PmWiki | Lab1 / Lab1Group7Question3

How accurate is the Wait Angle Command?

Design a simple experiment to gain a better understanding of how the Wait Angle command works and how accurate it is. What angle is being "measured?" DRAW A DIAGRAM to help describe the results of your exploration. How do you think the Create senses this angle.

Purpose: The purpose of this lab is to test the accuracy of the wait angle command and to discover what angle the Create is actually measuring in the process.

Materials : iRobot Create, marker, poster board, RealTerm program, protractor, ruler

Hypothesis: I hypothesize that the Wait Angle command measures an angle with a vertex of either the left or right wheel.

Procedure: Step 1: On the poster board, create some sort of "starting mark" that you will use as a place holder to show you where the Create started from before it began turning.Then, place the Create on that spot. Step 2: Measure the radius of the Create bot and draw a perpendicular line from the side of the Create (the side being the direction that is perpendicular to the robots wheels and is in the relative center of the robot) that is the same length as the Create's radius. The point at which the line stops will be the vertex of the angle that you are measuring. Step 3: Using the line that you just drew, draw another line that is perpendicular to it and starts from the vertex. This line will act as a marker for a 90 degree rotation. Step 4: Using the angle that you just drew, draw a 30 degree and 60 degree angle. Step 5: Using the RealTerm program, use the drive command opcode and wait angle opcode to make the robot drive forward with a radius that is equivalent to that you drew in step 2 and an angle measure of 30 degrees. Make sure that you also enter in the opcode of drive 137 0 0 with and equivalent radius so that the robot knows to stop once it has reached it's wait angle. You can enter these values in either hexadecimal or decimal form. Step 6: Send the commands to the robot and record your results. Step 7: Repeat steps 1-6 except use an angle degree of 60 degrees and then 90 degrees for step 6.

Results/Data:

                    Radius of Create: approx. 6.25 inches (158.75mm) 
                    Radius measured in the Drive command: 12.50 inches (317.50mm)

               Wait Angle (degrees)     Command entered into RealTerm (dec.form)         
                       30            128 131 137 0 64 1 62 157 0 30 137 0 0 1 62      
                       60            128 131 137 0 64 1 62 157 0 60 137 0 0 1 62      
                       90            128 131 137 0 64 1 62 157 0 90 137 0 0 1 62

Observations: As I was conducting the lab, I noticed that the robot stopped precisely on the degree markings that I drew out on my poster board. The Create was slanted at the exact degree so that the power, play, and advance buttons were lined up on the mark. This explanation is illustrated in the examples below:

One factor that could have altered my results could have been human error. I could have done a number of things wrong such as not placing the robot in the same position each trial or not measuring the angles correctly.

Conclusions : Using the data from our lab, I can conclude that my hypothesis was incorrect and that the wait angle command measures an angle with a leg that extends from the center of the Create bot, to the center of the turning circle. To measure the radius of the turning circle, first, calculate the radius of the Create and multiply it by 2. This will give you the distance of the turning circle. In other words, the radius of the turning circle is equivalent to the diameter of the Create. I also discovered that the wait angle command is very accurate and can surmise that the angle is being measured by sensors or wheel encoders found at the center of the Create bot.