Here's the root cause

Here's the short version: I've been playing with a GPS that transmits its locations on the MURS band around 150 Mhz. I inadvertantly had wires within the 5" dia x 12" long L3 avbay that were of a length conducive to being an antenna receptive to the transmitter frequency and subsequently induced a spurious RF signal into one of my altimeters. The altimeter detected a launch because of it (it looks for a 300 foot variation in barometric pressure before looking for an apogee event and evidently found it prematurely). Once the launch was determined, even though the rocket was happily resting on the rail, the altimeter saw neither a positive nor negative change in elevation, and determined that it was at apogee, and fired off the drogue charge. One second later, as 2/3 of the rocket was in the air above the rail, the altimeter discovered that it was below 1000 feet AGL and fired off the main, as it was designed to do.

In my 3" dia x 8" long L2 avbay which also contained a GPS/TX, the length of the wires were much shorter and was never affected.

After three days of late night testing, I have determined that I needed to reduce the length and number of wires in my L3 avbay and to move the GPS transmitter into the nose cone. All is well again. If I didn't have the tracking gear on board everything would have flown without a hitch. I love failures, its one less thing I have to learn.

I hope I didn't keep you guys on pins and needles too long.

Mike.

Mike. that is a great analysis and a lesson well-learned. Sounds like a positive ID of the problem - Thanks for the update---

8) No harm, no foul! A very cheap lesson. One that many members of our club, picked up for free. Once again a failure, and in this case, a non-failure to launch, taught the biggest leasons. So, under the month of February, mark DUES PAID, Mike. Looking foward to next month! 😀

My very first dual deploy bird had only a single altitude bleed hole into the avbay and it fired its charge on the pad when a gust of wind hit. Since then I've generally gone to 2 or 3 holes equally spaced around the avbay and have never had that kind of problem again. However, it was a specific altimeter that was known to have this problem - not a Missileworks.

I was told years ago by a manufacturer that you should always use 1 or 3 holes, not sure why but that is what I have always done. when using 1 hole I have the electronics on the opposite side of the board away from vent hole to help baffle against any abnormal air flow. I have never had a problem with wind causing an altimeter to go off.

Since that bird, I always use 3 holes and I try to make sure that the baro-sensor is somehow baffled from any direct airflow through those holes.

Warren

Greg here - the guy hanging with Jeremiah on the 2nd.....

Anyway, I just wanted to say a couple of things. I was impressed with how well Mike kept his cool, and the crew helped out. This was my first time out with NCR and came away with a pretty good impression of the group that was there.

Second, I found the analysis and side conversation on this post really informative and helpful. Thanks to those who put formulas up, sometimes people don't always remember newbs are lurking. Stuff like this may be directed at one problem, but put a few topics together and it reads like a tech manual..... I would never have though about RF problems in rocketry, I'm glad I took the time to read this.
I live by the principle of knowledge not shared is knowledge lost.

Glad to see Mike got it figured out. I was looking forward to seeing that thing go up...

Greg

I didn't think about it either to be honest. I hadn't considered Mike's secondary payload (GPS and downlink) or its possible impact at all. As I recall, I believe Mike said it was 2 Watts, which is a considerable amount of power at close range. Very nice example of difficult problem resolution too.

Warren

On Saturday, March 1, I launched both my L2 (J350W followed by a J420R) and my L3 rockets (K560W). I can reveal my GPS now that the March issue of Extreme Rocketry is now on the shelves. You need to buy it, it has some very informative articles in it.

You can see the entire build sequence of Slipstick III and full size pictures at
http://www.telerover.com

Both rockets had the Garmin DC-20 (hunting dog tracking transmitter) located in the nose cone (L3) or payload section next to the nose cone (L2). Both contained a MW's RRC2-X as the primary controller and an RRC2-mini as the backup with a 1 second delay. The later is the one that gave me the surprise pre-mature launch detection before initiated by the GPS/TX installed in the avbay with the altimeters. The avbays were lined with aluminum duct tape for RF shielding. The wiring between the altimeters and the charges/switches are the main receptors of RF that caused the original problem.

Recovery deployment and tracking worked flawlessly.All four charges went off on all three flights in the proper dual-deploy sequence. The Astro 220 handheld GPS shows the tracks of the three flights along with the path we took carrying them back.

Here's a link to video of the maiden Flight of Slipstick III. The video is 70MB:
http://www.telerover.com/rockets/video/Slipstick_III_L3_Shakedown.AVI

You'll see tiny puffs of smoke as the deployment charges go off at apogee (drogue chute). Look near the bottom of the window for the main deployment.and at 1000 ft elevation (main chute) you'll see two small puffs as well, the backup charge being delayed by 1 sec. I wasn't holding the camera very stable as I was looking over the top of the camera. I'll be flying with the M motor on April 5 for my L3 cert. It will be glorious!

Slipstick III will go into the paint shop on March 10.

Very nice, Mike! 😉

8) I must say that Mike's flights were as nice as it gets. The 75/K560 was nice and slow and low. You could get a great view of the flight, start to finish! Great job! 😀

For those that would like to see a couple of tests I performed in analyzing the previous false launch problem initiated by the transmitter in the GPS/TX, here are two videos.

The first shows how the proximity of the GPS/TX affects the altimeter. The altimeter seems unaffected until you are within 6 inches. The actual test moved the GPS/TX slowly toward the altimeter in 2" steps, letting it 'soak' for a 2 minutes before continuing on. (46MB)
http://telerover.com/rockets/video/GPS_Test_1.avi

The second test was to see if the altitude is affected by the GPS/TX. (55MB)
http://telerover.com/rockets/video/GPS_Test_2.avi

Shielding the inside ofthe avbay protects the wiring from becoming antennas. Someone with a CB radio nearby could have the same effect since both frequencies are around 150 MHz.

Before lining the inside of the avbay I tested the theory by wrapping kitchen aluminum foil around it. No false signals were encountered.

you can see the final product in the previous thread.

Those were some great flights Mike. Glad I was there to see them. Good luck on the M flight at MHM. I'll be there doing it too.

Warren

I made a comment while carrying Slipstick III past the small rocket launch pad, (being in good spirits after a successful flight) to the effect of "My rocket is bigger than yours". I received many chuckles, but evidently some took offense at my comment. I apologize, if that is the case. If you know me then you will know that I am just as involved in model rockets as I am in HPR, and every rocket that flies and shows good workmanship gets my respect.

You know Mike, if you wern't always carrying your "Big Rockets" around, you might not have those back problems! 😉

The multi-stage Estas Rocket I'm launching next month, well I dont really expect to get all the pieces back. So the workmanship (Fillets, Fins, Paint, and well, every thing Else) isnt up to my usuall stardards, which isnt very high anyway. 😉 Can I still have your respect tooooo?? 🙂 😉

You are right there. Every Rocket that flyies is a great achievement.
I think most People fly within a budget.

Just watched Your videos. Great video and explanation.

Look forward to seeing You at MHM.

The greatest flights are those flown by the Youth of the club.
Hope We (Old People) never loose the wonder and excitement.