Modifying servo motors for continuous rotation
TUTORIAL
mall hobby servo motors are
commonly found in radio-controlled
planes, in miniature robots, and in
many other types of projects that
require precisely controlled
movement, slow motion, and decent
torque. Servos are relatively cheap and come in all
sorts of sizes, and usually come with a set of ‘link’ or
‘control horns’, nylon plastic arms and disks that
attach to the motor shaft, and have tie holes that
allow you to attach control rods, wheels, and other
objects. It can position these fairly accurately with a
180-degree arc using pulse width modulation (PWM)
or pulse code modulation (PCM).S
Hacking servo motors
for more rotation
How to remove the control circuitry and mechanical stop on a standard servo motor
Right
A standard hobby
servo taken apart to
show the top plate,
the main body (with
gear-box), and the
bottom plate with
four screwsIf you don’t need this control, but do like the form
factor and need the ability to spin more than 180
degrees, you can convert your servo into a geared
motor. Let’s find out how.
To transform our servo into a regular DC motor
with gearbox, all you have to do is complete the
following two simple ‘hacks’.REMOVING THE FINAL GEAR TAB
The large ‘final gear’ in the servo’s gearbox has a
mechanical stop on it that prevents the motor from
travelling outside of its fixed 180-degree arc. To
remove this stop to allow continuous rotation, do
the following:Step 1: Remove the bottom screws and top plate
There are commonly three parts to a servo motor’s
plastic case: the top plate, the main housing, and the
bottom plate. All of these are usually held together
by four long Phillips screws located on the bottom
plate. Use a suitable driver to carefully remove these
screws. With the screws removed, carefully pull off
the top plate. You should now see the three main
gear assemblies.Step 2: Remove the middle gear
Carefully remove the centre gear from the assembly
and set it aside. It will go back where it came from.Step 3: Remove the final gear
The final gear will have a small, clearly visible tab on
it. Remove this gear.Step 4: Remove the mechanical stop
Using a pair of angle cutters, razor knife, or another
suitable tool, remove the little tab from the final gear.
File or sand it down so that nothing will interfere
with its full rotation when you put in back. Note: If
you have metal gears in your gearbox, the stop will
usually be a small pin. You can use the tip of your
side cutters to gently pry the pin from the gear.Gareth Branwyn
@garethb2Gareth has been a
lifelong practitioner
(and chronicler) of
DIY tech, media, and
culture. He is the author
of ten books, including
Make: Tips and Tales
from the Workshop,
and is a former editor
for Boing Boing, Wired,
and Make:.