Monday, January 19, 2015

...and a UV-mapped render seems in order


I wanna fly it now!!

Initial V2 modeling complete

This morning I added a shoulder to the nose cone and a shock cord attach hoop that's smooth to reduce stress points:

I also built a rail guide by downloading the .dxf cross section from 8020.net and extruding a virtual rail within which I could bevel/extrude:

The larger hole of the three near the motor mount will be the Kevlar shock cord attach point.  I'll just tie a square knot or two in one end as an anchor and thread the cord up through the airframe to the nose cone.  The two smaller, opposing holes in the base are guides for the wood screws to retain the motor. Finally I improved the leading edge taper of the fins and sharpened up the bottoms to maximize adhesion to the heated build platform.

The airframe alone will require 15 hours to print at 0.3mm layer height or 25 hours at 0.2mm layer height (!) so I want to minimize the risk that the part will pop off before it finishes.

Sunday, January 18, 2015

Slice-a-rific

There are many free, open-source programs to slice 3D models into tool paths that can be used by a 3D printer.  I downloaded a installed a few this morning including CuraSlic3r and PrintRun/Pronterface. There's another package called Simplify3D that looks interesting, especially via this forum thread, but it's very steep at $140 and there's no trial version.  I've used Slic3r before at work but I think I'm liking Cura more now and here's the tool path preview of the V2's fin can and motor mount:

Teal-green is raft and support material, red is the model's exterior shell, green are inner shells, yellow is volumetric fill (10%), and blue are travel moves without extrusion.  Niceness!!

Saturday, January 17, 2015

Better living through additive manufacturing of a V2!!

Some of you know that I've been dabbling in 3D printing for three-ish years.  I ceaselessly admire the astonishing progress of garage-based hardware hackers using intellectual property from patents that have expired in recent years.  It appears that the masses using democratized technology continue to move far faster than the corporations that developed the IP in the first place!! One new startup, 3D Printer Works, arose from a successfully funded Kickstarter campaign.  I like their style and recently ordered their first product, The CreatorBot 3D, for home use:

And yes of course I upgraded to the pro package with dual extruders, a heated glass build platform, acrylic enclosure to prevent drafts, and the Raspberry PI with OctoPrint to enable WiFi printing. Who wouldn't?!
   With a nearly unparalleled prosumer build volume of 2,592 inand 1 ft. x 1 ft build plate I decided that my first home project would have to be a V2 with a 24mm motor mount to take the full range of Pro24 reloads.  This is the first rocket I've attempted to design in my go-to 3D package, Modo, and I'm very pleased with the initial version.  I started with V2 scale profile images from the interwebs and used them as background images in Modo.  I then added a cylinder and adapted the cross-sectional hoops to conform to the airframe shape.  I added edge loops at the fin root locations and extruded the fins directly out from the airframe.  The entire model below is previewed in Catmull-Clark Subdivision mode for maximum smoothness and that's the format I'll use to export the .stl files bound for equivalently smooth 3D printing:

That black feature in the center wireframe is a hypothetical Pro24 6GXL casing as a worst case motor length.  While CTI presently offers only 1, 2, 3, and 6G casings in Pro24 I do see 4, 5, and 6XL on both David Reese's Wildman West page and CTI's page so I'll assume they're forthcoming some day soon.  I still need to add features like the nosecone shoulder, shock cord mounts, and rail guide(s) but the exterior form exceeds my expectations and took only about 2 hours to complete.  I also used Modo's powerful and astonishingly versatile bevel tool to build both the vented motor mount and the interior walls of the airframe in a single operation set:

I plan to print with ABS that flows and extrudes reliably at 230˚C but its glass transition temperature hovers around 105˚C (221˚F).  NFPA specifies a maximum casing temperature of 200˚C for 160 N•s or smaller so this could be an issue.  ;)  As such I think that venting the motor tube inside the airframe will decrease the likelihood of structural failure due to motor casing heat.  If I observe melt damage I can always add exterior vents to the airframe and maybe I'll make them whistle while I'm at it.  For the first flight I'm just planning to use two diametrically opposed, wide-head wood screws and perhaps washers for motor retention.  Here's a top view showing the virtual 6XL casing in it's vented motor mount:

Once the model is finalized I also want to cleave it into pieces such that it can be printed in black and white using the dual extruders and according to the scale painting pattern so no painting will be required (and you know I LOVE painting!):

This first design will be 3" in diameter and 24.5" long.  At the limit I should be able to design and print a roughly 10" diameter V2 in four vertical segments.  More on this soon as my printer should arrive in the next two weeks. Yay, 3Dp!

Addendum: The site 3DPrint.com recently published this article on Steve Jurvetson who's advocating 3D printing for hobby rocketry for many good reasons.  He also gives a genial introduction to rocketry and finishes with some cool SpaceX stuff.  The revolution will be webcast!!

Wednesday, January 7, 2015

Happy 2015, Holtville!!

Hi, all, and happy 2015 to you as well.  Last Saturday was a stunningly perfect day for flying with 0-3MPH winds all day and all the way to the top.  Here's the second installment of my 240-slowed-to-480fps liftoff vids (full-screen HD and crank that audio please):

Go, GoPro!!  I can't believe how much downward force is exerted on those steel pads!  They're bouncing awhile after liftoff in several sequences.  Here are are some photos I was able to shoot between flying and moving the GoPro.  As you might have noticed in the vid I made two errors involving our equipment manager, Mike Caplinger, at this launch:
  1. I missed his 2-stage liftoff because he was prepping intently and then was ready all of a sudden and I didn't want to interrupt his launch sequence by asking him to pause while I ran over to start my camera.
  2. I left my K2045 alligator clips dangling underneath the motor.  It wasn't until later when he expressed vigorous concern with the damaged clips that I realized ignition exposure isn't as brief as I had once assumed.  In my defense the e-match leads were very short and others flew after me but I'll be sure to somehow secure them out of harm's way in the future, Mike.  
I had only one flight that day because of all the video, photos, and helping others but it was a doozie. A couple of years back I crashed my 4" Nike Smoke at Lucerne, my buddy Megan rebuilt its replacement entirely herself (I was hoping she'd do her L1 and L2 with it), and I've been sitting on this 1408K2045 for way too long.  My 1D mark IV shoots at 10fps so these two sequential liftoff frames are 0.1s apart:

The ascent was neck-snappingly fast, loud, and straight with a nice 14+ second coast to apogee.  Unfortunately the 'chute fouled but, fortunately, it landed in some soft dirt and remains entirely intact and ready to fly again:

Darrel Kelley and I discussed the fouling and he recommended this Fruity Chute method to reduce line tangle so I'll try that next time.  Thanks for reading and cheers to another year of great flying weather at our new site.

Sunday, December 21, 2014

Updated: "Level 3 First Try!!" PDF

Hello, all, and happy holidays to you and yours.  In 2011 I had authored "Level 3 First Try" as an introduction to my TAP style and recommendations.  Just today I realized it needed some updating so here's v1f:

      L3-First-Try-v1f.pdf

Thanks for reading and cheers to burning vast quantities of AP in the new year accompanied by much rejoicing!

Sunday, December 7, 2014

Our first Holtville launch... 16x slower

I'm slow.  Only recently did I figure out that the GoPro Hero3+ I've had for a year features a 240 fps mode.  If I slow that down another 50% during editing I'm now showing hawt akshun at an effective 480 fps! Perfect for rocket liftoffs at our new launch site at Holtville Airport right?  [Watch on YouTube in full-screen, 720p with the audio cranked up for best results]:

My LOC Bullet finally bit the bullet with an old AT J420 Redline motor. Unlike a fine wine... Redline motors age the worst of any propellant I've yet encountered.  This failure was similar to an AT I366 Redline failure I experienced a couple of years back yet... only yesterday did I figure out that, upon ignition, the delay begins burning but the propellant takes several seconds to pressure up (even if one scuffs up the grain surfaces vigorously).  So, once it does lift off, there's little delay left and the ejection charge fires near Max Q thus shredding your recovery system, destroying your Comm-Spec tracker, and inexplicably hurling your nose cone several hundred feed away (despite a perfectly straight ascent).  Russ Sands spotted it right away yet I must have been in denial.  Yes I did find it positioned precisely as pictured:
I also flew my DarkStar Lite on a slightly less old AT H128 White Lightnin'. It's interesting to draw attention to the fluctuating thrust on the video.  Our new launch site is an extra half hour from my house but it's a cool, retired airport.  The concrete runways occupy only a small percentage of the land area on the site yet my DS Lite managed to miss the soft dirt by that much:
The motor retainer cap dented but still works fine... ahhhhhh, probability. I hope to fly an M6400 at the new site soon and really break 'er in!  Sound carries very efficiently there so ear plugs might be in order for the audibly sensitive.

ROCStock launch, Lucerne, November 2014

It was another beautiful day of essentially windless flying at Lucerne on November 8th.  I was mainly there to witness Scott Yeatons' Level 3 attempt but wanted to fly at least one rocket as well.  I've had this AT 2406K650 Blue Thunder sitting in my closet for awhile now but only my trusty Em-Sem-Fity 98mm minimum diameter vessel seems compatible.  This "coffee can" motor shot is probably as close as my blog will ever get to rocket porn:
Second time was a charm and Em-Sem-Fity flew well on the "Kay-Sikz-Fity" despite the first igniter burning yet somehow failing to ignite the motor; that never ceases to amaze me:


Here's the Raven 2 graph (click image for enlarged version):
 
[Tabular data here] Peaks... V: 548MPH  A: 10.4G  Baro Alt, AGL: 6,113 ft.  It was a clean flight that, shocker, landed about a mile away 'cause that's how I roll:
I  must also commend Scott Yeaton for a picture-perfect level 3 prep, flight, and recovery on a CTI 5506M1230 Imax:

Thanks also to Scott's other TAP, Kurt Gugisberg, because he rocks and I very much enjoy working alongside him.  Yay, another great launch!

Laster Blaster 2014

It's time to catch up on some blogging.  In my defense I've been moving more toward Agile or Lean Test development at work and both methods value "functional [stuff] vs. documenting [stuff]."  So I'm valuing flying rockets more than documenting them but I still need to complete the documentation portion some day.

Sadly our last launch at the Plaster City site was on November 2, 2014.  The FAA claims that we never should have been allowed to fly at that site yet they managed to make that mistake for a decade.  I'm not buying it but that's my uninformed-conspiracy-theory opinion.

In any event I did have two quick, fun flights to mark the occasion.  I flew my Aerotech Arreaux on a CTI 56F120 Vmax.  I'm sure it seems like sacrilege to fly one vendor's motor in another's famous rocket design but the Arreaux is the only rocket I had that was light enough with a 29mm mount.  For some reason the F120 chuffed a couple of times and then slowly ascended.  Luckily I had shortened the delay to like 5 seconds or something so I got it back safely.  I also flew my DarkStar Lite on a CTI 168H410 Vmax for the second neck-snapping flight and it was just as fun as the first.  I realize this picture is boring but it does sort of prove that I was there... kind of like the moon landing photos:

[I have no doubts that we visited the moon by the way and was merely prodding those conspiracy theorists]
With that we bid you adieu, Plaster City, and look forward to our new site at the now retired Holtville Airport east of El Centro.

Sunday, October 12, 2014

Der Red Mix mark II Skidfest at ROCTober 2014

After talking it up for over a year I finally flew my scratch-built Der Red Mix mark II on a full complement of seven burly Skidmark motors (as always switching to 720p in full-screen mode is the shit):

A formidable liftoff featuring loud, flaming titanium granules:

And notably angled ascent:

I arrived at the lake bed later than I'd have preferred but the conditions were perfect all day with light, intermittent wind and perfectly clear skies.  I had prepped all the electronics two months ago so I only needed to load up the seven Skidmark motors, set up the CD3 ejection system, mount the Flip Mino camera inside, and button everything up.  Upon checking in with the RSO he seemed confident in my design and flight plan but cautioned that the far pads were angled away from the spectators.  He specifically asked me not to adjust the rail to a more vertical orientation (and that's some foreshadowing).  Kurt Gugisberg was out at the pads and helped me to get the 30.5 pound rocket loaded up on the rail.  I powered up the two Ravens, installed the air-start igniters, started the Flip camera, closed the electronics bay door, installed the central motor ignitor, and was ready to go.
     The ignition of the central CTI 2010K675 was instantaneous as expected and, at a 7.3:1 thrust-to-weight ratio, the ascent was expeditious.  Now normally I would have set the launch angle at 1-2 degrees from vertical because this rocket is incredibly stable and there was no wind.  Instead the angle I was asked not to change was closer to 4-5 degrees from vertical so the angle you see it the picture above is real.  The one second air-start gaps I programmed into the altimeters seemed a bit long but the sequential pairs of 543I297, 258H180, and 176H123 Skidmarks otherwise popped as expected.  By the time the H123 pair fired the rocket appeared to be approaching a horizontal flight path but, in reviewing the onboard video above, that was mostly an optical illusion.  From the ground it also appeared that the ejection was 3-4 seconds too late but the video once again proves that wrong and the 'chute popped right at apogee.  Unfortunately the initial launch angle essentially lobbed the rocket on an arc rather than straight up so that extra velocity at apogee served to zipper the top of my rocket rather severely.  I can repair it but, from now on, I'm trusting myself to set the optimal launch angle. Once again DRMII stuck the landing:

Here's the zipper damage from the energetic ejection (Grrr...):

And here's the interesting thrust curve showing acceleration surges from the four motor phases in red on the left of the graph:


The altitudes from the Raven 2 (tabular, graph) and Raven 3 (tabular, graph) only differ by 10 feet (!) and average to 4,483 feet above ground level.
     So I'll repair the damage, shorten the air-start delays to 0.1-0.5 seconds, and fly DRMII again soon with a K815 Skidmark in the center. I'm not yet sure of the outboard motors but they'll likely max out the motor tube lengths.  Thanks for reading!