PropVario, A Talking Variometer/Altimeter For RC Sailplanes


Lift. For a sailplane pilot it means the difference between a nice relaxing flight, or searching for an open area to land. Finding lift isn’t always easy though. This is especially true when the sailplane is hundreds of meters above a pilot whose feet are planted firmly on the ground. That’s why [Tharkun] created PropVario. PropVario is a combination variometer and altimeter for Radio Controlled sailplanes. We’ve seen a few variometers in the past, most often for full-scale sailplane or hang glider pilots. Almost every full-scale plane has a variometer as part of its suite of gauges – usually called a rate of climb or vertical speed indicator.

R/C pilots don’t have the luxury of looking at a gauge while flying though. At altitude even large 2 meter gliders can appear to the naked eye as no more than a dot. It would be somewhat embarrassing to lose sight of your glider because you were checking gauges. The solution is actually simple. A varying audio tone indicates the rate of climb of the plane. Higher pitched tones mean the plane is going up. Lower pitched tones mean the plane is descending. This system, coupled with a simple radio transmitter, has been in use by R/C sailplane pilots for years.

[Tharkun] decided to take things to the next level – adding voice output for altitude. He started with a Parallax Propeller and an MS5611 pressure sensor. The pressure sensor was a good choice for determining altitude. Even in today’s world of GPS, barometric pressure is still the gold standard for altitude measurement all the way up to commercial jetliners. A microSD card provides samples for voice output, making it easy to adapt the altimeter portion of the project to any language. Finally, a standard family radio service radio was hacked to create the down link.  Using the PropVaro is as easy as listening to the tones and voice readout.  Great job [Tharkun]! We hope all your flights are filled with plenty of thermals!

23 thoughts on “PropVario, A Talking Variometer/Altimeter For RC Sailplanes

  1. Interesting idea!

    Especially listening to the beeps though, it makes me wonder if using intuitive musical indicators could be easier on the ear. For example, using ascending or descending note sequences for the variometer, but selected the starting note based on altitude (and/or number of notes).

  2. The variometer tone is standard and it can be turned on in most sailplane cockpits. After hearing the high pitched beep enough times and associating it with good lift in a pavlovian way, I think it’s one of the sweetest sounds to hear!

    Your idea for combining two different pieces of information in one melody of beeps is interesting, but flying a sailplane, you want to know the immediate vertical speed at all times, but only need to get updated on the altitude every now and then. Maybe instead of altitude, you could somehow incorporate your speed or slip angle ( to the beep sequence for better coordinated flight.

  3. We didn’t care how it sounded… it was incredible just to know if you were in or out of the thermal so you could fly higher and longer… It was just a dot, you couldn’t tell by sight.

  4. Hacking a FRS radio is illegal (not that the FCC pays attention, just saying). I don’t understand why more hardware hackers aren’t licensed amateur radio operators. You can get the kind of ham gear needed for this type of project cheaper than a pair of FRS/GMRS radios, it’s legal to modify, and opens up a whole world of radio fun.

    1. Could you describe some of the gear required for a ham to do this? I’ve looked into APRS and packet radio, but it seems to be quite a bit more expensive that just buying two handhelds like this.


      1. The closest equivalent to FRS radios in the ham world would be inexpensive 2 meter or dual band handheld transceivers. There are several selling for around 35 dollars or so. The baofeng uv-5r is one popular model to prime your google searches. The price isn’t a lot different than FRS systems, but they’re much more powerful, and it’s legal to make modifications and attach external antennas. I agree with kaidenshi; this is precisely what amateur radio was intended for. Hacking ham radios is not only legal, it’s encouraged. And now that there’s no morse code requirement for any class of amateur license, the license is easy to get.

        1. Indeed, I have a Baofeng radio and for what I paid ($40 shipped on Amazon) I was overwhelmingly and pleasantly surprised. When I first got my ham license the only real budget radio was a 2M HT from RafioShack that was over $100 and apart from repeater split and a few memory channels, was basically a toy. It wouldn’t even receive out of band. With my Baofeng I have a radio that can transmit legally on 2m and 70cm ham bands as well as licensed business bands (the radio is type-accepted for business bands in the US), and receive well outside those bands on VHF and UHF.

    2. except all he did to the radio is add a remote power switch and feed audio and PTT into the mic jack. he didn’t modify the transmitter portion of the radio at all, so his hacking of the radio is not illegal. Did you even bother to read his article?

      1. I hate being “that guy”, but FWIW, I believe all of this is illegal (in the US anyway). FRS is only for two way voice communication between two people. Radio Shack has a nice FAQ. Seems totally silly to me on one hand, but on the other hand, the point above about getting your license and it opening up a whole world is a very good one. In the US. Other places I have no idea, but it’s probably similar.

      2. Bill is correct, FRS radios are not allowed to be modified in any way and are meant for person to person communications. You can’t use them as a beacon, repeater or any other manner apart from normal conversation between two or more people.

        Besides, with the cheap Chinese HTs you can get these days (cheaper than some FRS models), you’re not limited to the 500mW on FRS. If weight is an issue you can strip the radio down to the barest essential parts necessary for tx/rx.

      3. We all read the article, but apparently you didn’t read the FCC rules. Title 47, part 95, section 95.193 prohibits data communications on FRS except in limited circumstances (initiated by a button press at the radio, no more than 1 second long, no more than one of these one-second data transmissions in any 30 second period). FRS is generally for voice.

        Of course I’m not making any claim about enforcement practices, just pointing out that the original legal objection has reasonable basis in the law, among those who bothered to read both the law and the article.

        1. True in Canada and some other countries as well. I don’t know the relevant law paragraph and sentence, though. I thought of using FRS for a digital project years ago only to find out it was illegal.

  5. Not that I would be worried about the FCC enforcing the rules, they seem to be fairly lenient these days for most minor violations, but I seem to recall FRS/GMRS radios still require a license to operate, even though they can be had on the cheap from many different stores and most people ignore this requirement. This also may have changed since the last time I looked?. You could get quite a boost in range with a HAM setup, I’m sure, but I think you’d also have to regularly transmit your license number or station ID, I’d assume, much like a repeater does.

    1. If you operate solely on the FRS channels, you don’t need a license. If you stay under 500mW on the shared FRS/GMRS channels likewise no license is needed. If your radio is capable of over 500mW on the shared channels and you choose to use it (called “high power” on most radios), or if you use the GMRS-only channels, you do need a license.

      Or, instead of spending $50/year on a license that limits you to 22 frequencies and low powered “toy” radios, you can spend $10-15 and a little study time to become a licensed amateur operator, with a much broader range of bands and power levels at your disposal. Not to mention the ability to legally transmit on a device you can build yourself, in just about any mode you want (voice, data, morse code, SSTV, etc).

      I’m not trying to be condescending, I just don’t understand the average hardware hacker’s aversion to amateur radio. It’s not all grouchy old men playing CB in the garage, it’s a lively hobby with operators from 8 years old (maybe younger) up to great-grandfathers, and the possibilities for experimentation and exploration are endless.

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