2. File or cut off the nub on the underside of the
output gear that prevents full rotation. This typically means
removing one or more gears, so you should be careful not
to misplace any parts. If necessary, make a drawing of the
gear layout so you can replace things in their proper
location, or take a photo. Important! When cutting off the
nub, you’ll want to “nibble” it away in smaller chunks. The
pressure of a single large cut may cause too much pressure
in the plastic, breaking the gear.
3. On those servos that have a retainer clip at the
bottom of the output gear, remove the clip to disengage
the potentiometer from the gear. In this way, the pot no
longer turns when the gear does. On some servos, there is
no retainer clip; the servo engages into a spline molded into
the bottom of the gear. On these, you need to carefully drill
out the bottom of the gear. One method is to temporarily
attach the output gear to a large servo horn disc, and
clamp the gear and horn steady with a pair of pliers.
4. Connect the servo to a microcontroller and apply
1.5 ms pulses to it. Carefully adjust the potentiometer until
the servo stops.
5. Reassemble the case.
Of course, I could go on for many more pages talking
about radio control servos for robotics, but we’re out of
space. For a hands-on look, check out my ArdBot and
ArdBot II series in past issues of SERVO Magazine.
The original ArdBot appeared starting back in the
November 2010 issue; the updated ArdBot II appeared
beginning in October 2013.
In both of these series, you’ll see how to build a small
Arduino-based desktop robot that uses twin R/C servo
motors for locomotion. SV
SERVO 07.2014 63