Turning the Nuclear Sledgehammer into the “Questionable Investment”

I  have had the rocksimfile for the rocket for quite a while, and made a few modifications

rocksim[5]

1) a few cosmetic changes to wings and fins to make them look ‘sleaker’
2) remove mid centering ring, drill holes in forward centering ring,
and fill booster section with Mega Foam prior to installing the tube
coupler / baffle plate subassembly.
3) Drill numerous 1/2 inch holes in the foward fin/wing root tabs to
allow foam to flow through
4) fill tail with mega foam to encapsulate rear fin root tabs prior to
installing tailcone
5) Replace included Polystyrene nosecone with a custom fiberglass 5:1
Ogive nosecone. This will increase the overall height by about 12″,
increase the nosecone weight (both reflected in the Rocksim file), and
allow me more flexibility in adding nosecone weight as I get closer to
final build and have actual weights for the booster and sustainer
sections.
6) Tip to tip lamination of both fins and wings using kevlar and
fiberglass. My usual procedure is fiberglass and Carbon Fiber with a
vacuum bag. Thanks to the lower maximum expected speed of this rocket I
don’t need the stiffness of Carbon fiber,which free’s me from using a
vacuum bag process.  I’m very comfortable with the lamination process,
but I have not yet finalized how I am going to accomplish this given
the wing / fin overlap. My initial thought is to mount the fins first,
then laminate the fins. re-cut the airframe wing slots, mount the
wings, then laminate the wings.

Here is a copy of the Rocksim file:

For recovery I will be abandoning my electromagnetic ejection
concepts. I am still working on them, but starting at MWP 8, I’ve had
a series of failures where the force of ejection was significantly
stronger than I had calculated, and ripped the electronics or magnets
out of the rocket. I think the high voltages are effecting the
electronics, but I’m still unsure.
I plan on using my Marsa4 altimeter for primary, and my Raven for
backup. Both altimeters have been flown several times, and have been
flawless in their operation. I received an Altus Metrum for the
Holidays, which I will add in the third AV bay. Since I have no
flights, nor any experience with it,  I don’t plan on utilizing it for
any part of recovery – Just a way to get some telemetry data, and test
out it’s transmitting recording capabilities. I already love this little guy because the hardware is ‘open hardware’, and the operating system, and flight software is open source! available here

IMG_2428_thumb[1]

My primary building epoxy is be Loctite Hysol E-120HP

. This is an Aerospace grade high viscosity epoxy that is just amazing.
Provides a long  pot life (~2 hours), and creates bonds stronger than the materials it’s connected to. It’s expensive, but worth it. I use JB Weld in areas that will be subjected to high temperatures (connecting the motor retainer), and US Composites for lamination. I *MAY* use Pro-Set for fin and wing fillets. I haven’t decided yet.

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This entry was published on January 11, 2011 at 11:33 pm and is filed under Rocket related. Bookmark the permalink. Follow any comments here with the RSS feed for this post.

3 thoughts on “Turning the Nuclear Sledgehammer into the “Questionable Investment”

  1. Thank you for choosing one of my altimeters. I’d like to know a little more about your decision to forgo the electromagnetic ejection. I thought it was brilliant, and what I saw of your electronics were of very high caliber. Could have been a software problem? :> Just kidding

    • heh…

      I *think* I have two issues that are blending together.

      The first issue is the mosfets. I am using an enhancement mode n-channel mosfet in saturation mode to control the current using the following formula here: http://upload.wikimedia.org/math/e/a/8/ea8ecd051837b6b88bd5036989637da6.png

      My overdrive voltage is extremely high (~400 volts). I believe the channel length is too short, which is causing the formula to become inaccurate. the end result is I am doubling, or tripling the voltage AND amperage flowing through the circuit, which is creating a force so strong it’s ripping the magnets (and often the electronics) out of the rocket.

      I’ve been compensating for this by dividing the end calculations by 2.5, which seems to put me in the right ballpark. The next issue then is the contraption I use for main deployment will consistently fail if the nosecone does properly eject. Here, I think the issue is the huge voltage spike through my electronics is not propery insulated, and is effecting the altimeter, so it doesn’t fire the second channel. I’ve been able to recover a few altimeters, and when I look at the data, I can see a massive spike, but my Kalman filter should have no issues filtering it out. For some reason, it’s not.

      In the short term, I could probably use different altimeters – one for apogee deployment, and one for main deployment, to avoid the voltage spike issues. This increases both complexity, and the probability of failure.

      I will still move forward on the concepts, just not in my level 3 bird!

      Oh yeah – this years Ski trip is to Utah unfortunately, so we probably won’t connect over the winter. Hopefully we’ll see each other at a launch over the summer.

      Alex

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