Download Controlling the Outside World

Controlling the Outside World
Servo Motor
Servo motor
• A feedback controlled motor
– The Parallax standard servo motor has built in
feedback
– Range of motion is limited
• Parallax also supplies continuous servo motors for
robotic applications but…
– This is not a continuous servo!
• That is, it will not go 360º
• It will hit “stops” at either direction around
The servo motor
Wiring the servo motor
• You can wire up the servo on the proto
board as shown in the schematic…
• …but, there’s an easier way
Wiring the servo motor
Wiring the servo motor
• The X4 and X5 connectors are
designed to control the servo motors
• But, the power source must be set
via the jumper connector
Power
• Check your power source!
– If using a DC power blocks, it may be 9V or
it may be 6V
– Set the Vdd/Vin jumper as specified
• Vdd if using a 9V source (or 9V battery)
• Vin if using a 6V source
– Power switch must be in position 2 to send
power to the X4/X5 (servo) connectors
How it works
• To light up an LED we send a
continuous, level signal (DC voltage)
voltage
5v
HIGH pin
0v
time
Controlling the servo
• To move the servo horn we send a
pulse train
1.5ms
voltage
5v
1.5ms
0v
20ms
Time (in milli-seconds)
Controlling the servo
• The pulse width will control the location
of the servo
• The time between pulses should be 20
milli-seconds
From PBASIC
• PULSOUT command
PULSOUT pin, duration
• pin is the pin number to which your servo is
wired (12, 13, 14, or 15 if you are using the
servo ports on the RevC board)
• duration is the pulse width
PULSOUT command details
• The duration parameter is in units of
2μS (2 micro-seconds)
• The servo prefers values in units of
milli-seconds
• The time between pulses is under
software control (PAUSE command –
units of milli-seconds)
Activity – in class
• Test the servo
– Test all 4 servo ports
• Find the values of the duration
parameter (in the PULSOUT command)
that cause the servo to hit the stops in
both the clockwise and counterclockwise directions
Homework
•
•
•
•
Design a system that continually moves the servo from one stop to the other
– That is, it goes from full counter-clockwise to full clockwise and back again,
continuously
Add two buttons to the board (B1 and B2)
– B1 is the emergency stop (EStop)
• When it is pressed all servo motion stops
– B2 is the reset button
• When it is pressed the servo motion begins again
Add two LEDs
– The red LED lights when the servo is all the way clockwise
– The green LED lights when the servo is all the way counterclockwise
– Both LEDs are off (not lit) when the servo is somewhere between clockwise
and counterclockwise
The servo should not “slam” into the stops
Deliverables
• A state-machine diagram depicting the
operation of the system
• Source code
• A schematic diagram of the circuit
• A working demonstration on the Basic
Stamp development board (in class)