standard servo limited rotation servo basics output shaft

standard servo limited rotation servo basics output shaft servo horn David Hall red wire = 5 V + black wire = Gnd white wire = control signal -

servo components 1. small DC motor 2. gearbox with small plastic gears to reduce the RPM and increase output torque 3. special electronics to interpret a pulse signal and deliver power to the motor 2

types of servos continuous rotation can rotate all the way around in either direction white wire tells servo which way to spin & how fast to spin standard (limited rotation) can only rotate 180 degrees white wire tells servo which steering position to hold 3

servos for a vehicle this wheel is not driven by a servo motor makes car move forward or backward (continuous rotation servo) David Hall motor makes car turn left or right (standard servo)

STEM Discovery types of servos http: //www. rccrawler. com/strongsteering. html 5 http: //articulo. mercadolibre. com. mx/

divide into two groups … Group 1 Group 2 Boe-Bot robot extra servo motor assembled car computer

hooking up servo motors servo ports red & black color labels back wheel motor plugs into 13 front wheel motor plugs into 14 image credit: www. turbosquid. com/3 d-models/parallax-board-education-3 d-model/705602 7

making back wheel go – continuous rotation servo ' {$STAMP BS 2} ' {$PBASIC 2. 5} DO DO DO PULSOUT 13, 650 PAUSE 20 LOOP PULSOUT 13, 750 PAUSE 20 LOOP PULSOUT 13, 850 PAUSE 20 LOOP STOP forward backward 8

centering back wheel servo if wheel still turns for the “stop” program, then slightly turn this screw until it stops ' {$STAMP BS 2} ' {$PBASIC 2. 5} DO PULSOUT 13, 750 PAUSE 20 LOOP STOP

how the control works ' {$STAMP BS 2} ' {$PBASIC 2. 5} DO PULSOUT 12, 650 PAUSE 20 LOOP full speed clockwise voltage (V) pulse width varies between 1. 3 ms and 1. 7 ms full speed counter clockwise 5 V - 20 ms 0 V - time (milliseconds) pulse width (μs) servo action 1300 full speed CW 1400 ½ speed CW 1500 stopped 1600 ½ speed CCW 1700 full speed CCW speed not linear with pulse duration 10

controlling standard servos ' {$STAMP BS 2} ' {$PBASIC 2. 5} DO change this to 14 for front servo make this number larger or smaller to control servo position PULSOUT 14, 750 PAUSE 20 LOOP Experiment to determine the numbers that makes the servo turn all the way left and all the way right. Write down these numbers! straight = ____ left = ____ right = ____ 11

putting it all together ' {$STAMP BS 2} ' {$PBASIC 2. 5} counter VAR Word GOSUB forward GOSUB turnleft END forward: FOR counter = 1 TO 50 PULSOUT 13, 650 PULSOUT 14, 650 PAUSE 20 NEXT RETURN turnleft: FOR counter = 1 TO 50 PULSOUT 13, 850 PULSOUT 14, 950 PAUSE 20 NEXT RETURN controls how long car goes forward use what works for your car! 12

play around with car to make it drive around an object control one continuous rotation servo (back wheel) and one standard servo (front wheels) object two continuous rotation servos (you don’t need the standard servo for a vehicle like this one)