Very nice, Scott. I know your altimeter will work and you'll nail L2! Before the thread police come in, we better get back on topic. 😉

Any body have any experiance testing altimeters? The instructions says use a tube on the baro senser and draw a vacume. Joe told me some in the club, have some neet ways of testing them. ??? Food saver? 😉

Scott e

I bought two used RRC2X's and had the same concern, not so much for the accuracy, as I think that is hardwired in, but whether they were working at all, not just for an altimeter reading as well as the deployment set points. These are the older thru-hole component types.

I put LEDs with pigtails (from Radio shack - 12V) on the deployment connectors, one green and one red, attached the battery, then sealed it up in my avbay. It has a 1/4" dia hole on each end. The mach delay was set to zero. Drogue at apogee, main at 800ft.

I slid it into my upper airframe tube which has the nose cone on it and is unpainted G10 (which is transparant enough to see LED's inside of it). I hadn't drilled any bleed holes in it yet.

When I put it in as far as I could and could still grab the quick-link, I put a piece of tap over the hole on the end that I was holding.

I yanked the avbay creating a suction in the upper body cavity, and then slowly brought it out the rest of the way out of the tube.

I saw the apogee deployment LED fire right after the jerk, followed by the main deployment. The beeps indicated that I hit 1286 ft.

I did this several times and got up to over 8000 ft. Since I have redundant altimeters, I tested them individually, otherwise I couldn't keep the lights straight. I never got around to testing them together to see how close they were to each other.

I'm pretty sure at least one of these will do the job if the other fails.

I was thinking about it yesterday. I Have a 3" Rocket(not much room)
In our redundent alt. ejection systems Ken had 2 Powder cups, Mike has 2 Powder cups, I have 2 Powder cups. If your testing ejection charges and getting the charge so 1 cup will work. Wouldnt 2 cups going off at the same time be too much??? Why not put both matches into 1 cup? 🙄
That might help solve some of my issues of room in a 3" body. 🙂

In practice, you'll find that it's pretty difficult to get two barometric altimeters to fire at the same time. Aside from sensor tolerances, altimeters like the RRC2 family just don't have the resolution or precision to fire at the same altitude. They're 8 bit devices which on the 25K model means that the LSB is +/- 97.5 feet. The 40K version is +/1 156.25 feet.

My 4" bird was originally two RRC2X altimeters and there is probably as much as a second of difference between the two altimeters when they fire the charges.

Besides, if your charges are a bit wimpy (something that's happened to me), the first one will pop your shear pins and kick the nose cone, the second will push the laundry out.

Warren

Scott,

I'm too new at this to take anything I say as Gospel, but I started my design with just one cup because of space reasons. The other location held an in-line terminal block.

In later discussion with folks it became obvious that to get full redundancy I needed separate cups for the two igniters, rather than two igniters into one cup.

How I understand it is, you set the 1st main deployment at a higher elevation with your standard charge. The backup charge has a bigger kick and is set at a lower altitude.

If the 1st charge goes off as planned the nose cone separates successfully you are OK, then when the 2nd charge goes off, it just blows out into the open airstream.

If the the 1st charge fails to go off or is not strong enough to pop the cone or shear the pins, 200 feet later the 2nd more powerful charge goes off to blast the cone and its innards away. And even If it's way too much and you've hurt the part of the airframe, at least you have deployment and you've saved the rocket.

So in short, there should not be an over pressure by two charges going off at the same time.

My original design:

My modification:

Some of the Innards:

Good points

Has anybody had 1 cup set the other cup off???

scotte

Never. You will also find folks who use a single charge with dual matches in situations with redundant altimeters. You better damn sure know your charge is sized to be absolutely reliable about kicking the laundry out though.

Warren

Any body have any experiance testing altimeters? The instructions says use a tube on the baro senser and draw a vacume. Joe told me some in the club, have some neet ways of testing them. ??? Food saver? 😉

Scott e

Not sure if your original question got answered but a easy way to verify altimeters with baro sensors is to place the unit into a glass or jar with the battery and Christmas tree bulbs installed and ready to go. Them place a rubber latex glove over the end of the glass/jar. With one hand hold the glove in place and with the other pull the glove away from the glass which causes a vacuum inside the glass them slowly release you should see both apogee and main deployment if it is setup that way.

You better be damn sure know your charge is sized to be absolutely reliable about kicking the laundry out though.

Absolutely! Had I not had an extra gram in my redundant charge for my last cert, it would have been bits and pieces on the prairie! You really don't need redundant on an L2 cert, though I really admire that. You will need that for your L3. I used to say I was paranoid, but Art Hoag said that it's best to say I'm cautious. Sounds better. Listen, the ground test blew that main out at 6 grams, but in flight, it required that extra gram--I credit Conway for that additional gram. Sizes may vary, and it takes time to know what different charges do based on materials used, etc. Mike Bennett is right on how to test altimeters, plus there are as many ways as there are those of us shooting our hopes and dreams up into the sky. Just isolate the altimeter and make a relative pressure change. Mike K., your way of testing your alts was very original. Don't forget vent holes, and not just the ones in your avionics bay. Pressure changes can and do pop things off. The only time I've ever heard and personally witnessed two altimeters getting the same resolution was with Jason C. getting the EXACT altitude from one of Jim's RRC2X's and a Perfectflite MAWD. That was rare.

Mike, why is that center hole uncovered? Obvious question, but since your two avionics bay rods are on the outisde, why do you have a center hole? I know you know this--and it comes that way, but that will defeat the purpose of a perfect seal to protect your electronics and screw up the barometers, plus damage them?