Monday, 22 May 2017

Checking out your new FrSky transmitter

Having set up a variety of transmitters for myself and friends, I thought I'd pen some tips on checking out your new transmitter, including a simple and foolproof method for checking the range.

1. Check the gimbal wiring
The quality on FrSky transmitters has improved steadily, however one recurring complaint is the lack of proper support for the gimbal cables, which can lead to wires fracturing through bending fatigue. So one of the first tasks is to open the case and check out the wiring especially on the inner (moving) gimbal. If necessary apply some hot glue as strain relief. I've done this on my own Horus and it's given that extra 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 particulary durable, indeed my second X9D suffered from a faulty 3-position switch. The Plus version 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'll be a loss of range (as I discovered, see below).

4. Do a comparative range check 
If you frequent RC Groups, you'll see a lot of talk about range. Most discussion is just anecdotal - what's needed are actual numbers, so different transmitters can be compared.

The test that I use involves recording RSSI readings at a fixed distance from a designated receiver. RSSI is a good measure of effective range as (a) it triggers the RF signal low and critical warnings and (b) it's supported by all radios using XJT or iXJT modules, i.e. X9D, X9E, Horus etc. Since the RSSI value is generated in the receiver, it's important to dedicate a single receiver in order to avoid sample variation issues - I use a spare X4R for this purpose.

Test rig with spare receiver and battery. The servo is not necessary.
The range check can be done in any convenient open space with say 200-250 meters between transmitter and receiver - the exact distance is not too important, what matters is that the same two locations be used for all tests. The test should be done with the transmitter in 'full range' mode, not range-test mode (since there's no guarantee that different transmitters have identical range-test implementations). The receiver board and transmitter should be held at a consistent orientation.

Obviously if you're testing several transmitters, it'll be necessary to rebind with each one but it only takes a minute or two.

Here are the results of tests with various devices at approx 200 meters:
  • Taranis X9D #1: 69 
  • Taranis X9D #2: 69
  • Taranis XJT ext module: 70
  • Taranis X9DP #1
    • RF firmware 2015: 52
    • RF firmware 2017: 72
  • X9DP #2: 73
  • Horus 69 (internal antenna only)
This method could also be used to compare effective range between EU and non-EU firmware, which would be very interesting. If anyone has tried this do let us know the results!

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