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View Full Version : Gearing Up Servos



BillW
08-09-2007, 03:39 PM
What I'm looking for is a servo that turns much more than the ~200 degrees that mine turn but still allows exact positioning. I'm looking for more like 1000 degrees but, other than some very expensive servos for sailboats, there doesn't seem to be such a thing. I have the Phidgets 4 servo controller and have confirmed that I can move in tenths of a degree. (maybe smaller but this is good enough for me) Geared 500% it would still be more than granular enough for my uses.

I had some continuously rotating servos on back-order but they have been discontinued. I was never sure they would work for me anyway because it didn't sound like they'd give me the exact positioning I wanted.

So:

Can I gear up the servo inside the servo case so that I can tell it to sweep more than the ~200 degrees or is the sensing portion of the servo tied to the angle of the output? Are there gears to even do this?

If I can't do it inside then does anyone reading this know of somewhere I can find gears to step up the rotation outside the servo? (I've been hoping to find a gear project kit that supplies gears and handy things to have properly oriented shafts, etc. I did get a meccano set but it unfortunately only has pulleys.)

Thanks. :)

Alex
08-10-2007, 09:47 AM
Hey Bill!

I think you might be searching for something that just isn't there. If it were possible to modify servos to turn continuously and still have positioning feedback, it would be all over the internet because it is one of the major topics that come up with hobby servos. I may be wrong on this, but I don't think so. Hopefully someone else can chime in on this topic.

Obviously you can hook encoders up to a modified continuous servo, but that isn't a very elegant solution.

Have you heard of the Dynamixel AX-12 series servos yet? Those things are sick! They have a operating angle of 300° and can switch between positioning and full rotation (no, full rotation doesn't get positioning) and are daisy chain-able meaning only one wire goes back to control board. They aren't your standard hobby servo, so you can communicate with them via PWM signals (Phidget 4-motor controller). Instead you communicate with them via serial communication.

Taken from the Dynamixel AS-12 page:


The AX-12+ Dynamixel is more than just a digital servo, it's a highly sophisticated robotic component. Each servo has the ability to track its speed, temperature, shaft position, voltage, and load. As if this weren't enough, the control algorithm used to maintain shaft position can be adjusted individually for each servo, allowing you to control the speed and strength of the motor's response. All of the sensor management and position control is handled by the servo's built-in microcontroller. This distributed approach leaves your main controller free to perform other functions.

The Dynamixels are where it's at!

http://www.trossenrobotics.com/bioloid-system.aspx