How to turn a stock Rival Charger into a full-auto powerhouse of destruction

Demo Firing:

In order to do this mod effectively, there are some tools you will need.

1. Dremel with large grinding wheel

2. Soldering iron and electrical solder

3.  Hot glue gun

There are also several parts you will need.  I will add Amazon affiliate links to the parts I used below.

1.  1x SPDT Switch:  link

2.  1x Male Mini Tamiya Connector:  link

3.  1x 11.1v LiPo Battery (Airsoft):  link

4.  1x LiPo Battery Charger:  link

5.  12 Gauge Stranded Wire:  link

Lastly, you will need the 3d printed auto seer.  There are currently 2 ways to get one.  If you have your own 3d printer, the model can be purchased here:  link.  If you do not own a 3d printer, don't despair! You can purchase a print from Shapeways here:  link.

Now, the tutorial...

First, you should remove the batteries from your blaster.  Do not reinstall the battery door, but set it aside in a safe place.

Next, you will want to unscrew all the screws from the blaster.  Be careful to note where the shorter screws came from, as you can damage your blaster if you put a long screw where a shorter screw originally went.

Once disassembled, you should see something like this:  

(image courtesy of BlasterHub)

There are several changes that must be made.  I have highlighted them in the next image, which shows what parts to remove, where to Dremel for the new switch, and where to desolder.

This looks like a lot, but it's actually fairly simple when taken one step at a time.  First, let's remove the PCB board from the motors.  Start by clipping the indicated wires.  After that, plug in your soldering iron.  Once the iron is heated, use it to heat up the indicated solder joints while pulling up on the board from the side.  You might have to wiggle it off by alternating which point is heated and slowly working the board off of the motors.  Once it is removed, you can save it or discard it.  We won't need it for the mod.  

Now, you should unscrew the screw holding down the plate by the battery compartment.  Once the plate is removed, pull out the battery contacts.  Also remove the white highlighted battery spacers from the battery compartment.  After that, remove all the wiring and switches from the blaster.  To do this, you will need to remove the ammo tube from the blaster.  Do not remove the wide-headed screws on the top of the tube, but rather the smaller screws that hold it in place.  While the ammo tube is out of the blaster, you will want to remove the ammunition flow regulator from the tube.  This is done by using a screwdriver to push out the small pin from the side of the tube.  

If you want to make the blaster semi-automatic again, then save the pin, spring, and small door that was held in by the pin.  This piece is a pain to reinstall, but without it the blaster cannot shoot semi-automatically.

Do not place the ammo tube back in just yet.  Now, we will install the auto seer.  Underneath the ammo tube close to the flywheels is a small orange piece with a spring-loaded flipper.  Carefully lift the assembly out of the blaster.  Now, remove the spring-loaded flipper, being careful not to lose the spring.  The spring on the flipper will need to be cut down slightly on the straight edge that shoots out to the side.  Cut the spring so that the small protrusion coming out of the side is no longer than ~6mm or 1/4".  Next, remove the spring from the original flipper and place it on the auto seer.  The side piece that you cut down should fit nicely between the notches on the face of the seer.  Now, align holes of the spring and the seer and slide the seer onto the original peg, making sure that the end of the spring that points down goes into one of the holes next to the peg on the orange piece.  Set this assembly aside.  It should look like this:

Back to the rewiring!

Take two small lengths of the wire purchased and run them vertically between the two opposite motor terminals.  It is easiest if you use red wire for the terminals on the right and black wire for the terminals on the left.  You should strip a small length of the wire's coating from the middle of these sections.  Solder the wires to the motor terminals.  Next, we will remove the long metal arm from the switch.  Carefully wiggle it out with some pliers.  Do not worry if it slightly damages the housing of the switch on the way out.  This is purely cosmetic, and this part of the blaster will be hidden inside, so it won't matter.  Now, you will need to Dremel out some of the grip to make room for the new switch.  Using the grinding bit of your Dremel, carefully remove material in the highlighted area until you can comfortably fit the switch into the area.

It should fit like this:

Do not glue it into place just yet.  First, we will want to attach the wires to it.  Run a length of red wire from the middle of the wire bridging the motors to the terminal on the side of the switch and solder it in place.  The wire should be long enough to comfortably snake its way through the blaster to the switch without getting in the way of anything.  Now, solder another wire to the switch on the terminal closest to the one we just soldered to.  This wire should snake its way through the small piece at the back of the pistol grip into the battery compartment through the largest hole made by removing the battery terminal plate.  The wire should be long enough to almost reach the back of the battery compartment through the hole.  Now you should run some black wire from the black wired motor bridge to the battery compartment, this time taking a more direct route through the middle of the blaster.  It should be long enough to end at the same spot as the wiring running from the switch to the battery compartment.  Now, use hot glue to glue the switch in place as seen in the image.  The small button protruding from the side of the switch should reach slightly beyond the small wall on the left side of the switch.  The orange rev trigger should press the button when the trigger is pulled. 

You will want to Dremel out the space on the other half of the shell above the switch so that the blaster can close again.  This area is not mechanically important, so precision is not entirely necessary.  Just be careful not to cut through the shell entirely.

Now, reinstall the orange plate with the auto seer into the blaster.  After that, install the ammo tube, follower, and spring into the blaster.  You will need to hold the auto seer open so that the flippy arm connected to the ammo tube goes behind the auto seer.  The arm should push down on the curved section of the auto seer when the trigger is pulled.  You are almost done.  The internals should look like this (with red and black wires instead of white):

Reassemble the blaster, making sure to put each screw in its proper place.  Now, flip the blaster over so that the battery compartment is facing up.  Connect an empty mini Tamiya connector to the battery.  Next, cut two of the small metal prongs from the line of prongs.  You want the prongs that have a hollow end.  Insert the red and black battery wires into the prongs and use pliers to bend the straight bits onto the wires to hold them in place.  Solder the wires to the metal barbs.  Now, take the battery with the empty connector attached and insert the wires into the exposed end of the empty connector.  Make sure you match the wire colors from the blaster to the battery!  You are now finished!  

I hope this tutorial was helpful.  If you have any questions, please feel free to leave a comment.