Components used:
HAC-LM96 radio modem - $52
Turnigy UBEC - 3A switched DC-DC converter - $8
Teensy 2.0 - Arduino compatible board - $19
To make it plug-and-play with my Futaba 9C radio I took the casing from an old defect RF transmitter module and put the UBEC and Teensy board inside. The UBEC is connected to the 9C V+ pin (9.6-12V) and supply 5V for the Teensy board and the HAC radio modem. Sadly the HAC modem is slightly to large for the transmitter module casing, so i had to use an extra box for the HAC modem.
The Teensy MCU converts 8 channel PPM from the 9C radio into serial data for the HAC modem. The Teensy board is my favorite Arduino compatible board, has more i/o in a smaller formfactor and a proper USB interface.
In the airplane the serial data is received by the HAC modem and either transmitted directly to the autopilot or converted back into servo PWM pulses using another Teensy board. This way I can use the HAC modems as a pure R/C control system if I need to, freeing up the 2.4ghz band for live video link etc.
To use the system as a two-way telemetry system you connect the Teensy board in the RF transmitter casing to a computer using a USB cable and either talk directly using the USB interface or use a virtual serial driver for normal two-way serial communication.
Edit: Here is the source code for the Teensy PPM decoder and rf433 transmission system.
Teensy_PPM_Decoder.pde rf433.h
Comments
At least in Norway 433mhz is a little used frequency, so I have never had any problems. I also used checksum error detection on the signal to prevent servos going crazy from any corrupted data. For extra safety you should also have the autopilot activate stabilization and RTH if signal is lost. I would say that a stable and well working RTH is critical for any type of radio and control experimentation in the air. :)
Hi Tommy. Sorry for the late reply.
As I mentioned earlier I built this system as a one of for myself, so the documentation is somewhat lacking.
But if you can make sense of it, I scanned my work diagram for you. It shown the connection I used between a Futaba 9C radio ( receiver module pins ), teensy 2.0 and the 433mhz modem. Power is taken from the 9C radio (9-12v) and converted to 5V using a cheap HobbyKing BEC.
The 500mW HAC should have even better range then the Xbee 868. The 9600 baud version (HAC-LM96) is rated at 2km ground level (Xbee 500m). And I have confirmed this myself. I had one HAC modem transmitting from inside the first floor in my house while I picked up my 9C radio and started walking. In a typical suburban environment with houses, trees etc. I got well over 2km before I got missing packets. Remember one of the modems was inside! So line of sight and high altitude location in the airplane have the potential for crazy long range. :)
I'v used my system on and of since I made it, and have never had a control issue. There is a slightly noticeable delay (12ms) if you try flying aggressively (aerobatics), but for normal UAV/FPV it is just fine.
Just read your blog about the Xbee 868.
I ordered mine directly from http://www.hactech.com/
If you do not need extreme range you can also get the 10mW version at sparkfun ( http://www.sparkfun.com/categories/113 )
mighty interesting project! :) I'm trying to do the same thing and have a long-range signal between my ardupilot and my UAV, and was considering Xbee 868 modules but due to some problems with the duty cycle I started searching for other solutions and found this! Whee!
Are these the RF modules that you used? : http://www.hactech.com/index.php?productID=672
May I ask why you didn't use any of the other modules with longer range, HAC-LAN RF or HAC-LEM RF? Because of the RF module weight or some other reason?
@dunk: Well done too. You have taken things to the next level. I see the value in using standard R/C gear for reliability, but I think it would be cool to bring this part of the system into the open source world eventually too. Your approach is getting closer to that goal.
o, absolutely. sorry if that reads a little more critical than i meant it.
i've spent a great deal more time than i expected implementing a 2 way communication method where as you've skipped that step with off the shelf modems and got 90% of the functionality with 10% of the time/hard work.
if the end goal is to get a system flying quickly and easily pre-made radio modems are the way to go.
it shows my stubbornness that i stuck with the CYRF6936 once i had started.
now i have my project working though i just thought it might be of interest.
other options are always interesting right?
dunk.
@dunk: I understand the need for talking directly to a chipset if you are doing a commercial grade low latency R/C control system. But remember the goal of my system was to get long range control and easy two-way communication with the autopilot. And since I did not feel like reinventing the wheel (for a change :p), using a modem that already has built in support for serial communication seemed like the logical choice. Also I wanted to keep the 2.4ghz band free for a video link in the future.
-
1
-
2
-
3
of 3 Next