Continuous servo with position control

[Alex3k]

Hey guys
Im trying to build my own dome CCTV camera.
To do this I need to get hold of a servo that moves in a full circle and still allows me to control the position. Can anyone help?


I also just literally as i was writing this had a brain wave. is it possible to use two motors one to go around continuously but only when i hold down a button or something and then go the opposite direction if i hold down another? and is it possible to do the same thing on the other motor however it needs to stop at certain angles?

 

[hippy]

You probably don't need a servo, just a simple DC motor or a stepper motor, and just one to rotate in both directions.

 

[papaof2]

DC motors are easy to reverse - just reverse the power connections. Having the device stop at specific points could be done with microswitches or hall effect devices and magnets (it's a little more complex than that).

If you have a servo with sufficient torque, you can gear it up so it drives a shaft that turns twice as fast as the servo output, giving 360 degree camera motion from a 180 degree movement of the servo. The control software would do the math to only turn the servo 90 degrees when the desired change of camera position is 180 degrees. Any PICAXE could do that. Using a geared-up servo also makes stopping at specific positions easy - just give the servo the new position and it goes there. Using a servo also ensures that you don't wrap the camera wiring around the mount many times while testing ;-)

John

 

[goom]

Looks like a sail winch servo for model boats would be ideal. Most can rotate several turns. The fancy ones can be programmed for specific amounts of rotation and end points.

 

[westaust55]

@Alex3k,

Consider the AMIS-30622 Stepper motor controller.
To use this chip you need a PICAXE with i2c comms capability and a stepper motor with a current rating of 800mA. The chip has current limiting so you could also use a motor with a higher current and using the current limit depending upon torque requirements.

With this chip you set a position as the "zero" positon and then you just send a command to move to a poisiton up to +/1 32767 steps either side of the "zero"/home position.
You also have 1/2, 1/4, 1/8 and 1/16th microstepping capability.

With a 200 step per rotation stepper motor and on 1/16th microstepping that still equates to approx 10 rotations in each direction from the home/"zero" position.

See my past thread here on using the AMIS 30622: http://www.picaxeforum.co.uk/showthread.php?15071

I purchased some of these SMD chips direct from ON Electronics.