Building a full-auto Nerf Demolisher Part 3: Getting that gearmotor in there and getting my 3D printing on

As the great sage Kool Moe Dee once said, “I go to work.” Welcome to part 3 of my retrospective on building my prototype full-auto Nerf Demolisher. At long last this was the phase of the build where I actually started to do some you know, building. I finally got my 3D printer in and I immediately cleared my weekend, and many successive weekends. First order of business was to get to a proof of concept – mounting a gearmotor in proximity to the semi-auto pusher system so I could see with my own eyes that this might actually work.

The first thing I quickly determined was 4 ways to mount the gearmotor poorly. It’s not that I wasn’t within a stonesthrow with my initial attempts, it was just that I needed to embrace the iterative nature of what I was doing. In other words I was about to have a lot of plastic scrap all over the place, a lot. The upside was, the shell of a Demolisher seemed to have just the right amount of space to mount the gearmotor, with the minor detail being the jam door already occupied that space. Something I conceded that I’d need to sort out, later.

“I now know 999 things that won’t make for a good light bulb filament.”

That’s probably nowhere near what Edison said, but whatevs. After some a lot of trial and error I finally came up with a solution that placed the gearmotor in (what I think was) the most optimal position. As soon as I got that sorted I noticed that the pusher was in no way aligned with the pinion. I’d planned to make a new pusher anyway and the discovery of the alignment issue was actually a beneficial thing since it allowed me to cut out some excess cycles out of the development process.

This thing sits here a little too nicely.

Show it to me from the back.

To be honest it was the quality of the pusher in the XSW kit that drew the most ire from me. It wasn’t necessarily the straightest piece of plastic I’d ever seen, seriously… it was straight up bent. I was actually looking forward to drawing up a new pusher. Into SketchUp I went and I did my best to remember everything Mr. Foreboard taught me in my High School drafting class. Yes his name was really Foreboard, very fitting if you knew the man.

After roughly 5 attempts I settled on version that I was willing to move forward with.

Now I break stuff.

I had made steady progress on my proof of concept, the gearmotor was successfully mounted and I had the pusher alignment ironed out. I already had an idea of where to start with the pinion gear settling on a 7 tooth design for both the pinion and the geartrain that drove the pusher. It was time to rig it up and see if the gearmotor was even gonna be able to move anything. Obviously it worked, but it worked a little too well. So much so that the force of the pusher snapping back after the pinion cleared the geartrain it eventually cracked then broke the post that the pusher rides on. Could be that this is the fate of all the Stryfes that have the XSW kit installed or it could be that I had the wrong screw holding the pusher collet down. Probably the later… for the sake of those running the XSW kit.

Oops. Could this be what will happen to your Stryfe if you have an XSW kit in it?

This lead me to revise the pusher collet, and the pusher throat to allow for more “meat” to surround that post. I had to make a version for a broken post, and later a version to protect that post.

This collet was meant to fit down and around what was left of that poor post.

Crisis averted, the collet and pusher back in place.

Don’t panic and carry a towel.

With a minor catastrophe behind me, I could finally move on to the balance of the interior shell work. It was now time to stuff some microswitches in there. With a hot glue gun at the ready a sudden rush of self-loathing came over me. Was a I really willing to splooge hot glue all up in the guts of my Demolisher? Was this inline with my builder’s ethos? Um no, no it was not. I have a 3D printer, that hot glue gun is now a paper weight. After some cleanup on the inside and a little dry fitting to guide the removal of any portions of the shell that might be in the way I had managed to workout some fairly solid mounting points for not only 2, but 3 microswitches. 1 for the trigger, 1 for the flywheels, and 1 for a pusher limit switch.

All your switch mounts are belong to us.

So there we have it. I’ve got that gearmotor in there, switches mounted in the cleanest fashion possible, and I was able to save my build development shell. Well I should say what was left of this particular shell after I tried melting away the gluedown between the outer and inner portions of the shell – that first Demolisher did not die in vain.

Pro-tip: you cannot melt the glue holding the outer and inner Demolisher shells together. Ask me how I know.

Next time.

Building a full-auto Nerf Demolisher Part 4: I bring balance to the Demolisher after printing a few bits a whole mess of scrap plastic.

2 Comments

2 Comments

  1. Hunter Dail says:

    Do you think you could print all the necessary parts so I can do this to my demolisher and maybe also give me a list of other things i need for this build??

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