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Announcements:
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Notes
on friction ID
Some of the teams have noticed that their
friction ID results are much improved if they hit the system with a torque
pulse to break friction before allowing the system to reach steady state
velocity:
(1) Give the system a large pulse of torque in the direction of
rotation to break friction. The duration should be somewhere around 0.25
seconds.
(2) While the system is still spinning, command your desired
constant torque value.
(3) Allow the velocity to reach steady state. Filter,
average, etc. to get a good velocity data point.
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Amplifier
gain: The nominal amplifier gain is 0.1 Amps/volt.
If you consider that the torque generated by the motor is proportional to
the current through the motor (this gain is the motor torque constant from the
data sheet) you can now calculate the relationship between D/A voltage and
motor torque (don't forget about the gears between the motor and the output
shaft).
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Important
notes about running experiments in the lab (from
The hardware that we have in the lab is real and the typical application
is industrial rather than educational. As such, there are no built-in
safety features to protect your experiment and the pieces will not magically
fit together nicely like the problems in the back of a textbook. Whenever
running an experiment, I suggest that you proceed cautiously,
think things through thoroughly, and take the time to do some planning before
powering up the experiment.
Here are a few things I do before running a new experiment or code:
1. Run new code on the tilt joint only. Disconnect the pan cable
from the electronics box. The tilt joint can spin indefinitely
without wrapping wires, so if the experiment goes unstable, nothing will get
damaged.
2. In the Simulink model, you can define how long your code will
run. For a new controller, set the program end time to a small value, such as 1
second. At worst, your controller will only be unstable for 1 second
before shutting off the motors.
3. Check the directionality of each component before running any closed
loop code. First, modify the Simulink diagram so that a constant source
of value zero feeds the D/A converter. This will ensure that the motor is
not powered up during the experiment. Run the code and turn the shaft by
hand. Take note of which direction is positive and which direction is
negative. Next, remove the belt from the drive motor (loosen the tension
in the belt first). Modify the code to give a small
positive value to the D/A converter. Run the code and take note of the
direction of motor spin. Refer to your understanding of feedback control
to determine if you need to reverse the sign of the encoder or motor.
4. Use very small feedback gains at first. Increase the gains slowly
as you build confidence in your controller.
BE CAREFUL!!!
·
Project proposal presentation will
be held on Wednesday, March 2 starting at
·
Conceptual design memo is due on
2/1 at
·
You should download MATLAB 7.01 to
your laptop from http://www.rpi.edu/dept/arc/web/licenses/matlab_license.html
Make sure you select at least MATLAB, Simulink, xPC Target, Real time workshop, and control systems toolbox.