Altimeters!

[Randy G]

I currently use a casio watch for an altimeter in my sailplane and zagi. It records the max altitude, and also temp and time at the that moment. It is ok but it is bulky and pretty heavy.

Ok, here is the challenge: if you could record the "perfect" on-board computer, what would it do? I think you could have two of them. One that would look like a post-it digital clock that would record max altitude, time, and temp. The other would transmit to a unit on the ground (you could put it on your transmitter) that would give gps, altitude and temp. That way, you could get a 3 dimensional view of exactly where you were at!

If there was such devices, what would you pay for them? I am researching developing this because I would like to have a dozen of them for my planes.

[Mr.RC-CAM]

Randy,

I have been toying with an ongoing project that is like that. I started it well over a year ago and I poke at it from time to time. It gets some attention in between my other projects. So far, it has been a lot like "the house that Jack built" -- a project that never ends.

Mine is a wireless telemetry system that I optimized for model helicopter use. The first prototype sent fuel level, rotor speed, exhaust temperature, battery voltage(s) and more. It also sent warning messages if I got hit with R/C signal interference.

The RF link is on 433Mhz (ham radio freq) and the range is a little shy at this point. Currently I get about 300 feet, but I could pump that up if I needed to. Most of my flying is close by, so the extra range is not needed by me.

The data is sent to a Lap Top PC Computer. I have a custom Win95/98 program (written in Borland C++) that displays everything in big hunky analog guages. They are easy to read, but while flying it is still not convenient for the pilot to watch them. I think that it would be better if I added a voice synthesizer to announce the data (or at least the alarm states). A Soundblaster card and more software would be the answer.

A screen snap shot of my prototype PC app is shown at the bottom of this post.

This month I started a redesign. I am adding altimeter and air speed functions. The extra features have forced me to scrap the old board, since I needed a new microcontroller with more ROM. I am up to 8K, a paltry sum in the PC world, but that is a decent amount of embedded code for such a project.

I may also port the PC's code over to a Palm handheld. That would make it very portable. My other choice is to overlay the data onto a wireless video link, but I am afraid that all the text would leave little for the airborne video image. Perhaps I will try to see if it has meret.

But as you may have guessed, this project has wandered around somewhat, so who knows what the final package will be like. Frankly, I have more fun developing personal gadgets, so "finishing" it is not my main focus.

There are some commercial systems out there. Here is one from a UK firm (there are more):
http://www.rtos-solutions.co.uk

Here are two examples of USA based telemetry systems:
http://www.geocities.com/eba1972/index.html
http://www.rc-experts.com/

As far as an on-board display that does not transmit any data, I think there is room to add several items to its functionality without substantially impacting cost. Like you, I would like a local LCD that showed the basic stuff. Perhaps max altitude, min battery voltage, average airspeed, Rx glitch count, etc.

When you returned home, a PC interface could be used to download entire data sets from each flight. With five second sample periods, lots of good data could be retrieved and plotted. I am not sure what you would do with the info, other than take a peek at what occurred during flight.

Here is a altimeter project site that may help you. It may soon include plans for an R/C telemetry verision: http://www.qsl.net/ok2xdx/Altimeter/altimeter.html

Good luck on your project. If/when I finish mine I will post a few words about it. Until then, it will continue to keep me entertained as I dork around with it.

[Mr.RC-CAM]

The PC screen snap shot did not show up on my original post. Here it is (I hope):

[ybanrab]

That's very cool, Mr-RC. I've been looking into doing something like this for a while but my Microcontroller skills aren't up to it. I've got a couple of questions if that's ok.

1. What microprocessor did you use? Any reason?
2. What did you use to measure rotor speed?
3. how are you planning to measure air speed? Differential pressure?

Thanks for any help.

Barny

[procrastination inc]

commercially availible unit here
http://www.thommys.com/html/body_picolario_english.htm

[docphi]

Here's a nice complete unit with video!

http://www.sky-spy.bigstep.com/

[Mr.RC-CAM]

I hope this helps:

1. What microprocessor did you use?
I originally used an MCU from Atmel. I switched over to a Flash PIC so that the project would be more appealing to other folks (in case I published the finished project).

There are no "best choices" when it comes to these sort of projects. If you ask me, it really depends on what software and hardware development tools you own. My migration to the PIC was based on my belief that the various Freeware development tools will make it easier to support by a guy/gal on a limited budget. The change certainly did not save me any money, but then I blessed with easy access to commercial embedded tools.

2. What did you use to measure rotor speed?
I have been using an IR opto coupler. I have a little index cam on the Rotor's main shaft that is just a standard mast stopper that I retooled. But, with the new design I am going to switch over to a Hall Effect sensor. I think mounting the magnet will be easier for most folks. For model heli's, either way will work fine. But if your application involves a model airplane then you would need to use a reflective optical sensor.

3. How are you planning to measure air speed?
So far, this element exists only in schematic form. The hardware design is nearly the same as the altimeter. I plan to use a single port absolute pressure sensor. I thought about using a two port differential type and installing fore and aft pitot tubes. I originally reasoned that this might reduce errors from rotor wash, but now I think that this is unnecessary over-kill.

The pressure sensors arrived last week. They are tiny little surface mount parts. Sadly, a work related project is still in the way, so it will be a few weeks before I can try them out.

I will admit that the plumbing aspects of the airspeed feature are uncharted territory for me. I am very slow-witted when it comes to fluid dynamics. For example, what are the dimensions to the pitot? How can I effectively use tubing to remotely mount it? How do I mount/aim the pitot to prevent airspeed errors? And so forth.

I would love to hear from anyone that has an accurate airspeed sensor on their model. For example, I know some of you are using the Sky-Spy TL100. If you are, can you please describe the mechanical aspects on the pitot and its connections? How is it mounted? Any suggestions to make it better?

[ohmite]

I've done quite abit of work developing a recording altimeter/accelerometer that I've been using for High Powered Rockets. Here are a couple of links to the altimeters: http://home.att.net/~e.ohmit/Version2-3/ROLAltimeter.htm and http://home.att.net/~e.ohmit/Version2-3a/ROLAltimeterv23a.htm .
These are earlier versions, I have a newer version that is smaller and faster, but not shown on the website. Also some of the links are still broken as it was moved from another site (which is still working BTW) but will eventually go away when the ISP decides to clean up space from former customers, the site is: www.concentric.net/~ohmit the links there still work.

Since most of the flight times for rockets are less than 2 minutes, and interest is mostly capturing high accelerations (for <2 secs) and proper deployment of parachutes. My sample rates are 40-50 samples per second (way overkill here). I've been using PICs for my work. This isn't directly applicable to RC, but....

Now that I've gotten back into RC, it seems like a logical progression to making this work for RC and meet the needs of the modeler(s). I've surfed over to the sites referenced above and they seem most geared toward gliders. Now I've got the bug to do some playing with this to make it work here.

From what I can see the following things would be good features:
- Time correlated data
- On board recording for post flight download
- Recording of model altitude and airspeed
- Recording of model acceleration(s) anybody want rates too?
- Interface and recording of GPS data (if available)
- Radio glitch counter/recording
- Battery health/status
- Ability to interface with Telemetry downlink (on a legal freq)

Any others? I'd like some ideas from you guys.

This will help give me some direction with my experimenting.

Next question, what would most people like:
1) Purchase the whole shebang
2) A kit to build it
3) Plans and direction how to do it yourself

Thanks for the time, I'm going to follow this thread with interest to see what people are thinking.

Cheers,
-Eric

[sguty]

To follow on Eric's post, the HPR folks have a number of lightweight altimeters available from companies like Adept, Cambridge, Blacksky, etc--if you're interested, take a look at http://www.rocketryonline.com and do a search on altimeters.
But the needs for HPR and R/C are pretty dissimilar. For R/C, AOA and attitude would be awfully interesting, especially if they could be correlated with control deflections (though it'd probably be easier to record the latter from the TX end to save a lot of additional electronics in the plane.)

[ohmite]

sguty,
You are correct the majority of the Rocketry products you mentioned are not directly related (these are meant to recover the rocket and deploy parachutes and some versions from each vendor even provide data logging capability), but the technology (processors, sensors, data storage, encoding, communication with GPS, etc) are the same and directly applicable. The work I've done (and is being done by the AED guys) allows expansion into so many other sensors.

The RC community doesn't need 50 s/s or 200 s/s and definitely needs more than 2 minutes of data storage (about average for most of the rocket altimeters). But 1 s/s or even 10 s/s would be good and it is easier to slow this stuff down than it is to speed it up.

That being said, my thrust was to find out what folks wanted to see, and whether folks wanted a DIY project or a ready made product and what it would need to have to be useful.

I agree AOA and attitude would be great and surface deflection would also be very handy. Getting surf position and recording that is doable (servo command that is). I've got some AOA and AOS ideas based on a previous life of mine. Attitude is hardest given the quality of the gyros that most people can afford, rates are much easier.
-Eric

[Ben C]

Originally posted by Randy G
Ok, here is the challenge: if you could record the "perfect" on-board computer, what would it do?
It would be great if it could be set up like a remote 'whattmeter', ie. the system measures amps, volts, watts and mAh used, and beams them 'live' back to a small LCD screen mounted on the top of your tx. An 'at a glance' milli-amp-hour reading would be SO useful that I'm sure it would be worth buying. You would know when the pack was about to cut out, how many climbs you had left in a pack, how much the prop and current 'unloaded' in flight, how much longer you could fly for, etc, etc.


Originally posted by Randy G
If there was such devices, what would you pay for them?
Price? Well, the current whattmeter is around £50, so is £80-£100 for a remote whattmeter reasonable? Or is a price like this wishful thinking? Perhaps the tx and rx parts could be sold/kitted separately?

The system would have to be easily interchangeable between planes if the cost of a single device was prohibitive. But you would not need a normal whattmeter as well as the remote one, so the overall price could be lower.


Just a few thoughts,
Ben C

[PunkerTFC]

I know that this would be bulky and quite un-feasable, but wouldn't it be cool if the data was displayed on a hud? then you could check it without looking away!

[Ben C]

Okay, now that we're talking un-feasable, how about a live video feedback from the plane to your heads-up-display? Hehehehe . . .

It would be cool for flying combat - until you were 'hit' at least!


Ben C ;)

[ohmite]

Volts would be easier. Current and thereby Watts is harder, especially when you get up to the really interesting values of 30+ Amps. Would Volts be good enough? If so that could easily be added.
-Eric

[BEC]

Welll......

I've wanted a data link to a PC or laptop that would record essentially the parameters a Whattmeter shows (current, voltage, power, cumulative mAh) plus RPM in real time (one sample per second would probably be just fine). I'd use this on a test stand as well as in the air. Remember current is just volts across a known small resistance.

For a remote application having airspeed and altitude would be great additions.

DIY vs. ready to go would depend on the cost difference compared to my available time (not alot). Or, how about the central unit being ready but sensor inputs at least partially DIY - particularly since the airspeed sensor and the pickup for RPM and their connections to the master unit would have to be customized to the airplane most likely.

Having a little bit of success with 2.4 GHz video (X10 based) I'd think a 2.4 GHz downlink could work well enough, especially with some sort of omnidirectional airborne antenna.

Stuff like attitude, AOA and surface deflections gets into parameters that full scale flight data recorders now do...... I'm not sure what I'd do with that data.

OTOH GPS would make precise positioning for survey type aerial photography much easier. Hmmmmmm.......

This is NOT getting my next column written :)

[LYHTSPD]

i am a big DIY-er so a kit would be more appealing to me.

[Ben Diss]

I'd like a small recording device to put in sailplanes that captures:

1. altitude (baro pressure)
2. temp

Optionally:

1. pitot pressure to determine airspeed
2. humidity

Really, really optionally:

1. GPS coordinates

I'd like a snapshot of these parameters to be taken every second and stored. I can envision some kind of IR transmitter to send the data to my PalmPilot after landing. I'd have to run on watch batteries and weigh no more than a couple ounces. I'd be willing to pay a few hundred for it.

-B

[Jeff Meyers]

Ben,

My business partner/flying buddy is already working on a commercial product that will do some of what you are looking for.

max altitude
air temp

a docking station will be available to download readings every 2 or 3 seconds.

The finished product is a ways off as we are about to finish our second product.

Regards,

Jeff

[Dsegal]

EMS has a series of onboard data logging devices for altitude, airspeed, voltage etc. The altitude guage costs $80 and it is necessary to buy the display module to read any of the devices- price is $55. See the website at www.emsjomar.com/

Dave Segal

[rkrishnan]

Originally posted by ohmite
Volts would be easier. Current and thereby Watts is harder, especially when you get up to the really interesting values of 30+ Amps. Would Volts be good enough? If so that could easily be added.
-Eric

Maybe a linear hall effect device could clamp around the battery lead and measure the DC magnetic field. At the higher current levels we operate in our hobby, this should be easier. Of course, it would have to be calibrated with an ammeter /whatmeter first.

[ohmite]

rkrishnan,
Interesting idea, I forgot about those types of transducers. I found two (25A LTS-25 and 50A LA55P from LEM) from Digikey. Bit pricy though ($19 & $25). They would sure do the trick though. The LA55P is a +/- 12-15V unit though so that complicates things a bit. The LTS-25 is a 5V unit. May be worth buying one and doing some experiments. They also make a 100A unit as well ;-).

I agree on the calibration as well.

Thanks for the brain jog!
-Eric

[Kimble_Schmitz]

If you want a real good altimeter check this relativly cheap logger out.

http://www.lomcovak.cz/lolo/lolo.html

Very cheap if you consider the work gone into this thing!
It can also be bought at f3x.com

[oldengr]

I am working on a telemetry system along the lines discussed in this thread. I was going to start a new thread to describe the project, but it looks like you guys are already into this subject. I'll compose something tonight and add it to this thread unless you all think we need to start a new one.

[markwild]

Early on in this thread, someone wrote that they could download the data to a PC, but they didn't know what could be done with it.

What would really be cool is an onboard device to measure and log the flight, then download and convert the data to a PC in some format that FMS could read. Then you could replay and watch your flight over and over.

I dunno if FMS has a record/playback feature though.

--Mark

[fregon45]

I just ran across this this morning. A single chip GPS unit....

http://www.motorola.com/mediacenter/news/detail/0,1958,1887_1513_23,00.html

I can't stop thinking about the possibilities. Location, speed, altitude...automation. An autonomus home brew airplane. This is easily the single most exciting home-brew gadget that I've heard about since learing how to use a PIC (other uC's included of course). I doubt that we'll get our hands on these in anything less than a year (if at all :mad: ). Quantity pricing will be on the order of $10/ unit, so I assume that for the average Joe it will be 2 or 3 times that much from Digikey or something. At any rate, I forsee a large price drop in consumer GPS equipment and lot more options from companies other than Garmin and Magellan. I can't wait.

[oldengr]

I'm currently working on a very small and light telemetry system to down-link interesting in-flight data. The project was inspired by a recent article in S&E Modeler describing an in-flight wattmeter flown on the SELFI during its flight across Long Island Sound. Recently I stumbled onto this thread and it seems like there are a few of us with similar interests. Personally, I'm just tired of not knowing what's going on up there. I have found Motocalc to be of marginal utility in predicting performance.

My system is completely designed and is under construction. The weight target is now 1.25 oz. complete including GPS receiver, down-link transmitter, micro-processor and antennas. I will be sending down the following data once per second for display and logging on a notebook PC:

Battery voltage and current
Motor or prop RPM
Motor temperature
Speed, heading and position (GPS)

The on-board transmitter and on-ground receiver are modules made by Linx (HP series). The GPS is a Motorols M12. The micro is an 8051 varient by Phillips (P89C688). Power is tapped off of the main battery.

I have flown the transmitter and the range looks to be at least the 1000 feet advertised by Linx. I'm leaving provisions to add an amplifier to boost output power should more range be needed in the future.

I would be happy to answer questions and listen to suggestions that could enhance the project. I'll post progress and photos if there is sufficient interest. Don

[Neil Stainton]

oldengr, your system sounds excellent. I would be very interested in something like that. Could you build in a spare input, so modellers could add their own sensor? I am particularly interested in airspeed. Also altitude and rate of climb are wanted by many.

[oldengr]

Neil: I will end up with a couple of spare analog inputs to the ADC as well as some spare port bits on the micro so almost anything is possible. Airspeed would be a nice addition as the speed from GPS is speed over-the-ground. Altitude will come directly from the GPS and it is pretty good now that SA has been turned off. Rate of change of altitude can, of course, be computed from consecutive altitude measurements but some software filtering would probably be needed to keep it from jumping around too much. The air speed seems difficult since you would have to keep the sensor completely away from the prop wash, like out on a wing tip! Thanks for the input.

I got a couple of hours today to work on construction but it is very slow going. Working with these tiny parts in a breadboard "one-off" environment is extremely tedious. But, it is coming along. Don

[jimsp]

Originally posted by Randy G


If there was such devices, what would you pay for them? I am researching developing this because I would like to have a dozen of them for my planes.

I don’t know about the telemetry stuff but onboard recorders would be quite easy. Little 8 pin serial eeproms that can record(many times) and hold(even when turned off) 16,000 numbers only cost $2 or $3. So if you measured and saved 3 parameters every second just one of these chips would be good for about a 1 1/2 hr flight. Of course you need the sensors with associated circuitry and a microprocessor to control everything.

I used a Basic Stamp in such a scheme to build a recording altimeter and speedometer for my bicycle. Later I added a recording heart rate monitor. What I did was to simply record the raw data in the eeproms and then later upload it to my computer to an excel file. I used Excel to do the calibrations, calculations and plotting.

I sure someone could incorporate the whole thing utilizing a pic for the microprocessor and the part cost would low but the per unit cost of developing such a devise for a low volume application like this would be quite high.

[AndyKunz]

Originally posted by ohmite
The RC community doesn't need 50 s/s or 200 s/s and definitely needs more than 2 minutes of data storage (about average for most of the rocket altimeters). But 1 s/s or even 10 s/s would be good and it is easier to slow this stuff down than it is to speed it up.

True. 2 minutes is too short, though.

On my data logger I used an Atmel Serial DataFlash (high capacity ones are a 3V part :( ) driven by a PIC (moving to 18F452-I/PT from '877). Data is stored in 32-byte records including RPM (derived by the PC. I actually keep a running count of shaft rotations in the logger), current (0-100A), volts (0-50V), (I and V are auto-scaled) and position of 2 servos, airspeed and altitude. The sampling rate is programmable from 1kHz to 6.5s but the filters are all tuned for 10Hz.

Andy

[jandirks]

GPS board

Maybe this is of interest for you guys. Don't have any info about weight and size, but look for yourself. I found it on eBay:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1384390870

Jan-Dirk

[zagisrule!]

I saw at Wal-Mart the other day a Estes rocket starter set with a peak reading altimeter for only $27.99. You could just pop the altitude recording capsule out and Viola!

Has anyone else seen it?

[oldengr]

Sounds like Andy is way ahead of most of the rest of us with a working data logger. Maybe he will tell us some more details about his design. I would particularly like to know how he did the air speed measurement. The auto-scaling is a good idea. I am presently fixed at 16 volts and 16 amps FS which is fine for the small models I'm flying right now. More info please, Andy.

Jan-Dirk's post on the Motorola GT receivers is a good find. This is a good performing eight channel board and at $20 it would be a good way for anyone to get some experience working with GPS. The board is a little big and heavy for the small system I'm working on but would be just fine for larger craft. I can lay my hands on one and weigh and measure it if anyone is interested.

I'm really impressed with Mr. RC CAM's display program with the guages and all. This is one area where I'm sadly lacking in DIY capability. Don't know how I'm going to solve that problem. I haven't thought past the simple logging of the data and raw display using a terminal program such a Procomm.

I'm hoping to fly my bare-bones unit in a few days sending down a dummy message on the down link to checkout actual data transmission and reception.

Don

[soren]

In the German super magazine for E-flight - Elektromodell (issue 4+, 1996) you can find a construction for a inflight datalogger, where you can measure the following:
Time, Speed, hight, power consumption (A), voltage, prop. rev/min, temp (eg. battery or motor), model acceleration(s) and the computer calculate used mAH.

The computer is app 30x30x10 mm - 20g, to that you have to add the size and weight of the transducers, where the combined speed and hight transducer is the biggest (app. 20x30x15mm 30g) the other transducers are wery small.
The total flying weight is app 80 g.
The system is able to store up to 510 data set (all the above mention is one data set).
You can operate the system with a switch from the transmitter or you can set the datalogger to start automatically when you start the motor.

The displayunit is not in the plane, but connected when you want to read data.
You read the data, when the plan is landed, with the display or by a PC.
You can also add a small transmitter (app. 50 g) then you can get the data down when the plane is in the air.

The datalogger is constructed by Milan Lulic and Ingo Star
You have to buy the computer-components from Milan or Ingo to get the SW - the price is OK low.

Ingo Star also have a homepage:
http://www.koeln.netsurf.de/~ingo.stahl/bc_src/bcomp_frm.html
...but unfortunately this page is not working for me today ??!!??

I have been using this system in a lot of planes, the system is working very fine. I was very surprised when the data told me that my El a' big (wingspan 2,4m, 30 cells, weight 7,5 kg) look at: http://users.cybercity.dk/~ccc16084/ was able to stay i horizontal flight only using 100W.

Soren
Denmark

[Nowell York]

GPS would be useful for autonomous flight out of visual range, however my highly evolved and rather low tech eyes display my model's 3D position.

My eyes also tell me the plane's altitude. There are two values that concern me: ground level and too high. If I was staring at a display on my transmitter, the former value would be achieved quickly. My back-up system (ears) would also register the ground level reading by detecting a muffled thump. The differential value computed by these auditory and visual systems would then tell me how far I need to walk to pick up the pieces of my once expensive and now valuless aircraft. The visual system also relays the plane's current attitude, rate of climb and even gives me an adjustable stall warning alarm.

Prop speed is estimated with my sophisticated, pitch sensitive, analyzing device. This lets me know when my battery is losing power even with my eyes closed. I have set an alarm value which is the low voltage cut-out on my speed controller. I can anticipate this eventuality by the stop watch and alarm on my transmitter combined with an average throttle setting correction factor. My auditory system also has the doppler decoding, stereo-acoustic upgrade, helping me estimate my plane's velocity, whether it is traveling toward or away from me, and automatically compensates for convergence angle through a visual interphase.

Finally, my system has temperature sensing capability. My skin transducer lets me know the ground temperature, and I'm able to calulate temperature at altitude through a simple linear correlation program I like to call "Cortex". I'm able to use this system in conjunction with my visual capability to create a variometer. When my plane suddenly speeds up and rises from level flight without any input from myself I am in a thermal. My temperature trasducer downloads average current draw when I pick up the battery at the end of the flight. My experimental olfactory system allows me to tell if any electrical component has been damaged. I call this latest upgrade "Burning Silicon".

All this information is downloaded to my memory storage system in real time. Unfortunately it has some half-life issues, and even modifies data as time goes on.

I'm working on several other parameters currently, but I think my system is pretty solid as it stands.

[Capt. Electron]

That's interesting Pilot Error, I'm running the same system.

Which version are you using, I'm currently running Jimmy 2.3.

It's pretty stable as long as I re-boot each morning.:D

Jimmy

[AndyKunz]

Don,

I did it for racing boats, where current draws of 100A are not uncommon. Kills your cells but man is it fast!

Air speed was the hardest part. I used a differential pressure sensor (MPX series as I recall). What I found was that the location of the static pickup was important to getting real numbers. I ended up going with an absolute input and ignoring altitude. As long as I don't try to compare data between too different flying conditions (altitude, barometer, etc) it was reasonably consistent. The pitot pickup was also sensitive. I found it virtually impossible to get the same readings from different pickups if there was any geometric difference between them. This is apparently a function of the small scale that we're working at. It's easier to just calibrate it for each pitot separately.

Auto-scaling was handled by starting sampling on the lowest gain. When the value was below the 50% mark, it would flip to a higher gain. When it went back up to 75% it would change to the higher gain. A total of 6 gains were available.

I wasn't so concerned about accuracy at the high end. For a shunt I used a length of 12 AWG.


Originally posted by oldengr
Sounds like Andy is way ahead of most of the rest of us with a working data logger. Maybe he will tell us some more details about his design. I would particularly like to know how he did the air speed measurement. The auto-scaling is a good idea. I am presently fixed at 16 volts and 16 amps FS which is fine for the small models I'm flying right now. More info please, Andy.

[BEC]

Originally posted by AndyKunz

Air speed was the hardest part...... What I found was that the location of the static pickup was important to getting real numbers.

This is VERY true in full scale aviation - where the static ports are and what the surface smoothness is around them and for how far. Maintenance of the area around the static port(s) (maintaining smoothness over time) is also critical. And you've got rather less real estate to work with on a model than on, say, a 757. :)

[oldengr]

Andy: Thanks for the additional information. The post from Pilot Error notwithstanding, I haven't given up on the idea that measuring is better than guessing if you care about the results. Therefore, I am proceeding with the telemetry project. I'm ready to fly a test of the data downlink - just waiting for the weather to settle down a bit. It's been a bit windy for my small planes and limited flying skill the past few days here in So. Cal.

The airspeed problem does seem difficult, especially when you think about trying to calibrate it. How did you approach that one? Don

[AndyKunz]

The only way I could - with a car.

Going with an absolute sensor works well-enough because we don't fly more than a few hundred feet AGL. A sailplane guy might want something more, but he has more room for a static pickup.

Mine is only a data collector - it saves the raw values read from the ADCs. Other systems include interpretation, which increases complexity. All the complex stuff happens in the PC for me. A spreadsheet makes most of the data crunching relatively easy. I figure that the more I do in the PC, the more "real" stuff I can put in the micro.

Andy

[eparkflyer]

Originally posted by zagisrule!
I saw at Wal-Mart the other day a Estes rocket starter set with a peak reading altimeter for only $27.99. You could just pop the altitude recording capsule out and Viola!

Has anyone else seen it?


The Max Trax isn't an altimeter.. it's a timer.

It pops the "altimeter" out, and it records the time it takes to hit
the ground. They know the drag/mass/etc of the module and it
does the math to figure out the "altitude"...

It would be awesome to find a true altimeter like this!!

I used to use a casio watch like others have said, but I lost it years ago...

[oldengr]

Got off two good test flights today after a less than successful attempt earlier in the week (notebook computer problems). Two flights totalling 32 min. sending down a short data frame consisting of a seconds count time-tag and a few dummy characters.

Results were good. Out of 1917 frames transmitted all but 89 were received correctly. The missed or corrupted data frames were almost all when the plane was nearly overhead. This makes sense since both antennas have a null at their zenith ( transmitting antenna on the plane pointing down and receiving antenna on the ground pointing up). Not bad considering that the transmitter output power is a measly 1 milliwatt! Flew the plane nearly out of sight so the range is good. The Linx modules are going to work fine for my purposes.

I may add an amplifier to boost power by 6-9 dB just to pick up some additional margin.

Next step is probably going to be to add the circuitry for battery voltage and current measurement.

Note to Andy: I hadn't thought of using a car. Must have done it on a very calm day! What do you think your final accuracy might have been?

Don