Lab 4(a): Open Loop Control (Real Robot)

Objective

    The goal of this lab is to change the remote control capabilities into an open loop control system within the car.

    Note: Code for Part A can be found here

Steps for Part A:

  1. Hooked up the Artemis and the motor driver using the Qwiic connector:
  2. Ran the code to find the address of the SCMD and it matches the one reported on Sparkfun:
  3. Took the car apart as shown in the figure in Part 1. Removed the shell and bumpers from the car, removed the battery, and took out the PCB. Finally, cut the motor wires and power wires and hooked them onto the SCMD. I faced two problems while doing this:
    • Screwing in the wires without a wire stripper and not enough length on the motor wires was difficult.
    • I stored the motor driver in place of the PCB, and made the hole (where the power button used to be) bigger to fit the Quiic wire through and to the Artemis board as shown in Figure 1.
    4. Used the Arduino IDE and installed the SCMD library.
    • In order to check if I can control both motors, I used the example "Motor Test" and made one small change shown below. I updated the address to the correct address of the SCMD obtained in Part 2:
      As shown below, both the motors work after making this change:
    • While exploring the lower limit for which each of the motors still turns, I noticed that the lower limit varies as I alter the value up and down. As shown below, I altered the third parameter in the "myMotorDriver.setDrive". We already know the upper limit is 255, and after experimenting a lot, the lower limit resulted to be 50. The value of the lower bound kept fluctuating as I performed the test but it seemed to alter around the value 50.
    • After running the robot without any factors, the robot started drifting to the left. This may be due to a number of reasons, friction due to the wheels or internal resistances within the motor, etc. So to solve this issue, I considered four cases:
      • Case 1: Robot's input speed is the lower limit 50.
      • Case 2: Robot's input speed is the upper limit 255.
      • Case 3: Robot's input speed is between the lower limit and the mid point between lower and upper limits.
      • Case 4: Robot's input speed is between the Upper limit and the mid point between lower and upper limits.
      I wanted to have one calibration factor that I can alter to lean left or right depending on the error, which I defined as Cf. The definition of this factor is as follows:
      • 0 < Cf < 0.5: Robot will lean left (where 0 is when it turns left the most)
      • 0.5 < Cf < 1: Robot will lean Right (where 1 is when it turns right the most)
      I can alter this calibration factor and consider the cases stated above to create conditional statement as shown below:
      These conditional statements provide the appropriate speeds for the right and left wheel individually (as shown above). For example, the robot tends to drift right in my case, the value I chose for Cf is 0.47, which will provide an appropriate left wheel and right wheel speeds such that right > left, which will allow the robot to drive straight by accomodating for the drift right. The reason I chose this approach is because it is generalized and can work for any value of speed I choose and any robot I pick. After making these changes, the robot follows a straight line as shown in the video:
  5. Assembled the robot completely. Closed the battery pack and the motor driver within the robot. Due to a lack of space the artemis board and the Lipo battery were taped onto the bottom side of the robot as shown below:
  6. To demonstrate the open loop and untethered control of the robot, I decided to use concepts from Lab 2 where we used the PDM to determine the frequency in the surroundings of the robot. I combined the code from Part 4 - Driving the robot straight, and the code from example PDM/Microphone output. I chose a threshold of the frequency to be 2000:
    • If the frequency is above this threshold, it starts acting crazy (rotating at full speed).
    • If the frequency is below this threshold, then it moves slowly in one direction.
    I created subfunctions within the main file to account for calibrating of the robot's motors to be able to drive straight when below the threshold, and the other subfunctions were responsible for the motion of the robot and the frequency reading. As shown below, by inputing a higher frequency I can control the robot to make turns. The issue I faced is that the frequency readings are incredibly noisy due to the motors of the robot. Since the Artemis is taped onto the bottom side of the robot, the noise is amplified from the motors (since it is right next to it). However, this provides an interesting motion of various unpredictable turns, and I can be seen in the video trying to avoid the robot from colliding into me due to this unpredicatability.

Lab 4(b): Open Loop Control (Virtual robot)

Objective

    The goal is to familiarize myself with the simulator and the virtual robot, and Jupyter.

Perform tests on the virtual robot

  1. Successful setup process after running the setup.sh:

  2. Range finder activated as shown below:

  3. Got the Robot's pose as shown below:

  4. Moved the robot as instructed in Jupyter:
  5. Created a rectangular trajectory by using an open loop control on the robot:

    Code

    
# Repeat 4 times
for x in range(1,5):

	# Move forward and stop
	robot.set_vel(v=0.2,w=0.)
	time.sleep(4)
	robot.set_vel(v=0,w=0)

	# Turn Left
	robot.set_vel(v=0,w=-0.4)
	time.sleep(3.9)
	robot.set_vel(v=0,w=0)