Autonomous Robotics Platform for Pico - Using the Servo Connections

By Kitronik Maker

Courtesy of Kitronik

Guide by Kitronik Maker

The ARP has 4 servo connections. These can be used to control standard hobby ‎servos. ‎

The servo connectors are located 2 towards the rear of the ARP, just outside the ‎motors, and 2 towards the front, by the ultrasonic connector. Power is fed, via the ‎power switch, directly from the battery voltage. ‎

The connectors are standard 3 pin, Signal, Voltage, and GND connections for ‎usual hobby servos. A brief guide to servos gives an overview and more ‎information about what servos are and how they are controlled.‎

PIO and Servo Control

On the ARP the servo control signal is driven using the Pico's Programmable Input ‎Output (PIO) functionality. ‎

PIO is a facility that allows the Pico's processor to control things using a very ‎simple state machine processor.‎

When the PicoAutonomousRobotics class is instantiated, it sets up the PIO state ‎machines ready for use.‎

The PicoAutonomousRobotics class defines 2 methods that control the connection ‎of the servos - registerServo(...), and deregisterServo(...)‎

registerServo(...) is called automatically for all servos when the class is ‎instantiated, but if you wish to use the servo pins for another purpose you can call ‎deregisterServo(...), which will stop the state machine running so the pin can be ‎driven as normal GPIO.‎

It is not necessary to understand PIO to use the servos on the ARP, but if you wish ‎to then start with this explainer from Raspberry Pi. ‎

Make Some Movement

Plug a servo into the SV0 connector (near the On/Off switch) and create the ‎following code in Thonny:‎

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from PicoAutonomousRobotics import KitronikPicoRobotBuggy

buggy = KitronikPicoRobotBuggy()

while True:
    if buggy.button.value():
        buggy.goToPosition(0,180)
    else:
        buggy.goToPosition(0,0)

Save and Run the Code‎

When you press the button on the Pico the servo should move from one end of its ‎travel to the other. When you release the button, the servo will move back again. ‎

Sensor Control

You can also control the servos using the ARP sensors.‎

Ensure the front ultrasonic sensor is mounted and create the following code in ‎Thonny:‎

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from PicoAutonomousRobotics import KitronikPicoRobotBuggy

buggy = KitronikPicoRobotBuggy()

while True:
        #multiply distance by 2 so 180 degrees range occurs over roughly a meter
        Dist = buggy.getDistance("f") * 2
        #check to make sure we are not driving past the end of a servo range
        if(Dist>180): 
            Dist = 180
        #drive the servo
        buggy.goToPosition(0, Dist)

Run the Code‎

This code will move the servo arm in proportion to the distance sensed by the ‎ultrasonic sensor. As the sensor detects an object getting closer the servo will ‎move towards its 0 degree end, and as it gets further away the servo will move ‎towards the 180 degree end. The code multiplies the distance detected by 2 so that ‎the full range of servo movement only takes 90 cm of detection distance.‎

Multiple Servos

The ARP can drive up to 4 servos at once.

‎This variation of the first piece of code moves each servo in turn as the button is ‎pressed and released:‎

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from PicoAutonomousRobotics import KitronikPicoRobotBuggy
from utime import sleep

buggy = KitronikPicoRobotBuggy()

while True:
    if buggy.button.value():
        buggy.goToPosition(0,180)
        buggy.goToPosition(1,180)
        buggy.goToPosition(2,180)
        buggy.goToPosition(3,180)
    else:
        buggy.goToPosition(0,0)
        buggy.goToPosition(1,0)
        buggy.goToPosition(2,0)
        buggy.goToPosition(3,0)

Controlling multiple servos allows the ARP to be used for more complex projects.‎

Can you build a Robot arm?‎‎ ‎

Coding Resources for Pico-ARP:‎

Online Tutorials - Pico ARP

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