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From just the equipment point of view:
Primary issue would be EMI from one device affecting the other. The could occur due to proximity of the units themselves or via the wires to the charges/batteries.
While this could be an issue you would find this in ground testing, with all systems active and setting off real ematches EMI wise the system will be very similar to in the air
Agree you should find it during ground test. There is a remote possibility that wires could shift under G forces and cause a problem but probably unlikely
Due to the differences in the units (Hardware and/or algorithms), while they are set to operate at different times/altitudes they could operate at the same time. With both charges being activated at the same time the rocket could over-pressurize (like - blow up).
The time frame for the ejection charges is in milliseconds, this is statistically very unlikely to happen. If you throw two darts at a target with 2000 possible locations determined completely random, what are the chances the two will hit at the same spot? Plus thisd wouldn't even been an even distribution like that, only the overlap time would be possible.
Again agree. I'm not sure about the exact timing of the pressure wave to the separation of the body/nosecone. My gut says to get the parts moving, including breaking shear pins may take more than a few milliseconds. And One altimeter I have only gives you the option for a 1 sec delay, not 2. But still probably remote
Minor risks could be a part from one falls off due to G forces and hits the other.
If you mount the altimeters per the instructions (Usually 4 4-40 screws) properly you would have to be pulling serious G's to cause those to fail.
I was more thinking of a large storage cap, such as on a Raven tearing off due to G forces. I know it is suggested to epoxy it to the card if you are going to hit high G's I don't know if other units could have a similar issue
Combined heating from the two units could impact operation - although I would think thermal heating from the sun would have a much greater impact
Mass of one unit versus two would change the resonance frequency of the sled which could cause a problem.
Most of these are running processors that are using less than 2 watts, these things will run on tiny batteries for hours. Overheating is not an issue, ambient airflow will be more than enough to prevent heating.
I did say this was a minor risk and just sitting in the sun is a much bigger impact
May be other failure modes.......
There are always other failure modes. That's why redundancy is important, a one point of failure system get increasingly unacceptable as danger from the rocket increases (complexity and size)
Agreed - that's why I will typically use 2 different altimeters, switches, power sources and 3 e-matches (see previous post to this thread)
Then from the human/operator issue, (which I believe is a bigger concern....)
Having more units means more wiring and complexity which can lead to erroneous connections (such as accidentally connection the main charge to the drogue channel).
Different units typically need to be set/programmed differently which could lead to errors.
These are absolutely the number one cause of errors, the correct solution is to properly checklist and verify working conditions pre-flight.
ABSOLUTELY - but I still once cross wired the drogue and main - hey - I'm human. It meant a longer walk but the rocket had a safe recovery
And since most units beep out continuity or other info having 2 units could make hearing one over the other a problem
You should be at the very least able to turn one altimeter on, check it, turn it off, turn the second on and check it then turn the first back on. In my case I turn the stratologger on and wait for continuity beeps, then turn on the Telemetrum and look for my phone to connect and verify continuity.
One of my units allows me to set the "beep" to either a low or high tone. I am able to set it to be different from the other and I can discern which is which
Bottom line - you can run into issues either way - with or without redundancy
Process, such as check lists can help minimize the human errors (but not totally eliminate them)
Redundant systems can help with both equipment failures (bad FET, wire, weak battery, whatever) and in some ways can HELP the human error. You may make a mistake on one system that prevents it from operating correctly. But hopefully you don't make 2 mistakes, one on each system.
I strongly believe in a redundant system -As I've stated - 2 different altimeter, 2 different power sources, 2 different switches PLUS using 3 e-matches.
I will admit I plan to build a 38mm min diameter rocket, and there just isn't the space for a tracker and 2 altimeters. I will probably use my Raven to make use of its backup, but I have to admit I am concerned by the lack of redundancy since I have a single point failure for the altimeter system
Primary issue would be EMI from one device affecting the other. The could occur due to proximity of the units themselves or via the wires to the charges/batteries.
While this could be an issue you would find this in ground testing, with all systems active and setting off real ematches EMI wise the system will be very similar to in the air
Agree you should find it during ground test. There is a remote possibility that wires could shift under G forces and cause a problem but probably unlikely
Due to the differences in the units (Hardware and/or algorithms), while they are set to operate at different times/altitudes they could operate at the same time. With both charges being activated at the same time the rocket could over-pressurize (like - blow up).
The time frame for the ejection charges is in milliseconds, this is statistically very unlikely to happen. If you throw two darts at a target with 2000 possible locations determined completely random, what are the chances the two will hit at the same spot? Plus thisd wouldn't even been an even distribution like that, only the overlap time would be possible.
Again agree. I'm not sure about the exact timing of the pressure wave to the separation of the body/nosecone. My gut says to get the parts moving, including breaking shear pins may take more than a few milliseconds. And One altimeter I have only gives you the option for a 1 sec delay, not 2. But still probably remote
Minor risks could be a part from one falls off due to G forces and hits the other.
If you mount the altimeters per the instructions (Usually 4 4-40 screws) properly you would have to be pulling serious G's to cause those to fail.
I was more thinking of a large storage cap, such as on a Raven tearing off due to G forces. I know it is suggested to epoxy it to the card if you are going to hit high G's I don't know if other units could have a similar issue
Combined heating from the two units could impact operation - although I would think thermal heating from the sun would have a much greater impact
Mass of one unit versus two would change the resonance frequency of the sled which could cause a problem.
Most of these are running processors that are using less than 2 watts, these things will run on tiny batteries for hours. Overheating is not an issue, ambient airflow will be more than enough to prevent heating.
I did say this was a minor risk and just sitting in the sun is a much bigger impact
May be other failure modes.......
There are always other failure modes. That's why redundancy is important, a one point of failure system get increasingly unacceptable as danger from the rocket increases (complexity and size)
Agreed - that's why I will typically use 2 different altimeters, switches, power sources and 3 e-matches (see previous post to this thread)
Then from the human/operator issue, (which I believe is a bigger concern....)
Having more units means more wiring and complexity which can lead to erroneous connections (such as accidentally connection the main charge to the drogue channel).
Different units typically need to be set/programmed differently which could lead to errors.
These are absolutely the number one cause of errors, the correct solution is to properly checklist and verify working conditions pre-flight.
ABSOLUTELY - but I still once cross wired the drogue and main - hey - I'm human. It meant a longer walk but the rocket had a safe recovery
And since most units beep out continuity or other info having 2 units could make hearing one over the other a problem
You should be at the very least able to turn one altimeter on, check it, turn it off, turn the second on and check it then turn the first back on. In my case I turn the stratologger on and wait for continuity beeps, then turn on the Telemetrum and look for my phone to connect and verify continuity.
One of my units allows me to set the "beep" to either a low or high tone. I am able to set it to be different from the other and I can discern which is which
Bottom line - you can run into issues either way - with or without redundancy
Process, such as check lists can help minimize the human errors (but not totally eliminate them)
Redundant systems can help with both equipment failures (bad FET, wire, weak battery, whatever) and in some ways can HELP the human error. You may make a mistake on one system that prevents it from operating correctly. But hopefully you don't make 2 mistakes, one on each system.
I strongly believe in a redundant system -As I've stated - 2 different altimeter, 2 different power sources, 2 different switches PLUS using 3 e-matches.
I will admit I plan to build a 38mm min diameter rocket, and there just isn't the space for a tracker and 2 altimeters. I will probably use my Raven to make use of its backup, but I have to admit I am concerned by the lack of redundancy since I have a single point failure for the altimeter system