Servo - September 2011

Spin, using the RoboProp library.

Check out the main body of the RoboProp-Bot roaming code, side by side with the Boe-Bot version in the Listings included here.

As you can see, the code is very similar; the greatest difference is how the bumpers are handled.

On the BOE, the whiskers use digital inputs declared as PIN variables which were used directly in the expressions. The BASIC Stamp does not support procedures or functions, so the movement commands had to be written as subroutines invoked by the GOSUB keyword. The servo speed is controlled by global variables, as is the time to travel.

On RoboProp, the analog short range IR sensors were connected to analog inputs, read using a function call, and compared to a constant BUMPER distance. Had I used whiskers, I could have written

“if ina[lwhisker] == 0 AND ina[rwhisker] == 0”

Initially, I wrote:

“if (robot.ain(lbumper) > BUMPER) AND
(robot.ain(rbumper) > BUMPER) “

However, to make it easier for readers, I added some helper functions allowing me to write:

“if left_bumper AND right_bumper”

54 SERVO 09.2011

Spin supports methods with arguments (think functions and procedures), so I passed the “time to travel” (in milliseconds) at the current speed as a parameter to the helper forward/backward/left/right methods. I could have also passed the speed, but I decided to use a global variable for that purpose.

Take a look at Listing 3 to see what the main body of code looks like after adding support for the rear virtual bumper. Robbie sprints away when any object approaches too closely from behind.