We use these servos for all sorts of things. From the trigger on our 'internet connected kettle', to the striker on our 'bell of notification'. They are easy to interface with an Arduino, not too expensive, and rugged. Given how much we rely on them we thought it was a perfect candidate for our first product teardown.
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Product: Standard Servo
Made By: Spring RC
Made In: Shenzhen, China .:Taking Apart:.
To take the servo apart remove the four screws found on the bottom. This allows the top and bottom plastic housing to slip off revealing the gear train on top and the circuit board on the bottom. The PCB and motor requires some convincing to be removed. Finally if you want to fully disassemble the servo you need to remove some hot glue that holds the potentiometer in place.
The servo is assembled from three plastic housings; a gear train (explored in more depth below), a PCB with motor and potentiometer (explored in more detail below). Plus two red rubber rings, which give the servo it's unique red stripe appearance.
The gear train has 5 gears (2 single and 3 double). These go from the motor (metal 10 teeth) --> first double gear (60 teeth to 11 teeth) --> second double (49 teeth to 11 teeth) --> third double (35 teeth to 13 teeth) --> output gear (42 teeth). These combine for a total gear reduction of 274.75:1.
The PCB is single sided and easy to read. The large chip is a servo decoder (KC2462). This takes input from the signal line (white wire) and compares it to the position of the servo (given by the potentiometer). The chip then produces a control output based on the error between the two values. The output signal is fed to 4 transistors (Q1-4) which are configured in an h-bridge (this allows the motor to be driven either direction). This simple closed loop system causes the servo to always be moving towards the desired position. (We'll delve deeper into how this PCB works and the parts used in a future post)
.:Sources, Helpful Links, Mentioned Products:.
(want to take a closer look, all images are available on Flickr Servo Teardown Photos (CC-BY-SA))