Mechatronics: Project 1

XBC Lego Car


System Description:

The system is composed of a microprocessor on an XBC board, a car driven by two DC motors (controlled by PWM signals), and a laser range finder measuring the distance to an object in front of the car (a wall in our case).  Control logic for the system is written in Interactive C (IC).

The output from the range finder is measured using the IC code:
y=analog12(0);
y will be a 12-bit integer measured from analog port 0.

The input is sent to the motors using the code:
motor(0,u);
motor(2,u);
where the motors are connected to ports 0 and 2 and u is an integer between -100 and 100 specifying the PWM duty cycle.


Phase 1:

Objectives:

  1. Develop a transfer function model of the car, where y (the range finder distance) is the output and u (the motor PWM duty cycle) is the input.
  2. Design a proportional controller for the system and implement it in IC.
  3. Accurately predict the step response of the system while under closed-loop control of your proportional controller.

Required Steps:

  1. System identification data will be collected in class.  Bring suggestions for inputs we should try.
  2. Analyze the system ID data and develop a transfer function model (y/u).
  3. Design a proportional controller using the Matlab® commands feedback and step (or equivalent Python® commands).
  4. Implement your controller in IC.
  5. Gather experimental data for the step response of the car with your proportional controller.
  6. Compare predicted and actual step response results.

Note:

You will be required to turn in your predicted response before you run the experiment.

Optional Step:

As an optional step, you may design your controller using Bode plots.  This would be a good learning experience, may be faster than iterating through the feedback and step commands, and will give you a head start on Phase 2.


Phase 2:

Develop a more advanced controller for improved performance.
  • Proportional control is not very sophisticated and may not lead to great performance.
  • Identify areas where the performance of your system could be improved.
  • Design and implement a control that improves the system response.


Phase 3: System Improvements with PSoC's

There are several problems with the existing system:
  • The range finder is noisy.
  • The XBC micro controller with IC does not do hard real-time control and is not very fast for computations.
  • The PWM control implemented by the XBC does not have very fine control and uses a lot of system overhead by doing additional things (like trying to track the motor position through back EMF sensing and integration).
Use PSoC's (Programmable System-on-Chip) to improve the system by first supplementing the XBC and ultimately replacing it.  Possible PSoC uses include:
  • Lowpass filtering the range finder signal
  • Implementing a better PWM controller with finer control
  • Implementing a hard real-time controller