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Anamatronic servo help! Answered

I'm building a basic anamatronic arm, and I need help in the land of servos. I am pretty much new, so could someone explain to me what oz. inches are, and if possible, reccomend arduino- compatible servos? Thanks a bunch! 

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frollard

7 years ago

Oz-in is a measure of torque. 1 oz-in is the force of 1 ounce hanging on an armature (lever) that is 1 inch long. It's like foot pounds, but different units. Torque can also be (properly) described in (metric) Newton-Meters.
http://en.wikipedia.org/wiki/Torque
More torque is more twist force. It directly translates to the ability to move a larger object essentially.

Torque in conjunction with speed gives total power, because if you can move an equivalent twist motion (same force) at a higher speed/acceleration, you'll use more power to do it. Servos can be rated in their wattage/voltage/amps which you will need to consider within the guidelines of your power supply.

Speed of a servo is expressed in the amount of time it takes to fully deflect from its minimum value to its maximum value. It can also be expressed in the amount of degrees per second it rotates. Ex.
A small servo I have deflects 170 degrees total, and it takes 1 second to make this move. A faster servo may have less torque (higher gear ratio), or may consume more power (bigger motor) (per the laws of physics)

Connecting to a microController (arduino) is pretty easy with a 'sensor/servo' shield. The good ones are only 10-20 dollars and allow you to inject a strong power supply (you'll need one if using multiple servos, my arduino can barely handle 1 small servo at load on usb). Each servo has a power, ground, and signal pin, which are connected to power and ground -- the signal pin connects to an analog output of the arduino and the processing environment has a library for driving servos.
http://arduino.cc/en/Reference/Servo
http://www.renbotics.com/products/servoshield.php
The servo has a small computer in it that takes a pulsed signal on the 'signal' line and converts it to an angle on the gear-motor output. In software you reference that signal as a value between (arbitrarily) 0 and the number of degrees you have to work with, it can be scaled.