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Re: Symet was anemic, now is inert

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  • J Wolfgang Goerlich
    And Eric gets the prize. My hat s off to you. From what Matt is showing, I think you are spot on. ... Connect the capacitor anode (positive) to cathode
    Message 1 of 26 , Sep 4, 2005
      And Eric gets the prize. My hat's off to you. From what Matt is
      showing, I think you are spot on.

      Now, on to Matt's questions:

      > PS, how the heck do I short the caps?

      Connect the capacitor anode (positive) to cathode (negative) with a
      wire. This discharges the capacitor, ensuring the circuit is reset
      and near 0V. Only short low voltage capacitors.


      > I have put the 2.2 resistor back in and the FLED does not flash
      > anymore, out the thing still just twitches.

      Good. You are moving in the right direction because the FLED should
      not flash.


      > The three in the bottom seem to be what I am getting out of my
      > symet. Not much.

      That is similar to how our Symets run.


      > Do you think I would get better action by replacing the 1000uf caps
      > with 2200uf caps?

      Would not hurt to try. The Symet will take longer to charge. When it
      fires, the Symet will have a longer "twitch"


      > how does one figure the amount of caps needed in a circuit? How
      > does uf convert to available voltage?

      The amount of storage capacitance one chooses depends on time.
      Specifically, time to charge versus time firing. The formula is:

      T = (C * V) / I, where

      T = Time to charge (Seconds)
      C = Capacitance (Farads)
      V = Voltage to charge
      I = Charge current (amps)

      For your Symet, with three 2200 uF capacitors and estimating the
      voltage and current:

      6600 uF = 0.0066 F
      10 mA = 0.01 A

      1.716 = (0.0066 * 2.6) / 0.01

      You can get a rough idea of runtime by measuring the motors current.
      I generally use my multimeter's current setting, run the motor from
      battery. Battery + to meter -, meter + to motor +, motor - to
      battery -. Since the circuit is firing the motor around 3V, use a 3V
      battery pack.

      The current will be a very rough estimate for several reasons. Motors
      use more current when loaded, the circuit itself uses current, and so
      on. Still, it gives fairly decent estimate. Let's suppose you find
      that the motor consumes 25 mA when free running.

      V = Trigger voltage - Reset voltage
      1.8 = 2.6 - 0.8

      25 mA = 0.025 A

      0.475 = (0.0066 * 1.8) / 0.025

      Such a setup would take about 2 seconds to charge, then run for about
      a half second.

      What is right depends largely on what you want. For Photopoppers such
      as Jon's Dogbot, you would not want the SE to fire for too long. The
      robot would over-shoot the target. For a Symet, you might make it as
      long as you can for more action. Gord, one of our members, likes to
      use 1F capacitors. He has a Symet called Taz that spins all over the
      place. Very active, just takes a very long time to charge.

      Regards,

      J Wolfgang Goerlich
    • Matthew J. Hannan
      Thanks for all the help, guys! My symet is now twitching around on the floor and the cats can t quite figure out what it is. I put the two 2200uf caps back on
      Message 2 of 26 , Sep 4, 2005
        Thanks for all the help, guys!

        My symet is now twitching around on the floor and the cats can't quite
        figure out what it is.

        I put the two 2200uf caps back on it and that seemed to help out a
        bunch. One bored night, I will probably add a third.

        On to the next project: Frankenmouse.
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