Each SimpleSumo robot uses two of these servos to drive the wheels. While they are durable little devices, they can break if you manually crunch the gears back and forth or if you hold the output shaft still while the motor is moving.
Its always good to have a spare!
The FS90R is a micro-sized servo that has been built by FEETECH (formerly known as Fitec) specifically for continuous rotation. At 6 V, it has a maximum rotation speed of around 130 RPM (no-load) and can produce up to 21 oz-in (1.5 kg-cm) of torque. The servo can be controlled using a direct connection to a single microcontroller I/O line without any additional electronics, which makes it a great miniature actuator for beginner robotics projects; just throw on a pair of wheels and your robot is ready to roll!
The FS90R continuous rotation servo converts standard RC servo position pulses into continuous rotation speed. The default rest point is 1.5 ms, but this can be adjusted by using a small screwdriver to turn the middle-point adjustment potentiometer. Pulse widths above the rest point result in counterclockwise rotation, with speed increasing as the pulse width increases; pulse widths below the rest point result in clockwise rotation, with speed increasing as the pulse width decreases.
The servo has a 10″ (250 mm) lead that is terminated with a JR-style connector and includes additional servo horns and mounting hardware. The following picture shows an example of the hardware that might be included (actual hardware could vary):
Max Speed @ 6 V:130 RPM
Stall torque @ 6 V: 21 oz-in
Max Speed @ 4.8 V: 100 RPM
Stall torque@ 4.8 V: 18 oz-in
Weight: 9 g
Size (mm): 23.2×12.5×22