Lead TAs: Avi J. Siegel, Mike Shum
Lab 4 Demo Times
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).
Evaluation:
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.
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.)
- Click here for a diagram
- Click here catalogue info
(Part number 3315C-1-006-ND)
- Tips from Chau
-
Using a PID-based Technique
For Competitive Odometry and Dead-Reckoning.
This is a great page for those interested in learning more about the PID
control scheme mentioned in class.
- Make sure your robot can go backwards as well as
forwards with the same accuracy. This is usually
preferable to turning 180 degrees if you need to turn back
(less error).
- The encoders we gave out are
**analog** encoders. At least one group tried to use the
digital encoder libraries for the Handyboard with
not-so-successful results. For those who haven't noticed,
analog encoder libraries are available for the handyboard
and are linked off the Handybaord web site (and of course
our links page).
- Lab 4
Grading Sheet
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