From: TonyL
Sent: Sunday, November 09, 2008 8:14 PM
Subject: Re: [arsabq] altimeters

Hi Kevin,
you know I have an opinion[ha ha].
don't forget the ARTS by ozark aerospace.

I think there are two categories:
1. cheap

These are typically pressure based. The guy selling them at a loss is great 
for people without much budget but ultimately hurts the folks who are trying 
to make a living supporting our hobby. When one of them can't survive any 
longer and that guy has stopped messing around then we all will have fewer 
choices. BTW his sensor's performance appears not significantly better than 
perfectflite's.

for small subsonic rockets without much ejection charge or motor ejection 
These seem just fine. I think the down side is that they can be spoofed, 
and quite easily for several of them. 

I am sure someone can tell me all the good things about how they work better 
than I make out. That is fine if that is all you need. 

For larger rockets the stored energy is higher and the responsibility still 
falls on the flyer to ensure the thing does not go off accidentally.

I can't agree that a pressure based flight controller is 'safe' unless it 
has a well though out safe/arm system added to it.

2. acceleration based [i.e. expensive]. these are typically as good as the 
hobby stuff gets. A pressure switch to arm the ejection charges in flight 
is pretty standard for NASA payloads, but I have not seen that level of 
complexity in the hobby stuff yet. The barometer based main deployment 
get the best of both sensors.

These are still not idiot proof. again a good safe/arm system added would 
make these realistically 'safe'. My altacc popped the charge on stubby 
because the arm switch was closed when it was powered on. Not particularly 
acceptable in my view but also hard to address in a uController based minimum 
size design. 

Any of the others that are not polarity protected [i.e. pop the charges when 
connected backwards, are too cheap to put a diode on the board in the name 
of saving space [or inexperience circuit designers who likely have never 
had one set off next to them or maybe just never learned even after that]. 
The right thing to do is to wire up a short harness so the battery connector 
has a diode on it. Diodes have quite high surge capability even for the tiny ones.

All this extra safe/arm & polarity stuff takes space. I have not done all 
of it on one rocket but these are things I think I want on my larger efforts.

All that said, a careful person can get by most of the time with any of the 
products out there. They should be commended on their care and thoroughness, 
but that does not make their rocket itself any safer.

Some particulars:

ARTS: got favorable responses when I asked about custom stuff, Nate had one, 
seemed OK except for the dip switches. Telemetry can be added, many functions, 
seems like the next altacc until the parrot. Popular in big bad rockets.

Gpsflight: starts with telemetry, can add other functions. hard to lay out that m
uch cash at once, but seems nice.

Parrot: the guy maintains a forum and answers questions. Manual is cryptic but 
defaults work fine and someone wrote a GUI for it since he uses hyperterminal. 
Clearly designed by a stereotypical software guy as he forgets how unintelligible 
his system is to a newcomer [no offense intend] and trades fairly complicated 
power arrangement for size. I have one, it worked fine for me straight out of 
the box. like a tiny altacc but watch that polarity! Also the external charge 
battery is unfortunate but at least makes the diode easier to include.

RDAS: So far DaveF's GPS does not work and while they answered other questions 
in the past, not sure what support he got. The manual is poor as I recall. Seems 
fine when it works and you may be hosed if it gets quirky. Many add-ons, popular 
in big bad rockets.

GWiz: 9 out of 10 fliers at BALLS17 think it is a POS. Heard that at RRS too. Sadly 
some guy inevitably only talks to #10 before buying it and his rocket augers in or shreds.

Missileworks: Several people at BALLS17 thought these were acceptable. Some folks 
have had good experiences.

Adept has been around a very long time. I have never heard anyone curse them.

I am satisfied with the parrot for typical deployment. Telemetry would lean me towards 
ARTS since I have seen it work and maybe Gpsflight, but would need to research that 
over a parrot and a big red bee.

cheers,

TonyL