Motion Following Robot





Introduction: Motion Following Robot

Hello instructables community!

After messing around with an Arduino for a couple months and avidly reading instructables, I decided that I would finally publish my own. I wanted to create something that moves by itself. I also wanted to create a system that reacts to the outside environment. After some thought I decided on a simple motion follower.

Potential Applications:

• Motion following camera
• Robots that will acknowledge their environments
• Motion following turret
• Educational projects
• Obstacle avoiding robots

Required Materials:

• Breadboard
• Ultrasonic Range Sensor x2 (I used the four pin version so if you are using the ping version you'll have to change the code a bit)
• Servo (I used a micro size)
• Arduino UNO or similar microcontroller
• Jumper Cables (female to male and male to male)
• Particle Board
• 9v Battery and connector
• Something to mount the servo on (I used some poster mounting putty)

Required Tools:

• Hot glue gun
• Xacto knife
• Computer with Arduino IDE
• Electrical tape or similar

Step 1: Build the Sensor Mount

First, we will need to build the sensor mount. For this I built a prototype out of cardboard and then built my final project in particle board. In the future I plan to 3d print a perfect mount for the sensor.

Cut a rectangle that is about the same height as one of the sensors and an 1/8th inch (about 3mm) longer than two of them together. Set the rectangle aside and cut out two identical isosceles triangles with the odd angle out being 120 degrees. I cut it at 120 degrees because the range sensors have a 15 degree cone that they measure, this allows for no blind spots while optimizing the area that is sensed.

Finally, place the sensors on the mount to determine where to cut the rectangular holes for them to fit in. Make the hole as small as possible because this snug fit makes up for not using any other adhesives or connectors. Now cut another small rectangular hole on the bottom triangle of the mount to allow for jumper cables to be passed through. Once the jumper cables are plugged in, the sensors should stay in place. If they don't, you will need to fasten them with some hot glue or pins.

When you are done with the mount, attach it to the servo.

Step 2: Wire Everything!

Now all you need to do is connect everything! I used Fritzing to create a circuit diagram. I have also provided some pictures of the final product.

The code provided uses digital pins 9 through 13. Pin 9 is the data pin for the servo. Pins 10 and 11 are the echo and trig pins, respectively, of the left sensor. Pins 12 and 13 are the echo and trig pins, respectively, of the right sensor. I connected the 5v and gnd pins from the Arduino to the breadboard and then used jumpers to connect the servo and sensors.

Step 3: Code

The code that I provided allows for the changing of the distance threshold. So in other words, how far the sensors can see. I will be uploading a new instructable soon to show how you can make the sensors even more accurate using a temperature sensor. Finally, my friend showed me a cool way of debugging really quick. All you do is use a boolean and some if statements. If the boolean is true, then serial communication will be on and communicating. If the boolean is false, then the program will run much faster but not communicate.

I will attach the .ino file, otherwise you can copy it from here:


Motion Follow Created by Calvin Kielas-Jensen

Using an Arduino UNO, check for the circuit diagram.

This script allows two ultrasonic range sensors to follow movement while mounted on the top of a servo. The distance threshold can be changed but should not be set too far as the sensors will begin to fail.

Anyone is welcome to use and modify this code as long as I am given credit. Thank you for respecting the open source movement!

************************************************************************************************** *************************************************************************************************/


Servo myservo;

const int Lin = 10, Rin = 12, Lout = 11, Rout = 13, serv = 9; //setting sensor pins and servo pin

// establish variables for duration // and the distance result in inches long Rduration, Lduration, Rinches, Linches;

int threshold = 10; //Sensor threshold in inches

int angle = 80; //Initial angle

boolean debug = false; //Serial communication for debuging. Set to true for serial communication.

void setup() { // initialize serial communication: if (debug) { Serial.begin(9600); } myservo.attach(9); //attach servo to pin 9 }

void loop() { //Most of the sensor code has been taken from David Mellis's PING sensor code //I modified it for a 4 pin sensor as oppsed to the 3 pin sensor // Give a short LOW pulse beforehand to ensure a clean HIGH pulse: pinMode(Rout, OUTPUT); digitalWrite(Rout, LOW); delayMicroseconds(2); digitalWrite(Rout, HIGH); delayMicroseconds(5); digitalWrite(Rout, LOW);

Rduration = pulseIn(Rin, HIGH); pinMode(Lout, OUTPUT); digitalWrite(Lout, LOW); delayMicroseconds(2); digitalWrite(Lout, HIGH); delayMicroseconds(5); digitalWrite(Lout, LOW);

Lduration = pulseIn(Lin, HIGH);

// convert the time into a distance Rinches = microsecondsToInches(Rduration); Linches = microsecondsToInches(Lduration); if (debug) { Serial.print("Left: "); Serial.print(Linches); Serial.println(" in"); Serial.print("Right: "); Serial.print(Rinches); Serial.println(" in"); } follow(); }

long microsecondsToInches(long microseconds) {

// According to Parallax's datasheet for the PING))), there are

// 73.746 microseconds per inch (i.e. sound travels at 1130 feet per

// second). This gives the distance travelled by the ping, outbound

// and return, so we divide by 2 to get the distance of the obstacle.

// See:

return microseconds / 74 / 2; }

void follow() { if (Linches <= threshold || Rinches <= threshold) { if (Linches + 2 < Rinches) { angle = angle - 2; } if (Rinches + 2 < Linches) { angle = angle + 2; } } if (angle > 160) { angle = 160; } if (angle < 0) { angle = 0; } myservo.write(angle); }

Step 4: Conclusion

Once the code has been loaded, plug in the 9v battery and watch it start following anything that comes within the threshold range!


  • If the sensors keep turning the wrong way, try switching the cables in pins 10 and 11 with the cables in pins 12 and 13.
  • If the sensors don't move at all, or just a little bit, check the wiring. It is really easy to accidentally move the jumper cables over one spot on the breadboard.
  • If the sensors are moving really slowly, go back to the code and make sure that the debug is false. The serial communications can really slow down the reaction time of the robot.
  • If you are still having issues, first make sure that the Arduino is on and that all jumper cables are in the correct spots. Switch the debug to true and check to see if the range sensors are working. You might also want to test the servo to make sure that it is also in working condition.

Some improvements I am planning on for the future:

  • Improving the accuracy of the sensors with the use of a temperature sensor
  • 3d printing the sensor mount and servo mount
  • Adding another servo and sensor to allow for vertical movement
  • Switching out the servos with stepper motors to allow for 360 degree following

I had a great time writing this instructable and hope to create many more! Please let me know how I did and how I can improve my future instructables.

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first off thanks for the help

but quick question

i have the design fully assembled, and i'm using the serial monitor, the device keeps printing linches 0 rinches 0. from my knowing this means that the sensors are functioning, but the micro servo wont even budge. i have tried slowly moving objects across it, im using the same sensors as you and the orange wire of the micro servo is connected to the arduino, so do you have any tips for a quick fix of a stationary micro servo?

I would first test out whether the servo is truly not working. Use the Arduino servo sweep example (I think that's what it's called) to see whether the servo is in fact able to correctly function. Next, the fact that the sensors are printing 0 means to me that they aren't working correctly. Very seldom do I ever see them measure zero.

additionally all the wires are in the correct postition

does it matter which way the sensors are placed

It does. You'll have to look at the specs of your sensors and do some testing on your own to determine the best placement of the sensors. If you look through the comments here, you'll see why I picked the angle I did for the sensors I was using. It was a simple approximation though and I did not perform any thorough engineering analysis so be sure to take that with a grain of salt.

@MagicByCalvin do you have any methods to print the real time data into the arduino serial monitor?

with still having a decent time reaction (not delayed by more than 4 seconds

Try increasing the Baud rate to 115200 (9600 is the default on Arduino). Even with a baud of 9600 though, you shouldn't be delayed by 4 seconds, you should be delayed for a couple milliseconds at most.

but will it track smoothly or stiffly