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Better than an Xbee and cheaper Hobby King 433Mhz or 900mHZ Radio Telemetry Kit 100mW

Posted by Nick Goodey on October 25, 2013 at 2:03pm

Better than an Xbee and cheaper Hobby King 433Mhz Radio Telemetry Kit 100mW

Ran this wee puppy at 57,600 full duplex no issues at 1/4 mile with the RX inside my neighbors brick post box. Seems to penetrate the masonry better than a 2.4Ghz Xbee and its half to a quarter of the price the price especially if you buy from Sparkfun. 

Like the Xbee it resumes comms very quickly after a power cycle which is pretty essential for RC usage. 

Arduino Xbee Receiver Arduino Nano V3.0 Microcontroller Board from hobby king

 http://kiwitricopter.blogspot.co.nz/2013/10/rx-tx-csharp-to-arduino.html
Features:
• Very small size
• Light weight (under 4 grams without antenna)
• Receiver sensitivity to -121 dBm
• Transmit power up to 20dBm (100mW)
• Transparent serial link
• Air data rates up to 250kbps
• Range of approx 1 mile
• MAVLink protocol framing and status reporting
• Frequency hopping spread spectrum (FHSS)
• Adaptive time division multiplexing (TDM)
• Support for LBT and AFA
• Configurable duty cycle
• Built in error correcting code (can correct up to 25% data bit errors)
• Demonstrated range of several kilometers with a small omni antenna
• Can be used with a bi-directional amplifier for even more range
• Open source firmware
• AT commands for radio configuration
• RT commands for remote radio configuration
• Adaptive flow control when used with APM
• Based on the HopeRF HM-TRP radio module, featuring an SiLabs Si1000 RF microcontroller

A quick test at 57,600 Baud seems like a great product and well priced at US$29.99

XBee Pro 60mW Wire Antenna - Series 1 (802.15.4) 

US$37.95 AND YOU NEED 2

xbee.jpg
FPV 433Mhz Radio Telemetry Kit 100mW
US$29.99 AND YOU GET A PAIR


433Mhz+Radio+Telemetry+Kit+100mW.jpg

An interesting price point comparison between Sparkfun and HobbyKing on another useful and in this case identical product. HK are almost 80% cheaper
HKlogo.png


Arduino 9DOF ArduIMU Controller ATmega328 (ACCEL/MAG/GYRO)

 US$29.99


9doHK.jpg

Same product from Sparkfun 9 Degrees of Freedom - Razor IMU 

US$124.95

9DOF.jpg

So HK sell this identical device for almost 80% less

But it get worse if are a Kiwi you buy from our local Sparkfun resellermindkits.png9 Degrees of Freedom - Razor IMU - AHRS compatible NZ$180.499DOF+Mind+Kits.jpg
 
To be fair on Mind Kits they do buy from Sparkfun but that said the bloke at Mind Kits has a way worse supply deal then Hobby King 
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Comments

  • Nick Goodey October 26, 2013 at 12:27am

    This is what I discovered

    Some things I have learned about Xbee from hands on experimentation.
    1) Keep the packet size to < 100 bytes in either direction
    2) Allow for 50% dead air on 20mS at 38,400 my TX packet is sent in 8mS so 12ms dead air, this value is sent in the TX packet header in a single byte
    3) Only send back a telemetry packet every other TX cycle minimum or you will crowd the airwaves, this causes drop oust and variable latency. I have chose (packcount %5) which is a good margin, and a packet size limit that keeps the transmission clear of the next TX update by 5mS minimum.
    4) Not really Xbee but have another CPU handle the telemetry packets not the TX micro. I am re-using my Netduino Plus as it has Ethernet & TCP/IP and a flash card socket just because i have one.
    5) Have your own checksum, the 802.15.4 will handle things in the air but you still have a wee bit of wire between you micro and the Xbee. Belt an braces is the best approach here.
    6) The Xbee should be treated as a simplex regardless device as I do it gives you better real-time behaviour overall 
    7) Learn about the Xbee config and configure sensibly, to many items to list here, however is set the 802.15.4 retry limit to 3 and the packetiztsion threshold to 3 also
    My timing chart
    Red is command control data to the aircraft servo positions ect
    Blue is response data from the aircraft
    xbee+timing+diagram.png
     
    This little bit of knowledge has be accumulated through practical experience and experimentation with the Xbee and has know basis other than my own meandering experinace
  • Nick Goodey October 26, 2013 at 12:23am

    I have flown planes with an Xbee Arduino based remote control with very low latency 

  • Renato Aranghelovici October 26, 2013 at 12:16am

    Xbee based RC attempts were made years ago, the creator of OpenLRS was the last who convinced himself they are not a solution due to latency and buffering these devices does.

    Telemetry yes, RC no, or anything where you need better than 0.1 second latency/feedback.

  • Sam Kelly October 25, 2013 at 3:29pm

    OK

  • Nick Goodey October 25, 2013 at 3:22pm

    Cutting the tracks no going back from there

  • Sam Kelly October 25, 2013 at 3:12pm

    I have not done that but it is possible. You will also need to disable the FTDI chip so it doesn't interfere with the communication between the Arduino and the radio.

  • Nick Goodey October 25, 2013 at 2:52pm

    i need to trace the RX/TX before the FTDI chip on the PC end so I can connect it directly to an Arduino have you done that with one?

  • Sam Kelly October 25, 2013 at 2:34pm

    Those radios are cool.

  • Admin
    Morli October 25, 2013 at 2:11pm

    HK is good for RC guys but you have to remember that HK downloads the eagle file and produces the board. So no R & D , design  cost over heads and hence lower price. 

This reply was deleted.