General Robotics Lab 4: Low Level Mobile Base Control Caleb Overman, Somchaya Liemhetcharat, Steven Nielsen Previous caretakers: Avi Siegel, Mike Shum

Introduction The purpose of this lab is to design a feedback controlled robot base that will be used in subsequent motion planning labs. The base will need to be able to translate and rotate precisely.

Challenge Statement Upgrade or redesign your mobile base so that it can translate and rotate with accuracy. (Or build a new one!) Measure the accrued dead-reckoning error (do not use feedback). Implement some form of feedback to minimize dead-reckoning error.

Design What should this thing look like? Tracks/Wheels? What’s a castor? Ackerman/DiffDrive? Friction?

Tank Treads 2 treads, each turned by a motor. Good all-terrain (surface) performance. Sadly, not able to turn very precisely (friction issues).

Wheels 2 main driving wheels, each turned by a motor. Some sort of steering. Ackerman DiffDrive Castors, placement of wheels, balance (3D).

Castors and Stability What is a castor? How do I make one out of Lego? What it does Smooth turning Support robot Actuated steering?

Going Straight This is harder than you think. Seriously.

PID Control Proportional Integral Derivative How fast are we drifting from the center? Integral How far are we from the centerline? Derivative Is the drift rate accelerating/decelerating?

Other Problems Charge your handyboard! Give the ECEs something to do… (encoders…) Stopping: not as easy as you think.

Grading (see grading sheet) Your grade will be directly determined by the percentage accuracy of your robot. i.e. if you are asked to move 10 inches and your robot moves 9 inches, you will receive a 90. The same goes for turns.

Testing Translate: Write a function that takes as input a number (in inches), waits for the start button to be pressed, waits five seconds, and then accurately drives the robot forward by the inputted value in inches (or reverse if the inputted number was negative). Try different values. Rotate: Write a function that takes as input a number (in degrees), waits for the start button to be pressed , waits five seconds, and then accurately rotates the robot counter-clockwise by the inputted value in degrees (or clockwise if the inputted number was negative). Try different values.