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Balancing robot – without gyros

Posted by Mike Redrobe | Posted in Arduino, robots | Posted on 25-05-2012

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Bot balancing without gyros … for a few seconds at least

No gyros, no accelerometers – only a sonar ranger and lots of code.

The motors used are standard servos modified for continuous rotation, sonar sensor is a HC-SR04 as detailed in a previous post

Code ? Well here’s a simplified portion of the PID loop:

    int Drive = 0; // PWM value sent to Servos
    int Error[5]; // array of 5 Error elements
    int P = 0; // proportional term
    int I = 0; // integral term
    int D = 0; // derivative term

    #define Current 0
    #define Sum 1
    #define Last 2
    #define SecondToLast 3
    #define Delta 4

    int PID() {
    Error[Current] = SetPoint – Ptime;
    P = Error[Current] * Kp;
    Error[Sum] = Error[Current] + Error[Last] + Error[SecondToLast];
    I = Error[Sum] * Ki;
    Error[Delta] = Error[Current] – Error[Last];
    D = Error[Delta] * Kd;
    Drive = P + I + D;
    Error[SecondToLast] = Error[Last];
    Error[Last] = Error[Current];

    return Drive;

Ultrasonic robot avoids walls

Posted by Mike Redrobe | Posted in Arduino | Posted on 21-05-2012

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Using an ultrasonic sonar ranger to avoid walls – and people’s feet – before hitting them:

At first I was getting plenty of false readings, so here’s the first run, pausing and verifying before turning:

With faster code, and not stopping:

Improved accuracy, so it detects smaller objects like feet:

Arduino and SR04 ultrasonic sensor – robot eyes !

Posted by Mike Redrobe | Posted in Arduino | Posted on 20-05-2012

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Hooked an SR04 ultrasonic sensor to my arduino board – robot eyes !

Ranger sensor uses sonar to give accurate distance measurement to objects or obstacles placed in front of it. They’re surprisingly sensitive / accurate – I was able to reliably measure to a millimeter at 15cm range.

These sensors are also now VERY cheap £2.37 (4$) delivered from HK, and accurate to a few mm.

Added a servo for visual feedback:

Arduino code is basically sending a trigger on one pin, receiving a timing value on another,
which can then be converted into a distance:


    digitalWrite(Trig_pin, LOW);
    digitalWrite(Trig_pin, HIGH);
    digitalWrite(Trig_pin, LOW);
    duration = pulseIn(Echo_pin,HIGH);