Then disassemble the HS-81MG and remove the bottom plate.
Remove the little circuit board and then the retaining screw for the pot
and then remove the top and the metal gears from the pot shaft side. I
used a small handle screwdriver to press the pot shaft down until it
slid as far as it would go loosening it self from the interior retaining
slot. Then I removed everything except the motor which seemed to be
glued in.. I cut the motor wires (brown and orange in this case) fairly
close to the circuit board so that you have about 1 1/4" of wire and set
the case with the motor aside for now.
The pot and circuit board with the plug is now all that is left. We
can't use the circuit board or the plug - but we will need the pot. Cut
the three wires (Yellow - Red - Green) as close to the circuit board as
possible and toss the circuit board over with the losi case - we won't
need it any more.
Now look at the Losi circuit board and you will see that the pot is
soldered directly onto it. Notice the orientation of the pot. It is
soldered so that the three leads are at the edge of the circuit board
and the pot sits over the circuit board. Keep this in mind for later
reference. This wont work in the HS-81MG because it's too large to fit
and even if it did fit the pot diameter is just slightly larger making
the shaft sit at a very slight but incorrect angle if you get it into
place (I tried this first!). But you will notice that the Losi pot and
the Hitec pot have one thing in common - the shaft length is the same!
You will need to remove the Losi pot from the Losi circuit board -
CAREFULLY - as you WILL be using this circuit board. It just needs to be
de-soldered and replaced with the pot and leads from the HS-81mg. (I
simply used a pair of dikes on the Losi pot and literally "cut" the pot
arms - then grabbed them singlely with needle nose pliers and applied a
soldering iron - they released easily!)
Strip the ends of the Red-Yellow_Green HS-81 pot leads.
On this circuit board (now that we have removed the old Losi pot) check
the holes where the pot was soldered. Are they open?
What I mean is are they free of solder obstructing the holes - if not
then you will need to open them using a pick or any method that works. I
used a pin vise drill and a small bit to just drill 'em out. You need
them clear for the wires from the HS-81MG pot.
Notice on the Losi circuit board that two of the pot's leads were
soldered in such a way as to shunt them together and the third was
separated. On the HS-81MG pot we will orientate the pot to be the same
as the Losi pot but with the wire extensions soldered to the Losi
circuit board. The green - yellow - red wires from the HS-81 pot are now
stripped so that about 1/16th or so of wire is bare at each end. I used
my fingernails for this not trusting dikes as I always seem to cut the
wires instead of stripping them. Twist each end of the wires after
stripping to keep the strands tight and then pre tin each wire end with
good resin core solder as this will help you to "thread" them into the
holes. Orient the wires so that the pot is in essentially the same
position as the Losi configuration. The GREEN wire is the separated one
then the yellow goes into the center and the red into the last - with
the yellow and red actually shunted. Now gently solder each of the wires
in place.
Finally strip the ends of the blue and red motor wires so
that there is about 1/8th inch of bare wire. Twist each and tin with
solder. Now get the HS-81MG case with the motor wires and strip each of
these similarly and tin. Just slightly twist the RED and ORANGE wires
together and solder them. Do the same for the BLUE lead from the circuit
board to the BROWN motor lead. After the wires are soldered - NOW you
will need about 3/8" of small heat shrink tubing for each of these motor
joints. Just slide it in place and use the hot soldering iron to shrink
it down by "circling" it with the hot iron until it is snug. This will
keep the wires protected from shorting in the case.
Almost done!! Now just reassemble the servo using your newly created
electronics. Place the pot back in the same place it came from -
oriented the same and replace the retaining screw. Make certain the
shaft seats properly ansd is oriented as there is a half moon section
for the shaft to fit into in the gear this is what makes the pot work!
There will be quite a bit of space in the case between the pot and the
circuit board - to fill this in a little for insulation I used a small
piece of foam - but you can use almost any NON-CONDUCTIVE material -
tissue - cardboard - whatever. Now place the circuit board in the case -
orienting the plug lead wires in the "slot" and press it into the case.
Fold the motor leads in after it and replace the case bottom. Insert and
tighten the four screws and your new HS-81MG-MOD servo is ready to rock
with the stock ESC/REC!!
