Sunday, April 5, 2015

Holtville Launch - April 2015

This last Saturday was amazing at Holtville and here's some slow-mo evidence...

I completed three simple flights using only my 3D-printed V2 and all with progressively longer CTI Pro24 reloads.  I didn't risk an altimeter in any of them so all I have is my visual memory:
  • 2G 50F51 Blue Streak:
    • In all three liftoff vids I see some lateral wiggle on the rod so perhaps the integrated rail guide isn't quite long enough.  That's odd though because there seemed to me too much friction in the rail channel so I was planning to reduce the guide's cross section by a few percent.  Dunno.
    • Jittery liftoff above the rod so there's still not quite enough lead in the nose tip.  
    • The altitude was lower than expected and the 10 second delay about 4 seconds too long.  More on this below.
    • The landing was in some rock-laden dirt in the bowl and one of the fin bottoms broke.  It was still attached, however, so I just CA-glued it back on for the second flight.
  • 3G 60F50 Skidmark:
    • Even these tiny 24mm Skidmarks ignite instantly and are impressively loud!  Good titanium times.
    • I had shortened this delay to 8 seconds but that was still about 2 seconds too long.
    • The parachute fouled after eject but, surprisingly, there was no fin damage after landing in our bowl.
  • 6G 140G145 Pink:
    • The liftoff was most expeditious!  I sort of noted some pink shades in the flame from a distance but it's hard to tell unless you're watching slow-mo video of the liftoff.  :)
    • Because of the higher thrust and total impulse I left this third delay at 8 seconds.  The flight still ejected about 2 seconds after apogee and, upon watching that, it finally sank in that the uniform, 0.3mm high, radially oriented bands resulting from 3D-printing induce MUCH drag.  For the next print I'll try 0.2mm layers and that will take several more hours to print but should reduce the drag coefficient somewhat.
    • This flight achieved a surprisingly lofty altitude.  Darrel had packed the parachute for me using the burrito method so it popped cleanly at ejection.  Wind was building a bit so I had to walk to the north runway to retrieve the vessel.
    • Having landed on concrete that same fin tip broke once again and this time the top 1/4" of the nose tip chipped off.  This was OK because testing of this version zero design is a wrap and I'll move it to archive.
Apart from the issues I found over the four total test flights everything else worked surprisingly well.  The structural integrity of the airframe and shock cord mounts proved more than adequate.  I observed no melting from the casing heat or black powder ejection.  But, in addition to the modeling improvements I'd planned previously, I think I also need to edit the following:
  1. Remove the vented portion of the motor mount - this doesn't seem to be necessary for robust motor orientation and it just adds complexity, tail weight, and print time.
  2. I think I'll maintain the rail guide length on version 1 and decrease the cross-sectional size by perhaps 2%.
  3. In the Simplify3D slicer it's possible to vary print parameters by layer height.  As such I think I'll go with 60-70% internal fill from the glass plate to above where the fins meet the airframe to reduce the likelihood of damage upon landing.
  4. I think I'll use the same trick to beef up the nose tip and reduce it's tendency toward damage on concrete impact.
  5. I'll try 0.2mm layer height but this will increase print time on the airframe from ~15 hours to ~21 hours.  Longer print times mean more opportunities for print defects so reprinting would necessarily delay the time to v1.  Fingers crossed.
  6. I just realized I forgot a vent hole but the nosecone didn't pop off during ascent so I just lucked out.  Rather than modeling and printing a hole I think I'll cheat and use a drill bit.  
Onward and upward on the 3Dp tip!

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:
Neato.

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.

Saturday, February 28, 2015

The airframe printed but with issues

I had hoped the airframe would have sufficed for a test flight but there are some layer splits that would likely fail. As such I've switched slicers and it's reprinting for another 15 hours. :)

Friday, February 27, 2015

V2 nosecone... PRINTED!


I found a flaw in the source model only after printing (note that ring/gap near the top).  I've since fixed the flaw but this 8-hour print will suffice for test flights.  The airframe is printing in black ABS now now and should be done tomorrow morning.  Yay, printer.

Sunday, February 22, 2015

More OctoPrint goodness

It turns out that OctoPrint also provides a real-time preview of the GCode toolpath in the 3D printer:

The solid black line is the current bead in progress and everything else translucent is the previous layer.  Nifty!

Saturday, February 21, 2015

It's aliiiive!

I've struggled with a learning curve since Tuesday but, with perseverance (and significant assistance from Alex on the forums), I'm now up and 3D printing at home!  I started by sending just the motor mount from the full-size V2 to test motor fit. Oh and all the print data moves wirelessly thanks to the brilliant Octoprint!  More soon.

Sunday, February 15, 2015

Updated^2: Lucerne on 2/14/15 with M3700 viciousness

I finally got around to crunching some data so I'm updating this entry. Here's the video you might have already seen but go ahead and watch it again anyway  (:

I'm astonished and pleased to note that I experienced two Saturdays in a row of impeccable flying weather. Holtville and Lucerne were similarly windless and a comfortable mid-70s all day.  It turns out that I've had this CTI 6800M3700 White Thunder reload in storage since November 2009.  Oops... tempus fugit!  I was throughly committed to preventing additional aging so I packed only that necessary to fly this vicious motor in my trusty DarkStar Extreme.  I bonded the grains into the liner the night before but, despite that and getting to the lakebed by 8:30AM, I still didn't fly until 11:30AM.  I was totally on my own and was unable to shoot photos but Gerald Meux was LCO and he and I agree that must have been an ~10' flame during the blistering ascent.  I lucked out for once and dual-deploy put 'er down less than 1/4 mile away from the pad:
I couldn't get the GPS transmitter working for some reason so you'll have to take my word for it.  The ARTS2 (table, graph, motor analysis, CD) and Raven3 250G(table, graph) averaged to the following maxima:
  • Altitude, AGL: 15,846' (3.00 miles!)
  • Velocity: 1,792 fps (1,222MPH, Mach 1.1... really?)
  • Acceleration: 44.7 Gees (Raven3 = 54.4, ARTS2 = 35)
  • ARTS2 Motor Performance: 7065M3605
The RocSimulation predicted a mere 15,300' AGL so I'm very happy with that altitude.  I'm surprised by the velocity of only Mach 1.1 but that must be due to the short 1.8s burn time and 28.3lb liftoff weight.  Finally there's quite a difference between the two altimeters on acceleration. The ARTS2 maxes out at 50Gees so I'm inclined to believe the Raven3 with it's 250Gee max.  
     The December launch at Lucerne was cancelled due to rain.  Two months later there remained some photogenic puddles so that's one benefit:


Addendum: David Reese captured a liftoff shot and kindly shared the link to his Flickr site:
It's not quite a 10 foot flame as I originally thought (rocket - 8.5 ft.) but I'll take it!  And he caught a proof-of-recovery shot as well:

Thanks for all you do, David!