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Lesson 4: Programming Sensors & Servos Boe-Bot Motion Programming (PBasic) P a g e 1 Summary of Servo PulsOut Commands Left (P13) Right (P12) Resulting Motion 850 650 Forward Full Speed 850 750

1 Lesson 4: Programming Sensors & Servos Boe-Bot Motion Programming (PBasic) P a g e 1 Summary of Servo PulsOut Commands Left (P13) Right (P12) Resulting Motion Forward Full Speed Forward Right Turn Forward Left Turn Backward Full Speed Backward Right Turn Backward Left Turn Counter-clockwise Pivot No Motion Clockwise Pivot 850 = 1700us = 1.7ms = CCW 750 = 1500us = 1.5ms (stand still) 650 = 1300us = 1.3ms = CW

Getting Set up: Centering the Servo-Motors P a g e 2 Before the BOE-bot is programmed, the servo-motors must be centered so that there is no motion when the pulse frequency is 1.

2 Getting Set up: Centering the Servo-Motors P a g e 2 Before the BOE-bot is programmed, the servo-motors must be centered so that there is no motion when the pulse frequency is 1.5 ms (ie, when Freq = 750). To center the servo-motors, perform the following steps: 1. Connect the motors to pins 12 and 13 as outlined earlier. (The motors should NOT be connected to the chassis). 2. Connect the carrier board to your PC, and set the power switch to 1. Then, enter the following PBASIC program: ' This code is used to center the servos... ' It should cause the servos to be motionless. DO PULSOUT 13, 750 'Left wheel - no motion PULSOUT 12, 750 motion LOOP 'Right wheel - no 3. Click the Run icon ( ) to burn the program to the BASIC Stamp chip. 4. Set the power switch to 2 and observe the motion of the control horns. If they are turning (even slightly), they must be re-centered by inserting a small Philips screwdriver into motor s access hole, then gently turning the screwdriver clockwise or counter-clockwise until there is no motion from the control horns.

3 5. When both motors have been centered, the motors can be mounted to the chassis and the wheels can be attached to the motors. Determining Time-Based Motion The short program to make the BOE-bot move forward at full speed is shown again below, along with the time required by the processor to execute each instruction: ' Move forward at full speed DO PULSOUT 13, 850 ' 1.7 ms PULSOUT 12, 650 ' 1.3 ms ' 20.0 ms LOOP ' 1.6 ms (overhead) Each iteration of the loop requires ( ) ms = 24.6 ms (= seconds). Therefore, for motion to last 1 second, the loop must execute (1 / ) = times. This can be more efficiently implemented using a count-controlled loop as follows: ' Move forward at full speed for 1 second X VAR Word FOR X = 1 TO 41 PULSOUT 13, 850 PULSOUT 12, 650 NEXT P a g e 3 In general, to make the BOE-bot move for n seconds, divide n by The resulting value becomes the max value in the FOR-NEXT loop. For example, to move the BOE-bot for 5 seconds,

4 max = 5 / = P a g e 4 Therefore, the loop would use FOR X = 1 TO 203 etc. Determining Distance-Based Motion It is more common to program the BOE-bot to move a specified distance, rather than for a specified amount of time. For example, suppose that you wish to move the Boe-Bot forward 6 feet. First, you will need to determine the speed of your BOE-bot. To calculate the BOE-bot s maximum forward speed, 1. Program the BOE-bot to run for 5 seconds at maximum speed using the following code: ' Move forward at full speed for 5 seconds X VAR Word FOR X = 1 TO 203 PULSOUT 13, 850 PULSOUT 12, 650 NEXT 2. Measure the distance traveled by the BOE-bot (in inches). 3. The speed of the BOE-bot is the distance traveled divided by the time (5 seconds). Therefore, if the BOE-bot traveled inches, the speed is / 6 = 6.65 inches/second. Now that you know the speed of the BOE-bot, distance-based motion can be calculated as follows: 1. Determine the distance (in inches) that you want the BOE-bot to travel. 2. Divide by the BOE-bot speed to determine the time. 3. Divide the time by to obtain the loop counter value. For example, suppose you want the BOE-bot to travel 6 feet:

5 1. Distance = 6 feet = 6 x 12 = 72 inches 2. Time = 72 / 6.65 = Loop counter = / = P a g e 5 Therefore, the loop would be FOR X = 1 TO 367 to move the BOE-bot forward 6 feet. This process must be repeated every time the BOE-bot must be moved a different distance and / or at a different speed.

Gripper Kit for the Boe-Bot Robot (#28202)

Gripper Kit for the Boe-Bot Robot (#28202) 599 Menlo Drive, Suite 100 Rocklin, California 95765, USA Office: (916) 624-8333 Fax: (916) 624-8003 General: info@parallax.com Technical: support@parallax.com Web Site: www.parallax.com Educational: www.stampsinclass.com