Electronics bays/altimeters in LPR

I'm working on a DIY altimeter for my low power fleet to begin with, hoping to move to MPR one day.... It seems you need to have the altimeter inside the tube, likely exposed to ejection gases.... Has anyone noted or suspected this is causing probs eventually with the electronics, given the corrosive nature of the gases?? It might be academic, the life shortening event in these is likely to be from being stranded in a tree rather than gassed.... curious though....
Lee

Hi Lee- Welcome to TRF! Cruise around in the 'recovery area' here and you'll find all of the designs are based on isolating and protecting the altimeters. Even the simplest alt is shielded or 'sealed' because the carbon from the ejection charge is conductive and over time corrosive too. Obviously baro based alts are more sensitive to pressure spikes than acel based units because of the exposed circuitry. Look into Jolly Logic's units and John still recommends protecting the fully enclosed unit from gasses. Because of the added structural elements, it gets a little easier in MPR where the motors can lift the added mass easily. It's a real challenge to build light and strong but don't let that deter you. That 's the whole beauty of our sport-the physics and material properties we use to get the most performance out of our motors, no matter what size. I have altimeters I've flown for 10 or more years, the trick is to get them back! Straight smoke and good chutes, brother. Welcome to the wide open skies!

I fly altimeters whenever i can and fly LPR almost all the time. I often create payload sections in models that wouldn't have them already - it only takes a stage coupler, a plywood disk and a screw eye. Often larger Estes kits already have a joint that involves a stage coupler in them - one that comes immediately to mind is the QCC Explorer and another is the Eliminiator - that lend themselves to this even without cutting a tube.

Thanks to the tiny size of some units - most notably the Altus Metrum MicroPeak - you can add a tiny payload section in a model as small as one made from BT-20 - and get altitude data.

The Jolly Logic units and the Estes Altimeter are designed to be able to be flown without a dedicated payload section, though it does make sense, as noted above, to make sure the altimeter is above the wadding, the shock cord and the recovery device. That way they're pretty well protected from all those nasty gases. Even for these I most often fly them in a payload compartment, not "in with the laundry".

A note one some payload sections: sometimes the coupler has openings in it that would allow gases from the main body through into the payload section. These are usually plastic couplers. Two that come immediately to mind are the bases of the payload sections in the Nova Payloader kit and the Sky Trax RTF. I always seal them with tape both to keep the nasty stuff out and to keep pressurization from the ejection event from messing with the readings.

Fyrwrxz is right - a key is getting them back. Otherwise you won't get the data (at least with anything this side of the Altus Metrum TeleMini).

Note that the *new* version of the Jolly Logic 2 does not fit in a BT20, whereas the old one did. But the display on the new one is really nice.

The first few will likely be evolving prototypes - I had thought of making a little bay for one, or somehow sealing the upper fuselage section of one from the lower section.... I'm hoping to shrink one enough to squeeze into a BT20 tube also, the problem will be keeping the altimeter short enough as it is made more narrow.... tinkering ahead!
Lee

Lee- checkout the Pico Alt P-1 altimeters! .6 x .3" only masses a few grams with a battery! Red SMT led flashes last altitude. I have two of these and they are super easy to use because they use smt chip based software with the batt holder built in. These will fly on gliders, mini motors and even slingshot loads! They still need to be protected.

Mine will be goliath compared to those - just on 3/4" wide, about 2" long, 0.25" thick.... half the fun is in the making of them though.... What good is my electronics bench otherwise....

Lee697 said:

Mine will be goliath compared to those - just on 3/4" wide, about 2" long, 0.25" thick.... half the fun is in the making of them though.... What good is my electronics bench otherwise....

Click to expand...

Ah, about the size of a Perfectflite Pnut then.

Lee697 said:

Mine will be goliath compared to those - just on 3/4" wide, about 2" long, 0.25" thick.... half the fun is in the making of them though.... What good is my electronics bench otherwise....

Click to expand...

ooooohhh-now I'm jealous!

Actually there are a couple Altimeters that can be flown in model Tubes as small as T4 (.448").
I have and fly two different tiny altimeters in Micro powered models as well See below.

I love it when people design their own product. Keep up the good work and do what works for yo.

Well.... here is my prototype v0.1..... it certainly felt more compact before I heatshrinked it....
I gave it a toss in the air outside tonight and it reported a 3.5m altitude - so that's a good start. Hopefully will flight test on the weekend some time.

It uses a "micromite" microcontroller and a BMP085 electronic barometer chip, connects to laptop via a usb-serial adaptor to report flight data post-flight, has a 100mAh lipo, shown being charged in pic 3.