RC or hobby servos provide a convenient actuator to be used in a small-scale robotics project.

Inside a servo there are a DC motor, a gear reduction system, a potentiometer as a position sensor, and some electronics that control the motor based on the desired position.

A hobby servo is great, as it provides all the above in a convenient small package. Due to its popularity, hobby servo is quite cheap.

However there are shortcomings in using a hobby servo in a robotics project:

• No position feedback. Once commanded to move to a target position, we don’t know when or whether the servo has reached the target position
• No torque sense. We cannot tell if the servo mechanism is unexpectedly obstructed.
• Sub-optimal control system. The servo manufacturer cannot know what load the servo will be connected to, so as a result the control system will not be optimal. The problem shows up as: overshoot, slow response, and steady state error.

My plan is to use all the mechanical components of a servo, but replace the electronics with one that I design myself to solve the above issues.