BASICS / CAMERA CRADLE / 360° SERVO CONVERSIONS
Method 3 - Servo Pot ReplacementFigure 6 Figure 7 Figure 8 Figure 9 This conversion will produce a servo that rotates continuously in either direction depending on which way you move the joy stick. This is based on the Futaba S3003 servo but could possibly work with other servos. This conversion was first described by Brooks Leffler in the Aerial Eye 4:2.
The servo is opened and the pot leads are cut as close to the pot as possible (Fig. 6) leaving enough of the "Pot" lead on the circuit board to solder a small 5K ohm trimmer (this is another word for a pot). Brooks recommended the Cermet Trimmer Part #3299W-502-ND from Digi-Key Corporation ( http://www.digikey.com). It is just the right size to fit inside a S3003 servo and the leads match up perfectly with the stiff leads left after you cut out the servo's original pot (Fig. 7).
When soldering the Cermet Trimmer in place make sure the center lead from the original pot connects to the center lead of the trimmer. You may need to bend the leads on the trimmer to allow for clearance when the servo case is replaced (Fig. 8). You will also need to cut out some of the structure inside the servo case, that used to hold the "Pot" in place, to allow the case to fit back over the modified assembly (Fig. 9). Drill a small hole through the case to allow a small screwdriver access to the adjustment screw on the Cermet Trimmer.
If your servo is constructed such that the pot is necessary to support the final output gear and can not be removed, then remove the guts of the "pot" so that the "pot" shaft can turn freely 360°. Then solder three wires to each of the leads of the gutted pot. Drill a hole in the side of the servo large enough to accommodate the three wires. Run the wires through to the outside of the servo case and solder them to the Cermet Trimmer, being careful to keep track of the wire coming from the center lead. Glue the Cermet Trimmer to the side of the servo case.
Once the Servo is reassembled connect it to the receiver and turn on the transmitter. Set the trim for this channel to the middle and leave the joystick in the neutral position. Adjust the Cermet Trimmer until the Servo stops turning. The trim on the transmitter can be use to re-zero the Servo when you first turn the rig on in the field.
External gears are not required
(some KAPers go ahead and gear the final output down 4:1 to make the panning action slower.)
With no external gears the panning action will be at the servo's normal operating speed.
With no external gears the servo requires minimal space on the KAP rig.
Servo must be open and modified, including some soldering.
Can not use most mini-servos because of partial gears.
This method has been surpassed by a much simpler and more elegant solution that accomplishes the same goal without replacing the pot. (see next method)