Redundant. Redundant.

While reading posts and seeing peoples setups at launches I am noticing that most people, it seems to me, are using different brand deployment altimeters in redundant systems.

Is there a benefit to this? I was contemplating getting another altimeter, SL100, for a redundant system simply because it reduces the software needed and all I have to do is modify the timing of charges. All else is the same and in my mind easier to deal with.

Am I missing something here?

True redundancy depends on your definition of redundancy. Some say that you should use two brands of altimeters because if there is a bug in the coding of the altimeters, then both of them will be in error. On the other hand, two different brands of altimeters mean that any errors will be different (normally). Not to mention, the same altimeters beeping on the pad give you the problem of figuring out which one is beeping what. On the other hand, 2 different brands of altimeters have different beeping patterns, so it is easier to tell.

I would use two different brands of altimeters in my rocket (working on setting up the altimeter bay). However, that is because I only have 2 altimeters.

You can change the frequency of the tone on the RRC3 so you can tell them apart.

I use 2 of the same easier to program less chance of screwing something up

I don't think there is a right or wrong way. I have heard many different reasons why people choose there altimeter combinations.

Some as mentioned are about tones at the pad.

Some are about there personal definition of redundant systems.

Some people use a less sophisticated altimeter( same brand or non same brand) as a back-up ( possibly no data recording) and the thought there would be minimizing dollars lost if something happened such as a water landing ( possible at our launch area).

I've seen people use a redundant system (again same brand or different brand) to help them prove out a new unit or check calibration on an older one. I'm doing this very thing at our next launch.

As with many items in rocketry, one person may do one thing and another something entirely different and their are pluses and minus's to both ways, I see redundant altimeters as one such item.

There are excellent, well reasoned arguments to be made for both schools of thought - same model altimeters vs. different models.

g zilla said:

I use 2 of the same easier to program less chance of screwing something up

Click to expand...

^ Personally I went this way too, I believe the chance of human error (on my part) is greater than a congenital machine error.


All the best, James

You do not have true redundancy unless 2 separate PEOPLE set up your altimeters. The weakest link in the chain is the human not the electronics.

Fdog said:

There are excellent, well reasoned arguments to be made for both schools of thought - same model altimeters vs. different models.



^ Personally I went this way too, I believe the chance of human error (on my part) is greater than a congenital machine error.


All the best, James

Click to expand...

I believed in this as well, but at a recent launch where I had two entacore AIM dual-deployment altimeters in my rocket, both were fooled by a spike in pressure (and so perceived drop in altitude to below 500') due to the apogee charge - and despite the fact it only lasted for 0.1 seconds both triggered the main at apogee.... you would think that there would be some sort of filter to see that going from 1500 feet to 500 in under 0.1 seconds (~7,000 mph) is physically impossible... I am now replacing one of them with an RRC2+ to try to prevent a single problem causing a failure in both my altimeters.

Telemetrum - distributor changed the battery to include a little circuit to detect shorts and shut down the battery. It's a nice safety feature with LiPOs. Of course, firing a pyro charge is a short. Electronics disfunctional after drogue event, if it could even fire the drogue which might be in doubt. Found by flight errors. I hit this one twice before we figured it out. Flight saved in each case by having another flight computer of different type active. Interesting in this case that the telemetry was total BS. If we didn't have eyes on it each time, we'd not have found it by telemetry. It indicated an LZ about two miles away from where it really landed. Fixed by removing circuit in battery, and verified by successful operation in subsequent flight.

Raven - some bug in some particular version failing to fire pyro above 50Kft? Found with shovel. Not mine though; going by what I've read and heard. Having something else on board as well might have saved the flight. I think a firmware update fixed that one.

A friend's altimeter reliably puts his main out much higher than it should. But only that one altimeter - other "identical" ones work correctly. I'd name it but I've forgotten.

I'm not picking on those fine products; there are plenty of examples. Our stuff is not mil spec. It isn't terribly bug free or terribly reliable. We don't pay enough for those features, or buy in sufficient quantity for economy of scale to pay for those features. Plus, a rocket isn't exactly the most gentle environment into which one can put electronics!

I consider rocket control functions to be safety-critical, and believe in true redundancy as a method of minimizing the chance of catastrophic issues.

GoPro Hero2 - had some issues with launch G loads... It would stop recording as soon as the rocket stared to accelerate. It would resume recording a few seconds after the motor shuts off. Solved by going back to older Hero.

Nothing is immune to issues. Nothing.

Gerald