The original servo mod was done with a Losi servo and a HS-55 by cagedmax on

That mod can be seen by going to the link here:

The following is simply carrying this one step further to apply to a HS-81mg and stock electronics.

The mod is essentially the same - remove all electronics from the losi servo. Now cut he motor leads - red and blue and toss the motor. Notice that the Losi pot is soldered directly to the circuit board. Click on an image to enlarge it for clarity.


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!!


I didn't create this - 22benjamin22 of did and here is the link to the article if it is still available.

I merely cleaned up the images and corrected the for gamma - they seem a little clearer now and I also added my own.



Chassis uncut with RED box showing area needed to be smoothed flat.




Chassis after dremeling of area.(You really don't need to have the chassis bare to do this mod - but it does make it easier!)

Here you see the servo laid in in a preliminary fit. Yep it fits!

Here are several shots of the servo after installation. The servo hold down bracket which serves as the battery hold down clip needs to be modified also for a good fit.

The bracket - if you look closely at the first photo you will not the area to be flattened is markes with a marker - unfortunately it is black and hard to see in this photo.


The second photo shows the bracket AFTER the mod.

Here it is AFTER the mod and fully installed in my Mini-T. After this mod the stock four cell battery box will NOT fit - but if you want to run four cell stock class - just solder up some AA Nimh's and you're in business as I checked and AA's will fit in the tray without the battery box.


The HS-81 is SOOOoooooo fast that I needed to turn the steering rate down almost completely to be able to steer the car. But wow is it solid!! I really like it! And since it will work with the stock electronics it's even better!!

All of the real work on this project was done by cagedmax and 22benjamin22 at so I will not take any credit for that. I simply didn't want their effort to disappear so I made this page incorporating it all in one area. I will include other mods as I find them - most especially if I fine them to actually work. These guys did their homework and I appreciate it! Thanks fellas!