Monday, 22 May 2017

Checking out your new FrSky transmitter

Over the years I've set up a variety of transmitters for myself and friends and as a result I've got to know what to look for and what to check out with new kit. So in this post, I list a few tips, including an effective method for checking the range.

1. Check the gimbal wiring
The quality of FrSky hardware has improved steadily over the years. However one recurring complaint is the lack of proper support for the gimbal cables, which has in rare cases led to wires fracturing. So one of the first tasks is to open the case and check out the wiring at the pot or hall sensor. Pay particular attention to the moving axis and if necessary apply some hot glue at the junction. I've done this on my own Horus and it's given me that extra bit peace of mind.
A dab of hot glue will help prevent fractures

2. Check switch operation
Early X9Ds came with cheap switches which were nor particularly durable, indeed my second X9D suffered from a faulty 3-position switch. The Plus has better switches, and those on the Plus SE are further improved. Nevertheless, it's a good idea to check the switches on a new transmitter. This is easily accomplished in the Info menu, just cycle them back and forth and check that each position is correctly registered.

Info menu showing switch monitor panel
If replacing a switch, note that the switch housing is different with the X9D, D+ and D+SE, so be careful to order the correct type.

3. Use the latest RF firmware
If flashing your RF firmware (e.g. from EU to non-EU), be sure to check the FrSky site for the latest firmware version. Watch out in particular for silent hardware changes. For example, if you have an X9D Plus which has been manufactured since November 2016, you must use the latest 2017 XJT firmware. The 2015 firmware will appear to work correctly but there will be a loss of range (as I discovered, see below).

4. Perform a range check 
If you have access to a second transmitter which is known to be working correctly, it's worth using it to check the range of your new transmitter.

The method I use involves comparing the RSSI values returned by each transmitter at a certain fixed distance from a 'standard' receiver. The test is done with the transmitter in full range mode.

This method offers some major benefits over other ad-hoc methods: first, it provides hard numbers of your transmitter's range performance. Secondly, the transmitter is tested in the same state as for flight. Finally, the test can be used to compare different models of transmitter, for example Horus and Taranis. Or you could compare different firmware (EU-LBT v. non-EU)... The only requirement is that the RF modules support RSSI telemetry.

The first task is to make a simple test rig using a spare receiver. I used an X4R receiver, with the antennae oriented at right angles on the back of the board.

Test rig with spare receiver and battery. The servo is not necessary.

For the actual tests, a helper will be needed to hold the receiver rig. Here's the test procedure in detail:
  1. Find a convenient open space, and choose two locations 200-250 meters apart. The exact distance is not important, what matters is that the same locations be used for all tests.
  2. Get your helper to hold the receiver rig at the first location. 
  3. Carry the transmitter to the second location. Note that the transmitter should be in full range mode.
  4. With the receiver board and transmitter at a consistent orientation, take a reading of the RSSI value from the transmitter's telemetry screen.
  5. Repeat with other transmitter(s) as required (of course it will be necessary to rebind each time).
Here are the results of some tests which I made recently with various devices. Separation was approximately 200 meters, the figures are the RSSI values:
  • Taranis X9D #1: RSSI 69 
  • Taranis X9D #2: RSSI =69
  • Taranis XJT ext module: RSSI =70
  • Taranis X9DP #1
    • 2015 firmware: RSSI = 52 
    • 2017 firmware: RSSI =72
  • X9DP #2: RSSI =73
  • Horus (internal antenna only): RSSI =69 
Note how the method has identified an issue on an X9DP transmitter. It turned out I'd flashed an incompatible version of the RF firmware. Reflashing with a newer version restored the range.

The same method could also be used to compare effective range between EU and non-EU firmware on the same transmitter. If anyone has tried this do let us know the results!

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