servo or dc stepper motor

fzeitgeist

Hi everyone. I am new to this forum. I am trying to control two motors which will position a telescope. I am not sure if I should use a servo or a dc stepper motor. The bs2 can handle both, but i need the motors to do the following:
1. Rotate 360 deg.
2. Rotate in reverse direction.
3. Have some kind of an encoder to determine the motor position.

Also, I will be having 8 inputs and 1 output apart from the 2 motors. The stepper motor has more wires and the bs2 can only handle 16 I/O, if a stepper motor is a better choice for this project, how can I use less pins to control them.

Thank You
·

Donoho

A compass might be a good way for your BS2 to locate the direction the scope is pointing to the nearest degree. Although anything magnetic close to the compass won't allow the compass to work properly, which is my problem with my project.

Don Buczynski

I'd use a stepper motor. Checkout the signature link below; specifically the model railroad "turntable" links.·It will give you some ideas for·using a·BS2 and stepper motor. You could integrate a second Allegro controller·for the other axis. You can get encoders separate or built into the stepper motor.

More than you probably want to know about stepper motors:

···· http://stepper-motors.globalspec.com/
···· http://stepper-motors.globalspec.com/directory/Motion_Controls/Motors/Stepper_Motors



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Don Buczynski

http://www.buczynski.com

fzeitgeist

Hi Don. I think the turntable example on your website is an excellent sample for my porject. I gues if the stepper motor moves at 3.6 degree/step I do not need an encoder. The no. of steps can help me determine my position. I see on your website that the allegro takes up 5 pin positions on the bs2 and i need 2 of these. And I will also be adding a key pad, that takes up another 5 pins.

·This does not leave place for my LCD connection. What do you suggest for that?
·Also, if the reset is activated on the allegro, will this move the motor to its initial position?

Thanx agian for the help.

Lee Harker

Stepper motors are better for precise positioning and they have less chance of exibiting jitter like servos. You don't mention what the 8 inputs are from but if they are just switches you may be able to matrix them to save lines. Also, you can share some of the lines that are used by the LCD display and your keyboard. There are examples of this on the Parallax web site.
Lee

fzeitgeist

Hi. Could'nt find examples how the lines from LCD and key pad be shared. Can you please post them here.

Thanx.