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Need advice on backup altimeter delay
#1
New to dual altimeter setups and it was suggested, as well as I read, to add a 1 second delay for my backup altimeter apogee event. I thought I would see what others are doing.

If it matters there are two rockets I will be launching with this config.

One I have already launched twice with a 1 sec delay but the main worked fine so the delay event was irrelevant. It is a 54mm min diameter rocket that I will be launching to 17K @ Mach 1.1

The other is a new 3” build that will hit 14K @ Mach 1.3

If there is anything else that I should take into consideration please let me know. It would be good to know if the delay should change based on the flight profile?
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#2
The main concern people seem to have is two events going off at once and blowing things apart. To me, it's very rare two altimeters will hit at exactly the same time, but a one second delay on one of them really can't hurt. The flight profile doesn't really matter much, the only reason to add a delay on one is to avoid both hitting at once. Personally, the way most of my rockets are built a simultaneous blow wouldn't affect much.

One thing to test on the ground is if you can fire one charge and not have the other (on the same side) go off. I had the cups on my darkstar too close, as soon as the main blew, the backup lit off as well.


Both main and backup charge should be big enough to independently separate the airframe.
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#3
the delay between events cant hurt but probably not needed. The biggest problem IMO even using 1 altimeter is POWER. 2 batteries FRESH or LiPo, Two Switches. I prefer the 110/220 switches but there are a LOT to choose from. A lot of the battery holders for sales even from rocket vendors are bad news. The power attachments wired are connected to the battery clip via a rivet, those rivets suck and loose connection turning OFF the altimeter. The best way is to use LiPo as they are factory wired.

This guy 3d prints awsome sleds some are dual capable, they are even setup with the switch holes. https://www.etsy.com/shop/Landru13?ref=l...eader-name


Bill Clune L3 | NAR#88583
Been a launch Director
Founded a Club
MARS Club|SRC|MDRA - Forever
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#4
I, like the other posters above have 2 entirely separate systems for redundancy purposes.
There is no point in having separate batteries and altimeters, and then using the same power/arming switch, as you are still left with a single point of potential failure for both systems.
I use a 1 second delay, but I agree even without a delay it's unlikely they would both fire at the same time.
The way I look at it is that if they did I would likely cause significant damage to the sustainer/payload section, which a one second delay would prevent.
So my bottom line is I won't take a chance. I add one second delay, and not worry about it! Smile
Greg Young - L3
TRA 00234
NAR 42065
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#5
Thank you Dave, Bill and Greg for your responses.

The altimeter electronics are fully redundant.  1 freshly charged to 4.2V 1S Li-Po per altimeter, zip tied through a G10 board both horizontally and vertically.  1 solid state magnetic switch per altimeter securely fastened to the G10 board with stand-offs.  The 54mm AV bay has 2 Garry Tortora small blast caps per bulkhead.  This altimeter and setup has been bench and ground tested about a dozen times to get everything dialed in and confirmed correct.  The other AV bay bulkheads are the new ProLine dual AV bay lids which have a through hole inside the blast cup to pass the e-match directly through the bulkhead.  This setup I have not bench or ground tested as I am still getting this rocket complete for LDRS.  I will likely bench test it this coming weekend but not get the opportunity to ground test it until LDRS.

Here are some pics of the bay.

3" SL100 side
   

3" SLCF side
   

3" exterior bulkhead showing the dual cups
   

3" interior bulkhead showing where the e-matches pass through the cups
   

54mm bay all buttoned up with batteries, I believe this is the SLCF side
   
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#6
Your approach sounds pretty solid to me! Smile
Greg Young - L3
TRA 00234
NAR 42065
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#7
Pitter thanks for sharing! Very NICE!
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