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Converting an RC servo so that it rotates continuously through 360 degrees is a fairly easy modification to do. I am using the Futaba FP-S148 servo, which lends itself particularly well to this task. Be aware though that not all servos can be converted in this way.

I like to put a small gear on the servo that will drive a larger gear to move the camera rig. That way the servo will be stressed less and the rotation it provides will be very smooth.

Click on the thumbnail to see a larger image.

Servos09.jpg (29449 bytes) Remove the 4 screws that hold the case together.
Servos10.jpg (29052 bytes) The inside view.
Servos11.jpg (29386 bytes) Remove the shaft/gear unit. The brass tab that is revealed is the rotating shaft of the servos potentiometer. Now is a good time to set the brass tab to the exact center of its travel--otherwise the servo will rotate when the transmitter joystick is in the neutral position. An alternative to this is to de-solder the potentiometer from the servo circuit board and replace it with 2 resistors of equal value.
Servos12.jpg (29474 bytes) A small insert with a rectangular slot, located inside the shaft/gear, fits over the "pot" shaft tab.
Servos13.jpg (29360 bytes) Remove the insert. This allows the gear to rotate without moving the shaft of the servo pot.
Servos14.jpg (29652 bytes) The top of the gear shaft has a small tab that prevents it from moving beyond the stops located in the top of the servo casing. This limits its travel to 270 degrees.
Servos15.jpg (29786 bytes) Off with the tab. One cut parallel to the shaft . . .
Servos16.jpg (29400 bytes) . . . and 4 or 5 slices in the other direction does the trick.
Servos17.jpg (29470 bytes) Pop the shaft/gear back into the top of the servo case and reassemble.
gear08.jpg (29917 bytes) The pinion gear from an r/c car ready to be modified.
Lathe01.jpg (29785 bytes) This is an EMCO Unimat 3 lathe loaned to me by a coworker at the guitar shop. By the way, all my camera rigs were made side by side with some very nice acoustic guitars.
Lathe02.jpg (29683 bytes) The round outer shaft of the pinion gear was chucked in the lathe. A 6mm drill was plunged into it to a depth of 3mm. It just so happens that the splined shaft of the servo measures 6mm. Hmm.
Gear06.jpg (29872 bytes) This is what that hole looks like.
gear09.jpg (29859 bytes) After the hole was drilled the round shaft that was held in the chuck was ground off . .
Gear07.jpg (29445 bytes) . . . and then cleaned up.
Servos02.jpg (29226 bytes) Servo and gear weigh in at 1.6 ounces. 1.6 x 28.35 = 45 grams
Servos01.jpg (29663 bytes) The hole drilled in the gear fits very snugly over the shaft of the servo. It goes on very nicely. Not so tight that excessive force is needed to get it on, but not so loose that it will slip as the servo rotates. And you can use the original screw that comes with the servo to hold it in place. The gear rotates with virtually no wobble.