60 Actuators (Robotics related products)
Description
This article is from the Robotics FAQ, by Kevin Dowling nivek@cs.cmu.edu with numerous contributions by others.
60 Actuators (Robotics related products)
Most actuation uses electro-magnetic motors and gears but there have
been frequent questions regarding other forms of actuation including
'muscle-wires' and inexpensive RC-servos. How do I get a motor under
computer control? What kind of motor should I use? What are the
differences between actuator types? What other types of actuation
are there?
Types of motors:
* Synchronous
* Stepper
* AC servo
* Brushless DC servo
* Brushed DC servo
10.2.1 RC-Servos (Robotics related products)
R/C servos for model airplanes, cars and other vehicles are light,
rugged, cheap and fairly easy to interface. Some of the units can
provide very high torques speed. For prices and specs see one of the
many Radio Control magazines on the market.
What is the wiring for R/C servos?
Three wire connector for RC-servos:
Pin 1 = White = Signal
Pin 2 = Red = +5
Pin 3 = Black = Signal and Power Ground
[Tang = pin 1]
The signal is a variable width pulse ranging from 1-2ms in duration
and repeating every 12-20 ms. The output shaft rotates to a position
porportional to the input pulse width. Input pulse width is compared
to an internal timer pulse. The timer period is controlled by a pot
coupled to the servo's output shaft. The difference between the two
pulse widths is an error signal. The servo attempts to reduce or
eliminate the error signal by driving the output shaft in the
appropriate direction. When the error signal is within about 5
micro-seconds the drivers are turned off to preventing oscillation
or 'hunting'.
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1 to 2 ms width pulse goes from full CCW to full CW rotation
20 ms pulse to pulse.
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