Need to pan 360 degrees

OLIRIC56

I am a newbie working on my first project. I need the ability to pan in a 360 degree arc with the ability to position at any given degree position. I am using a Parallax Servo Controller card USB #28830. The documentation for the card says the range of the card is 250 to 1250us. If 750us is neutral (750 x 2 = 1500us) then that means the card can accomodate a range of 100 degrees in either direction from center. A continous rotation servo won't give feedback so I don't think I can us it for what I need. I did find a servo R298-1T-SERVO (1 turn) from Acroname Robotics http://www.acroname.com/robotics/parts/R298-1T-SERVO.html but the specs don't say if it gives feedback. If the servo does give feedback how would I send a pulse width that would turn the servo more than 100 degrees in either direction. I'm sure I'm not the first to have to solve this "Turret" problem so what do the experts here recommend?

erco

You can only get ~180 degrees out of a servo, so you can gear it up 2-to-1 for 360 rotation.

Martin_H

Budget Robotics sells a 360 turret which has been on my buy list for a while.

http://www.budgetrobotics.com/item/360-Degree-Pan-Turret-329

GeorgeCollins

First- I have never worked with the particular servo you mention. From the description it looks like a servo that is geared to rotate 360 degrees, as opposed to the 135 or 90 degrees which is more typical. That would mean that it is different then a "continuous rotation" servo, which is a servo that spins around but cannot be stopped at particular angles.

With a servo like that, used as a turret, you should not need to get position information. When a servo is allowed to travel freely it should always turn to the same angle at a given pulse width. So you should know what direction the turret will be pointing at 1500us, 1250 us, 1800us, etc.

If you want a servo that will spin 360 degrees with accuracy and feedback I would suggest using an AX-12. The problem with that servo is that it will not be controlled easily with Parallax Servo Controller. You can program a propeller to control one, but it is not nearly so easy as using a Parallax Servo Controller to control a hobby servo.

Here is some general information about servos that could be helpful:
http://www.backyardrobots.com/Servo/servoguide.shtml

This question gives me another topic to explain and hopefully do some research on. Good luck!

W9GFO

There are multi turn "sail winch" servos which may work, such as this one. They use a multi turn potentiometer so they do have feedback unlike a continuous rotation servo.

Rich H

GordonMcComb

OLIRIC56 wrote: »

I am a newbie working on my first project. I need the ability to pan in a 360 degree arc with the ability to position at any given degree position.

Use a geared UP servo, like the one Martin talks about, a sail winch or 1T (one turn) landing gear retract (like the Acroname; the Servo City model is a 3T model and more expensive because of it), or switch to a stepper motor. You won't be able to use a servo controller with a stepper, but small unipolar steppers are easy to control.

Though they don't say it, the Acroname servo is a GWS S125 (or one virtually identical), and several outfits sell it --unfortunately not Parallax, though. Just do a Web search and you'll find it. If you use a small stepper, consider a way to provide an index position once every turn (or tern if you're building robotic birds), so you can re-home the motor upon startup.

OLIRIC56

I called Parallax tech support and got a clarification on the documentation I mentioned regarding the 28830 servo controller card. The 250 to 1250 pulse width range mentioned was meant as the limit if you had a standard 180 degree servo, the technician said if I have a 360 degree servo with feedback that the card will accept any pulse width the servo can accomodate. He also mentioned that the servo being a 360 degree servo may have a pulse width higher than 1500 for neutral and that I would have to play with it to determine what it is. Thanks to all who replied.