1st B.E.A.M. bot attempt - Symet

Discussion in 'The Projects Forum' started by skullforger, Nov 3, 2008.

  1. skullforger

    Thread Starter Member

    Nov 3, 2008
    14
    0
    Hi,

    I was wondering if I could get some help on my first steps in electronics? I decided to start with a very basic B.E.A.M bot : the Symet of which you can find the circuit and the explanation here:
    http://www.solarbotics.net/library/circuits/se_t1_fled.html

    This is the picture I used to put the components in my breadboard:
    http://junkbots.solarbotics.net/sample_chapter/hirez/F07-03-Breadboard-DSCN6783.jpg

    ...but it doesn't work :(

    I have done some tests and this is what I came up with:

    - solar cell + lead : 3.13V
    - capacitors : 3.13V over each one
    - resistor + lead : 3.13V / FLED-side lead : alternating between 0 and 3.13
    - motor : 3.13V on BOTH ends
    - if I disconnect the motor, the FLED flashes
    - if I use a 1K to 10K transistor, the FLED flashes
    - if I use a 22K transistor, I cannot see it flash


    My BEAM book also mentions that if I can see the FLED actually flashing, the resistor is too low and I should put in a higher value resistor (I used a 22K to stop seeing the FLED flashing, although my book says it should be somewhere between 1K and 10K)

    I don't know what kind of motor I have, but it runs great on a 12V battery and it looks very 'normal'. I think it is from an old cassette player.

    Sorry for being such a noob, and thank you in advance!
     
    Last edited: Jan 26, 2009
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The motor has to have a voltage rating of about 3.5V and not 12V because the fled trips at about 3V. Also, i dont think this solar cell can output up to 12V. When you use this 12V motor it looks like a short circuit because it does not rotating and the capacitor discharges quickly. If you use a 3V motor it will work for a few seconds and then stop.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Solar cells that small have a VERY low current output. You'll need a very small, very low-voltage hobby-type motor in order to get even a short run-time out of it.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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  5. skullforger

    Thread Starter Member

    Nov 3, 2008
    14
    0
    Thank you very much for the information!

    I think they should mention it in their book. Because I asked the electronics supply shop owner for a motor that doesn't need much, and on the one he sold me, there is the word 'sunmotor' engraved on its plastic side, so I thought it wouldn't need much charge to fire up... But still too much for the Symet it seems. I'll try to get one out of a broken cell phone then.
     
  6. skullforger

    Thread Starter Member

    Nov 3, 2008
    14
    0
    Hi guys.

    I just tested my motor with a 1.5V battery and it works! Does this mean that my solarengine has enough juice to power it after all? Or is it a current problem? I know the power of a solar cell is too weak, but I thought that was just what the whole circuit was all about, to overcome the weak power problem? Please note that the motor doesn't need to spin all the time, just very short burst every 40 secs, when the capacitors are full enough.
     
  7. skullforger

    Thread Starter Member

    Nov 3, 2008
    14
    0
    Hi,

    My problem is solved now. About a month a go, I was doing some beginner experiments with transistors, and I also had troubles. I posted them in another post and 'beenthere' pointed out my problem : I had misidentified my transistor leads because I assumed the pinout was the same with every transistor (emitter-base-collector). My transistor was (E-C-B), that's why it didn't work. Anyway, thanks for al the help!
     
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