When FrSky R9M long range transmitter and FrSky R9 receiver series started to pop up some time ago, there was a lot of speculations "it is any good?" "is it a Team Black Sheep Crossfire killer" "cheap Crossfire alternative?". In time, new firmware started to appear, new receivers and so on. And oh yes, EU LBT version finally also appeared. And what… FrSky even was giving R9M for free with X10S Horus.
- FrSky makes radios. Good and very good. Dominates the market. Taranis, Horus and all of them
- TBS makes bloody good long range 868/915MHz long-range radio system called Crossfire that is commonly used by FrSky radio users
- FrSky tries to make its own 868/915MHz long-range system called R9
- FrSky releases new R9 firmware called Flex, new receiver, and new antenna. The new antennas look the same as TBS Immortal-T antennas for Crossfire receivers
- Hell breaks loose and Team Black Sheep steps in and makes a policy that any dealer that restocks and tries to sell both TBS products and FrSky R9/R9M system, is removed from official TBS dealer list
After weekend tests of Betaflight 3.5 and some discussions with Betaflight developers, here are two things you have to (yes, have to) change in Betaflight 3.4 and 3.5 if you did not did that yet. Worth to do it!
Details for halfwave dipole for an 868MHz band are quite simple:
- two 0.8mm copper wires (used for welding) cut to 77mm and solder to the end of coax cable. Here I've used RG174
- put that thing into a 3D printed casing
- put antenna tubes around wires. I got mine from here: https://goo.gl/HrWNcY
- glue everything together
- you are done!
FPV, right? Long range maybe? With a 5.8GHz system, it’s really hard to call it a long-range but what if you put a ridiculous amount of power on transmitter module? 500mW? 800mW? Nope, not enough. Let’s go big and have a practical look at AKK X2-Ultimate which says it does 1200mW of RF output power! 1.2W put into the aether. Wow…
When little more than 3 months ago I announced iRangeX iRX-IR8M multiprotocol radio transmitter I did not expected it will take that much time to get the radio from Banggood. First it was delayed, than it was delayed and then sent via slowest post you can imagine.
Either way, it is finally here and this is my review of it (vol. 1 now, vol. 2 will follow).
Sometimes you win, sometimes you lose. This time I've lost. Not by much, but always. During testing of my DIY LoRa RC link, radio caught a glitch during a flip few meters above a ground. It was not even a failsafe situation. Link recovered a few milliseconds later, but it was too late and quadcopter crashed into the ground.
During a roll, while being behind a tree, RX antenna got hidden behind a carbon fuselage and both antennas were at 90 deg. That was enough.
Damage is not severe, nothing I can not 3D print in one evening. It's more like a discredited honor or something.
The glitch was so short that is was not even recorded in blackbox log. RSSI was fine, no locked rcData. Quadcopter just kept 90deg attitude for too long.
There is a slight chance it was not faulted in software or hardware. Maybe there was a strong rouge TX polluting the aether. Why? I've caught a failsafe on a different quad (2.4GHz FrSky link) while being only a few meters away and a friend caught a failsafe on a TBS Crossfire. So maybe it's not entirely my fault after all.
Looks like I was able to solve all major known problems with my DIY long range radio system Crossbow. I'm writing known, since no idea what lies beneath… Anyhow… What changed? Quite a lot:
- I've extended Arduino-LoRa library with ability to transfer full packet in single SPI transaction. Right now, each read of write to SX1276 uses single transaction. Previously, there were 2 transactions per byte…
- The same library now has ability to send packets in async mode. Previously it was blocking code execution until LoRa packet was transmitted. Huge waste on processing time
- With OpenTX 2.2.1 on the loose, I was finally able to drop PPM input from Taranis to TX module and replace it with S.BUS. But not without problems. According to specification, S.Bus should be
SERIAL_8E2. But my Taranis clearly outputs it as
- For now, OLED display is disabled. It was taking too much time to update it using I2C and TX module was loosing S.Bus packets
- I've improved RC channels processing time, time required for encoding/decoding went down by 1ms
- It is still LoRa32u4 II 868MHz based but I'm considering different hardware. For example ESP32 with LoRa. Time will show
Next test hopefully this weekend. If weather allows, of course. We have very wet autumn this winter in central Europe this year…
LoRa modulation has some advantages. Like superb receiver sensitivity and immunity to interference. Has some problems, true, but at the end, it's a great way to send small packets of data to long ranges using low power.
Anyhow, today only one picture: how LoRa spectrum compares to FSK signal spectrum? Like this:
Those two peaks are nearby FSK stations, while plateau is 250kHz wide LoRa signal. Difference is at least clearly visible 😉
Finally, much later than I originally expected, Crossbow LRS, my DIY medium range RC radio link was used to control something that flies. Not much, and not far. It was only my experimental 6" GPS Racer quadcopter. And I reached only 350m. Small steps, I had no intention to beat and records after all.
Just as reminder, by RC link is as follows:
- Based on LoRa32u4 II development boards
- Semtech SX1276 868MHz
- Programmed with Arduino
- Planned range: up to 5km
Next test, this time without twitching, in a few weeks.