problem

Quest Courier About ten years ago, my sister and I were launching model rockets that we built together. She built a Quest Courier. After some initial trouble with getting the nosecone’s parachite to deploy, I got it to work.

Too well.

The last I saw, it was floating over the freeway about three miles away

She’s still annoyed with me.

solution

could go buy a new kit, or write Quest asking for a replacement, but that’s not how makers work. Instead, I decided to use my hackerspace’s 3D printer. HeatSync Labs recently acquired an Ultimaker, and I recently acquired some modeling skill. Using OpenSCAD, I designed and printed a replacement nosecone for her rocket.

process

#### measure To make the nosecone fit and behave like the original, the nosecone had to meet a few specifications: - connector section must fit tightly in body tube - payload capsule must snugly hold a chicken egg. - outside diameter must not exceed launch rod standoff height


#### design OpenSCAD model My current preferred 3D design system is OpenSCAD, so that’s what I used to design this nosecone. I ended up making it modularly by generating several segments of hollow cylinders. Rather than create each segment individually, I built a parametric tube function. It takes a length and two radii, and generates a tube with those dimensions, tapering as necessary.


#### print printed nosecone After resolving some print issues, it came out great. I used our standard slicing profile, generated gcode, and started the print. The biggest issues I encountered were:

  • The tip kept melting. Playing with the extrusion head travel rate, I was able to reduce this effect. I still had blobs, which were easy to sand down, and some pits, which I filled with cyanoacrylate.
  • The connection at the shoulder was weak. The rocket tipped over, and the bulk of the nosecone just snapped off. Reprinting the lower piece with a thicker shoulder seems much stronger.


#### paint painted nosecone I applied two coats of spraypaint to protect the outside and make it look more like the original. When painting the new base, I didn’t take notice of which black paint I grabbed, so the top is glossy, and the base is shiny. Oops.


### lessons learned #### Measure carefully and plan ahead. After designing and printing the cone, it occurred to me that I might have made it wide enough to obstruct the launch rod. Thankfully, it ended up being just small enough to work. #### Make sure equipment is working The printer had a broken Bowden tube mount, so the filament easily lost tension, fouling the print. I discovered the broken piece after the third attempt failed, wasting several hours. After replacing the connector and adjusting the feed mechanism, the prints were much more consistent #### Pay attention Once the prints were completing, I ran into heat trouble. When reaching the tip of the cone, the plastic wasn’t getting enough time to cool, causing blobs and other unevenness. Increasing head speed only made the problem worse. After noticing that, I slowed it about an inch from the tip, allowing a clean, sharp finish.

conclusion

This project really helped improve my understanding of the 3D printing process, and my ability to use OpenSCAD. I’m really pleased with how it finally came out, and my sister is excited to be able to fly her rocket again.

Courier ready to fly again



Published

11 November 2012

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