1 reducing the 360*3.5 = 1260 reduced at 1/3.8 to get 331.6 degrees which is almost exactly the range I need.

Dave