VFC HK416 CAG AEG High Cycle Custom Gearbox Custom

Last time, I mentioned that the ball bearing in the gearbox broke while I was setting up the FCU and doing some test firing.

To briefly recap, the ball bearing in the spur gear of the gearbox has failed.

The outer laces are completely torn.

Let's take it out.

Upon closer inspection, the shape of the ball bearing retainer seems somewhat unsatisfactory. Even if it were made from sheet metal, the shape seems far too simple.

Because the retainer is made in a very simple shape to be easy and inexpensive to produce (making it difficult to drill holes for the balls), it seems to have fewer balls than its diameter would suggest. The number of balls is roughly equivalent to durability, so this is an important point to check.

In any case, all the bearings will be replaced, so I'll reassemble the gearbox.

Gearbox readjustment

We'll start by removing the bearings from the gearbox.

Since I wasn't going to use the ball bearings anyway, I figured it was okay to destroy them, so I pushed them from the opposite side of the picture with a punch and they came off easily.

I decided to use ORGA's high-precision metal bearings for the new bearings.

Personally, I was planning to go with Oiles Metal, which contains lubricating components rather than stainless steel, but I was half-asleep so I ended up ordering this on Amazon.

Let's compare it to the ball bearing that was removed.

It doesn't seem to have any particular problems, and there doesn't seem to be anything especially noteworthy about it.

Let's start assembling this right away.

After thoroughly cleaning the bearing area, I pushed it in with my finger, and it went in with just the right amount of load.

My initial thought was that I might need to attach a thick shim to the gear and then close the gearbox to press it in, but that doesn't seem to be the case.

Incidentally, I used Loctite's high-strength threadlocker for bonding.

Loctite High-Strength Threadlocker 263
I think a high-strength threadlocker is a good choice because you probably won't need to remove the bearings very often.

Leave it like this for a while and it's done.

This is where things get complicated, but since we've changed the bearings, we'll have to redo the shim adjustment.

While adjusting the shims, check to make sure that the left and right bearings are not misaligned.

I turned the gear by hand and it seemed fine. By the way, lubrication is even more critical with metal bearings than with ball bearings, so I strongly recommend applying grease thoroughly to the bearings.

All that was left was to assemble the gearbox as usual, but when I looked at the cylinder, I found that it was damaged and unusable because some foreign object had gotten stuck in it.

It appears that a piece of bearing debris got stuck in the mechanism.

I didn't have a suitable acceleration cylinder on hand, but I had a full-size stainless steel cylinder from Laylax, so I'll drill holes in it to make an acceleration cylinder.

First, mark the approximate location.

We'll use a rotary tool with a tungsten bit attached to process this.

I made a mistake with the marking location, so the processed part skips over the marking (I was working late at night, so I was pretty sleepy).

As expected, the cylinder was made of stainless steel and was quite hard, so the hole ended up being an odd shape. In theory, as long as the position is correct, the shape of the hole doesn't matter, so I'll just ignore it.

We will compare the hole positions for confirmation.

They're roughly the same, so I'll accept it.

After checking the airtightness of the newly made cylinder, I found that the O-ring on the piston head was also worn out, so I'll replace it with a low-friction O-ring from GAW.

Now we'll assemble the parts.

I didn't really like the shape of the tappet's fins, so I'm going to modify them.

I have a hunch that the tappet retraction timing is too long, so I'll shorten it a little.

Once you finish this, you're done.

In addition to this, I made a simple modification to reduce the difference in initial velocity between semi-automatic and fully automatic modes.

The modification itself is simple: insert the velocity adjustment ring as far as it will go, right up to the point where the spring is almost fully compressed. This time, I used GAW's internal piston velocity adjustment rings in 5mm and 3mm lengths, for a total of 8mm.

The logic behind this technique is illustrated in the following picture.

This is the normal movement of a piston.

In semi-automatic mode, the piston's retraction position remains relatively constant, resulting in a stable muzzle velocity.

However, in full-auto mode, the piston's retraction position is unstable due to the inertial force caused by the weight around the piston. The reason why the muzzle velocity is often higher in full-auto mode than in semi-auto mode is thought to be because the piston retracts more due to the inertial force compared to semi-auto mode, causing the spring to compress more.

As a countermeasure, the piston's retraction position is stabilized by making the spring tightly attached at the very edge of its range.

If the spring is tightly compressed, the piston's retraction will be forcibly stopped, so its retracted position should stabilize.

However, the thing to be careful about with this method is

This is how it works. If you do it wrong, it will break instantly.

Incidentally, this is a technique I often use to stabilize the valve behavior in automobile engines (to prevent surging).

If successful, this should reduce the difference in initial velocity between semi-automatic and fully automatic modes, and also reduce the variation in initial velocity during fully automatic mode. As a side effect, the piston's behavior should also become more stable, which should slightly help prevent piston crash in high-cycle firing.

Finally, although unrelated to the gearbox, I decided to replace the stock barrel because I was concerned about its precision and dirtiness.

I chose the BC Bright Barrel 275mm from Laylax as my new barrel. I simply had it in stock at home.

I'll modify the hop window as usual.

I like this barrel because it's relatively inexpensive, yet accurate, and made of brass, which is easy to work with.

Expensive items are often made of stainless steel or have high precision, making them difficult to modify further, so we don't use them very often (and they're expensive to begin with).

The readjustment is now complete.

FCU Leviathan settings

We'll now install the gearbox into the main body and set it up.

7.4V setting

I'll be looking for settings for a 7.4V LiPo battery.

After trying various options, I decided on the following values.

The ET-1 7.4V LiPo battery, Red Line (probably 30C) 1200mAh, operates at a fully charged 8.4V as follows:

It's a video.

VFC HK416 CAG AEG Re-customized Semi-automatic 7.4V

VFC HK416 CAG Re-customized Full Auto 7.4V

The data on the FCU looks like this:

It feels pretty good.

By the way, these are the measured values ​​for initial velocity and cycle rate.

The conditions are G&G Bio BBs 0.2g with a slight hop-up setting.

After firing several shots, the dispersion settled within 95.0-95.6 m/s.

Personally, I'd like to keep it under 0.9J, but I'll accept this as the absolute limit.

This is a fully automatic cycle.

It went exactly as planned.

Also, with high-cycle setups, the initial velocity tends to increase in full-auto mode, but it actually decreased slightly, so the adjustment was successful.

11.1V setting

Next, we'll look for settings that work with an 11.1V battery.

After searching around, I decided on the following values.

This shows how this setting works.

The battery is a DCI GUNS LiPo 11.1V 30~50C 1200mAh, fully charged to 12.6V.

It's a video.

VFC HK416 CAG AEG Re-customized Semi-automatic 11.1V

VFC HK416 CAG AEG Re-customized Full Auto 11.1V

The data on the FCU is as follows:

I'm glad I was able to beat my target of a 30ms cycle time for the cicada. Apparently the actual lock time is around 50ms, so I was aiming for 30ms.

Next, we'll measure the cycle time.

That looks good.

Most importantly, I was relieved that the initial velocity was stable.

This completes the initial stage.

Regarding durability, I ended up firing about 7,000 rounds while I was setting it up.

It doesn't seem like it will break anytime soon.

That settles the matter.

Normally, I would show the finished product and the recipe, but this post has gotten quite long, so I'll share it next time.

Please come along if you like.