SpringRC SM-S4303R Continuous Rotation Servo

Surplus units available: Pololu have made a one-time purchase of surplus new SM-S4303R continuous rotation servos that Pololu are able to offer at specially discounted pricing. They are functionally identical this stock SM-S4303R servo except for the direction of rotation, which is reversed, and Pololu are selling them as pairs under a different product number (item #3448) to differentiate them. Please consider them as discounted alternatives to the Pololu's stock item #1248 servos while supplies last.

The SM-S4303R is a standard-sized servo that has been built by SpringRC specifically for continuous rotation. At 6 V, it has a maximum rotation speed of 54 RPM (no-load) and can produce up to 71 oz-in (5.1 kg-cm) of torque. It features two ball bearings on the output shaft for reduced friction, and it offers easy access to the rest-point adjustment potentiometer. 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 actuator 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 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 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-CCW.

Continuous rotation servo comparison

54	71	43	46	41	41.3 × 20.7 × 40.2	CCW?CW
140	35	–	–	41	40.0 × 20.0 × 37.2	CW?CCW
130	21	100	18	9	22.5 × 12.1 × 23.4	CW?CCW