\ 16-311 Lab 4: Low Level Mobile Base Control

Lab 4: Low Level Mobile Base Control
Lead TAs: Michael Edelson, Karim Shaban,
Igor Avramovic

# Introduction:

The purpose of this lab is to design a feedback controlled robot base that will be used in subsequent motion planning labs. PowerPoint presentation

# Challenge Statement:

Step 1:
Upgrade or redesign your mobile base so that it can translate and rotate with accuracy.

Step 2:
Measure the accrued dead-reckoning error (do not use feedback)

• Record the location of the point of contact for each wheel. Drive the robot forward 18 inches, drive in reverse 18 inches. Repeat forward and reverse nine more times. At the end of the 10th lap, stop the robot and record the point of contact for each wheel. Report what happens.
• Record the location of the point of contact for each wheel. Drive the robot forward 12 inches, turn ninety degrees to the left, repeat three more times to make a square. Drive around the square five times. Record the location of the point of contact for each wheel. Report what happens.

Step 3:
Implement some form of feedback to minimize dead-reckoning error.

• 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).
• 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).

# Design Tips:

• Make sure your robot really goes in a straight line because you will need this for future labs
• Avoid a four-wheeled base to minimize errors from slippage when turning. Two drive wheels and a single castor for balance works well.
• Keep your encoder as close as possible to the actual wheel in the gear train. This will minimize errors between the wheel and the encoder.
• When testing, check the grading sheet to find out what values could be asked. Test either all possible values, or a decent sampling of those values, for both translation and rotation.
• Have your encoder spinning faster than the wheel by as much as possible. This will reduce the amount the robot moves for each encoder signal.
• Encoder info:
• Click for info (note that you should hot glue over the wires to the encoder to help prevent leads from breaking off.)