Perhaps I’m just nostalgic, but I miss the engineering blogs and build logs that seem to be so scarce now. A lot of it has moved to short form, ephemeral social media, which doesn’t give readers the same depth of insight into the engineering process, or have the long term reference value of a blog post. Vlogs are similarly easier to digest, but lacking in searchability and the ability to carefully curate your words. I’ve tried blogging before, but I’m serious this time. Even if they’re not in depth as I would like, I’ll write weekly updates on what I’m working on, or explaining some physics or electronics concept that I think hasn’t been covered properly, or I just find interesting. If a post hasn’t come out by Sunday, please bug me about it.
This week, a status of my projects. As most of the people reading this will know, I’ve gotten pretty involved in Nerf over the last couple months. As you can see from this website. I love how this hobby is both very technology heavy, and not so advanced that one person can’t push the boundary of the state of the art. It makes for a great hobby for engineers and makers. I got a Tevo Tarantula 3D printer about a month ago now, which will be the subject of another post, and have been selling Open Flywheel Project flywheel cages, a few of my own designs, and reselling some other parts, on this site.
First up, the last project I actually completed, a Rapidstrike flywheel and pusher motor cover set for 180 motors. I think they look pretty good, and fit into the Rapidstrike aesthetics well, but they haven’t been selling for some reason.
The flywheel cover is also unique in that it’s the first one to use the screw from the stock Rapidstrike attachment rail to hold itself on, and so doesn’t require any adhesives. Fasteners are always better.
Also, barrel attachments. I prefer functionality over aesthetics, so wouldn’t actually use the Barrett 50 cal muzzle brake, but some people are into that. The smooth and fluted attachments look pretty good in my opinion, and are very practical in that they hold the Rapidstrike battery door on without needing any screws. There’s also a ring version for people who want a lighter and cheaper option and don’t care about aesthetics. Thanks to LordSquiggles and Eli Wu for the battery door retention idea.
I’ve been trying out PETG for flywheel cages, as there are some new motors, like the Titan Hyperions, that might run too hot for PLA cages. As many people have said, PETG doesn’t print as well on overhangs and bridges, as you can see here on the bore of a Hyperfire cage.
This happens a bit with PLA, but is much worse with PETG, and the long, deep bore makes it difficult to clean up with an X-Acto knife. That picture was with flat top to the bore, which came out a bit worse than the round bore.
It was alright on the front and back, where it can bridge across the flat spot, but since there are cylindrical cutouts for the flywheels, there’s no way to bridge across the center section. A teardrop shape, which was commonly used in early 3D printed parts for this reason, works better, but the bottom edge of the bridge in the center of the cage is still unsupported.
Today I’m trying some support material in the bore and see how that compares. Even though removing the strings only takes a few minutes, it will never leave as clean a finish as will come straight off the printer.
I also switched from the flywheels-down orientation that the cages were designed for to a flywheels-up orientation with support material inside the motor holes, with much better results. The bore in particular used to be fairly messy and needed cleaning with a knife, and now comes out totally smooth. I run my nozzle too close to the bed to compensate for not having automatic bed leveling compensation, which makes the bottom 2mm of my prints slightly bulged out. That used to cause a problem with the motor bearing holes being too small, which is better now that the prints are flipped. The bearing holes in the files are still about 0.8mm too small though, because so I have my own modified copy of each file with enlarged bearing holes, and a chamfer on the 20mm motor holes to keep the bulge at the bottom of the prints from being a problem.
OFP also released Cycloneshotgun cylinders a while ago, which I’ve been tuning in. Unlike the cages, where my printer prints holes too small, it’s printing the barrels too loose for a proper springer fit. Go figure. They have both full 3x 50 caliber shotgun, and 1/2 shotgun and half mega dart versions.
For my own designs, I have too many ideas and haven’t followed through on them. The Stryfe Battery Door I posted 6 months ago still hasn’t been test fitted and refined. The idea is to have custom sizes for specific battery sizes, so I made a poll to see what people use. Unfortunately they don’t fit flat in the battery compartment, so you have to turn them on their side, which makes the door stick out way farther. Maybe I can have the walls of this door overhang past the original door and make enough room to sit the batteries flat inside.
I’ve also been working on a fully 3D printed, scratch built bullpup blaster called Openfire. The idea is to make it modular, so people can easily swap in different flywheel cages or front ends if they want, and open source so people can easily design their own upgrades. I printed the flywheel cage and butt plate, and the design for the back half is pretty much done, consisting primarily of the Rapidstrike-style pusher and magazine well. However that piece is a 20 hour monolithic print, which I’m not sure I trust my printer with just yet. I’ll try to get auto bed leveling working first.
There’s a couple other ideas that have been floating around in my head, like an afterburner cage that goes on a Nerf barrel attachment point, and looks something like the Modulus barrel. I might call it the Long Range Barrel. The tricky part with this one is how to power it. One option is connecting it to the existing wiring of a flywheel blaster, which is a bit complicated to install, and leaves a wire sticking out of the blaster when you remove it. The other option is to have the battery and rev switch built into the foregrip on the barrel. That means it would quickly attach to any blaster, including a springer, but you have to remember to rev the attachment before you shoot, or you’ll jam the barrel. And of course there’s another barrel attachment point on the front, so you can do shenanigans like Coop. Let me know which version of this you would use. Here is the current state, without the sideplates.
Another project is the DIY chronograph. Put two infrared detectors and LEDs in a tube, measure the time between the pulses, and you know how fast it’s going. Simple right? You can even keep the hardware costs extremely low by using an audio input on a computer or phone for data acquisition. I started writing an Android app for this, before realizing that was stupid, and switched to a web app. It kind of works, but has some serious bugs. I also 3D printed a chrony tube that attaches to a Nerf barrel attachment, which is pretty cool. If the software ever gets working, I’ll get some circuit boards made with the infrared detectors and LEDs on them.
I was also thinking about a Rapidstrike SMG foregrip and front cover, but I have enough projects going on right now, as you can see.
And of course, there’s SmartRapidstrike. A select fire, ammo counter, OLED screen, lipo protection, burst fire, chronograph circuit board for full auto blasters like the Rapidstrike. I assembled one circuit board, the buck voltage regulator works fine, but the STM32F072 microcontroller doesn’t respond to anything. I may have killed it during my many attempts to get it soldered down correctly, or I may have messed something up with the circuit board layout. I’ll get to this at some point, but even once the electronics are done, the software is another huge task. Thankfully Josh Esbrook and Lachlan Sneff kindly volunteered to help out, though this was many months ago. We haven’t even really started, but I’ve changed frameworks like 4 times so far, and am currently planning on ChibiOS + uGFX + GoogleTest.
In other business news, I’m going to be stocking wire, battery connectors, and both MTB Hellverine and Foamblast Meishel 2.0 motors soon. Keep an eye out for them.
This ended up being a long post, but I did say it was long form content. It’s good to get my thoughts out there. Let me know which project you’re interested in, it helps me know what I should work on.