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

servo components 2 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

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

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

types of servos 5 STEM Discovery

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

hooking up servo motors 7 red & black color labels image credit: servo ports back wheel motor plugs into 13 front wheel motor plugs into 14

making back wheel go – continuous rotation servo 8 ' {$STAMP BS2} ' {$PBASIC 2.5} DO PULSOUT 13, 750 PAUSE 20 LOOP STOP ' {$STAMP BS2} ' {$PBASIC 2.5} DO PULSOUT 13, 650 PAUSE 20 LOOP forward ' {$STAMP BS2} ' {$PBASIC 2.5} DO PULSOUT 13, 850 PAUSE 20 LOOP backward

centering back wheel servo if wheel still turns for the “stop” program, then slightly turn this screw until it stops ' {$STAMP BS2} ' {$PBASIC 2.5} DO PULSOUT 13, 750 PAUSE 20 LOOP STOP

how the control works 10 time (milliseconds) voltage (V) 5V - 0V - 20ms full speed clockwise full speed counter clockwise pulse width varies between 1.3ms and 1.7ms pulse width (μs) servo action 1300full speed CW 1400½ speed CW 1500stopped 1600½ speed CCW 1700full speed CCW speed not linear with pulse duration ' {$STAMP BS2} ' {$PBASIC 2.5} DO PULSOUT 12, 650 PAUSE 20 LOOP

11 ' {$STAMP BS2} ' {$PBASIC 2.5} DO PULSOUT 14, 750 PAUSE 20 LOOP make this number larger or smaller to control servo position 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 = ____ change this to 14 for front servo controlling standard servos

putting it all together 12 ' {$STAMP BS2} ' {$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 use what works for your car! controls how long car goes forward

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