Date: Mon, 16 Aug 93 11:00:30 EDT
Message-Id: <199308161459.AA06088@terminus.cc.gatech.edu>
Comment: Discussions of Robot controller boards
Originator: robot-board@oberon.com
Errors-To: gkulosa@oberon.com
Reply-To: Tucker Balch <tucker@cc.gatech.edu>
Sender: robot-board@oberon.com
Version: 5.5 -- Copyright (c) 1991/92, Anastasios Kotsikonas
From: Tucker Balch <tucker@cc.gatech.edu>
To: Multiple recipients of list <robot-board@oberon.com>
Subject: Servos as motors


If someone else has already posted a similar message, sorry.

I opened up a futaba servo and found that it is incredibly simple to
convert it into a high torque fwd/stop/rev motor.  This is handy since
servos don't require a power driver circuit and since we've got
code for controlling servos.  I've found that they can be "throttled"
to some degree, but not reliably without some sort of feedback.

Here is the procedure for the modification (for a std futaba):

1) Remove the 4 screws off the bottom of the servo.
2) Lift the top off carefully and remember where all the gears go.
3) Lift off the main drive gear (the one that goes to the outside world).
	Underneath is the top of a potentiometer (the servo uses it for
	feedback control).
4) Set up your miniboard to output a neutral servo position command,
	and connect the servo to it.
5) Adjust the potentiometer until the motor stops or jitters just a little.
6) Turn off your miniboard and disconnect the servo.
7) Put a couple drops of CA glue into the potentiometer (no turning back now).
	Epoxy works too, but don't use too much.
8) Look under the main drive gear and you will find a small plastic
	piece that engages the pot.  Remove it.  Other types of
	servos may require that you drill it out.
9) On the top of the drive gear is a ridge that limits its rotation,
	snip it off and trim it with an xacto.  Test it to make sure
	there is no binding.
10) When the glue dries, reassemble the servo.


Any questions, e-mail me at tucker@cc.gatech.edu  .

Tucker