Sunday, March 22, 2015

First flight of 3D-printed V2 a marginal success

I headed off to a local park this morning to test fly the 3D-printed V2 on a one-grain, Pro24 CTI 26E31 White Thunder:

It was tail-heavy so I predicted metastability and that's just what I got:

I've epoxied some lead shot in the nose tip and that's curing now.  Next up will be a two-grain, Pro24 CTI 50F51 Blue Streak.

Saturday, March 14, 2015

Holtville March 2015 launch report

It was another beautiful day in the desert although a tad windier than we're used to. I've been wanting to get my drone in the sky to shoot some liftoffs and that worked our rather dandily:
For some reason I forgot to set the controller to GPS mode so I was struggling to keep the thing where I wanted on the first few clips.  The 480 fps liftoff of Mark Treseder's Skidmark is quite nice although I think that slow mo is generally wasted from the air. In the future I'll probably switch to 720p 120 fps mode as a nice balance between spatial and temporal resolution.  Also, for the first time, I used Pocket Wizards to remote fire my DSLR while I flew the drone.  Shit's gettin' complicated!  Also Google rocks overall but I've officially switched from PicasaWeb to Flickr for my image posts from now on.
     I had only two flights but was pleased with both.  The first was the trusty 4" fiberglass Madcow Nike Smoke on an AT K1103X Propellant X reload for the 54/1706 casing.  I should note that AT included the wrong seal disk O-ring but Paul Snow saved me with a spare from his archive.  Thanks, Paul!  Thermite seemed in order so I ran with 2g which was a bit higher than the 1g/1000 N•s guideline.  Ignition was instantaneous according to Darrel who pushed the button for me (these two frames are 0.5s apart):
Darrel and I trekked my standard mile to retrieve the thing in a depression.  Even with line-of-sight on descent I think I would have lost the rocket without the CTI tracker:

Upon recovery I noticed that all of the nozzle's divergent section and most of the throat were missing:

Lucky for me no other issues arose as a result of this blow out.  I'm not sure if that was a faulty nozzle or perhaps the 4,500˚F Thermite caused a thermal gradient in the glass-phenolic nozzle and it shattered on pressure up.  Dunno.   The CTI 217H170 Blue Streak was next in the similarly trusty DS Lite and it landed in site of the launch pad:

Third time's a charm

Photos of 3D prints always make them appear far more coarse than they do to my eye but this third print is now ready to test fly:

This took 14 hours to print so, at some point overnight whilst I slumbered, that region near the top of the fins suffered from at least a one layer gap.  My extruder is running very reliably after cleaning it out so I'm not sure why that happened.  To patch it I simply ran a bead of thick CA glue around the perimeter and the airframe feels solid. Even before the test flight there are already things I need to change: 1) The bottom ring needs to be wider to ensure the motor retention washers do not hang out beyond the airframe edge.  2) I'm using #8 machine screws there but I think I'll switch to long #6 diameter equivalent wood screws and size the pilot ports accordingly. Right now they are very narrow so I ended up drilling out a bunch of material to fit the #8s.  Again this should be good enough for a test flight... which I should have done today at Lucerne but I awoke wanting to continue sleeping instead.  3) There's a slicer setting in Simplify3D that's either "inside out" or "outside in" for shell print order.  I'm quite certain I used "inside out" above so I'll try "outside in" next time and hope that it minimizes exterior noise.  Now it's time to edit that vid...

Monday, March 9, 2015

I fixed my 3D printer!

After a grace period of seeming success I managed to clog my left nozzle and even shear the right one off! I fixed the left extruder and now I'm trying, for the third time, to print the V2 airframe:
On a hunch I suspected that I've had a mild to severe clog in the left nozzle ever since I bought the printer.  I rolled the dice and ordered a tiny chuck and miniscule 0.38mm drill bit that cleaned 'er out and now I have yet to hear even a minor filament feed hiccup:

I just ordered a hand chuck and that, combined with a reverse-threaded extraction tool and replacement nozzle, should fix the right extruder.