Something a little different....

Discussion in 'Rocketry Electronics and Software' started by Blackfly, Mar 30, 2012.

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  1. Mar 30, 2012 #1

    Blackfly

    Blackfly

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    Some time ago, there was some discussion about the survivability of barometric sensors & altimeters. A few comments were made suggesting that High G's will shred electronics, and high pressures will bust barometric sensors.
    Though I'm sure it applies in some cases, it didn't in this one.

    I'm happy to say that Entacore Aim USB altimeters successfully and repeatedly deployed the recovery system in a large projectile, which was fired from one of the worlds largest pneumatic cannons. This was very much a rocketry project, but with a little air pressure used instead of a commercial motor. Here's the rough details:

    Project: the "SABOT-CAM"

    Client: Discovery Channel, "Punkin Chunkin World Championship"

    Objective: Capture the perspective of a pumpkin, in HD-Video, as if you were shot from the worlds biggest pumpkin cannon. No CG, but real footage from a camera carrying projectile. The projectile must travel the same distance as a competition pumpkin(4500' downrange), and capture both front and rear views, from muzzle to ground.

    I'll let the pictures do most of the talking:

    P Thompson SABOT1.jpg
     
    Last edited: Mar 30, 2012
  2. Mar 30, 2012 #2

    Blackfly

    Blackfly

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    Initial CAD drawings and Vectorworks renders:

    P Thompson SABOT3.jpg

    P Thompson SABOT2.jpg

    P Thompson SABOT11.jpg
     
    Last edited: Mar 30, 2012
  3. Mar 30, 2012 #3

    Blackfly

    Blackfly

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    CAD Renders of flight concept, showing the projectile nested in a SABOT, within the barrel, and exiting the Muzzle:

    P Thompson SABOT4.jpg

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    P Thompson SABOT9.jpg
     
  4. Mar 30, 2012 #4

    Blackfly

    Blackfly

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    Flight & recovery renders:

    P Thompson SABOT10.jpg

    P Thompson SABOT12.jpg

    P Thompson SABOT13.jpg

    P Thompson SABOT14.jpg

    P Thompson SABOT15.jpg
     
  5. Mar 30, 2012 #5

    Blackfly

    Blackfly

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    The Build:

    P Thompson SABOT16.jpg

    P Thompson SABOT17.jpg

    P Thompson SABOT18.jpg

    P Thompson SABOT19.jpg
     

    Attached Files:

  6. Mar 30, 2012 #6

    Blackfly

    Blackfly

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    Fin Can & lower gimbal receiver:

    P Thompson SABOT21.jpg

    P Thompson SABOT22.jpg

    P Thompson SABOT23.jpg

    P Thompson SABOT24.jpg

    P Thompson SABOT25.jpg
     
  7. Mar 30, 2012 #7

    Blackfly

    Blackfly

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    Camera Domes, SABOT thrust ring base with casing runner hinges, completed projectiles in sabots. In the last photo, you can make out the GoPro camera gimbals on the table. These were modular units that fit in either the nose or the tail of the projectile, and contained a motorized tungsten gyro. The cameras were mounted on a free spinning axle, which allowed the gyro to counter the roll of the projectile, regardless of its actual roll rate.

    P Thompson SABOT26.jpg

    P Thompson SABOT27.jpg

    P Thompson SABOT28.jpg

    P Thompson SABOT29.jpg
     
    Last edited: Mar 30, 2012
  8. Mar 30, 2012 #8

    Blackfly

    Blackfly

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    The electric winch, used to draw the projectile down the 100 foot long barrel. As the projectile/sabot combo was about 44" long, it had to me muzzle loaded into the cannons; most of the breeches at the "punkin Chunkin" were only about 14"X8". We shot a loose bale of synthetic 1/8" winch line out the barrel, then attached it to the rear of the sabot. With the winch secured to the breech, we used a cordless driver to power it, drawing the sabot smoothly and quickly down the long barrel.

    P Thompson SABOT30.jpg

    P Thompson SABOT31.jpg

    P Thompson SABOT32.jpg
     
    Last edited: Mar 30, 2012
  9. Mar 30, 2012 #9

    Blackfly

    Blackfly

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    ROAD TRIP!!! Toronto to Delaware. 9 hours, plus a 6 hour stop at customs in Lewistown, as US Border Agents gave us a thorough, but friendly inspection....

    P Thompson SABOT34.jpg

    P Thompson SABOT36.jpg

    P Thompson SABOT39.jpg

    P Thompson SABOT35.jpg

    P Thompson SABOT38.jpg
     
  10. Mar 30, 2012 #10

    Blackfly

    Blackfly

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    Arriving at the Pumpkin Chunk and meeting Alan Duckett, designer, builder and owner of "Mac Daddy", an incredible pneumatic cannon with a fully hydraulic control & breech system. He was one of the nicest fellas we've ever met.

    P Thompson SABOT40.jpg

    P Thompson SABOT41.jpg

    P Thompson SABOT42.jpg
     
  11. Mar 30, 2012 #11

    Blackfly

    Blackfly

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    Load'n her up!

    P Thompson SABOT55.jpg

    P Thompson SABOT60.jpg

    P Thompson SABOT43.jpg

    P Thompson SABOT56.jpg

    P Thompson SABOT44.jpg
     
  12. Mar 30, 2012 #12

    rockets4kids

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    So, when do we get to see the video? ;-)
     
  13. Mar 30, 2012 #13

    Blackfly

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    OVERPRESSURE SHRED!!! The first shot, which we guessed the barrel pressure of(Beer + Ballistics Physics = Moon Shot), left the barrel at a sabot shredding velocity. The Raven II altimeter, used for data-logging only, showed 220 G's.

    There was such a large volume of air behind the projectile, that as it left the barrel it turned about 140 degrees counterclockwise; possibly due to the huge margin of stability and large aerodynamic drag of the ring tail.

    The sabot had also snagged an inner seam of the barrel, causing the shear pins to prematurely break; separation occurred just outside the muzzle, and the chutes deployed about 200' from the barrel, somewhere upwards of 800fps.

    As the projectile descended under chute, safely, the charges were fired by a single Entacore Aim-USB altimeter, at a pre-set altitude of 100 feet.

    P Thompson SABOT45.jpg

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    P Thompson SABOT47.jpg

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    P Thompson SABOT49.jpg
     
  14. Mar 30, 2012 #14

    Blackfly

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    Back to the drawing board....

    After completely rebuilding the #1 Sabot casing, I added eight shear pins to the carbon fiber airframe coupler, and bumped the separation charge up juuuust a little.....:y:

    If I could keep the airframe together, it would eventually straighten itself out and carry on its flight path. The Sabot was just a casing to guide it through the barrel, and with a little modification, I eliminated the chance of it snagging the seam.

    One of the camera domes was damaged, but other than that, she was perfect. The domes are 1/4" 5.5"X2.75" optical cast acrylic, (sourced from an ROV company in Cali), bonded into 5" CF tube and ground smooth. Aside from cracks, even heavy scratches buff out easily.

    My apologies to the folks in room 414 at the Comfort Suites in Delaware, for the sawing, drilling, sanding, cursing and horrendous smells of BP & epoxy coming from room 412, at 3 am...... My bad.

    P Thompson SABOT50.jpg

    P Thompson SABOT51.jpg

    P Thompson SABOT52.jpg

    P Thompson SABOT53.jpg
     
    Last edited: Mar 30, 2012
  15. Mar 30, 2012 #15

    Blackfly

    Blackfly

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    Second time around...

    On day two, lady luck shined on us. The wind had died, the weather was perfect, and we had all day to prep the Sabots and run simulations.

    The Cannon was dialled back to 40 psi(it's capable of over 300 psi!), and the #1 SabotCam from the previous days carnage was loaded down the barrel. At 5pm, we said a little prayer to the Pumpkin Gods and sounded the horn. seconds later, Alan pulled the valve actuator and set her free.

    P Thompson SABOT54.jpg

    P Thompson SABOT57.jpg

    P Thompson SABOT58.jpg

    P Thompson SABOT59.jpg

    P Thompson SABOT70.jpg
     
  16. Mar 30, 2012 #16

    Blackfly

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    The shot was perfect. The Sacrificial Sabot broke away from the projectile(albeit not as gracefully as my renders visualized), and the projectile carried on its course, following a beautiful ballistic arc down range. As predicted, the extra shear pins helped it stay together as it fought the rush of air from the cannon. Initially exiting the barrel on a cocked, 45 degree angle, she straightened out with a little tail flick, and raced down range.

    As the arc became a vertical arrow pointing to China, I prayed that all of the electronics had survived the shot, which later turned out to register 87 G's, and over 600fps, at a 46 degree barrel angle.

    A few screen shots from the on board cameras explain my goofy smile:

    P Thompson SABOT72.jpg

    P Thompson SABOT73.jpg

    P Thompson SABOT74.jpg

    P Thompson SABOT75.jpg

    P Thompson SABOT83.jpg
     
    Last edited: Mar 30, 2012
  17. Mar 30, 2012 #17

    Blackfly

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    Over the top!

    As the projectile arc'd over, it became apparent that the recovery was going to be ballistic and hard. To maximize the shot, I'd set the Aim USB altimeter events to 150 and 100 feet, agl. Now remember, this is not an HPR launch, but a sanctioned, insured event, with a secure, controlled range.
    As we watched , the projectile, which was worth thousands, picked up speed and raced towards the horizon. Fortunately, the big frontal area of the camera dome and the drag of the ring tail kept deployment velocity under 300fps, and I was quite comfortable with the capabilities of the Mil Spec mortar chutes I'd employed, which were purchased from Bob Fortune at Aerocon Systems.
    With phenomenal accuracy, the charges blew, just above the treeline, three quarters of a mile away. The huge charge detonated with a brilliant flash of excess, and the chutes snapped open, looking like two giant popcorn kernels popping. If you've never witnessed deployment that low & that fast before, its really quite amazing.
    The projectile landed intact under dual chutes(single deploy, of course), just beyond the 4500 foot marker in the field. Hoots and High Fives abounded as we'd witnessed the first successful flight and landing, of a camera from a pumpkin cannon. Now that seems a little silly, but its worth noting that a team of aerospace engineers had tried three years earlier, and failed on all four of their attempts. Just sayin'.....

    P Thompson SABOT77.jpg

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    P Thompson SABOT82.jpg
     
    Last edited: Mar 31, 2012
  18. Mar 30, 2012 #18

    Blackfly

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    Touchdown, lets do that again!

    The light was fading fast, but we managed to get another shot off before the range was closed. In the twilight, the flash of the deployment charge, which was the equivalent of about 40grams of FFFF, lit up the field, much to the pleasure of the thousands of drunken "Chunkin" patrons, who'd gathered to watch our final attempt.

    Later that night, Andrea, Alan and a good friend from Arkansas went out on a drunken scavenger hunt to retrieve the projectiles and all the Sabot parts from the field. Good times had by all, and a fantastic project which I'm proud to call my own.

    I'd like to personally thank the following people:

    Allan "Pedro" Duckett, for treating us like family and letting us play with his giant masterpiece called "Mac Daddy".

    Bob & Neil from MDRA & rockets magazine, who drove all the way just to give me ignitors, BP and a ton of encouragement. Thank you so much, and for the amazing photos and video you took. (ps... Neil, I've almost got your article done...:blush:)

    Bob from AEROCON SYSTEMS, who's chutes, switches & recovery gear were AWESOME. 16lb projectile, 800fps deployment, dual 60" chutes. RESPECT!

    David from ENTACORE electronics, whose AIM USB altimeters survived hundreds of G's, hundreds of PSI of baro-trauma, and one of the hardest deployments I can think of, and worked perfectly the next day. Thanks for all your support with firmware and flight profiling.

    Tom, from Cresthill farms, who helped us get back on our feet after a regrettable first shot.

    My better half Andrea, who drove through the night to get me there on time, and didn't complain when I dumped CF tube dust all over her make-up case during the hotel room rebuild..... Love ya' honey!

    For Darrel, because somewhere, out there, I know you're watching.

    Finally, thanks for a great forum, I look forward to going for my L3.

    Patrick

    P Thompson SABOT84.jpg

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    P Thompson SABOT91.jpg
     
  19. Mar 30, 2012 #19

    Wingarcher

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  20. Mar 30, 2012 #20

    WillMarchant

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    Congrats, Patrick! Great project and thanks for keeping us up to date!
    Best wishes,
    Will
     
  21. Mar 30, 2012 #21

    chadrog

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    Way cool! I lawn darted an Enticore USB 1.2 and it still works fine, great products. Will your project be part of the next installment of "Punkin Chunkin"?
     
  22. Mar 30, 2012 #22

    Blackfly

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    They used about four seconds of our flight footage for "road to the chunk", and thats about it. Not a bad gig, but it was definitely a freebie, once all the costs were tallied up.

    We did get an invite to a few more events, and made some great friends along the way, which was well worth the investment, IMHO.
     
  23. Mar 30, 2012 #23

    JimJarvis50

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    Excellent job. Won't be long before you're ready for this bad boy ...

    http://www.youtube.com/watch?v=M3Ia-o_PnDY

    We had a trebuchet at a launch a few months back. Very cool, but I couldn't figure out how to launch a rocket from it.

    Jim
     
  24. Mar 30, 2012 #24

    Fe Dude

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  25. Mar 30, 2012 #25

    Blackfly

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    Jim, thanks for the kind words; your immaculate CF airframes were a huge inspiration for the Sabot project, thank you.

    As for "VERA", well that's just plain cool. I'd love to know what he's using for a release valve. Some guys have been seriously talking about air starts from cannons, much like the old ARCAS variant launch system. Any thoughts on this?

    Patrick
     
  26. Mar 30, 2012 #26

    chadrog

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    You'll do a build thread I hope?
     
  27. Mar 30, 2012 #27

    troj

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    Patrick, not only an awesome job on designing and building that, but also a great job writing it up, so you could share it with the rest of us!

    -Kevin
     
  28. Mar 31, 2012 #28

    GDJ

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    Most impressive!
     
  29. Mar 31, 2012 #29

    JimJarvis50

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    Thanks Patrick. No idea on the release valve. Most of the associated discussion was on what cause the fire and how pumpkins might be encased to survive the launch (none of which would apply to rockets). My first impression was on how to get it pointed up.

    Jim
     
  30. Mar 31, 2012 #30

    Rex R

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    a few years back I heard of a similar oversize 'spudgun' in its design phase. this might be from the same folks. as I recall the that one was a 'light gas combustion cannon' using a burst disk to seal the combustion chamber And one at the muzzle so they could pull a vacume in the barrel. anywho that is what came to mind when I saw VERA.
    rex
     

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