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How sensitive is RF200 to mechanical vibration?

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  • How sensitive is RF200 to mechanical vibration?

    I am thrilled to report that the following system works and this after only three or four days of working with the new-to-me Synapse gear.

    An RF200 and a TI TM4C123GXL LaunchPad are plugged into a custom board. The 400ma LDO regulator on the LaunchPad also powers the RF200.
    The LaunchPad is powered via a high efficiency 5volt switching regulator connected to a 12V SLA battery which also powers a pair of brushed drive motors which also have encoder outputs. The whole system when running uses 65ma and with both motors freewheeling uses 150ma. This construct is bolted to and controls a wheeled mobile robot base prototype (a 16" x 16" 1/2" thick polycarbonate plate). The robot base is very rigid and there is no suspension.

    An RF200 is plugged into a Synapse-to-FTDI Adapter plugged into a breadboard and powered by batteries (all very standard I'm sure). A joystick and several pots are attached to some of the RF200 analog inputs. This is used to send motion control signals to the robot base.

    When I took the system into the garden (lots of paths and circles surfaced with slightly domed pavers (each ~9" x 4") so lots of joints causing lots of vibration (one can hear the bumps via the polycarbonate plate sounding board!)): for its first test, I was able to drive it around for 7 or 8 minutes. What a thrill!. BUt then it suddenly stopped.

    Investigation reveals that when the RF200 is unplugged the system powers up normally. When the RF200 is plugged in the system does not power up and the regulator voltage output is very low. I've replaced the RF200 with a new one, downloaded the 'image' and voila, the system works again! (Note: also, there was no RF200 bypass cap installed during the test).

    Would someone speak to the mechanical sensitivity of the RF200 (and/or speculate on alternative failure modes) before my next ground test?
    Last edited by DavidGenge; 11-15-2013, 11:43 AM. Reason: Clarity

  • #2
    Hey DavidGenge

    I'm unaware of any vibration testing, but I'm still researching. As for your configuration; I didn't see any mention of how you are securing the RF200 to the proto board so it doesn't become disconnected. One option is to use stand-off's or zip ties. Or both depending on which RF200 you have and which proto board you are using.

    If you have one of our SN-171 proto boards available? I'd recommend trying to reflash the firmware, Factory Defaulting the NV RAM and erasing the script to see if the module starts working via a serial connection.

    Speaking of which, which board are you using to mount on your custom HW? The Solarbotics Synapse-to-FTDI Adapter Kit looks to have a row of solder in pins which could short to the casing under the RF200 if you had enough movement.


    RPS.

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    • #3
      RF200 connection

      Hi RPS,

      The modules are RF200PF1 (didn't realize there were versions).
      The replacement is an RF200P81 (they were out of stock of the PF1s) and as I mentioned it works fine.
      I'm plugging the module directly onto my HW on the robot end and there are no projections in the vicinity at all. I've followed the guidelines pretty well (except for the cap). No, I didn't use any securing mechanism at all, only the force of the sockets on the 24 pins. When I inspected the system after it failed the module appeared to be well and firmly seated in the sockets. In future I'll mount the system on a block of lead glued to a sponge or something like.
      Haven't made a board for the remote control (joystick, buttons etc..) end yet. It's the Solarbotics adapter in a breadboard but that end works perfectly).
      I will try your suggestion about recovering the damaged? module. Have to solder up another Solarbotics adapter first. Let u know soon.

      Thanks very much, hope some info about vibration shows up soon.
      Cheers,
      Dave

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      • #4
        Synapse does not conduct any type of vibration testing on the RF modules. We have in the past used a small amount of glue on the outside of the socket and the RF module to help hold the RF module in. It is just a small amount applied after the RF module is plugged into the socket. (on the side)

        We have also used zip ties as mentioned by RPS. In my personal experience in a hobby involving very expensive RC planes we do not use zip ties because they seem to transfer the vibration into the object you are trying to secure. We use Velcro.

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        • #5
          Mechanical sensitivity

          Hello gvoce & RPS,
          Haven't had time to investigate the 'dead' unit but I will soon and report back. Thanks and
          Cheers,
          Newbie Dave

          Aside(Been busy: To save battery power the system was designed with a SS-Relay to disconnect power to the motors when the joystick is centered. An important unforeseen effect (perhaps the influence of years of working on dead level floors) was that when the relay cut the power, yikes!, the platform rolled downhill! . So have been writing code to implement parking brakes. Now when the joystick is centered the current motor location (as tracked in the QEI interface) is immediately sampled. The parking brake algorithm uses that value minus the current motor location to produce a Proportionate power level (and a direction) which holds the platform firmly in place regardless of slope.
          (I imagine some kind of latching-solenoid activated mechanical parking brakes would be a better battery power saving solution...)).
          Last edited by DavidGenge; 11-18-2013, 02:19 PM. Reason: Clarity

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          • #6
            I use mine in a fairly high vibration environment using those little plastic standoffs and hot glue across the outside of the socket, with the board bolted down and the antenna connector secured to the case. Mostly they stay put.

            I do have a box of dead modules from bad power though, and those symptoms sound familiar. Motors make voltage spikes, and sometimes those get through the regulator. They can also be nearly impossible to detect with a multimeter, and a mobile application makes it even harder.
            It complicates things, but consider separate batteries for motors & logic.

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