Not sure what motor I need. Stepper VS Servo OR something else?

Other Hardware Motors, Mechanics, Power and CNC
1

I'm sorry it's come to this but the more research I did the more confused I got. I am using Max/MSP with an Arduino Uno and need to control a motor that will turn 30° every time a condition is true. The motor needs to turn in the same direction every time and at the exact ° every time. I thought I needed a servo motor because of the position feedback. But (and correct me if I'm wrong) it seems servos can turn a certain ° but only up to 180° and then it needs to rotate in the other direction. My thought was I could use a continuous servo motor, but it seems I can only control the speed and time of the continuous servo motor. And I thought a stepper motor won't work because it doesn't give feedback on it's position.

So the question is: How would I have a motor turn 30° in the same direction every time a condition is true and make sure stays within that tolerance and doesn't get out of position?

Thanks so much for your help. You are welcome to talk to me like I know nothing.

2

If you are content to turn a max of about 3 revolutions in one direction then a sail-winch servo should do the job and it would be by far the simplest option.

If you need more revolutions in the same direction then you probably need a stepper motor. But you should be aware that stepper motors cannot detect where they are - they can only move X steps from the current position. To determine a Home or Zero position you need an external microswitch or optical detector. Stepper motors also need a stepper driver board that sits between the Arduino and the motor.

See stepper motor basics

...R

3

Well the usual for something like that would be a stepper with a reference home sense.

But since you mention in the title "something else" I thought I would throw something out that I always get a kick out of. The mechanism is used on some cnc's to index the toolholder carousel.

4

Thanks for your responses. Looks like I will have to go with a stepper motor and determine a zero position. The Geneva mechanism is very cool but still looks like I would need something to control the position of the rotation.

5

With an r/c servo maybe use a pawl ratchet system. Notice the actuator moves like a servo.

6

Depending on yours parameters (torque, voltage, size, etc.) you may want to consider a geared motor with a built in encoder. You can probably find an inexpensive source. - Scotty

7

Justone and Scotty thanks for the input. The ratchet and pawl system seems like something that could work great for what I need. Will investigate further. Looking into the encoders as well.

8

With the encoder setup you would need it to have a home sense (just like the stepper).

With the ratchet If you need to know what 30 deg. position it is sitting at then a home switch would be needed.

I have a 3d printer so I'm playing around with a simple ratchet system using a single servo to drive and also steer a robot.

9

The motor needs to turn in the same direction every time and at the exact ° every time.

How exact do you mean by exact? With what torque?