The road to L2 is paved with practice. PSII trainer fleet

Discussion in 'Mid Power Rocketry (MPR)' started by Nytrunner, Jun 4, 2017.

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  1. Jun 4, 2017 #1

    Nytrunner

    Nytrunner

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    With the arrival of my L2 airframe, I'm continuing to work on my mid-power fleet in order to get familiar with preparing electronic recovery. I honestly figured I'd be further along by now, but a lengthy Blackstar Voyager build and a two week business trip in Alaska have slowed things down.

    IMG_20170429_131831178.jpg Nice to visit, not sure I'd want to live there. I'm finding out I'm kind of a flatlander.

    Adding to the pause in rocket activities was the tree-loss of my first PSII trainer BroncBuster II in March. It was a Leviathan built stronger than stock and incorporated a Chute Release with the intent of reducing recovery footprint on G's and H's. Definitely was successful until bad wind direction took it behind the nearby treeline. Lesson: Learn when not to fly!
    BroncBuster II
    I've already ordered a Scion to replace it, but that build'll have to wait until the rest of the PSIIs are done (maybe behind an undisclosed H-I flyer too) New Goal: Don't Lose AnyMORE of these until the fleet is complete!

    So! On to business......

    I present Vertigo II!
    IMG_20170528_242928278_HDR.jpg IMG_20170603_130543747.jpg

    An Estes Ventris with reinforced shock cord mounting, converted av-bay transition, nose weight adjustment, and rod/rail capability.

    Its basically fully constructed, and I'll be starting the prime/sand cycle. That should give me time to do system overview posts, some cfd analysis, and tell the story of the original Vertigo, the first "Big" rocket I worked on when introduced to rocketry! Plus, I'll post my journey into ground-testing deployment, and hopefully its first flight at Southern Thunder '17!

    I'm on a schedule to try and certify L2 at NARAM next year, and I consider this training fleet an important part of preperations.
    We'll see how things go! (with bonus pictures from Alaska because)
     
  2. Jun 4, 2017 #2

    MikeyDSlagle

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    Carry on sir. In pursuit of my level 2 as well.

    But know if Vertigo II meets an untimely end, I have a Ventris here if you need it. Last guy looking to buy it must've sailed too far and fell off the Earth. Haven't heard back from him.
     
  3. Jun 4, 2017 #3

    John Beans

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    Which release altitude have you used with your Leviathan? Leviathan was one of our test rockets during development...
     
  4. Jun 4, 2017 #4

    Nytrunner

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    Well I've discovered your plan now. Selling me all your PSII leftovers!

    First flight was 400, subsequent flights were 300. I would have been comfortable trying 200, but figured I'd play it safe at 3.

    It functioned beautifully every time for all my rockets that used it. My loss was totally because of wind direction and rod angle combined with where the owner located us in his field. (Wind blowing straight to the trees)

    The CR just meant it got stuck in 70' trees 500 feet from the pad instead of 70' trees half a mile from the pad lol.
     
  5. Jun 4, 2017 #5

    MikeyDSlagle

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    Drat. I've been compromised. This one is in better shape. Unopened.
     
  6. Jun 5, 2017 #6

    Nytrunner

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    you-cant-replace-5934b2.jpg
    Memorial day weekend was productive (plus my schedule gave me that friday off too!)
    I've started trying techniques to improve adhesion, so I peeled off the motor mount glassine to attach the rings and fins. I also glued in a Kevlar line that came with an Apogee av-bay since the 2" airframe doesn't leave enough room for an eyebolt.
    IMG_20170526_235839043.jpg IMG_20170526_235854520_HDR.jpg IMG_20170524_214608862.jpg

    The kevlar should give me some heat resistance near the end of the motor mount which will help since I can't get my hand down there to ductape the cord like I normally do.

    The fun part was tying the elastic to the kevlar a few inches below the tube mouth to combat zippering. Ended up using some sort of hybrid sheepshead/canoe knot by slipping it into place, cinching it at a good spot, then securing with the kevlar. I gave it some energetic tugs and am pretty confident it'll stay in place.
    IMG_20170604_153401729.jpg IMG_20170604_153417299.jpg

    Today's state:
    Filler primer!
    IMG_20170604_163302748.jpg

    Tonight's Alaska picture:
    The ground gets a lot closer to the plane than I'm used to.

    IMG_20170427_143310547_HDR.jpg
     
  7. Jun 7, 2017 #7

    Nytrunner

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    Between work and going to see Wonder Woman (excellent movie), haven't done any sanding or write-ups in the last couple days.

    So I will leave a question for anyone that cares to ponder:
    Where would you put the vent holes?

    650 ft/s cutplot showing pressure distribution. Black squiggle is roughly where the AV-bay volume ends.
    (~2116 lb/in^2 is atmospheric pressure; green with a hint of yellow)
    Vent Holes.PNG Transition bay.PNG
     
  8. Jun 7, 2017 #8

    John Beans

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    Don't forget you can vent that section to another section if the other section has a more favorable venting location. I kinda don't trust that any part of that slanted section won't have reduced pressure at speed...
     
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  9. Jun 7, 2017 #9

    BDB

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    That's a good idea, particularly in this case.

    I would have thought the pressure on the backwards transition would be lower too, but, unless I'm reading it wrong, the heat map is showing more pressure there. I guess that's why I'm not an aerospace engineer.
     
  10. Jun 7, 2017 #10

    Nytrunner

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    Excellent suggestion from both of you! I intend to try it someday, but, for this particular rocket, I don't think it's a good fit.
    The volume behind the bay will be subject to the motor's ejection charge, and the volume ahead of it will be where the main chute deployment charge is.
    Since the bay will be riveted to the forward section, there's a chance a tube could be fixed on the bulkhead to line up with a hole in the forward section, but then its vulnerable to being yanked or broken during deployment.

    I'll outline the recovery setup fully in the next post. Or I'll just prepare more flow studies at various speeds to chart the pressure variations in that area!

    It's puzzles like this that make me pretend I'm a mechanical engineer again (before I got shanghaied into Systems)
     
  11. Jun 7, 2017 #11

    dvdsnyd

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    Very cool flow simulation. What software do you use to model flow?
    Thanks,
    Dave

     
  12. Jun 11, 2017 #12

    Nytrunner

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    I use the toolkit from Solidworks '15. It's rather crashy, but if you're patient, it can produce some nice analytics.


    More about the AV-bay;

    I permanently borrowed some spent brass from y mo over the holidays. Since I don't predict this using more than about half a gram, I'm sure a .38 cartridge will be fine.

    I designed the lids using the aforementioned Sworks and met a local printer through 3Dhubs.com.
    IMG_20161227_214549577.jpg IMG_20170417_195030357_HDR.jpg IMG_20170417_195110536_HDR.jpg

    Chinese ematch fits through a tiny hole in the bulkhead, and a 10-24 rod keeps everything together. The wooden sled came from Apogee's 1.9" bay kit. It also serves nicely to transmit the loads directly through the sled instead of the bulkheads. The muffins keep me from going hungry.
    IMG_20170420_211711126_HDR.jpg IMG_20170604_153746400.jpg IMG_20170522_222855702_HDR.jpg IMG_20170603_132357249.jpg IMG_20170603_132341514.jpg

    Alaska pic of the day, someplace east of Anchorage. Maybe Chugcah Nat. Park.

    IMG_20170429_152344804.jpg
     

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  13. Jun 11, 2017 #13

    cwbullet

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    Pretty cool design.
     
  14. Jun 11, 2017 #14

    Nytrunner

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    Thanks! Unfortunately, I've designed myself into a corner. I didn't measure a 9V battery properly, so the sled is offset 1.5mm too short. I'll have to switch to a battery with a slimmer form factor.

    The good news is: When I do this for L2, I won't have that kind of problem in a 5.5" Bay!
     
  15. Jun 11, 2017 #15

    michigander

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    Here is a shot of 300 mah lipo next to 9 volt

    lipo.jpg
     
  16. Jun 12, 2017 #16

    Nytrunner

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    That's a great start for the thinking process!

    I'll probably run by hobbytown to see what they have for rc planes.
     
  17. Jun 12, 2017 #17

    Nytrunner

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    Yesterday's activities: Ground testing!

    I don't actually have the Stratologger yet, so I just used my E-launch controller.

    Although I have holes and brass strips for 3 shear pins, I'm only planning to use one at a time, and tested accordingly.
    IMG_20170603_131836512.jpg

    I calculated 1/4 gram, and decided to use half a gram to make sure everything popped. I may back that down a tenth so I don't wear out the tube.
    Or I'll just sleeve the interior reinforce that area. The pins sheared perfectly clean.

     
  18. Jun 20, 2017 #18

    Nytrunner

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    Busy week behind me, with some good progress on the transition-bay, painting progress, and some package arrivals.

    First a picture of the chute section. Now no longer filled with empty volume like the stock kit. Let's just say that it is no longer that color.
    IMG_20170611_161311632_HDR.jpg

    Because of my miscalculation in placing the sled, I ditched the threaded rod and glued in the mounting tab from the original apogee e-bay kit. It came with a couple weld nuts and these nifty thumb screws. The other lid is permanently epoxied onto the sled (is there even a way to non-permanently epoxy something?).
    IMG_20170618_205819483.jpg IMG_20170618_205846195.jpg

    With the threaded rod gone, I can effectively use the whole bay volume. Which brings me to my package: a stratologger! I powered it up with an E-flite 2s lipo and all the beeps check out. having an e-match installed in the main terminal gave a nominal 2 beeps, and the Datacap software is picking everything up fine.
    IMG_20170619_204707791.jpg IMG_20170619_204750728.jpg

    For flight, the battery will be zip tied down at a notch I cut into the sled. There's also a stop block glued down in front of it to prevent it sliding forward.

    Current plan is to do a vacuum ground test with a club member on Friday before Southern Thunder this weekend (if it doesn't get rained out...)

    Now for some history:
    The original Vertigo was built by three Nasa interns that were introduced to rocketry while on loan to help develop the USSRC's Robotics Camp. This is a good time to mention that these interns had never had any model/sport rocket experience whatsoever. Being engineering students all, and quickly getting bored with the standard spacecamp rockets (B's and C's) the interns trekked over to Hobby Lobby and bought the Biggest rocket they could find: the Ventris. And not settling for half-measures, they bought the biggest Motor they found also (Estes G80)!

    Having built the Ventris stock and wrapped masking tape around it to create this legit spiral paint pattern, they christened it Vertigo and planned a launch with some of their intern and crew trainer friends watching. Come launch day, they went to their location and read the motor paper. "1000' clearance? Well, we've got 800' in that direction.....that should be fine." Have you figured out where this is going?

    It launched, and went up. Really far up. And stayed up. And when it came back into view is floating.....into the lake? no Over the lake? Crap, into the woods....wait, was it over the woods too? Cue 45 minute tromp through the woods looking for Vertigo. With no luck, the interns retreated. But one of them decided to hop in his pickup and drive around the woods to see what he could see. There, hanging over the fence of a little water treatment building, was the rocket! Lessons were learned that day. When the internship ended, the intern that found Vertigo took it back home to Florida with him.

    But not before the intern in the photo below got a picture with it prior to going back home to Texas. Coincidentally, a few years later that intern would end up moving back to Huntsville as a full fledged engineer when he graduated. Fortunately he's learned a thing or two about rockets bigger than C since then.

    1008180_167112630134093_745933961_o.jpg
     
  19. Jun 21, 2017 #19

    Nytrunner

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    Further reading is giving me the impression that the LiPo I bought has a good chance of frying the stratologger. Time to scramble for a less powerful one! (Low mAh 2s batteries seem to be in shorter supply these days....)
     
  20. Jun 21, 2017 #20

    MikeyDSlagle

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    On some of my setups I put a 1.4 ohm resistor between the igniter and return (-) side of your altimeter. It should be enough in case your igniter shorts. On Danger Close I have the resistors mounted on the sled, I have several different ways I do it. I haD one setup with a terminal block in line with the return side. Using a LiPo I can insert a resistor, if I use a 9 volt I replace the resistor with a jumper.
     
  21. Jun 21, 2017 #21

    Nytrunner

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    See, this is why I'm doing all this Mid-power before jumping on L2 lol (or even complex 1's)

    I was noodling around with ideas for messing with the current the last couple of days. One was to use another ematch in parallel, but that's just as susceptible to a short.
    Another was to use a resistor on the same vein of what you're describing.

    If my battery is 800mah 30C and outputs 24 amps peak with a 7.4 (nominal) volts,
    That could translate into ~.31 ohms circuit resistance (Man, this forum needs a symbol palate)

    If I want to drop that down to <5A I'd be looking for a ~1.2ohm resistor counting the circuit resistance, or (like Mikey D) a 1.4-1.5ohm ignoring circuit resistance.

    The question that leads me too is, where the heck do I get 1.2/1.5 ohm resistors on short notice.....
     
  22. Jun 22, 2017 #22

    MikeyDSlagle

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    How short notice? I can drop some in the mail in the morning. Not sure how fast snail mail will reach you though, Priority would be a little pricey for a few resistors.
     
  23. Jun 22, 2017 #23

    Nytrunner

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    Well, if you're offering, I can't complain about shipping speed.:eek:

    There's also a little tropical system that's threatening to drown out Southern Thunder, so the criticality of flying on Saturday is dropping logarithmically.
    I may be able to borrow a 9v connector and wedge that battery in now that the threaded rod is gone, but I'm committed to learning how these LiPos work now.
    I'm imagining the possibilities of the resistor setup. With inline current reduction on the igniter, that 800mah battery could power a flight computer for awhile!

    Possibilities are electrifying!
     
  24. Jun 22, 2017 #24

    OverTheTop

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    Remember if you are putting resistors in series with the eMatches that they will have a voltage drop you need to consider. A 1 ohm circuit with a 1 ohm eMatch means the eMatch only sees half the supply voltage.
     
  25. Jun 22, 2017 #25

    MikeyDSlagle

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    Deleted
    Somehow I posted twice
     
    Last edited: Jun 22, 2017
  26. Jun 22, 2017 #26

    MikeyDSlagle

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    I think my batteries are 2 cell 480mah 30C, not 100% sure. OvertheTop is right but with charged LiPos I've never had issues with using resistors, or not using them for that matter. I'll get a few in the mail. I think the C rating has something to do with how much current it can put out before it experiences a voltage drop...something like that.

    And that little tropical system is heading right for me and my mail man doesn't really believe in that "neither rain, nor sleet, nor snow" nonsense, so that may slow the snail a bit.
     
  27. Jun 22, 2017 #27

    OverTheTop

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    Correct. It relates to the internal resistance of the batteries. A 20C (20 x capacity) means it can be discharged at 20 times its rated (hourly) capacity, so a 120mAh would be able to supply 20 x 120mA = 2400mA (which incidentally it could supply for approximately 60/20 = 3 minutes) at the defined (by the manufacturer) voltage droop on the output. It may actually supply more than this (with more associated voltage droop), so don't assume this is the actual maximum limit :). This is what it is specified to.

    I personally run 120mAh typically (sometimes 180mAh) 25C LiPos for the eMatches on my Raven and TeleMega deployment circuits. I use a separate battery to power the altimeter usually. That way a shorted eMatch does not effect the altimeter operation. Never had a problem with deployments. The batteries are quite small. If you need more pad time you could go for a bigger one on the avionics supply.
     
    Last edited: Jun 22, 2017
  28. Jun 22, 2017 #28

    Nytrunner

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    Great points.

    I'm not too concerned with the voltage drop after the resistor, since that's only on the firing circuit. The altimeter should still be getting full battery voltage for power.
    Hmmm....has anyone done a study on minimum firing current/voltage for Chinese e-matches? I may have to borrow a bread board and power supply.....


    And a sneak peak before the masking comes off

    IMG_20170621_230417595.jpg
     
  29. Jun 22, 2017 #29

    MikeyDSlagle

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    I think I have fired one with a AAA battery but not positive. I don't know off the top of my head what kind of amps those put out. It may have been a Christmas light starter I am thinking of.

    Got 6 resistors headed your way. That should help you experiment a bit. Didn't have as many as I thought I did.
     
  30. Jun 22, 2017 #30

    Nytrunner

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    Fantastic! Heck, I'd be fine with 2 or 3. (As long as they aren't toasted after each use that is)

    The google tells me this about AAA batteries (cue 'More you know!' shooting star):

     

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