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45444Re: [SeattleRobotics] Neato wifi

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  • Weston Turner
    Jul 2, 2011
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      The XBee Pro 50mW RPSMA - Series 2 supports 30 kilobytes/second. It has a max data rate of 250kb/s. http://www.sparkfun.com/products/10419

      And:
      (250*1024) / (30*1024*8) = 256000 / 245760. The spec supports the requirement, but maybe that is not enough headroom for the application. 802.11b gives you about 45 times more bandwidth, more flexibility if you want to extend the project by embedding more controllers, sensors, etc. 

      I don't have personal experience with long range Bluetooth communication. Only read specs on modules such as:

      SparkFun's Bluetooth Modem - BlueSMiRF Gold:
      The data-sheet claims it "delivers up to 3 Mbps data rate for distances to 100M."

      I've used short range Bluetooth communication for remote control and robotic telemetry applications without latency issues. In fact I was surprised at the responsiveness of the system (tens of milliseconds), but maybe that is not fast enough for this application.  

      Using Wifi will give you much more bandwidth and flexibility but at a cost of a greater integration effort. Form a software engineering perspective, you would go from interfacing with the simple RX/TX pipe of Bluetooth SPP to developing an interface to the command set of whatever Wifi module you chose to use. In other words, chose between something I would spend my free time playing with to something I would get paid to work on for eight ours a day five days a week.

      Also, I have doubts about the actual bandwidth needs of the application. Surely some pre-processing could be applied to the data stream to make it sparser. Often using LIDAR is like sipping from a fire-hose, it provides you with an overwhelming amount of data, while only a small subset of it is actually useful for navigation and object avoidance.

      Best Regards,
      Weston

        
      On Fri, Jul 1, 2011 at 11:55 PM, Nathan Monson <nmonson@...> wrote:
       

      On Fri, Jul 1, 2011 at 6:10 PM, Weston Turner <wstnturner@...> wrote:
      If you are not embedding significant compute power in the robot, why would you want to use a heavyweight TCPIP stack and wifi? Why not use a lightweight wireless protocol like Zigbee or Bluetooth

      Zigbee is too slow, since the XV-11 can generate over 30KB of sensor data per second.  There's a lot more going on than in a Roomba.

      I'd be interested to hear about your experiences using Bluetooth over 100m. Which product did you use?  I've attempted to use Bluetooth in a couple of robots and just can't get the range or reliability needed.  Indoors, it is prone to bursts of lag as the robot moves around, which just sucks with a mobile robot that needs good responses.  I've used USB Bluetooth dongles and standalone UART modules.

      For me, only Wifi has been sufficiently reliable/low-latency/functional-in-homes.  And of course it's not perfect either, but it sure beats Bluetooth!

      Nathan


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