Hi! This is Chau again. When doing these labs, I decided to try a different kinematic configuration for the two DOF arm. This figure contains the INCORRECT kinematic configuration for the assignment. Please see photo of requirements

Making Sense Of and Using Potentiometer Reading.

While playing around with potentiometers, you'll notice that for about the first 30 degrees worth of turns, the potentiometer will consistently output 0 and for about the last 30 degrees worth of turns, the potentiometer will read 79 (or some number similar to this). And the relationship between the output values between the first and last 30 degrees are nonlinear. Here is one way to dealt with the problem. It may not be THE BEST way to tackle it, but it works.

1. Position the potentiometer and the legos attached to it so the potentiometer reads 2 or 3.
2. Mark the potentiometer and the gear it is attached to with a single ink line that connects the two. This way it will be obvious if the potentiometer is turning along with the gear or if slippage is occurring. (I found some of my gears fit snuggle onto the potentiometer, while others did not.)
3. Turn the potentiometer 15 degrees or so and record the output.
4. Repeat part 3 until you reach the end of the potentiometer's ability to turn.
5. Discard the last few data sets where the potentiometer readings are the same.
6. Plot the data with some program like Matlab.
7. Use some command to create a line that closely resembles the relationship between the potentiometer reading and the angle.

Design Constraints to Keep in Mind

Potentiometers, because they can only turn a set number of useful degrees, will be one of the limiting factors in your arm's ability to turn and move. When I say "useful degrees" I am referring to the fact that about the first 30 degrees worth of turns (which all output 0) and about the last 30 degrees worth of turns (which all output 79) are useless to you. This makes only the turnability between these two extreme angles useful. So when designing the arm, consider how to maximize your arm movement with the potentiometers.

When I first designed my robot arm, I realized that, when I incorporated the potentiometer into my robot arm, my arm lost most of its ability to turn and move. Then it took me some time and effort to regear the arm so it would be able to turn/move a greater degree then it did when I first put the potentiometers in.