Jolly Logic AltimeterTwo versus Altus Metrum MicroPeak

[mh9162013]

I've done a few flights with both of these altimeters in various rockets. Here are their apogee readings:

1. Estes Patriot with C5-3: JL = 253 feet. MicroPeak = 41.7 feet (12.7 meters) (likely glitch in the MicroPeak). During this flight, the JL was packed with paper towels in the nose cone payload bay while the MicroPeak was dangling in the "regular" payload bay (or maybe it was the other way around).
Launch conditions: cold and sunny with little to no wind.

2. Estes Patriot with C6-5: JL = 152 feet. MicroPeak = 146.0 feet (44.5 meters). Both altimeters were packed with paper towels in the nose cone payload bay.
Launch conditions: 48 degrees F and 61% relative humidity; little to no wind.

3. Scratch-built BT-50 AMRAAM with A8-3: JL = 103 feet. MicroPeak = 113.5 feet (34.6 meters). Both altimeters were dangling from the nose cone.
Launch conditions: 73 degrees F and 78% relative humidity; slight winds from the north

4. Estes Goblin clone with A8-3: JL = 62 feet. MicroPeak = 60.4 feet. Both altimeters were put into the nose cone payload bay, but not packed with paper towels.
Launch conditions: 81 degrees F and 68% relative humidity; slight winds from the north-west

That's only good 3 flights with both altimeters working properly (presumably), but it's interesting to see the seemingly random variations in the flight data.

Just thought some of you (ahem @BEC) might find this interesting...or not surprising and simply mundane.

 

[cerving]

You're likely to see higher percentage variations with lower LPR flights. With HPR flights, they will be somewhat less. I recently did a test flight with six altimeters (four Eggtimer altimeters and two "others"), and on a flight in the upper 2600's they were all within about 20' of the average.

 

[BEC]

I agree with Cris that those pretty low flights will make things look a little worse. I'd be a little curious to see the MicroPeak plot on flight #3. But dangling an altimeter, even one pretty much designed for that (AltimeterTwo) is asking for chaotic data around ejection and during descent, some of which might not be handled well by the filter software.

 

[SolarYellow]

I'm not sure I even see the point of flying an altimeter for flights that low. There's discussion of at least one altimeter not even being expected to register a flight below about 100', so I'd not expect much from flights at 100' +/-.

 

[mh9162013]

I'm not sure I even see the point of flying an altimeter for flights that low. There's discussion of at least one altimeter not even being expected to register a flight below about 100', so I'd not expect much from flights at 100' +/-.

Please explain.

As for the 100 foot ceiling, apparently my MicroPeak will register alitudes as low as 38 feet.

 

[SolarYellow]

Just my personal feelings, I guess, which others might not share. They obviously aren't extremely low-power competition rockets. For me, those rockets at those altitudes would be visual estimates and I must be trying to keep it on a really small field, so the metric would be, did it stay on the really small field? Was it a nominal flight with deployment at a safe altitude? I'm unlikely to bother flying instruments on something less than using the full delay of an A8-5.

 

[cerving]

I recently shipped a customer a special firmware build for the Quark, with a 100' launch-detect altitude instead of the standard 200'. He's using it on a large saucer... which by TRA rules must have some kind of active recovery. He only expects it to go about 150', so the 200' arming altitude is too low for this project.