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48094Re: [SeattleRobotics] Predicting Robot Position in a Differentially Steered Robot While Turning

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  • robotMaker
    Oct 18, 2013
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      Peter:

      I hope that you get this post. You're the first that speaks what I say about using BT and Android phones. They're cheap, $20 used on Ebay or craigsList and they work just fine. There's no need for service contract to use the Android phones as controllers for the Bots. They have wifi too that does work just like a tablet.

      I'm using a cheap Android phone in my Autonomous carpet walkingBot ( http://www.flickr.com/photos/96504930@N02 ) I'm just using a BT module (HC-05) from www.dealextreme.com that is nothing more than an equivalent to a serial cable connection from the Pololu motor driver to the Android cellPhone. To test it I use the Android blueTerm app (equivalent to Hyperterminal, TeraTerm or Minicom) to send commands to the Pololu motor drive module. It's just like having an actual two wire serial connection to the cellPhone. I could probably do the same to replace the Pololu motor driver using an embedded controller (such as an Arduino), but then it would be an overkill (a waste of time and money), I would have to write the firmware, test it and connect it to an H-bridge for each of the motors. I do still believe that the embedded micro-controller is indispensable, since it offers important embedded hardware peripherals that are not on an Android device. But I do believe that there are more brains for the bot in the program running on the Android device than the micro-controller can offer.

      For now I've momentarily stopped working on the carpterWalkingBot, to work on DIY 3D printer. To control the printer I'm using my Acer Tablet BT and BT HC-05 module to control the printer, the BT makes everything so simple. I plan to use the printer to make parts for the Bot.

      Cesar




      From: Peter Balch <peterbalch@...>
      To: SeattleRobotics@yahoogroups.com
      Sent: Thursday, October 17, 2013 5:29 PM
      Subject: Re: [SeattleRobotics] Predicting Robot Position in a Differentially Steered Robot While Turning

      David

      When you say DB25 do you mean you want an RS232 connection with RTS/CTS or
      do you mean something else (such as a parallel printer port)?

      (I haven't really been following this conversation - I only seem to get a
      few of the SRS messages. Yours come through fine but, say, Matthew's and
      Tony's didn't. I can't see how my setting could get that to happen!)

      Let's say, you're using an android phone as a hand-held remote control or
      debugger.

      If all you want is RS232 then use something like an HC05/HC07 or (more
      reliably) RN41/RN42.

      We use RN42s every day to android phones/tablets and they work extremely
      well (at 9600 or at 115kb/s). We found HC07s would work well with some
      phones but not with others so we swapped to RN42s. I personally found HC07s
      worked just fine with every Windows PC I tried.

      Given how cheap HC07s are, why would anyone fit a serial cable umbilical to
      a robot?

      I've used FTDI chips in a different project and found them to be a bit of a
      pain. We _had_ to use them because we wanted high bit rates but I reckon an
      RN42 at 115kb/s is enough for most hobby robot work.

      Alternatively, if you're using an android phone inside a robot as its brain
      then, once again, use an HC07 to do the comms from the phone to the robot
      hardware. It may seem crazy to use bluetooth over a couple of cms but it's
      very easy compared with the alternatives. We've done it that way putting an
      android tablet as a display inside a vandal-proof box connected (inside the
      box) via BT to an HC07 on our hardware. The alternative (a serial cable) was
      ludicrously difficult.

      Maybe I've got the wrong end of the stick - as I say, I don't see all the
      messages.

      Peter



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