Very Strange Futaba s3003 Behavior

Other Hardware Motors, Mechanics, Power and CNC
1

Hello,

I bought a large number of Futaba S3003 servo motors believing them to be standard servo motors. By standard I mean they rotate between 0 and 180 degrees. I am controlling 4 with an Arduino Mega. I have a separate power supply powering the four. The board is powered through a USB connection from my computer. It needs to communicate with some software through the serial port so I decided to route a wall wort to the four servos to power them directly.

The problem is, the motors act as though they are continuous rotation servo motors. I've researched these as thorough as I can and had thought they were standard servos. I do not understand why they are acting the way they are. Even with a single motor connected to the board and run with the Sweep example, they rotate continuously.

Here is a link for the motors on Amazon:

Futaba S3003

Here are the specs:
SPECS: Speed: .23 sec/60° @ 4.8V or .16 sec/60° @ 6V /
Torque: 44 oz-in @ 4.8V or 56.8 oz-in @ 6V / (3.2 kg-cm @ 4.8V or 4.1 kg-cm @ 6V) / Size: 1.6""L x .8""W x 1.4""H (41x20x36mm) w/o output shaft /
Weight: 1.3oz (37.2g) /
Connector: ""J"" type with approx. 5"" lead / 9/20/95 / ir/jl / updt jxs 10/29/03 / updt jxs 4/13/04 / updt mcw 5/19/04 / updt jxs 10/29/04

I've interpreted the Speed as a spec for standard servo motor, meaning non continuous rotation. This is based on the specs I've seen for continuous servos show the speed in RPMs and not in degrees.

Attached is a rough wiring layout.

Any advice on what my error could be or how to fix this is greatly appreciated.

Servo Sch.png
Servo Sch.png819×460 4.16 KB

2

I have Futaba 3003 servos bought from a reputable model store.
They do not rotate more than about 170°, simply because they have mechanical stops built in to the final gear.

3

Exactly what I thought. I believe I found the error. On a hunch, I opened the case of one of my motors. I see the shaft of the potentiometer looks broken. This could be causing the motor to spin continuously since there is nothing to tell the motor to stop. Its odd though. No material fell out when I opened the case. I think there must be a manufacturing flaw. A shame since I have about 70 of them.

Any advice on how to replace the shaft?

4

Why not return them if they are faulty?

5

I see the shaft of the potentiometer looks broken.

You should be able to do a close examination to determine the issue. Usually the pot shaft is attached to the output gear using a collar, or the inside of the output gear is molded to fit the pot shaft. The output shaft also usually has a tab that acts as a mechanical stop for the output gear to prevent complete rotation. As usual, if a deal seems to be too good to be true, it probably is.