HS Produkt VHS-2 Airsoft Replica Build [Part 3: Grip and Fire Controls]

Okay, so now we get to a real pain in the ass part of this build: the grip, trigger, and fire selector.

 

The grip and fire controls are comprised of the following parts:

• Grip (housing)
• Trigger
• Trigger PCB button
  
• Trigger switch mount
• Trigger spring
• Rotary potentiometer
• Rack
• Pinion x2

As you may have figured out from that list, the trigger just activates a PCB button. The real meat and potatoes of this fire control group is the fire selector. We're spinning a rotary potentiometer to select the firing mode, but this introduces challenges. 

Namely, I can't just hook up a potentiometer to the selector switches themselves. This would employ two potentiometers that are not synchronized (one for each half). There are rotary pots that allow a keyed shaft through the center, but this requires more machining than I'm capable of doing with my current setup. 

The solution, of course, is a rack-and-pinion:

Imagine another pinion sitting between the trigger and that pinion on the potentiometer. This translates the rotation from the fire selector downwind to the potentiometer, allowing an Arduino to pick up the position. Also imagine a PCB switch on that little shelf in front of the trigger - that translates trigger movement into a readable position as well. Clever, huh? Big shoutout to janssen86 on Thingiverse for the parametric helical rack and pinion model he made, though I did modify the hell out of it to fit in the grip and to not be helical. 

I printed the rack and pinion out of Dr.3D ABS-like resin, which I have been VERY impressed for at the price (it costs about as much as normal UV resin, but comes in 500g bottles instead of 1kg).

 

That's it for the grip and fire controls. Took far too much effort, too many re-prints of tiny resin parts. See you next time for the lower receiver. Worth noting, there will possibly be a significant amount of time before the lower receiver part is published - I have to do more test fitting prints, which means more hours into printing parts destined for the garbage can. I have queued posts to release once per week to prevent this from being too bad, but if you're keeping up with the project, just be aware.

-Craig, ETW

HS Produkt VHS-K2 Airsoft Replica Build [Part 2: Upper Receiver]

Alright, with the barrel assembly done, now it's time to do the rest of the upper receiver.

I split the upper receiver into four parts due to the size - two for the top rail, two for the actual upper receiver body. 

The longest piece of this assembly is 300mm. This would unfortunately end up being slightly tool tall to print on the Ender 3, so I had to take... action:

I also have a Creality CR-10S5, which is an absolutely enormous printer - so enormous that it prints everything poorly unless I have it print at a snail's pace even after hundreds of dollars of upgrades, so it's mothballed. I decided to take the Z axis extrusions and lead screw off to put on the Ender 3. The E3 can't travel all the way up the new Z axis due to the cable loom length, but I'll make an extension later. It's long enough for this part, at least.

Printing the rear receiver half was much simpler, as it's only around 150mm long.

The extension to the chamber block is now serving part of its purpose - to affix the rear end of the barrel assembly to the upper receiver using two M3x8 screws. There is a slight protrusion on the back to lock the upper into the lower - more on that later.

And there it is, the upper receiver all printed. The gap between the two rail sections is an unfortunate result of stacking tolerances - luckily, these aren't critical, but I will probably end up replacing the top rail with an adjusted version later. I haven't started the charging handle yet because I may be having part of it machined out of aluminum for me, as 3D printed options for the "knuckle" will probably end up being too fragile long-term.

So yeah, upper receiver's all done. On to the grip and fire control group. Next time!

-Craig, ETW