Which Hybrid do YOU think is the best for HPR???

Can't ask for a more definitive answer than that! Thankee kindly, Anthony. I'll crank the regulator above 80 psi from now on.

Any statistics on how long we can expect a fill stem to last? I'm on my second fill stem, having gotten 24 firings off the first one, which seemed pretty good to me. It failed on a flight that was otherwise perfectly normal; there was no indication during ignition that the GOX tube was banana-peeling. I'm assuming it was just age, possibly assisted by my habit of cleaning the fill stem with a pot scrubber at the end of the day.

Doug Pratt

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Reply to
Doug Pratt
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You may be on to something here, Ray. I experimented a few years ago with a very simple pull-pin arrangement: the contacts stuck out the side of the electronics bay and were angled down. A shorting plug was tied to the pad with Kevlar thread. Worked like a champ. There was some concern that the rocket rotating on the rod in a breeze would pull the pin, but using a rail solves that (and so many other problems) neatly!

Doug Pratt

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Reply to
Doug Pratt

I have no experience with the Accelo-Rocket product, but every hybrid flight I've ever made was with a G-Wiz, except for one with a Missile Works altimeter. I have had a total of one failure, and that was from improperly installing the G-Wiz so the battery slid backward at ignition, ripping the wires out of the connector block. The G-Wiz guys tell me that their launch detect sequence is programmmed specifically to deal with hybrids, and I believe them. It certainly matches my personal experience.

So, it's an over-simplification to assume that accelerometers have a problem with hybrids. I would say that it has more to do with the way the accelerometer is used.

Doug Pratt

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Reply to
Doug Pratt

I regularly use 35-45PSI for my motors, but the start sequence is different-- getting a "good 'ol fahr" going at the top-end of the motor is precisely what is needed to get U/C valved hybrids started.

For Kline-valved hybrids, you really want "plenty-o-flame(tm)" coming out the nozzle to break the tie downs.

The available pressure in those disposable GOX cylinders is fairly low--I think they run them at about 100PSI, and they're designed to be regulated down to about 2-3PSI. They won't give you more than a launch or two for Hypertek flights, and maybe 3 or 4 for U/C-valved hybrids.

I don't know about in the U.S., but up here a little "pony" bottle for GOX can be obtained from Home Depot. They filled to the standard 2200PSI pressure for GOX and last a long time between ($15.00) refills.

Reply to
Marcus Leech

Brings up and interesting question. How do you store high flammables in and about the house?

Mine are in several fire safes.

Joel. phx

My hypertek grains are laying about, as inert as the kids toys.

Reply to
Joel Corwith

In Their shipping boxes id the prooper method. I suggest within 3 steps of the door or where possible in an outbuilding.

Reply to
Jerry Irvine

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Aerotech motors look like a pain in the rear. You have to assemble those loose grains, o-rings, and even the nozzle, which you apparently have to drill out yourself. Then you have to try to pour those black grains from that little red cup, which it seems you can open wrong spilling the contents on the table, into that little port on the top. I've even seen multiple ignition failures from what they call 'copperhead' igniters which really look like the paper out of my office's paper shredder.

So someone flying Estes motors says RMR flying looks like a pain in the rear. Would you want to explain after a few times you can practically assemble them blindfolded? That they cost less per flight than single use?

Same is true of hybrids.

I don't recall the thread 'flaming you', but if it was perceived that way, I'm sorry. My interpretation is it was a discussion about the relative 'pain in the rearness', not a 'you don't know so you're a moron'.

Then again, how many times are you willing to repeat the same information....

Joel. phx

Reply to
Joel Corwith

Without wide open ranges, or an eagerness to chase rockets for miles, high power flights benefit from dual deployment which, AFAIK, require electronics.

Joel. phx

Reply to
Joel Corwith

Hybrids have high-frequency (~20hz) instabilities in their output--some more so than others. If the CPU under-samples the output of the accelerometer, there can definitely be serious trouble. In the worst-case scenario, the CPU will always be seeing the valleys, and not the peaks, and thus coming to entirely the wrong conclusion about what's going on.

There's no excuse not to sample whatever sensors you have at least 100hz, and apply a smoothing filter to them (no hardware necessary!). A simple N-point moving average filter can work wonders, and it's very simple to code up. A more brutish approach would be to put a hardware low-pass between your sensors and the CPU, but that add components, board space, and weight. Modern PIC chips have plenty of beef for computing simple filters at sample rates on the order of 100-200hz, and still have memory and cycles left over for the other things you need to do...

Reply to
Marcus Leech

Accelo-rocket samples at 25HZ. The hybrid noise component is somewhere in that vicinity. If you run a simulation of this, the sampled output looks nothing like the input. I think accelo-rocket should up the sampling rate to at least 100hz, and implement a simple filter.

Reply to
Marcus Leech

Doug Pratt wrote: > I have no experience with the Accelo-Rocket product, but every hybrid > flight I've ever made was with a G-Wiz, except for one with a Missile > Works altimeter. I have had a total of one failure, and that was from > improperly installing the G-Wiz so the battery slid backward at > ignition, ripping the wires out of the connector block. The G-Wiz guys > tell me that their launch detect sequence is programmmed specifically > to deal with hybrids, and I believe them. It certainly matches my > personal experience. >

I said that accelerometer based altimeters that do not pay attention to basic sampling theory (ala Mr. Nyquist) have problems.

There are certainly good implementations available but as the Accelo product indicates, the same mistake keeps getting repeated.

I also failed to mention that I found the use of a new altimeter in a rocket where it was the only means of deployment was just asking for trouble. I like to fly new altimeters (new to me anyway) in a rocket where there is some other means of kicking out a parachute. Be that motor ejection or another altimeter with which I am comfortable. When I fly a hybrid, my standard setup is to use an altimeter along with a timer backup for the apogee event.

That way, if I make a mistake or the altimeter is faulty in some way, my rocket will not fit into a glove compartment. :-)

Reply to
David Schultz

Even 200Hz isn't a fast enough sampling rate for some motors. See the graph at the bottom of:

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Which is data captured by an RDAS (no low pass filter) at 200SPS.

Moving average filters require too much storage and computation, especially on some PIC's which don't have a lot of RAM. A simple recursive filter is just as effective, needs only a single word of storage, is easily tuned, and is extremely easy to code.

But PIC's do have the horse power to compute a simple Kalman filter at

128Hz. It ain't easy though. And is not a substitute for good data sampling.

Which reminds me I need to start work on that little project again now that Level 3 is complete.

100hz, and > apply a smoothing filter to them (no hardware necessary!). A simple > N-point moving average filter can work wonders, and it's very simple to code > up. A more brutish approach would be to put a hardware low-pass between > your sensors and the CPU, but that add components, board space, and weight. > Modern PIC chips have plenty of beef for computing simple filters at sample > rates on the order of 100-200hz, and still have memory and cycles left over > for the other things you need to do...
Reply to
David Schultz

I know size dont matter but I am pleased that this thread has proven so popular and contraversial...

site.

Reply to
TheOutcast

Ray and Doug,

Thank you for the best tips and tricks posts this week! A twofer' in one thread!

HEY: what about a Dr. Frankenstein switch, you know the kind with the blade on a pivot and forked contact? Starts counting when circuit is broken. That would look _perfect_ on some of my recycled creations. Time to hit the flea markets and find one I can experiment with on a

24mm rocket. I wonder if ratshack even carries these anymore?

Now to find something at the new Lowes in Georgetown to use as a low power rail...

A twofer' AND next weeks project! The weather babe predicted rain all weekend anyway.

Thanks guys, Patrick

Reply to
IceAge

Every time I read about how reliable pull pins are, I remember reading David Stumpf's excelant book on the Titan II. The very first silo launched flight test didn't work quite as planned. The umbilical disconnects didn't, ripping assorted wires from deep inside the missile body. The guidance didn't work and worse still the range safety package never armed.

The missile somehow managed to clear the silo without hanging up on anything and then was flying wherever it wanted to go.

Very scary.

OK, not quite the same thing, but that is what it reminds me of. :-)

RayDunak> of something 100% reliable like pull-pins.

Reply to
David Schultz

Reply to
Alex Mericas

Just as long as I know you guys still love me. ;-)

Reply to
Kurt Kesler

There was an early Mercury Redstone test mission that rose a mere 4 inches off the ground, when a plug disconnected prematurely. Amazingly, the rocket fell back onto the launcher and didn't topple (just some minor damage to the fins).

What happened next was amazing. The flight sequencer, assuming the shut- down was normal and everything was hunky-dory, then jettisoned the escape tower. Then a few seconds later, the capsule staged, just as it would have upon booster shutdown.

Then, the (very green) NASA flight controllers had to figure out how to disarm and de-fuel this potential catastrophe without getting anyone killed. They even discussed shooting holes in the LOX tank with a high-powered rifle. Calmer heads prevailed and they figured if they let the batteries run down, the LOX valves would open up and it would boil away all by itself.

Reply to
BB

Can you give us the title of that book? I'll put it on my wishlist at

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I've been absorbing the three-DVD set "Project Gemini" from Spacecraft Films for the last week. Wonderful footage of "fire in the hole" staging and all sorts of other neat stuff. I sure wish I could get some of those neat covered switches they used in the cockpit. They have great footage of erecting and stacking the GT-3 as well. I never really understood how the erector worked until I saw this DVD. Fascinating!

Reply to
Doug Pratt

snipped-for-privacy@rocketryonline.com (Doug Pratt) wrote in news: snipped-for-privacy@posting.google.com:

From AbeBooks.com, search on author = stumpf, keyword = titan:

Stumpf, David K./ Kelley, Jay W. (Frw) Titan II : A History of a Cold War Missile Program Univ Arkansas Press. Brand New Hardcover (All books with dust jackets Protected in New Brodart Covers) - 320pp - Diagrams - Photos - Color Illustrations - Index Publisher List Price= $49. ISBN:1557286019 Bookseller Inventory #37817 Price: US$ 44.00 (Convert Currency)

Ain't the internet wonderful?

Reply to
Leonard Fehskens

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