Re: [SeattleRobotics] Motors, controls, and an IR question for micromouse
- Ben Estroff wrote:
> Hello, again.I looked for 370 size motors and the first hit I got was this one:
> 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?
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?
>There is no point in using a regulator to supply motor voltage in this
> 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.
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.
>The SN754410 can do about 1A per channel I think. You could use both
> 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?
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
>I don't know about that one. Several mice have been built with one of
> 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?
the various Sharp distance sensors. Can't remember the part numbers now.
GP2D12 or GP2D15 or something like that.
- Ben Estroff wrote:
> We are, of course, going to use gearings that will make our 35-36My apologies - I rather thought you had dropped a zero.
> mm diameter wheels rotate at an appropriate rate.
have you looked here:
<shameless self promotion>
</shameless self promotion>
> On 13 Mar 2007 12:43:27 -0700, Peter Harrison <peter.harrison@...>
>> 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
>>> 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