Servo motor changed to continuous rotation

Any servo motor can be converted to a bidirectional variable speed motor. Generally speaking, controlling the speed and direction of a motor requires a motor driver chip and some other components, which are already available on the servo motor. Modifying a servo motor is the most common and cheapest way to obtain a digital control transmission method used in robots, so that a servo motor with continuous rotation is obtained. This modification is partly mechanical and partly electrical. The electrical modification is to change the potentiometer to two fixed resistors of the same resistance value, and the mechanical modification is to remove the limit device that prevents the motor from rotating in all directions.

First, disassemble the servo motor. The HTX500 servo motor housing is made of three pieces of plastic snapped together. We can pry them apart with a small flat-blade screwdriver or similar thin piece. Pull the gear apart from the top, and then carefully pull out the servo motor control circuit board from the bottom (see Figure I). There are two mechanical stops inside. Use needle-nosed pliers to bend and remove the metal stop next to the rotating shaft, and use an angled cutter to remove the plastic stop on the top shell (see Figure J). Replace the 5kΩ potentiometer with two fixed resistors that add up to about 5kΩ. Two 2.2kΩ resistors will do. Desolder the three wires on the potentiometer and solder the two resistors as shown in Figure K. Wrap the new assembly with insulating tape or heat shrink tubing (see Figure L), then stuff the circuit back into the servo motor housing and install the housing. The modification is complete. Now you can calibrate the continuous rotation servo motor to see where the starting point is. If the two resistors are exactly equal, the motor will stop when the servo motor is at a 90° angle. Your motor may have a little deviation, so try experimenting with the previous program to see what angle stops the motor. Remember this value, as each servo motor is different.

Two continuous rotation servo motors complete a drawing robot

Using two continuous motion servo motors, we can make a drawing robot. We use two servo motors, a 9V battery, a small breadboard, an Adafruit Boarduino control board (an Arduino clone), a Sharpie marker, and a few plastic turntables. The circuit is the same as the panoramic camera, and all the parts are glued together with hot glue. Any turntable with a diameter of 2 to 7 cm can be used as a wheel, such as a plastic screw cap. You can also wrap the edges of the wheel with tape to increase the gravity. The servo motor settings are the same as before, and the code uses the variables for the starting position of the motors obtained in the previous experiment (the starting position of your motors may be different). The logic of the code makes one motor move in a certain direction for a period of time, and then switches to the other motor. Now you are done, you can go and try your robot (see Figure M).