Basic electric car build given 4 AA batteries

Discussion in 'The Projects Forum' started by TheRanchero, Apr 9, 2009.

  1. TheRanchero

    Thread Starter New Member

    Apr 9, 2009
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    Hey guys,
    I'm new to the site and have a basic knowledge of electronics but am always willing to learn more. We have been assigned in a collegient course to build a basic electric car given the following design criteria.
    -must fit within a 1' X 1' X 1' box
    -must use only 4 AA Duracell batteries in which the instructor provides

    The competition is scored in various ways however the most important being time (seconds) to travel
    1) a 100 ft flat distance
    2) an 30 degree inclined surface for a distance of 8 ft

    I would think developing a circuit to fully utilize the batteries in such a short distance would be key. What kinds of circuits and motors should I be looking at and are there any other suggestions for this project?

    I thank you in advance and look forward to any responses.
     
  2. leftyretro

    Active Member

    Nov 25, 2008
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    One tip, built it as light as you can.

    Lefty
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Another tip: MOSFETs and PWM.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    One limit you cannot avoid is the maximum discharge current the batteries can provide. You might consider having the batteries power up a flywheel -- either mechanical or electronic -- over a longer period from which you could then draw the full power more quickly.

    John
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Use jpanhalt's flywheel, but use a set of NiCd, or sim. re-chargeable batteries instead. How long do you have your batteries before contest?
    The discharge rate will be much higher, amps rather than mA, use one or two model aircraft electric motors [used?] direct , or gear reduced drive, two to 4 wheel drive. Should burn rubber for first 10 ft. @ 20 A then drop as speed builds up. Switch off power as soon as possible to conserve batt. for next run. Pick jpanhalt's brain for motor application.
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Best inf I can come up with: DURACELL AA[ Alk.?] discharge rate 1 A; NiMH AA, 5A; NiCd AA , 18A
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
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    I would couple JPanhalt's electronic flywheel with a joule thief to get the most bang out of the batteries.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    The Joule Thief really isn't very efficient; it's just a cheap and clever way to light LEDs from batteries that wouldn't normally power the LEDs.

    I'd use a low-frequency PWM circuit with a MOSFET that had a low gate charge, to gradually bring the car up to speed, reserving maximum power for the climb up the ramp and the sprint to the finish afterwards.

    Were I one to make a wager, I'd put my money on the student who spent the time to learn how to program the power demand vs availability into a microcontroller to drive a MOSFET.

    A suitable logic-level power MOSFET might be something like an IRLR7807/IRLU7807.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I'll wager on the student who experiments and doesn't wait until the last minute for a pre-packed solution from the Internet. :)

    The OP's first and only post on this subject was two weeks ago.

    John
     
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