# ALTS-2 or HiAlt45K?

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#### timothyterpsalot

##### Well-Known Member
These are the two that I have been looking at... I see that there is a difference in the way that they handle mach transitions. Is there an advantage to either of these? I was thinking the ALTS-2 seemed to be the way to go since I wouldn't have to account for how long the rocket will be in mach. That is a tricky variable if the rocket is to travel just above mach. Thoughts? Input?
If anyone has a better suggestion for an altimeter I would appreciate that as well. Thanks!

#### JimJarvis50

##### Well-Known Member
These are the two that I have been looking at... I see that there is a difference in the way that they handle mach transitions. Is there an advantage to either of these? I was thinking the ALTS-2 seemed to be the way to go since I wouldn't have to account for how long the rocket will be in mach. That is a tricky variable if the rocket is to travel just above mach. Thoughts? Input?
If anyone has a better suggestion for an altimeter I would appreciate that as well. Thanks!
I have both of these altimeters (and a number of others), and both of them are good altimeters. They do differ in terms of how they handle Mach, but there are many other differences between them that are probably more important than that particular difference. The HA45 has the capability to read up to 45K feet, but it does not have the ability to "download" the flight data. If you are not planning to fly above 25K feet, you might consider a MAWD instead, which does download altitude versus time. The ARTS2 is an "inertial" altimeter as opposed to a barometric altimeter. It is larger (a disadvantage), but it has the capability to do things beyond just dual deployment. Many people like to use one baro and one inertial altimeter for redundancy.

I use altimeters for many different things in different kinds of flights. Consequently, I have many different kinds of altimeters because of the differences in the features. I think you could get more specific recommendations on specific altimeters if you describe what sort of rockets you are flying now or plan to fly in the future.

Jim

#### timothyterpsalot

##### Well-Known Member
I wanted this altimeter for flying my level one rockets. I figured if I wanted to go pretty high I could just buy another one. This would probably fly between 1,000 and 10,000 ft. I won't be flying very large rockets with it, probably 3" dia, 6 ft tall max. I will probably only use it for dual deploy.
I was looking at the HiAlt45K because it was cheaper but the way it handled mach seemed like it could cause problems/be complicated. I would like the minimum altitude to be able to fire at around 300 ft which is why I was looking at the ALTS-2.
Also, if the ALTS-2 is an interial altimeter how does it fire the second charge at 700 or 250 ft? Does it also use a barometric altimeter as well?

#### JimJarvis50

##### Well-Known Member
I wanted this altimeter for flying my level one rockets. I figured if I wanted to go pretty high I could just buy another one. This would probably fly between 1,000 and 10,000 ft. I won't be flying very large rockets with it, probably 3" dia, 6 ft tall max. I will probably only use it for dual deploy.
I was looking at the HiAlt45K because it was cheaper but the way it handled mach seemed like it could cause problems/be complicated. I would like the minimum altitude to be able to fire at around 300 ft which is why I was looking at the ALTS-2.
Also, if the ALTS-2 is an interial altimeter how does it fire the second charge at 700 or 250 ft? Does it also use a barometric altimeter as well?
OK, either of these altimeters would work (as would most of the others). I would still recommend the MAWD over the HA45. Getting the flight data was one of the things I enjoyed most when I got my first altimeter. You can verify the apogee altitude (that it's not a spike for example), calculate the velocity and acceleration, and calculate the descent rate under drogue and main. Lots of good data for the $20 difference in the cost. The Mach part of it is simple. You do your flight simulation to estimate how long it will take the rocket to reduce speed to about Mach 0.7 (roughly), and you set the delay at that time or the next higher time. This works fine for many people, but I've got no problem with the ARTS, which avoids having to do this. And you're right, the ARTS is barometric for the main. However, I think most people would recommend deploying HP rockets at higher than 300 feet, just in case the chute needs a few extra seconds to open. Jim Looks like$40 total cost difference (with the data transfer wire). Still worth it though.

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#### Handeman

##### Well-Known Member
TRF Supporter
I have a HiAlt45 and it works great. The mach delay is pretty easy to use. It doesn't record data, but it does put out more current for lighting the charges then the MAWD.

I know everyone says to put a fresh battery in every flight, but I flew a whole season on the same battery and it's voltage was only down to 8.7V. I did put a fresh battery in this year, but I'm sure the original would have lasted this year too. I have three flight and have been testing homemade e-matches in a vacuum chamber and have fired 2 dozen already and the battery voltage only dropped from 9.0 to 8.9. For the Alt45 ability to sink a lot of current, it is still very easy on the batteries.

#### MarkM

##### Well-Known Member
My personal favorite is the ALTS25, very similar to the ALTS2. Two differences 1) it is a bit wider, but still fits within a 3" altimeter bay...I haven't tried it in anything smaller 2) it has many more options for main altitude deployment. Both altimeters are barometric; they are not inertial. They are "armed" once the barometric sensor detects a 300ft difference between rocket position and ground starting state (based on an air pressure logarithm). My ALTS25 is the altimeter I use for ~ 95% of my flights....love it, easy to setup, high reliability, fires all the commercial ematches I've tried and will work with the ematches made from the Quickburst kit.

#### bobkrech

##### Well-Known Member

1.) The PF Hi4Alt5, the MAWD and the ALT-2 are barometeric altimeters, not inertial. The PF units employ a Mach Lock out timer to prevent false deployments at Mach transitions whereas the ATL-2 calculates measures the changes in pressure vs time and calculates air speed to prevent false Mach transition deployments.

2.) The MAWD and ALT-2 are have capacitor discharge pyrocircuits and use small, low capacity "dog collar" batteries. Check the AH rating of the batteries and devide that by the current draw of the altimeter to determine then maximum number of hours that you can have the altimeter on befroe the batteries die. To account for temperature effects, I would change out the batteries after half the time determined by this method.

4.) The HiAlt45 needs a bigger battery to fire the pyros. It is probably best to use a separate pyro battery.

5.) Never use battery voltage alone as an indication of a good battery. If there is no current draw, a bad battery may test as good. Batteries should always be tested under load. A 1 Kohm resistor in parallel with a dog collar 9-12 volt battery will draw about the same current as an altimeter, and check the manufacturers data sheet for the capacity vs voltage curves under load. Alway change the battery at the 50% point to account for hot or cold conditions where the capacity is reduced.

Bob

#### Handeman

##### Well-Known Member
TRF Supporter

4.) The HiAlt45 needs a bigger battery to fire the pyros. It is probably best to use a separate pyro battery.

Bob
Bob, I agree with what you say about the batteries, but the thing about the HiAlt45 is that there is no way to wire in an additional pyro battery without modifing the circuit board. The HiAlt45 does use a capacitor to hold voltage in case of intermittent opens in the battery during flight. It will continue to operate for about a second after the battery is disconnected. I'm not sure if this will provide power to the circuits if the ypro channels drag down the battery during firing.

#### bobkrech

##### Well-Known Member
Bob, I agree with what you say about the batteries, but the thing about the HiAlt45 is that there is no way to wire in an additional pyro battery without modifing the circuit board. The HiAlt45 does use a capacitor to hold voltage in case of intermittent opens in the battery during flight. It will continue to operate for about a second after the battery is disconnected. I'm not sure if this will provide power to the circuits if the ypro channels drag down the battery during firing.
You are correct. The HiAlt45 requires that the battery supply all the required igniter current, but the uC is protected from brownout for 4 seconds by a robust capacitor and the igniters are only powered for 1 second, so uC brownouts won't be issue.

Differences between HiAlt45K and miniAlt/WD (from the manual)

Users of the miniAlt/WD should note that the HiAlt45K and miniAlt/WD have some internal differences in their power and igniter firing circuitry:

1. The miniAlt/WD will ONLY fire low current, low energy electric matches. The HiAlt45K will fire anything that requires less than 5
amperes of current.

2. The miniAlt/WD firing outputs are turned ON for 50 milliseconds, the HiAlt45K outputs are turned ON for a full second.

3. The HiAlt45K requires that the battery be able to supply the current necessary to fire the igniter, while the miniAlt/WD supplies the firing current itself.

4. The miniAlt/WD can survive a 2 second loss of power during flight without resetting, while the HiAlt45K can survive for up to 4 seconds.

5. The miniAlt/WD can still fire igniters during the 2 second power loss, the HiAlt45K cannot fire during power losses since the firing power is provided by the battery.

The Parrot altimeter is another option. It is also automatically immune to mach transitions, and compares favorably to the ARTS-2 in terms of price, data recording capability, size, and number of outputs. The battery for the board circuitry is built-in and rechargeable, and the deployment battery is separate, so there is no issue with brown-outs. The Parrot fires charges with up to 4 Amps for 1 second. The default configuration for the apogee and main outputs will work right out of the box for almost anyone. The main deployment altitude can be set down as low as you want (though I wouldn't recommend anything below 300 feet)

There was a time when the Parrot did not have a GUI-based interface program for modifying the altimeter configuration and downloading the data, but that has changed with the introduction of the Featherweight Interface Program (FIP) which provides an easy-to-use GUI for altimeter setup and nice graphing of the data. I still need to update the manual on the website to reflect the new FIP.

The HiAlt45k is significantly less expensive, but it does not record any data and has no on-board accelerometer.

#### timothyterpsalot

##### Well-Known Member
Oh wow, thanks for that info!! What increments can the second deployment be set at? Will I need software for my computer to be able to read the data? I think I am more interested in the Parrot than the ALTS.

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Oh wow, thanks for that info!! What increments can the second deployment be set at? Will I need software for my computer to be able to read the data? I think I am more interested in the Parrot than the ALTS.
The increment for the main deployment altitude is about 30 feet.

Yes, the Parrot only tells you the altitude via the downloaded data. But there's room in memory for 5 flights, so you can fly several times between downloads. The software for downloading the data and setting the outputs can be downloaded from Kevin Small's site: www.here-and-beyond.com, under altimeters. One of these days I'll get it up on my own site.

By the way, I did a deployment test recently at 250 feet, and it still had plenty of hang time, because it's a small rocket and the chute inflated right away.

#### cwbullet

##### Obsessed with Rocketry
Staff member
TRF Supporter
Global Mod
It would be nice to have a Mac compatible interface. Has anyone developed one?