There are a number of servos that can be used as motors for
robots. In this article I will tell you how to modify Hi-Tech HS 300 servo.
The Hi-Tech HS 300 is a very simple servo to modify and
works well in robots.
Here are the steps.
- Remove
the servo wheel from the shaft. Save the screw and wheel for later use in
mounting wheels.
- Remove
the four screws from the bottom of the servo. Be careful, when the last
one is removed the servo comes apart easily.
- By pushing
on the output shaft on the top of the servo, remove the top part of the
case. Pay attention to the arrangement of the gears.
- Remove
all of the gears and set aside for later reassembly.
- Take
the large gear with the output shaft. Find the square tab that projects
out of the gear. Using an exacto knife remove the tab. Set aside the gear
for later.
- Holding
the servo loosen the nut on the metal shaft.
- Remove
the bottom of the servo.
- Carefully
remove the circuit board. Do not break any of the wires.
- Pull
the silver potentiometer out of the servo.
- Cut
the wires attached to the pot. Leave about ¼” of the wire attached to the
pot. You will use this later to determine how to connect the new pot.
- Put
the threaded end of the pot in a vice and break off all of the body so
that you are left with the shaft and the threaded part.
- Put
the shaft and threaded part back into the servo and reinstall the nut
removed in step 5.
- If you
are going to have a left and right servo drive, reverse the motor wires on
one servo. This reduces the number of constants you need when writing your
code. You only need one forward and one reverse constant.
- Drill
a hole large enough to feed the three wires cut free from the pot through.
This hole should be above the signal wires coming out of the servo.
- Reassemble
the servo.
- Obtain
a 5k ohm 10 or 20 turn miniature (trim
- Using
the remains of the original servo pot as a guide, solder the wires to the
new pot. Use heat shrink to insulate them.
- Use
shoe goo or goop to glue the pot to the side of the servo. Make sure that
you make a left and a right.
- Set up
your controller (stamp, BX24…) to connect to the servo. Send a command of
stop to the servo. This should be a pulse 1.5 mili-seconds long repeated
every 20 to 30 mili-seconds.
- Adjust
the pot on the side of the servo until the servo stops turning. Repeat
this process for the other servo.
- You
now have a set of motors which you can mount wheels on to drive your bot.
