Wednesday, August 18, 2010

Lucerne, 8/14/10 - Der Red Mix FAIL on maiden flight

Let's start with the onboard video and then I'll explain:
First off can you BELIEVE my Flip MinoHD video camera survived that high-speed impact?! That has to be one of the few surviving onboard video accounts of a high-power rocket crash. Props, Flip!
OK so this was to be the maiden flight of my scratch-built, 7.5", clustered upscale of Estes' Der Red Max but cluster = Mix in my case. While I had access to 7 motor slots I wanted to walk before running so I chose to ground-start a CTI K500 Red Lightning, wait 1 second, then air-start 2 x I345 White Thunder motors. It shoulda kicked ass. However, operator error resulted in a great ground start, no air-starts, and no ejection of the main parachute at apogee. Jenius.
After the flight I downloaded the data from the Parrot2 and Raven altimeters from www.featherweightaltimeters.com. Those little devices never cease to amaze me as they're tiny yet record a large number of data streams at high temporal resolution. Nothing leapt out at me at first so I decided to e-mail the data to Adrian at Featherweight. SERIOUS props to him because, independent of his workload at NASA, he quickly responded that none of my four e-matches had shown continuity. Despite reading both manuals numerous times I'd made the following three mistakes:
  • Raven - responsible for air-start ignition & main parachute ejection - This was my first time using the Raven. While I thought I understood the wiring of this device I had clearly allowed my familiarity with other altimeters to lead me astray. The 9V battery does not connect directly to the altimeter as in most other altimeters. Instead it's grounded in the altimeter but the positive lead is connected to one of each of the e-match leads and optionally through an arming switch. The other leads of the e-matches feed into the relevant output connectors in the terminal block. [Addendum: if not using an arming switch you can also gang the second e-match leads in the + terminal slot. I verified this with a test connection.] Lesson learned: RTFM ad nauseum!

  • Parrot2 - backup altimeter for main parachute ejection - I lost my original Parrot2 (250G) model a few months ago in the J1520 minimum diameter flight. I was able to purchase an unused Parrot2 (70/30G) model from a fella on the forums. In re-reviewing the wiring diagram I mis-marked the power inputs for the 9V pyro battery so the thing was running solely on the LiPo battery the whole time. The apogee e-match never had a chance of igniting. I don't use separate arming switches so this wiring option consistently confuses me. Lesson learned: When in doubt get a second opinion.
  • Finally I left the K500's motor ejection in place as a secondary backup for parachute ejection. I was so confident that one of two altimeters above would do the trick, however, that I didn't shorten the delay from 17 seconds to 14 seconds. Let me tell you that 3 seconds is a LOOOOONG time when a rocket is coming in ballistic! Lesson learned: When possible trim the motor delay to simulated apogee + 1 second.
Here are some other pix:

Oh and KO and I were finally able to run our "Squat redemption" drag race on matching CTI I140 motors:
I edged her 'Cheshire' out by a length but the the motors look slightly different to me. I bought them at the same time so I'm not sure what's up with that. I will say that it appeared to be a tie to me until I downloaded the photos.

2 comments:

Kris said...

ko: the still frames esp of the sunlight are gorgeous. call drm flight a beautiful disaster. good thid you worked out the alrimeter kinks so sparkle motion will not suffer needlessly.

Kris said...

c'mon cisco, provide that flip sponsorship. the still frames with the sunlight are gorgeous. it's a beautiful disaster. glad you worked out the kinks on the altimeters so sparkle motion does not suffer the same fate. i demand a squat re-match!