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Global Positioning System. Telemetry. GPS data loggers. Batteries
Most people in western societies and many people in third world countries have at least heard of the term GPS. If they haven't experienced the personal use of a GPS unit such as a car navigator, they have at least been impacted by their use by governments, surveyors, mining companies and the military. Just 20 years ago GPS was for the military or the privileged few. In fact it was developed by the US military to enhance their operations including navigation, battle strategy, weapons deployment, asset tracking and troop location. It's full capabilities were only made available to the public after commercial interests purchased the rights from the US Government with lobbing from the Congress but with its accuracy detuned to avoid hostile use by foreign forces and terrorists. GPS is now used for literally thousands of tasks including land surveying, asset tracking, vehicle navigation and aircraft navigation. In recent years the US military have removed some restrictions on the GPS standards which have allowed very accurate tasks such as land and building surveying to be carried out. This improvement of accuracy also makes my kite altitudes easily measured within 10 meters for altitude and 2 meters for position. This represents up to 0.2% accuracy for height and 0.04% accuracy for position. There have been a number of technical advances such as DGPS or Differential Global Positioning System and WAAS to make the GPS even more accurate. These units are relatively inexpensive, the cheapest Garmin units such as the Geko are only $A99. Originally the smaller unit, the Geko, had more memory and track points so could record a 10 hour flight. The cheaper unit, the etrex, had only enough internal memory for 3,000 track points. Frequently it would only record the last 4 hours of a flight cutting off the record of the first 1/3 of the flight.
After the Garmin Geko was discontinued the new Garmin etrex gained the ability to store 10,000 track points so is now capable of 10 hour flight recording. The Garmin units are used as a secondary or backup of kite altitude records. The GPS data is virtually uneditable so represents rock solid verification for record authorities.
Here we have an array of communicationn and tracking devices. L - R front: Motorola Walkie-talkie, 2 Garmen etrex GPS units, Garmin geko GPS unit, Titley Electronics 161 Mhz tracking transmitter. Rear: Alinco Scanner/Reciever and Yagi Directional Antenna.
The early model Garmin etrex had limited track recording memory.
Late models have almost identical appearance but inherited more features from the Garmin Geko including larger memory for more track points.
Above: (L) is a GPSFlight radio telemetry module and (R) the RX3 base unit.
This model is a STXe 900 Mhz spread spectrum radio with Garmin 15H GPS module. It collects the GPS signal then relays the positional data back to the RX3 - base unit. The base unit connects via USB to a laptop and the data is displayed on proprietry software developed by GPSFlight. The altitude and position of the kite is displayed in real time which is an enormous benefit to our flight strategies.
Above is a vertical kite track as produced by the GPSFlight telemetry system and software. The GPS receiver and integrated telemetry transmitter is on board the kite inside an insulated high density foam box. The low temperatures at high altitude may affect the batteries. The black line at the bottom is sea level or zero altitude. The short horizontal lines at the start and finish of the flight shows the ground level which is 630 ft. above sea level. This altitude is subtracted from the GPS altitude. The GPSFlight software subtracts the ground level and displays ft above sea level and ft. above the launch point at ground level then continues to subtract this difference for the entire flight. The GPS Telemetry has a minimum accuracy of 99.87% and maximum of 99.9% for altitude and better for horizontal position. The GPS chips in all the telemetry and GPS tracking devices have SA & WAAS embedded which provides increased accuracy compared to earlier GPS devices.
GSP users expect lower accuracy in the City because less satellites are in view. The expectation is that 4 - 6 satellites are acceptable in built-up areas but here in a remote area with clear skies and no trees, 10 - 12 satellites are available at all times. This increases the accuracy of GPS "triangulation" by several times. GPS accuracy is not measured in percentage terms but absolute values. That means that an absolute error of 10 ft. for altitude at 630 ft ground level is 1.587% and at 16,000 ft is 0.0625%. This level of accuracy would be extremely difficult to achieve with any other method of measuring altitude.
Above is an altitude profile as displayed by the Garmin Mapsource program. This data is transfered via serial cable to laptop to save and display permanently. The internal memory of each logger is sufficent to record most flights then transferred to computer via serial cable. The memory is ten cleared for another tracking session unless using a log file to track another object. GPS cordinates of the last know position of a breakaway kitecan be input to use the hand held GPS device as a search tool. as shown by the search tracks of a ground walk above right.
Garmin geko is smaller than etrex yet has a few more features, the most important is the ability to record 10,000 track points or over 10 hours of air time compaired to 3,000 points for the etrex.
These tracks are produced by GPSFlight telemetry software, GPS Dash which runs on a Windows laptop. On the left is the horizontal track and on the right, the vertical profile. Underlying these graphs are the data streams which can be produced in a number of formats, particularly valuable for record verification and also can be exported to MS Excel for display and graphical presentation.
Big Red Bee GPS telemetry transmitter. Matching ground receiver not shown. Untested on high altitude flights.
FrSky R9M 900MHz Long Range Transmitter Module With R9 Slim Telemetry Receiver. This may be my next aquisition in 2019 if it passes reviews.
Canmore GPS logger. Not field tested as of 07/01/2019 but inbrief local testing it seems OK.
Holux M241 data loggers which I have 4 in various packages.One recorded the entire record flight after the GPSFlight unit failed during kite retreival. has really good proprietry software but logs in multiple standard data formats for analysis by several programs. Data standardisation is true for most GPS devices so I have no difficulty converting to any data format that displays NMEA (National Marine Electronic Association).
Screen gauge of GPS Flight software emulates an analogue dial. Easy to read on field with strong sun light although laptop screen is shielded by a shroud. The ground reference is in the centre at 630.8 ft above sea level.
The maximum altitude is displayed just below and this was 11,068 ft. on this day. The kite had just landed hence the zero altitude shown by the red needle. Other gauges above right show vertical speed and horizontal speed. The data listed to the left and right of the gauges is populated by altitude, longitude, Latitude, horizontal distance, horizontal speed, vertical speed, and heading and if the optional barometric module and temperature module are include, air temp and air pressure plus barometric altitude. The barometric altitude is calibrated from GPS altitude which is ironic as there are some critics who claim that barometric altitude is more accurate than GPS altitude. It may be, but under very limited conditions and for short periods only. Barometric altimeters must have temperature compensation embedded in the on chip algorithms to maintain some degree of accuracy.
Egg Timer GPS telemetry transmitter is a kit constructed by the user. My sight is not great so Dave Thompson from New Zealand assembled the transmitter (above) and receiver. (on the right). As of 07/01/2019 has not been flight tested.
915 Mhz 4.5 - 20 V, 100 Mw
Range 20 km with external aerial
Default data: NMEA
Battery: 2S LiPo 7.4 (5 hrs) or 2 x 2 SP LiPo 10 hrs +
Batteries for these devices have been a special part of my learning curve. I spent an inordinate amount of time, studying, contemplating, sourcing, testing, trialling and evaluating batteries. The best battery combinations give the greatest performance and duration to power all these devices. The least demanding are the GPS data loggers as they have no transmit functions. The most demanding are the 12,000 ft + flights were the telemetry may need to transmit for up to 14 hours and tolerate low temperatures.
Extensive battery tests were carried out at Baulkham Hills in my back yard, especially at temperatures between 0 - 10 degrees C
These battery duration test were designed to determine what combinations of batteries and GPS Telemetry units provided the greatest duration and reliability. The tests were conducted in Western Sydney winters where temperatures reach about 2 or 3 degrees C or just above freezing.
Temperatures at 20,000n ft. may be -10 degrees Celsius which is most important with carbon and alkaline batteries. Ni Cd, NMH and LiPo batteries have much lower temperature ranges. For altitudes up to 16,000 ft., alkaline batteries are a viable and very economical battery. Over 16,000 ft. and up to 25,000 ft. will require NNMH and over 25,000 ft, LiPo. 6 V lead acid was used on one flight but proved inadequate and may be prone to freezing above 10,000 ft.
Good quality Alkaline batteries are very cost effective on high altutude flights up to 16,000 ft. Performance may deteriorate at temperatures below -10 deg C
These offer excellent duration and performance at very low temperatures. An affordable battery as prices come down to compete with LiPo batteries. Requires a dedicated charger.
Lithium Polymer or LiPo batteries are the latestest in battery technology on the market, relatively expensive but high performance and duration with good low temperature performance. Requires a special charger to match battery voltages sense charged state. This example is used for drones.
Kite Altitude World Record