Surplus SpringRC SM-S4303R Continuous Rotation Servo Pair (Two Servos)

These are surplus SM-S4303R standard-sized servos continuous rotation servos that Pololu are able to offer at specially discounted pricing. They are functionally identical to Pololu's stock SM-S4303R servos except for the direction of rotation, which is reversed, and Pololu are selling them in pairs to help differentiate them. Pololu got them through a one-time purchase of surplus new inventory, and Pololu do not expect to restock them once they are sold out. This product is a two-pack of servos, so ordering one unit will get you two servos.

These servos have been built by SpringRC specifically for continuous rotation. At 6 V, they have a maximum rotation speed of 54 RPM (no-load) and can each produce up to 71 oz-in (5.1 kg-cm) of torque. They each feature two ball bearings on the output shaft for reduced friction, and they offer easy access to their rest-point adjustment potentiometers. They can be controlled using a direct connection to a single microcontroller I/O line without any additional electronics, which makes them great actuators for beginner robotics projects.

The SM-S4303R 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 positioner. Pulse widths above the rest point result in clockwise rotation, with speed increasing as the pulse width increases; pulse widths below the rest point result in counterclockwise rotation, with speed increasing as the pulse width decreases. Note: This behavior is different from Pololu's item #1248 SpringRC SM-S4303R servos, which turn in the opposite direction (otherwise, they are functionally identical).

The servo has an 11" (270 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):

This robotics servo is compatible with Pololu's servo controllers and has a Futaba-compatible output shaft, which means it works with Pololu's servo wheels for standard servos (25T, 5.8 mm spline). This servo is also compatible with Pololu's Mounting Bracket for Standard-Size Servos:

If you are looking for a similar servo that is capable of limited-range position control as opposed to continuous rotation speed control, consider the FEETECH FS5106B servo or Power HD standard servo 6001HB, which have comparable size, weight, speed, and torque.

Note: The spline on this servo is slightly bigger than on Pololu's other continuous rotation servos, so some servo horns and wheels might have a tight fit. If you find it difficult to push a compatible servo horn or wheel on by hand, please try the installation method shown in the video below. Similarly, the servo’s mounting tabs are a tight fit with Pololu's mounting bracket, so you might consider filing them or the mounting bracket down a little if you want to use them together.

Note that, as with most hobby servos, stalling or back-driving this servo can damage it.

Note: This servo is SpringRC part number SM-S4303R-CW.

Continuous rotation servo comparison