Servo 360 Rotation Mod (Parallax)




About: Evo 8, Honda K, B Engines Mods
In this instructurable I will expalin and show you how to make a Parallax servo rotate 360º. And againI have search the internet to see tutorials clear enough to make this posible with no luck. Don't get me wrong they are some how good but not clear. This mod will help you to use the mod servo for robots that need a fully 360º rotation servo. Also some of the pictures were taken from other instructurables and google to help new users understand this instructurable. This mod is useful for your robotics needs.

Enjoy ;)

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Step 1: Materials

Parallax servo
Cutting pliers
2X 220Omh resistors 
Soldering iron
Desoldering pump.
Soldering iron.

Step 2: Step 1

1.  Remove the control horn attached to the top of the servo.
2.  Remove the four screws on the bottom of the servo and take off the bottom plate. 

Step 3: Step 2

1.  Unsolder the 2 connections you see in the picture. This will help to remove the PC board, without the motor.(Picture 1)
2.  With a small screwdriver, carefully pry out the PC board motor control unit from the plastic case. It will be tight so go slowly. (Picture 2)

Step 4: Step 3

1. I have soldered together the 2 220Ohm resistors. (Picture 1)
    Put them together like the picture.
The two resistors will replace the potentiometer for the continuos rotation

Step 5: Step 4

1. Remove the potentiometer by cutting it from the PC board.

Step 6: Step 4

1.  Attach the resistors where the potentiometer was installed before.
In the Drawing you will see the resistors attached together were the potentiometer was installed.
2.  Then cut the plastic mechanical stop.

The resistors will help the servo last longer. Also they are in place of the potentiometer so you can control the servo using the digital pins on the Arduino.

Step 7: Step 5

Assemble everything back again
Try this code to try the 360º rotation:
// Sweep
// by BARRAGAN <>
// This example code is in the public domain.

#include <Servo.h>

Servo myservo;  // create servo object to control a servo
                // a maximum of eight servo objects can be created

int pos = 0;    // variable to store the servo position

void setup()
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object

void loop()
  for(pos = 0; pos < 180; pos += 1)  // goes from 0 degrees to 180 degrees
  {                                  // in steps of 1 degree
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position
  for(pos = 180; pos>=1; pos-=1)     // goes from 180 degrees to 0 degrees
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position

Step 8: Trubleshooting

1.  When I took apart the servo all the gears were loose how do I put them in the right order?
A.  Look at the picture to see the gears in place.

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    15 Discussions


    1 year ago on Step 7

    Your code is 0 to 180 in one direction and 180 to 0 in other direction.

    How are you mentioning that it is 360 degree rotation code ?

    1 reply

    2 years ago

    Please tell me how do i set its mid point ? it just never stop. i used it with arduino mega.


    Reply 3 years ago

    the connections stays the same it is just for a full 360 rotation purpose ;)


    Reply 4 years ago on Introduction

    Even though Arduino wants you to use a PWM port, I've found you can use ANY digital port, and the Servo library will still write in PWM to it. Simply use 0 for full reverse, 179 for full fwd, and 90 for stop. Though the Arduino has an on-board regulator, DO NOT use it for more than 2 full-sized servos. I highly recommend running a +5V regulator, (7805 for example) for a 'Servo Power' supply, external to the arduino.. (I.e. GND for the regulator, the Arduino, and BLK wire for the servo can all be common, But.. run the RED wires from the servo to the output pin of the regulator, and NEVER back-feed the +5V from the regulator back to the 5V pin of the arduino. (could fry the switching circuit for the USB/Ext Pwr. circuit.)) the WHT signal wire on the servo can still be driven directly from the Arduino digital outputs.


    4 years ago on Introduction

    A small side notes... Though they have Parallax's label on them, they're actually Futaba A3003's. I've used A3004's (ball-bearing version) and easily modified them to constant rotation... Uhhh.. mid photo, the 2 resistors, Red-Red-Red= 2.2K, not 220-Ohm (red-red-Brown).. (the POT inside is actually 5K rated) The ones I've modified, I "Z"-bent the pot strips and drilled a hole through the side of the case, routing the trim adjustment out, (still works same as the 2x 2.2K resistors, but with fine-tuning adjustment.) for replacing the two Parallax Constants on a BOE-BOT, when the motor bearings started squealing. (reusing the POT which Parallax replaces with a 5k PC mount, screwdriver adjust.)


    5 years ago on Introduction

    black ground ,red 5 volts, white signal analog connection


    6 years ago on Introduction

    And I correct you they are 220 Ohm resistors. They worked perfectly


    7 years ago on Step 5

    assuming you have a solder sucker you can easily unsolder the pot from the board and use it in other projects :)


    7 years ago on Step 4

    Just to be clear, the POT is a 4.7K variable resistor. be sure that you replace it with two 2.2k ohm resistors as seen in the picture above. the instructions are a little fuzzy and make it sound (to me) that two 220 ohm resistors are being used.

    resistor color code

    220 ohm: red red brown
    2.2k ohm: red red red

    Good tutorial


    7 years ago on Introduction

    Parallax was one of the first companies to have a continuous rotation servo for its robots. I have seen other articles too. Many companies now have continuous 360 degree servos in most of the formats.