Modified Go Devil 29 build thread

Alright, I'm not gonna lie. Sanding more than 6" into a 29mm body tube is a pain. I thought I could use one of the die grinder extensions I have, but they were all just a tad too short. It would have been easy that way, so...boo.



So, the power tools got ditched. I taped some sandpaper onto the end of a long piece of PEX tubing and used that instead. It worked. Not perfect, but I think it's good enough.



This photo is pretty tough to decipher, but the non-shiny part is the inside sanded part of the body tube where the 3d printed recovery harness mount will go.



After I got it sanded, I used the end of the PEX tubing to slop some epoxy in the body tube. The masking take worked very well to keep things clean. I pushed the retainer mount into place from the bottom using another piece of the PEX tubing that I marked the appropriate depth on. The mount weighed just enough that it'd move if I held the rocket vertical. So, I checked its placement and laid the rocket flat to dry.

My hands got a little messy pulling the tape off, but the inside of the body tube stayed really clean.



I also put the nosecone on a drill and spun it around to sand the tip. Stock, it's square with maybe a 3/32" flat spot. It's nicely rounded now.

The last two things that needed epoxy were the coupler tube and the recovery harness retainer in the nosecone. For the coupler, it's going to live attached to the body tube since it'll have the avionics clinging to it. When I test fit the coupler, there was a little slop in the fit (the coupler was slightly too small). It was just enough slop that I could change the alignment of the coupler relative to the body tube if I pressed on the coupler one way or the other. I really prefer my body tube and nosecone to be perfectly aligned, so I added very thin lines of medium CA to the outside of the coupler. I let it dry then did a couple quick passes with sandpaper to make sure the fit was just how I wanted. The CA held the coupler in place while still allowing plenty of epoxy to bond everything.



The 3d printed recovery harness retainer in the nosecone is probably overkill for this sized rocket, but it only weighed a few grams (maybe 5 total with the epoxy). Here's a view down the nosecone with it in place...swimming in epoxy.



That's it for the epoxy! Avionics, harness stringing, and finishing is all that's left. Getting close!

P.S. I also finished the design for my rocket for this quarter's geometric rocket challenge. I'm 3d printing my rocket. Here's a sneak peak.

GrouchoDuke said:

Thanks!!

EDIT: I'm toying with designing & making my own GPS tracker to fit in a 29mm coupler tube using a LoRa telemetry radio & small UBlox GPS. I'm kinda hoping someone else will do it first & make it available for cheap.

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Working on it...

Adrian A said:

Working on it...

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Does LoRa require a radio license? I don't speak ham yet and don't plan to for a while.

That's great to hear, Adrian!

For licensing, it depends. If it uses 900MHz, then no. If it trons in the 430MHz range, then yes. My personal preference would be for a 900 radio since it uses a smaller antenna (even though I'm a ham). If the baud rate is set low enough, the range should be awesome on either one.

No pictures today, but here's an update on the project...

I got my order of Top Flight parachutes in. I have a 12" and 15" thin mil that I'll mess around with. The 15" will be really tight for the space I have left in the nosecone, but it might work.

I messed around with the friction fit of the nosecone for way too long. I used CA to build small ridge-shaped bumps to use to set the friction. I could get a separation in the 3 pound range or one in the 15lb range, but getting anything in between just didn't want to work. The upper range friction also seemed to be unpredictable. I didn't want the separation force of a 2-56 nylon screw, so I ordered some Plastruct 0.060" styrene rod to use as a shear pin. I haven't done calibrated tests yet, but it feels pretty good in a simple hand pull test.

I had the av-bay assembled and ready to fly, but my prefecture's monthly launch was rained out (again...yay for desert rain). I've since pulled apart the electronics and coated everything (except the inside of the EasyMini's baro chip) with Corrosion-X. My av-bay isn't perfectly sealed since the recovery harness Kevlar goes through it, so the Corrosion-X is for some added protection. The electronics all fit in the 25mm diameter x 65mm tall 3d printed sled with about a mm to spare on all sides. The load out is: EasyMini, TBeacon, RTFQ Micro Ublox M8N GPS, Featherweight magnetic switch, and a 1S 150mAh lipo battery.

I'm going to do some separation tests with the styrene rod shear pins sometime in the next couple weeks. My next flight opportunity is March 18th. Somebody send some good weather!

After more than a year with my Modified Go Devil 29 sitting on the shelf, I finally flew it. Sadly, the recovery harness broke when the ejection charge went off. The nose cone & chute floated down together. The body tube/tail section/avionics core sampled about 6 inches into Jean Dry Lake.

I did a quick post about it over in the "What did you do rocket wise today" thread. Which generated the question:

woferry said:

So what went wrong? My Go Devil 38 core-sampled 2 Saturday's ago...

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I've been chewing on it a bit. I can share the story of its life so far, but I don't have any hard evidence of why it broke.

I finished the rocket a while ago, but other rocket priorities have kept me from flying it. I built the rocket as a single deploy setup with a 3d printed avbay and fiberglass nosecone coupler on the body tube side of the rocket. The nosecone houses a 15" custom lightweight Spherachute and the Kevlar harness made from 300# Kevlar from Apogee. I ground tested it a couple months ago with a vinyl tube 0.35g charge. There isn't much room for wadding in the nosecone, so I just put a couple squares of Estes toilet paper-type wadding in there.

When the 0.35g charge went off, it was very energetic and it cut the Kevlar in half. It's tough to tell from my video if it broke when the charge went off or when the nosecone hit the end of its leash. There were a few black marks on the harness, but nothing major. The break happened near the body tube side of things, so I was able to cut off some of the harness and retie it to the Y harness glued to my body tube.

A month or so later, I did a test with a vinyl glove fingertip and 0.25g of BP. That was considerably less energetic, but the nose cone still popped off. I decided to not fly with that and then tested it with the same 0.2g vinyl tube charges I've been using on my 29mm I-motor record rocket. The ground test looked perfect, so I flew the Go Devil 29 with a 0.2g vinyl tube charge.

The flight was straight as an arrow. It simmed to about 2000' and the CTI F59W was a nice first flight motor for it. As expected, the Eggtimer Quark fired the charge at what looked like apogee with almost no downrange travel. So, I don't think horizontal speed or bad ejection timing were factors. A second or so after ejection, I noticed that the chute wasn't next to the body tube. The nosecone and chute floated down very slowly and the body tube core sampled into the dry lakebed.

I have a few thoughts on it.

• This is the same Kevlar I use in my 29mm record rocket. I've noticed that it frays easily, but it's held up to a handful of flights & ground tests in the other rocket. It's pretty thin stuff, so with a little bit of fraying and the very close proximity of the ejection charge to the Kevlar maybe the Kevlar just can stand up to the ejection charge.
• Maybe my initial 0.35g vinyl tube ejection test did more damage that I noticed to the Kevlar. I just cut off the section that looked bad. The potentially damaged Kevlar maybe couldn't stand repeated 0.2g charges.
• Maybe the Apogee 300# Kevlar just isn't enough. A more tightly braided or heavier test Kevlar might be the answer.
• A better barrier between the ejection charge and the Kevlar would probably help. The way I built the rocket, I don't have room for that though. A mini-Nomex blanket might be a way to improve what I have.

The good news is that the rocket is still in great shape. It needs new avionics and a new harness, but everything else looks perfect. Gotta love fiberglass rockets. I was planning on an F flight for its maiden and then ramp up to H & I motors. 29mm min-diameter rockets are a little bit of a pain to get a flight computer, GPS tracker and battery to fit, but it's awesome how high they go on small motors.

This Go Devil 29 will fly again. I haven't decided when that'll be or with what avionics though. I have a TeleMini V3 that I'm trying to modify to work with an external GPS. That might be the way to go with it. I could also put the electronics in from my Vanish 29 (I designed that avbay to be interchangeable between these two rockets, but it has its own quirks to consider). I might also just build another Quark and Eggfinder Mini like was already in it.

I have a couple record attempts I'm doing this summer. Those will take priority over getting the GD29 going again. If all of that goes well, I'll plan on getting it ready to fly after the Vegas heat breaks in the fall.