Causes of altimeter failure?

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Hal8472

Hal8472

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Hi

I was launching a rocket on the weekend and can’t explain the failure. It was a perfectflight altimeter launched dual deployment in a mid sized rocket. G motor. Altimeter was in the nose cone with plenty of ventilation. Charge cap was used for the drouge. Cable cutter was used for the main. No problems setting up, had continuity, three chirps. It took four tries to get the motor to light so it was on the pad longer than usual, but I turned it off when there was a long wait. At launch it made a nice lawn dart. None of the charges fired. Stratologger was pretty beat up so I am not sure how much testing will reveal.


My possible options are
1. Not enough ventilation. Don’t think so. Nose cone unscrews at the top so there was lots of room for air flow.
2. Not enough battery power. While there was probably some drop in current over time the battery should last an hour on the pad without problem. I was using a alkaline 9v.
3. Hooked up wiring wrong. Well, I did inspect carefully and had continuity at launch
4. Old altimeter. I have had it for about four years and moved several times. I thought I was taking care of it but perhaps not.

Any thoughts?
Andrew







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Battery should last a whole lot longer than an hour so I don't think that would cause failure. What brand of battery was it? Have read where some 9 volt battery cells are soldered together & some are not. What motor? High G flight? Possible cell separation! Maybe wire came loose?
A friend had a similar experience with 2 Stratologgers in same rocket. Neither deployed drogue or main. Came in ballistic and all was lost.
Is the stratologger data available?
 
timbucktoo said:
Battery should last a whole lot longer than an hour so I don't think that would cause failure. What brand of battery was it? Have read where some 9 volt battery cells are soldered together & some are not. What motor? High G flight? Possible cell separation! Maybe wire came loose?
A friend had a similar experience with 2 Stratologgers in same rocket. Neither deployed drogue or main. Came in ballistic and all was lost.
Is the stratologger data available?
Click to expand...

Not a high G flight so unlikely cell separation.
I was using the speaker connection which is pretty good retention at low velocity. Nose cone was pretty banged up and I didn’t check if the wires were still connected at the time. Should have, lesson learned. I have seen other people use these (forum idea bin) so I think they are reliable.
I have not checked the strat data. Good idea, I will check after work. Had totally forgotten about that.




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I have seen rockets lost from using cheap 9V batteries. If your altimeter still boots up download the data and see what you get. If data is lost about 2 seconds after launch I would say you lost power to the altimeter. That was the case for the one flight where the cheap battery failed due to high G forces. Perfectflite altimeters carry a large capacitor to prevent altimeter shut down due to momentary power loss. They stay powered up for 1 to 2 seconds if power is completely disconnected.
 
What size, how many, and where did you locate the sampling holes? Beyond that I would look at power, was the battery secure, was it good and was it the correct battery. You need to post more specs. Was this a CRC launch?
 
Hal8472 said:
Hi

I was launching a rocket on the weekend and can’t explain the failure. It was a perfectflight altimeter launched dual deployment in a mid sized rocket. G motor. Altimeter was in the nose cone with plenty of ventilation. Charge cap was used for the drouge. Cable cutter was used for the main. No problems setting up, had continuity, three chirps. It took four tries to get the motor to light so it was on the pad longer than usual, but I turned it off when there was a long wait. At launch it made a nice lawn dart. None of the charges fired. Stratologger was pretty beat up so I am not sure how much testing will reveal.
Click to expand...

Um, don't :kill: me, but did you turn it back on before the launch?
 
Hal8472 said:
1. Not enough ventilation. Don’t think so. Nose cone unscrews at the top so there was lots of room for air flow.
Click to expand...

This statement confuses me. The altimeter needs constant sampling of the surrounding air pressure from power-up through main deployment altitude on the way down. Maybe I'm misunderstanding your setup based upon your statement, however?

mpitfield said:
What size, how many, and where did you locate the sampling holes?
Click to expand...

I think we might be on to something.
 
Bat-mite said:
Um, don't :kill: me, but did you turn it back on before the launch?
Click to expand...

That was my first thought too.

It sounds like a power loss, either from a bad battery or loose connection. Although I also don't understand what was meant by the airflow through the nosecone, and pressure sampling could be the issue.

Can you post a photo of your altimeter set up and the nose cone? That would help.
 
IMG_3906.jpg
I found an old photo of the nose cone. Top unscrews while still connected. Their is a generous gap. Didn’t take a photo with the electronics in but it was on a sled around the central spine. All was secure including the battery.
Also, yes it was on when launched. Had to listen to the chirping.
Just back from work. Will try the data after dinner..
I didn’t put in a new battery (which I had in my launch box) so thinking thats a possibility in the meantime.






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No data. Strat didn’t want to turn on. Noticed at least one SMD resister off so I think it was unhappy with the landing.


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1. had this ever flown before?

2. any breather holes for altimeter baro reading?

3. I only see 3 wires, normal configuration for a Stratto requires 4 to function correctly...2 for each match. How were charges wired?
 
No this has never flown before.
There was adequate air
Picture was from a few years ago, only to show the nose cone ebay. Can’t take a current picture as the nose cone didn’t survive. Older version had different electronics. Experiments.


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You say there was adequate air, does that mean you had the appropriate sampling holes?
 
Air needs to be able move freely in and out of the av bay so that the pressure in the av bay is more or less equal to the outside air. Otherwise your av bay will remain at the same pressure through out the flight and your altimiter will not detect launch never mind apogee.
 
Just a simple question to OP, did you have holes or not? From your posts no mention of them at all.
 
Sorry, I don’t get it. The top screws on. This part is outside of the body and doesn’t make a seal. There are lots of holes. A complete ring of them. I actually think its fairly obvious.


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Hal8472 said:
Sorry, I don’t get it. The top screws on. This part is outside of the body and doesn’t make a seal. There are lots of holes. A complete ring of them. I actually think its fairly obvious.


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Click to expand...

If it was obvious, we would not all be hammering that question! How many holes and what’s the diameter of each hole?
Perfect Flight has a pretty good procedure for venting an AV Bay. Did you follow their procedure?
 
timbucktoo said:
If it was obvious, we would not all be hammering that question!?
Click to expand...

No, that does not follow logically.

Anyway, I appreciate the input from those that contributed but I think this is where it can die off.

I will ensure I use new batteries in the future (best suggestion).

Thanks
Andrew


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"The cows can tape something by now!" LOL

Sampling holes go from your bay to the outside of your rocket. They allow the altimeter to sample the air outside the rocket to read how high the rocket is. Without the holes, the altimeter never reads any change in air pressure so it thinks it is still sitting on the ground. A large gap doesn't help if it just goes into another sealed area. Drill some holes from outside the nose cone to inside the bay. Small holes, maybe 3 holes 1/8" diameter. Something has to allow outside air in.

Neat idea to screw the bay together like that. I would pin it or an least us a lock nut to keep it from spinning loose under the chute.
 
Just trying to help out. I think I understand now what you mean by a gap. ??? Nose cone cut above shoulder, top of nose cone screwed down on bottom part, but not all the way, leaving a gap around the total circumference of the nose cone??? In other words, top not butted tight to bottom??? How much gap??
 
rcktnut said:
Just trying to help out. I think I understand now what you mean by a gap. ??? Nose cone cut above shoulder, top of nose cone screwed down on bottom part, but not all the way, leaving a gap around the total circumference of the nose cone??? In other words, top not butted tight to bottom??? How much gap??
Click to expand...

Would that not just effectively result in the coupler of the nosecone recessing deeper into the BT. The shoulder would still rest on the BT, closing the gap or at least almost closing it, but certainly not ideal for sampling.

The whole thing is odd that the OP asked for advice and then when it was given he dismissed so quickly. I am not sure what to make of that, except I would say to him don't sweat it there likely isn't one rocketeer who has replied to this thread that hasn't likely made a silly mistake. Personally I enjoy my mistakes because I learn so much, but not so much from the successes. You could look at it as the mistakes feed the need for knowledge and growth, whereas the successes feed the need for validation or ego.
 
Quote Originally Posted by rcktnut View Post
Just trying to help out. I think I understand now what you mean by a gap. ??? Nose cone cut above shoulder, top of nose cone screwed down on bottom part, but not all the way, leaving a gap around the total circumference of the nose cone??? In other words, top not butted tight to bottom??? How much gap??
Click to expand...



mpitfield said:
Would that not just effectively result in the coupler of the nosecone recessing deeper into the BT. The shoulder would still rest on the BT, closing the gap or at least almost closing it, but certainly not ideal for sampling.

The whole thing is odd that the OP asked for advice and then when it was given he dismissed so quickly. I am not sure what to make of that, except I would say to him don't sweat it there likely isn't one rocketeer who has replied to this thread that hasn't likely made a silly mistake. Personally I enjoy my mistakes because I learn so much, but not so much from the successes. You could look at it as the mistakes feed the need for knowledge and growth, whereas the successes feed the need for validation or ego.
Click to expand...




This is what I see according to OP's explanation and picture. If you take a close look at OP's picture, the bottom part of the nose cone, I see what looks like the ridge of the shoulder. Cut and gap is above the shoulder.

Nose cone.jpg
 

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