How To Get Into Hobby RC: Recording Flight Data

Last month, we covered the basics of RC telemetry systems – including how they work and why they’re useful. Despite the apparent benefits, telemetry is not for every modeler or every RC aircraft. In fact, many hobbyists feel that only large, high-dollar models warrant the expense and added complexity of telemetry components. That opinion is debatable, but there are alternatives for those who would like the benefits of in-flight performance data without the overhead of telemetry. One way is to use a GPS recorder.

Modelers often wonder how fast their airplane can fly or how far it travels during a flight. A GPS logger can answer these questions without the need for a real-time telemetry system.

There are numerous GPS recording devices available, and many are tailored for the demands of specific activities such as hiking or driving. The Hobbico Big 5 GPS Meter ($90) is intended for use in RC airplanes. It collects time, location, altitude (present and peak values), and speed (present/average/peak) data. Following a flight, you can scroll to read selected parameters on the Big 5’s LCD screen. Or, you can upload the data to a computer and plot out the entire flight on Google Earth.

The Unit

The Big 5 unit measures 2.56″ x 1.57″ x 0.82″ (65mm x 40mm x 21mm) and weighs 1.4 ounces (40 gr). To invoke a common yardstick, it is very nearly the same physical size as a GoPro Hero 3 (but lighter). This size and weight make the Big 5 unit compatible with a wide array of RC airplanes. I’d say that most models weighing at least 12 ounces are fair game.

Power for the Big 5 comes from a built in 200mAh LiPo battery that is recharged via USB. You can expect up to 150 minutes of operating time. This is adequate for any RC application that I can think of. It may fall short, however, if you want to repurpose the Big 5 for something else, such as a long bike ride. In any event, you can operate the unit with external power via the USB port or the 3-pin RC-style plug.

The Hobbico Big 5 is a GPS recording device created specifically for use in RC airplanes.

Up to six hours of data can be saved to the built-in flash memory. There is no provision to expand the storage capacity.

This GPS unit can be attached to your model using whatever method you like. I use self-adhesive Velcro. The prime consideration when mounting the device is to avoid placing it such that electrically conductive material (metals, carbon fiber) are blocking the signal path up to the orbiting GPS satellites. You will also want to ensure that the Big 5 does not upset the model’s center of gravity.

The Software

For those who prefer to playback the full data log, Hobbico provides Gpslogger, a free program that reads from the device via USB. Sorry Mac users, this program is PC-only. Once the data file has been read by the program, you can plot the course of the flight over a Google Earth map. A summary box displays the start/stop times (UTC), data point interval, peak speed, peak altitude, and distance travelled. When you mouseover any segment of the mapped flight path, a data box appears. It provides the speed, altitude, time, latitude, and longitude for the nearest data point.

The flight mapping is a neat graphic, although it is not exact. I noticed that some of my log files show me overflying areas that I purposely avoided. I would guess that the error was somewhere around 50 feet. The paths of other flights appear to be spot on.

The free PC interface software that is provided with the Big 5 allows you to plot flight data on Google Earth.

One thing about the path of an RC plane is that you tend to overfly the same areas during a flight. So the mapped path can sometimes resemble a bowl of noodles. Even when fully zoomed, it can be difficult to select a precise data point among these myriad intersections. It would be nice if there was also an option to read the data as a spreadsheet, but that capability does not yet exist.

The program has some minor bugs that will give you pause. For instance, selecting the option to open a log file will spawn a pop-up window labeled “Save As”. The window works as it should by opening the selected file, but it’s strange to click the “Save” button to do so. For what it’s worth, the Save pop-up functions and is labeled correctly.

The Experience

I found the Big 5 very easy to use. If you simply want to answer a question such as “How fast does this thing go?” All you have to do is turn the unit on and wait for it to get a lock on satellites. This usually takes less than a minute. You can then place the unit in your subject vehicle (plane, car, boat…whatever) and make a speed run. Afterward, the answer is right there on the screen.

The Big 5 provides a compact and low-fuss way to garner the most basic performance data from RC aircraft.

If you’re going to log data, you must also press the “Enter” button to start and stop the recording process. The Big 5 records in metric units by default, but this can be changed to imperial units via the configuration screen of the PC interface software. The software is also the gateway for clearing log files from the internal memory.

If you don’t mind navigating the nuances and petty shortcomings of the Gpslogger software, the path mapping feature is also easy to use. Whichever method of data retrieval you prefer, the Big 5 provides a compact and low-fuss way to garner the most basic performance data from RC aircraft. I’ve created a spot for it in my field box. I suspect that it will be used to settle many flightline bets.

An Alternative

If your motivation for collecting data is to tweak your model for optimum performance, you’ll probably need more information than the Big 5 can provide. You’ll also want to know things like motor RPM, battery voltage, and component temperatures. There are other non-telemetry recording devices that can fill that information void.

The Eagle Tree Systems eLogger ($70) is a hub that can record the data delivered by a wide array of sensors such as tachometers, temperature sensors, and even G-force sensors. Designed for electric powered models, the eLogger can record cumulative milliamp-hours used, system amperage, wattage, voltage, and throttle position without any external sensors.

The eLogger from Eagle Tree Systems has built-in sensors to record electric power system parameters. It can be also be mated to a separate GPS sensor to attain a more complete performance analysis. (Eagle Tree Systems image)

One of the sensors that can be attached to the eLogger is a GPS module ($80). It provides essentially the same sensing and path mapping capabilities as the Big 5. When combined with the power system data from the eLogger (and whatever other sensors are attached) you can get a very complete picture of what’s going on during every segment of a flight. The data can be graphed, mapped, or viewed on a dashboard-like display.

Having this array of data is helpful for making informed changes that will improve performance. Of course, gathering more data elements requires a more complex recording set-up. It’s a matter of determining your data needs and then selecting the right components. A simple GPS logger like the Big 5 may be all you need, or you may find that an expandable system like the eLogger is better suited to give you the data that you crave.

Terry spent 15 years as an engineer at the Johnson Space Center. He is now a freelance writer living in Lubbock, Texas. Visit his website at TerryDunn.org and follow Terry on Twitter: @weirdflight

SOURCE:http://www.tested.com/tech/537792-how-get-hobby-rc-recording-flight-data/

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