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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. |
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Remove the 4 screws that hold the case together. |
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The inside view. |
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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. |
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A small insert with a rectangular slot, located inside the shaft/gear, fits over the "pot" shaft tab. |
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Remove the insert. This allows the gear to rotate without moving the shaft of the servo pot. |
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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. |
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Off with the tab. One cut parallel to the shaft . . . |
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. . . and 4 or 5 slices in the other direction does the trick. |
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Pop the shaft/gear back into the top of the servo case and reassemble. |
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The pinion gear from an r/c car ready to be modified. |
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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. |
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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. |
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This is what that hole looks like. |
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After the hole was drilled the round shaft that was held in the chuck was ground off . . |
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. . . and then cleaned up. |
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Servo and gear weigh in at 1.6 ounces. 1.6 x 28.35 = 45 grams |
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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. |