n 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
(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.
n 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).
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.
· Project proposal presentation will be held on Wednesday, March 2 starting at in JEC 4304. Each team presents to the entire class the scope of the project, approach, and initial modeling result (appr. 15 min each, starting with Team 1).
· Conceptual design memo is due on 2/1 at in JEC 4304. Each team should hand in a typed memo (a good example is group 2 of 2004). There should also be a signed copy of statement of contribution of all the team members. Each team should be prepared to discuss their proposed project for about 15-20 minutes (all team members should participate in the discussion). We’ll start with Team 5 and end with Team 1.
· 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.