A servo is a device comprising of a two wire DC motor, set of gears, a position-sensing device (usually a potentiometer), an integrated circuit and output shaft. Unlike the DC motor, Servo has three wires. One is for power, one is for ground and the third wire is a control input line. Through the input line we can send a code that represents a desired output position of the servo shaft. The shaft does not rotate freely like in a common DC motor, but can only turn maximum of 180 degrees back and forth. Therefore, mainly servo is used in RC controlled models. Example can be steering front wheels of remote controlled car, turning rudders of boats or ailerons of a plane etc.
Hacking a Servo to spin 360 degrees:
Here the question rises, why would one need to hack a perfectly good working servo to spin 360 degrees of continuous rotation just like a DC geared motor does? Lets say we need to make a micro-controlled robot, for it’s wheels we need a continuous rotation. If we use DC geared motors we will have to use a motor driver circuit and may require external power supply for the DC geared motors. But, if we make the cheap high torque compact servos work in continuous rotation, our robot can be much more simpler, because when using servo we don’t need to have a motor driver circuit. After all, it has that cute sound that makes it really traditional to be used in robots.
So now, lets get started on this. I would recommend you to try this with an extra servo available, because its little tricky and you might end up with ruining a good working servo. So make sure you be very careful with each step. I recommend you to first go through the video so that you have an idea of what you will be doing in this tutorial.
So after watching the video, you must have a little idea of what you would be doing now. So first of all you need to have the following instruments.
Tower Pro SG90 Micro servo
A small sized screwdriver (Phillips)
Soldering kit (Stand, Soldering wire and solder)
2 Resistors ( for me 2.2K worked )
1. First remove the attachment from the Servo’s main shaft and unscrew the four screws. Make sure you don’t loose any of them.
2. Remove the top cap and you will see set of gears and a axle that will be detached. The top main gear will make a little trouble getting off, so deal with it precisely and carefully.
3. Now remove the bottom cap and you can see the three wires following a circuit. We see three red wires that are connected to a potentiometer inside which we need to remove. We need to cut these wires from both ends ( potentiometer + Circuit ). Leaving only the two DC motor wires which are connected to the circuit.
4. Now this step is most crucial, we need to have good soldering skills. Here, first we need to solder the two resistors in serial connection. That gives us three pin resistor. We need to connect each pin to each knob where the three red wires were connected. This is very delicate work, we need to make sure that we don’t make them short. If we do so the servo might not work properly. It should look like this after soldering. After this, we need to fit the circuit back into place. and close the bottom cap.
5. Now its time to chop off the mechanical stop on one of the gears. You can do that with any blade.
6. Last step is to put all the gears and axle back in place and in the end you need to pack the set with the four screws. I hope you don’t loose any of them.
So you have successfully modified the servo to spin continuous rotation. You may use arduino program “Sweep” in order to check whether it is spinning 360 degrees or not. Best of Luck!