VFC HK416 CAG AEG High Cycle Customization: FCU Installation Guide

In my previous post, I introduced my customization of the VFC HK416 CAG AEG and my major failure.

Now that the preliminary work for assembling the gearbox is complete, we will proceed with assembling the gearbox.

Assembling the gearbox

As usual, I'll check the compatibility between the installed components and the gearbox.

First, check the clearance between the piston (SHS full steel gear, 14 teeth) and the gearbox.

There's quite a bit of play, so I'll adjust it by attaching a 0.2mm thick plastic sheet to the piston groove.

This plastic sheeting process is easy; basically, since the piston groove is 2mm wide, cut a long piece of plastic sheet 2mm wide, glue it in place, and then trim off any excess.

・Tamiya plastic sheet, 0.2mm thick
I choose Tamiya because it seems to have good precision and quality.

Now I'll assemble it again and check it.

It's a little on the tight side, so I adjust it by filing it down a bit to find the right point. Personally, I think the ideal point is when the piston has a slight resistance when grease is applied and falls down under its own weight.

Next, we'll temporarily assemble the cylinder head onto the piston and check the angle of effect (AOE).

The piston head I'll be using is DCI's side-intake POM.

This is to confirm the AOE (Area of ​​Effect).

It's not in bad condition, but since we're pushing the limits this time, we'll be making some adjustments.

There are several ways to adjust AOE, but since I don't want to increase the piston weight and also want to absorb shocks from the cylinder head, I adjust the thickness of the mounting area on the cylinder head. The downside is that the air volume of the cylinder decreases, but I adjust that with the spring strength.

Based on how it looks, two 1mm thick sheets of Haneite rubber seem to be just right, so I'll cut and paste them onto the cylinder head.

• Haneite, 1mm thick
I always use it for adjusting AOE. I'm hoping that the shock absorption makes it quieter and more durable.

By the way, a tip for applying Haneite to the cylinder head is that it's difficult to cut out a perfect circle from the start, so cut it out to a suitable size, punch out air holes with a punch, and then apply it to the cylinder head, aligning the air holes.

If you stick it to the cylinder head and then trim off the excess, you can achieve a fairly neat application.

This will allow us to check the AOE (Area of ​​Effect).

I apologize for the slightly off angle in the photo, but it turned out pretty well.

Next, we'll temporarily assemble the remaining parts.

Now let's focus on the fins of the tappet plate. Rotate the gear by hand to observe the movement of the tappet.

Upon inspection, it appears the tappets are engaged for extended periods, so I will modify the vanes.

I mostly rely on intuition, but I cut the feathers by about $ \frac{1}{3}$ and round the corners.

Next, check that the tappet nozzle is at a perfect right angle. Since it's a genuine part, there shouldn't be any problems.

It was absolutely perfect, as expected.

Next, we will check the installation of the FCU Leviathan, which is the highlight of this project.

First, assemble it according to the instructions.

Install the included trigger.

Upon installation, I discovered that the leaf spring, one of the selling points of the FCU Leviathan, wasn't reaching the trigger. So, I adjusted it with needle-nose pliers.

Once the adjustments are complete, we will check if the FCU Leviathan is functioning correctly.

Connect the battery and then connect to the app via Bluetooth. Once connected, switch to the sensor check screen.

While looking at this screen, manually move the gears and triggers to check them. If everything is working correctly, you will see that sensing was successful for each item.

The process is complete once you've confirmed that each sensor is detecting correctly.

However, this is where the incident occurs.

Trouble #2

The incident that occurred was that while adjusting the leaf spring that contacts the trigger, I ended up destroying the trigger switch.

Normally, the switch has a protrusion like this:

I messed up.

The instructions warned me repeatedly to be careful, but I still did it.

The cause seems to be that I lost focus while repeatedly adjusting the trigger pull, trying to find the perfect feel since there's no single right answer, and ended up snagging it with pliers. I tried to fix it by finding the broken switch and attaching it with super glue, but it didn't work.

I thought about finding and procuring an equivalent part for the circuit's switch and resoldering it, but I gave up because I didn't know the switch's model number (if anyone knows, please let me know).

By the way, everything is working fine except for the trigger switch, so I'd like to replace the detection switch and reuse it. If anyone knows the model number, please let me know. Also, if there's someone who can fix it, I'll give it away.

Having no other choice, I made up my mind and bought a brand new, new model FCU Leviathan OPTICAL V2 (it took about three days to arrive because I ordered it online, which was quite frustrating).

When I opened the lid, the item that should have been there wasn't.

I quickly contacted the seller and they sent me the item (thank you for your prompt response).

After waiting for about two days, the selector detection sticker arrived.

Now that we have everything we need, let's take a look at the new Leviathan.

FCU Leviathan Optical V2

Let's open it.

The included accessories are the main unit, a dedicated trigger, pan head screws for securing the circuit board, a selector detection sticker, and several stickers.

First, let's take a look at the main unit.

The most significant changes are that the sector gear timing detection has been changed from a physical switch to an optical sensor, and the trigger switch has been changed from a detection switch to a push-button switch.

Were there many people who broke it like I did? This is a great change.

This is a close-up of the trigger switch (optical sensor).

The connector is a large T-type connector and a 40A fuse is installed.

The circuit board has a two-layer structure and is connected by a connector, so it should come off, but it was stiff, so I got scared and stopped.

When disassembled, the FCU has ports that can send signals and power to external devices other than the motor. Therefore, these can be used to control electric magazines or hop-up chambers with integrated tracers.

Next, we will perform an integration check.

New Leviathan integration confirmed.

First, as instructed in the manual, attach the selector detection sticker to the selector plate.

In the case of VFC, the seal will be narrow. Also, the VFC selector plate cannot be removed from the gearbox (because the bearings interfere), so you have to be careful when applying it.

Next, I mounted the circuit board into the gearbox and assembled the trigger (the trigger was the same as the old model).

As expected with VFC, the trigger doesn't reach the leaf spring, so careful adjustment is necessary. The switch shape has been changed, making it much easier to adjust.

Next, let's assemble the sector gear.

I checked to see if the sector gear was making contact with the optical sensor, and coincidentally, there was clearance without shims when using the VFC ver2 gearbox and SuperShooter gear combination.

Now that the mechanical checks are complete, we will verify that each sensor is functioning correctly.

Similar to the previous model, you connect it to the app and check the operation of each sensor on the check screen.

The process is complete once you've confirmed that all the sensors are responding after moving the gears and triggers. At this point, since the sensors have been changed to optical sensors, a sensor calibration procedure is required, which will be explained later.

There are also tasks and checklist items that are not covered in this article, so we strongly recommend that anyone performing the installation carefully read the included instruction manual before starting work.

This completes the initial check of the FCU.

If I were to write about the events up to this point, it would take one article, but I was shocked when I damaged my old Leviathan at 1 AM when I was sleepy, so I reordered it and waited for about 3 days, then the product arrived and I noticed that some accessories were missing, so I negotiated, waited 2 days for the accessories to arrive, and then it took almost a week to check everything, which made me quite anxious.

It was 100% my own fault, but it was very difficult.

The moment the trigger switch broke seemed to unfold in slow motion, and I followed the flying fragments with my eyes.

EveryoneWhen adjusting precision equipment, avoid doing so late at night when you're sleepy, and take breaks if your concentration starts to wane.

Next time, I'll finally introduce how to assemble the gearbox.