The new AGM Altimax, featuring pyro and servo outputs.

The hand-held LCD programming and review device.

The 15 pin HD D-Sub receiver has connections for pyro and servo outputs.

ZEVEN, Germany EU — A German hobby rocketry enthusiast is working to bring a new altimeter to market featuring a hand-held LCD field interface that would replace the traditionally-used personal computers to program the device.  It also incorporates a unique connection interface to allow quick switch-out.

Louis Schreyer, of Zeven, Germany, is working to bring his AGM Altimax altimeter to the market to overcome the lack of easy-to-use altimeters in Germany.  His initial system was completed about six months ago and has been through an extensive testing phase, testing over 100 flights on a base of 50 units.

His desire was to create an easy system that everyone could use without having to lug a laptop around on the field.  Plus, he wanted to add outputs onto a device to drive servos instead of simply firing a pyrotechnic device, for those tho want to utilize mechanical ejection devices, or both.

His unit, built around an ATMega644 16Mhz 8-bit microprocessor by Atmel, uses a barometric sensor that utilizes a Kalman filter.  The developer claims the two pyro outputs are capable of delivering 17A using a single operations battery, using either a 7.4V lithium polymer battery or regular 9V batteries. 

The two additional servo outputs utilize a separate power convertor, allowing the flier to use either pyrotechnic or servo-driven recovery systems. Visual and audible unit status are communicated to the user via a beeper as well as two light-emitting diodes (LED). And, a built-in bootloader allows for firmware updates to be installed by the end user via downloads from the Internet.

The device calculates how high it is by the air temperature at the launch site, and the designer claims an accuracy withing 3 meters, based on the Kalman filtering system.  He states the filter calculates acceleration and speed based on calculations using the barometric pressure, compensating for a common error range.  Using the Kalman filter, the device looks for where speed is zero, using that as the point of apogee, rather than other system that use rising air pressure to indicate descent.

"This filter is very effective, it calculates the acceleration and speed out of the barometric pressure. It calculates an allowed error for the pressure, which allows to filter out wrong data," Schreyer said in an online communication. "We can even switch off the sensor two seconds after launch, and it finds the apogee still quite well, its like magic."

Another unique design element is the use of a 15 pin HD D-Sub (HD-15) connector on the device, which allows quick change-out to move the device to a new rocket.  By removing a couple of screws, the altimeter is removed, switched to a new rocket and connected to a 15 pin HD D-Sub receiver there, allowing the device to be moved without having the rewire everything during the move.  The 15 pin HD D-Sub receiver has connections for the two pyro charges and two servo charges, and stays located in each rocket.

To allow configuration at the field, Schreyer built a hand-held LCD terminal which allows for quick changes in device setting, testing the servo and pyro outputs, or even allows you to review the data of the last six flights.  The unit measures 3.5" by 2.75" (90X70mm) and just about completely replaces the need for a personal computer. But for the computer enthusiast, he has written a software package that also lets you do the same on your computer, plus allows analysis of the Kalman-filtered data from the device.  The software is currently in German but is being converted to English at press time.

Measuring just over 3" by 1.5", the unit isn't the smallest on the market, but Schreyer is working on a smaller device that will fit in a 24mm tube and has all the features of the Altimax, just without the servo outputs.  The new features are an exciting addition to the electronics market, making the new device an interesting twist on an old idea.

Website: http://rockets.aquarix.de/elec/altimax.asp

11-11-2008 11:17 AM  #1
UncleVanya If pigs had fins...   Joined: Sep 2007 Posts: 4071	Re: Article: New German altimeter sports hand-held LCD control This looks like a great product. Does anyone know if an English language version will be made? Also does anyone know the projected pricing?

11-11-2008 07:46 PM  #2
StuBarrett Certified Level Eleven   Joined: Aug 2006 Posts: 154	Re: Article: New German altimeter sports hand-held LCD control re: "The device looks for where speed is zero, using that as the point of apogee, rather than other system that use rising air pressure to indicate descent" Wish other barometric altimeters were this smart. The "mach delay" is a kludge IMO. Stu

11-11-2008 08:08 PM  #3
Steve_Shannon Super Moderator   Joined: Aug 2006 Posts: 2434	Re: Article: New German altimeter sports hand-held LCD control Quote: re: "The device looks for where speed is zero, using that as the point of apogee, rather than other system that use rising air pressure to indicate descent" Wish other barometric altimeters were this smart. The "mach delay" is a kludge IMO. Stu Quote: He states the filter calculates acceleration and speed based on calculations using the barometric pressure So, if he is uses barometric pressure to calculate speed and then watches for speed to reach 0, he must be watching for some adjacent samples where the change in pressure is less than some small amount (unless I totally misunderstand). Would that never occur during mach transition?

11-11-2008 10:33 PM  #4
jderimig Certified Level Three   Joined: Sep 2006 Posts: 109	Re: Article: New German altimeter sports hand-held LCD control Quote: So, if he is uses barometric pressure to calculate speed and then watches for speed to reach 0, he must be watching for some adjacent samples where the change in pressure is less than some small amount (unless I totally misunderstand). Would that never occur during mach transition? I think the Kalman filter takes into account how a real mass could actually accelerate/decelerate in a real flight, there is a model behind the calculations. The large volatility in altitude (as inferred by pressure) around a mach transition would not be possible in a real flight profile.

11-12-2008 12:01 AM  #5
Steve_Shannon Super Moderator   Joined: Aug 2006 Posts: 2434	Re: Article: New German altimeter sports hand-held LCD control I agree that Kalman filtering is the answer. I just didn't understand the part about watching for 0 rather than a change in direction. I'm no expert on Kalman filtering, but I wonder if low pass filtering would also help filter out mach transitions.

11-12-2008 04:30 AM  #6
Juerg Certified Level Three   Joined: Aug 2007 Posts: 353	Re: Article: New German altimeter sports hand-held LCD control Yes, the Kalman filter is the answer. I am glad I could persuade Louis to implement it. It predicts "plausibe" future development of the data and validates the actual data against this. It's a complex method, but it largely eliminates all the well known problems of "baro-only" altimeters. The second advantage is the accurate determination of apogee! No late deployments, right on the spot. Every time! Juerg

11-12-2008 06:12 AM  #7
swissflyer New Member   Joined: Apr 2008 Posts: 7	Re: Article: New German altimeter sports hand-held LCD control yeap..i can confirm.. i did myfirst flight..double ejection with the altimax..and i "fall in love" with

11-12-2008 08:21 AM  #8
UncleVanya If pigs had fins...   Joined: Sep 2007 Posts: 4071	Re: Article: New German altimeter sports hand-held LCD control Still curious about the possibility of English language version... Also about price...

11-12-2008 08:38 AM  #9
swissflyer New Member   Joined: Apr 2008 Posts: 7	Re: Article: New German altimeter sports hand-held LCD control Quote: Still curious about the possibility of English language version... Also about price... i did pay the altimax some more than 100€ i'm sure soon or later the SW will be too in english.. in the worst case..german is a nice language.. Alessio

11-12-2008 08:48 AM  #10
Juerg Certified Level Three   Joined: Aug 2007 Posts: 353	Re: Article: New German altimeter sports hand-held LCD control I did talk to Louis on options to promote the product internationally. I don't know about his last plans. But we talked about an english language version at that time. Only Louis really can comment on that currently. I also doubt that the pricing is known yet, the initial run was on a "non profit" base. Juerg

11-12-2008 10:28 AM  #11
jadebox Roger Smith   Joined: Jul 2008 Posts: 63	Re: Article: New German altimeter sports hand-held LCD control Quote: re: "The device looks for where speed is zero, using that as the point of apogee, rather than other system that use rising air pressure to indicate descent" "Speed" should be "acceleration" in the quoted quote, right? A rocket doesn't stop at apogee. Edit: Nevermind, I just realized that the vertical component of the rocket's velocity does become zero at apogee. -- Roger

11-12-2008 11:04 AM  #12
ddmobley Administrator   Joined: Jul 2006 Posts: 4553	Re: Article: New German altimeter sports hand-held LCD control For heada: Quote: The software is currently in German but is being converted to English at press time.

11-12-2008 11:05 AM  #13
Juerg Certified Level Three   Joined: Aug 2007 Posts: 353	Re: Article: New German altimeter sports hand-held LCD control Yes, that was meant. Actually, this description isn't completely accurate (speed becoming zero), the more accurate description would be "validated speed" becoming zero. And validation is happening by taking into account that accelerations cannot be higher than a certain level, so speed can increase/decrease at certain limited rates only. That's the "illustrated explanation", the Kalman filter is a mathematical method, at the end of the day. Juerg

11-12-2008 12:34 PM  #14
GDiener Certified Level Two   Joined: Mar 2007 Posts: 50	Re: Article: New German altimeter sports hand-held LCD control OK, stupid question on the filter. What happens if the rocket goes off at an angle and therefore never achieves a zero speed, that is that the vertical component of the velocity will be zero, but the horizontal component of velocity will not be zero. Does the filter "look" for the minimim speed, or does it truely look for "zero" velocity?

11-12-2008 01:22 PM  #15
UhClem Certified Level Three   Joined: Oct 2006 Posts: 203	Re: Article: New German altimeter sports hand-held LCD control More than you ever wanted to know about the Kalman filter: http://home.earthlink.net/...nd/2002/KalmanApogee.pdf If that didn't put you to sleep then this will: http://home.earthlink.net/.../2004/KalmanApogeeII.pdf

11-12-2008 01:35 PM  #16
LarryC Certified Level Two   Joined: Jul 2008 Posts: 90	Re: Article: New German altimeter sports hand-held LCD control Quote: OK, stupid question on the filter. What happens if the rocket goes off at an angle and therefore never achieves a zero speed, that is that the vertical component of the velocity will be zero, but the horizontal component of velocity will not be zero. Does the filter "look" for the minimim speed, or does it truely look for "zero" velocity? If the trajectory is ballistic, the minimum speed will likely be the very point where the vertical velocity is zero.

11-12-2008 01:49 PM  #17
UncleVanya If pigs had fins...   Joined: Sep 2007 Posts: 4071	Re: Article: New German altimeter sports hand-held LCD control Quote: i did pay the altimax some more than 100€ i'm sure soon or later the SW will be too in english.. in the worst case..german is a nice language.. Alessio LOL - I have no delusions about my ability to speak and read German. I have recently interacted with a neighbor's guest from Germany. While I could make myself understood more than my wife could - my ability in German is beyond bad. I would not want to trust my altimeter programming to my very bad German. [beat dead horse mode> I still don't see pricing info... [/beat dead horse mode>