This "How to" guide will show you how to configure the Heng Long recoil unit for more accurate and realistic recoil effect. Following each step, as outlined in this guide, will make this a simple modification that anyone can do.

Now to start

First, remove all the screws in the recoil unit and separate the case halves.

Now that you've separated the case halves, you'll need to remove the stops on the traverse slots, as shown in the pics below...

As you can see, the stops are located on both halves of the case. On the upper and lower tracks, use a pair of flush cut snips to remove them, then, using a sharp exacto knife, clean the tracks of all remaining pieces.

Now that the tracks are clean you'll need to elongate the slot to allow extra recoil travel. With a sharp knife cut the slot out as far as the tracks, as seen in the picture below.

Next step: Now, you'll need to remove a small amount of plastic from the corner of the slide to make room for the extended travel.

With the slot now elongated we can move on to the outside of the case. You'll need to remove the old spring pin. Be careful how you cut the spring off, as it will be reused in the next step.

Now, with the pin removed, we will be remounting the pin in the new location using a 2mm by 28mm long  screw. Attach it to the rear hole in the case where the old gun stop was located.

After you've installed the new screw, using a bit of Abroid Pro Weld, glue the pin in place.

Now drill your holes for mounting the micro switch. You can see in the picture the hole just ahead of the old pin location...

Next step is to mount the micro switch on the outside of the unit by inserting the screws from the inside of the case half. If the switch has a long lever, bend it in half so you can use it to fine tune the recoil unit.

Now reassemble the recoil unit but leave the motor out at this time as there is work to be done to it.

Motor modification: you will need to install new capacitors as the ones on the motor is not up to task to filter out all noise. I use 22 nano farad caps they seem to be the best choice to job. They will be installed from the positive (+) post to the negative (-) and from the positive (+) post to the motor case ground as shown in the pictures...

Once you've completed the above step, you'll now reinstall the motor by pressing it back into the case. Be sure when installing the ground lead from the capacitor to case you don't "over-solder", as it will interfere with the case hole when pressing the motor back in. With the motor back in place, you can now wire it up to the new switch and power leads.

First you need to solder on a positive (+) lead to the neg side of the motor and two negative (-) leads to the old positive (+) side of the motor.

Then attach one of the negative (-) leads to the center pin on the micro switch. Then attach a lead between the top pin on the micro switch and a negative source on the main board.

The positive (+) lead on the motor goes to a B+ source on the board.

The last negative (-) lead on the motor goes to the trigger wire on the main board. This is the yellow wire on the 8 pin connector on  RX13, RX14 and RX18 boards.

The the B+ lead gets a 22 ohm resister soldered inline and the lead wire going to the trigger gets a diode with the silver end facing away from the recoil, soldered inline also.

As you can see in the pictures, the positive (+) wire is green, the negative (-) wire is blue and the fire wire is white. The jumper from the switch to negative (-) side on the motor is black.

Now just fine tune the micro switch and your done. Enjoy your realistic recoil action!