Saturday, August 21, 2010

On the mend

So I've now overcome the sadness of Der Red Mix and embarked on DRM mark II:
  • Last night I think I thoroughly mastered both the Parrot2 and Raven altimeters via manuals, testing, and marking of the terminals. I will not repeat my mistakes of last Saturday.
  • I decided that DRMII will use all BlueTube 2.0 rather than phenolic and just ordered four tubes. This should greatly improve strength overall and will reduce my finishing time demonstrably over mark I.
  • I made some small positional adjustments to the mark II design in RockSim as refinements. I think I'll need less nose weight this time for a typical flight.
  • In mark II I can revert to the original position of the Flip video cam cowling so there should be no fin visible this time.
  • I'm considering cutting my own fins and centering rings this time but might still go with laser cutting at BMS. TBD.
  • I'll combine some of Kurt Gugisberg's painting advice with a new support rig I've devised to minimize dust kickback. Hopefully I can avoid car paint pitting this time. I'll also apply the decals before flying to underscore confidence in my revised approaches.
Cathartically this rebuild is now more important to me than attempting 2000MPH at Plaster Blaster in November. Also I just bought my own Pro75 6G hardware set for that flight but I wanna put some miles on that casing elsewhere first. Oh and KO sent her shot of the DRM fail. It better shows how the Flip camera landed safely:

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 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.