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Motor Speed Control

Discussion in 'Electronic Design' started by Marcus, Nov 12, 2004.

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  1. Marcus

    Marcus Guest

    I'm just wondering of anyone has any alternative for using an RC Car speed
    controller ? I'm building a robot and need speed contollers and the PWM
    input and analog voltage output of the premade speed controllers is ideal,
    however, the cost is not. From towerhobbies.com the price is $80+ which is
    a expensive.

    Any ideas how to vary voltage (high current too) via PWM would be
    appreciated.

    Thanks,

    Marcus
     
  2. Marcus

    Marcus Guest

    Oh yeah, and they need to be able to handle Reverse as well.
    Cheers,
    Marcus
     
  3. Tim Wescott

    Tim Wescott Guest

    Well, if you don't like that price I'm sure that there are industrial
    drives out there that'll add another zero on the end.

    Seriously, for what you're getting $80 ain't bad. You probably won't
    get below that unless you roll your own, and then you'll spend all your
    time on the amplifier instead of the robot.

    If you must, check out MOSFET drivers, and MOSFETs, and consider driving
    them directly from your PWM output (which will have to reflect your
    desired gate drive instead of the 1-2ms RC servo signal that your speed
    controllers accept).
     
  4. Er, no, it's *dirt* cheap, actually. If you can find ready-built
    controllers that will do the job needed at that stinking, low price,
    you'd be a fool to try to roll your own for anything other than fun.
     
  5. Marcus

    Marcus Guest

    Very Well, Out comes the visa :)

    Thanks Paul,

    M/K
     
  6. Rich Grise

    Rich Grise Guest

    Mr. Burridge is right about this. I did a little 8051 project once
    where we translated an ASCII string to control PWM. I didn't mess
    with the controller, but you couldn't build any thing like this
    for anywhere near that price.

    One thing to be aware of - when you're using RC servos, they're
    designed such that if they lose the signal, they just sit in
    the position they're at - they don't "home" or anything - I
    guess the reasoning is, if you lose the RF signal, the airplane
    just continues in whatever turn or dive it's in, so the damage
    will be predictable. ;-)

    But with a motor controller, this can be dangerous - if you lose
    the signal, the default command is "Stay where you are." With
    a motor controller, "where you are" is actually "How fast is
    the motor going" so it crashes into the end stop before you can
    resync your little control mock-up. Well, you get the point. ;-)

    Good Luck!
    Rich
     

  7. Wow. This one claims maximum continuous current of 232 amps
    and maximum peak current of 800 amps, for $65.

    http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LL4926&P=1
     
  8. In Robot Wars in the UK., we're compelled to use FS1s or equivalent to
    counter this problem.
     
  9. In Robot Wars in the UK., we're compelled under the rules to use FS1s
    or equivalent to counter this problem. They return the servos to a
    predetermined, safe default setting in the event of signal
    loss/interference. They only cost about 25 bux a piece in your dough.
     
  10. Rich Grise

    Rich Grise Guest

    You're right. That's not "dirt" cheap. These days, that's _cheaper_
    than dirt! ;-) (If you think dirt is cheap, go downtown and try to
    buy an acre or so of it. ;-) )

    Cheers!
    Rich
     

  11. Hmmm... Surely they must have gotten a decimal place wrong or something on
    that? 232^2*0.0035 = 188 Watts. I think that small a package would have a
    very hard time handling that continuously. Additionally I don't think 14
    AWG wire would much like 232 Amps flowing through it for very long. Surely
    23.2A continuous and 80A peak would be much more likely for a 0.0035 Ohm on
    resistance and 14 AWG wires...
     
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