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Re: [SeattleRobotics] Motors, controls, and an IR question for micromouse

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  • Peter Harrison
    ... I looked for 370 size motors and the first hit I got was this one:
    Message 1 of 41 , Mar 8 3:53 PM
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      Ben Estroff wrote:
      > Hello, again.
      >
      > Motors:
      > We have acquired a pair of RC car motors, INSANE 370 MLST. I can't
      > find any information on their current requirements/tolerances, just a
      > suggestion that they not exceed 7.2 V driving voltage.
      >
      > What would be a good way to determine their limits without damaging them?

      I looked for 370 size motors and the first hit I got was this one:

      http://www.jperkinsdistribution.co.uk/detail.php?JPNO=5510321&activepage=1&Navmain=Electric%20flight%20items&subcatname=Motors

      You may be upset by the figures there. It would not surprise me to find
      your motors to be similar. Even if not, they are likely to be able to
      draw several Amps when stalled. Measure their DC resistance with a
      multimeter. Take readings with the armature in several positions and
      average the answer. This will give you a crude indication of likely
      stall currents. Alternatively, if you have access to a lab power supply,
      set the voltage to 6V or so and see how much current they draw with
      various loads. Try setting the current limit to, say, 1Amp and stall the
      motor. What happens?

      >
      > Batteries:
      >
      > The batteries we plan to use are 6V Ni-MH rechargables rated for
      > 600mAh(150) and I'm not entirely sure about what that means as far as
      > maximum sourcable current goes. For powering the motors, I've gotten a
      > MC78XX 5v Voltage regulator (1 Amp max), and will be using some caps
      > to limit the noise, as well as having a common ground but seperate
      > v-regs for the controls and the motor circuitry. Since the batteries
      > shouldn't supply 1 A at any point, I think this regulator should be
      > sufficient, but I'd like to know if I'm making an error in judgement.
      >

      There is no point in using a regulator to supply motor voltage in this
      application. The motor supply should come direct from the battery. Bear
      in mind that the regulators may need 1.5V or more to do their job and
      you may find that there is not enough battery voltage to allow the
      regulator to reliably supply 5V to the logic stuff. A typical symptom of
      this would be the processor resetting when the motors run. Especially
      since the motors are likely to draw large currents when starting up
      unless you are very careful to control that.

      >
      > Motor controls:
      > We are going to use the PIC18F4431 as our controller, which is
      > designed for PWM. I don't think it will be able to adequately source
      > the current we'll need, so I'm looking for H-bridge ICs for the
      > Motors. Would TI's SN754410 controller suit our needs?

      The SN754410 can do about 1A per channel I think. You could use both
      channels in a chip for one motor to increase the current handling.
      However, if your motors really do draw multiple Amps, you may need to
      look at a more beefy h-bridge like the LM298
      >
      > IR:
      > Is the 38 kHz receiver module that Radioshack sells a good choice for
      > a distance sensor, or are there other modules that would be better
      > suited to that task?
      >

      I don't know about that one. Several mice have been built with one of
      the various Sharp distance sensors. Can't remember the part numbers now.
      GP2D12 or GP2D15 or something like that.
    • Peter Harrison
      ... My apologies - I rather thought you had dropped a zero. have you looked here: http://micromouse.cannock.ac.uk/motors/index.htm
      Message 41 of 41 , Mar 13 1:25 PM
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        Ben Estroff wrote:
        > We are, of course, going to use gearings that will make our 35-36
        > mm diameter wheels rotate at an appropriate rate.

        My apologies - I rather thought you had dropped a zero.

        have you looked here:
        <shameless self promotion>
        http://micromouse.cannock.ac.uk/motors/index.htm
        </shameless self promotion>

        Pete

        >
        > On 13 Mar 2007 12:43:27 -0700, Peter Harrison <peter.harrison@...>
        > wrote:
        >> Ben Estroff wrote:
        >>> I believe we'll be using three Sharp GPD120 IR range sensors.
        >>>
        >>> And, are these motor specs acceptable? We're hoping to have a maximum
        >>> velocity of 1.6 m/sec.
        >>> **
        >>> *MO-201 GEARBOX WITH MOTOR REVERSIBLE 12V 70RPM *
        >>> Torque 2.1kg/cm
        >>> Rated Voltage 12.0V
        >>> Operating 4.5 - 18V max
        >>> Current - No load 30mA
        >>> Current - Full load 390mA
        >>> Gear Ratio 82:1
        >>> Shaft Speed 70RPM
        >>>
        >>> I'm not sure of the dimensions, but this gearhead motor should fit
        >> inside
        >>> our desired footprint, and be much better in terms of power consumption.
        >>>
        >> I am sure you can do the sums as well as me but...
        >>
        >> To get 1.6m/s with wheels doing 70rpm you will need wheels that are
        >> 436mm diameter.
        >>
        >> Pete Harrison
        >>
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