need help understanding flight data charts

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Well-Known Member
Feb 10, 2017
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The attached charts were made by AltOS with flight data recorded by my TeleMetrum. I understand most of the data but there are a few things I don't follow.

First we flew the PAUL DZ (LOC Expediter). As you may have seen from my other post, the tie bar broke and the payload section, with the Telemetrum, separated from the rest of the rocket. I'm trying to understand what happened at the 9 second mark: there's an uptick in the green acceleration line, does that mean the delay charge fired the payload higher into the air? On the green line, negative numbers mean descent speed? And what does the big spike on the blue line mean, was the rocket accelerating that much faster than it was at liftoff?

Next we flew the PAVEL 3 (Wildman Darkstar Jr), and it was a perfect flight. Seems the chute deployed right around apogee. But why does the graph stop at 14 seconds? I think we could still hear the Telemetrum beeping when we recovered the rocket, but perhaps I'm imagining that. Only thing I can think of is the Telemetrum turned off at that point in the flight.

graph of flight of PAVEL 3.jpg

graph of flight of PAUL DZ.jpg
Your first chart shows a large acceleration jolt as the payload ejected and broke off the shock cord. The apogee deployment can be a large acceleration event.

From there, the payload fell at a speed around 50 fps and hit the ground with a thud at 33s. I have no idea why the green velocity required another 10s to reach zero.

The second chart looks typical, other than the truncated data.

I am not familiar with Telemetrum. I assume all the data shown is accel-based.
Wow! What size apogee charge did you use?
The chart's a little small, but it looks like you pegged the 100G accelerometer!
This takes the cake on most violent ejection I've seen posted.
No wonder you broke the little plastic loop.

You need to size your charge with just enough to get the laundry out.
Then make the backup larger.

Looks like you went straight to the BLOW IT UP mode.
It was just the standard charge that comes with the AeroTech H115 motor. The instructions said to use the entire vial if the rocket has a diameter of 4" or more.
Would you mind uploading the .eeprom files? The pictures are rather low resolution for my old eyes.

Take a look at your GPS height as well. During the descent the GPS height goes down to -200 feet and then jumps back up to 1200 feet. Very odd.
Take a look at your GPS height as well. During the descent the GPS height goes down to -200 feet and then jumps back up to 1200 feet. Very odd.
Anytime I see a weird bounce I assume barometric lag is entering the algorithm somewhere.
Where is your Telemega located at inside the rocket? Is is protected from the separation charges?
Only time I've seen a jolt that big was when my Wilman Jr Catoed at 1000+ km/h.

Truncated data is a battery / electrical issue. Not sure if your alt has a voltage or amp logging, if so you'll want to look closely at it. The delay is a bit interesting, usually you'd expect it to loose power when firing the charge, so possibly this is a short that occurred while bouncing around under drouge? I'd be going through your electrical wiring very carefully looking for posible issues.
See attachment, battery voltage was steady until the moment of loss. The device was in a payload bay several inches away from the ejection charges. It seems to be working now, at least I hear the usual beeps every few seconds when I turn it on. I had it wrapped in bubble wrap but perhaps not tightly enough and it got jarred at ejection.

battery voltage.jpg
Thought it would better not to pack tightly to keep the vent holes unblocked, didn't fully consider the problems a loose pack can cause.
If battery & altimeter were just wrapped and stuffed....a less than optimal ejection charge, could cause a jolt, hard enough to send electronics slapping around inside.

This would give you skewed data, as both rocket AND altimeter are slamming around.
Possible that a bump could also result in a "momentary'' battery or switch disconnect, then reconnect. This would reset altimeter to "ready for flight mode and stop data recording.

These are just a couple of possibilities when things are not firmly mounted.:wink:
Anything is possible if bubble wrapped. Wire could short, button could be pressed, dodgy wire could open circuit.

The idea behind mounting the altimeter to a sled is to prevent these sorts of things occurring as much as possible.
Thanks for the replies, the only explanation that makes sense is that the TM was not packed well enough and it got kicked around on ejection. I use this unit on different rockets, so mounting on a sled is not really a good option. I could have used more wrap and packed it much tighter but was worried about blocking the vent holes.
Mounting on a sled is a fine option. It's four screws. Not a big deal to swap.
Is there a picture somewhere showing a sled-mounted altimeter that is easily movable from one rocket to another, even rockets of different sizes?
This is a pricey piece of electronics. It deserves better than bubble wrap, especially the acclerometer. Secure the payload with the provided mounting holes.

Even if the altimeter was banging around and/or losing power, that doesn't explain the 10s lag between altitude and velocity at the end of graph #1. Does the Telemetrum attempt to combine and massage acel, baro, and GPS data at the same time?
Is there a picture somewhere showing a sled-mounted altimeter that is easily movable from one rocket to another, even rockets of different sizes?

If you do a google search for ebay or avionics bay with the "" tag, you'll get plenty.
I know there's an av-bay thread around here where people show off their designs. And the Apogee website has lots of instructables about dual-deployment and similar.

A lot of people do multi rocket sleds.
Sled that will fit in the smallest body coupler you plan for it.
Common threaded rod locations (This may mean moving the U-bolts or Eye-bolts to the sides in a larger diam bay)
Unless you just run long e-matches directly to your charges; Quick disconnect wire connectors on bulkhead leads and altimeter leads. (Set these up so its Impossible to hook up incorrectly. Otherwise you'll have to file an ID-10t report with the RSO at your launch)