>
>
As noted previously, it sounds like you have something hooked up
wrong, or your oopic code is buggy.
> Ok, this morning I set up the bot so that I could measure the
voltage to the
> motors. When I set the motor speed at 127, the voltage across the
motor pins
> was 8.7, which is pretty reasonable. When I changed the motor speed
to 120,
> the voltage across the pins was just below 1. It held steady around
0.6V.
> That's certainly a bit low for those motors.
>
> The second time I tested this, I got the same voltage at 127, the
same at
> 120, about 0.4V at 100, then I tried 126. The voltage first showed
about 2V,
> at which the wheels bumped forward some, but the voltage dropped
rapidly
> down to 0.8V.
>
> That's not a very smooth curve. Can you point me towards a solution?
>
>
>
> rtstofer wrote:
> >
> > --- In oopic@yahoogroups.com, Shaggy <charrington@> wrote:
> >>
> >>
> >> The motor is a 7.2V motor, which I am running off a 9.6v NiMH
> > battery pack. A
> >> 4V drop certainly suggests that this won't work, but what I'm not
> >> understanding is why the motors are flying at 127, but not
moving at
> > 126. I
> >> think I have a misconception as to how the output values from
the OOPic
> >> translate into motor speed.
> >
> > If you use the oDCMotor2 object the output pulse width varies.
At low
> > speeds, the pulse width is narrow and at high speeds the pulse
width
> > is wide. The total period (off time + on time) is related to the
> > frequency and, for PWM, that frequency is 19.5 kHz (call it 20
kHz).
> > So, the total period is about 50 uS and the pulse width can vary
from
> > 0 to 50 uS. Half speed would have a 25 uS wide pulse in a 50 uS
window.
> >
> > You can take the output pin, add a 220 ohm resistor in series
with an
> > LED connected to GND and you will see the effect of larger
numbers.
> > High numers = high brightness. Remember to connect the cathode
of the
> > LED to GND.
> >
> > Remove the motor from the output of the driver and substitue a
> > voltmeter. You should see the voltage vary up and down with the
duty
> > cycle values. This is one place where an analog meter is nice:
you
> > don't particularly care about the absolute value, you want to see
than
> > change.
> >
> > There is some relationship between motor voltage and motor speed.
> >
> > You can also use that analog meter on the output pin to watch the
> > voltage change. It isn't really the voltage that changes, just
the
> > duty cycle of the pulse. But, an analog meter will integrate the
> > pulses and display a voltage. A digital meter will work but you
may
> > need to add a 220 ohm resistor and 1 ufd capacitor in series to
> > ground. Measure across the capacitor.
> >
> > Forget the numbers! Measure the voltage at the motor terminals.
> > That's what the motor sees!
> >
> > Don't forget to put capacitors between the motor leads and the
motor
> > case and one across the motor leads (total 3). Use 0.1 ufd
ceramic.
> > Make sure the motor case is connected to ground. Separately.
> >
> > Richard
> >
> >
> >
> >
>
> --
> View this message in context: http://www.nabble.com/H-Bridge-
issue...maybe.-tf4867316.html#a13936854
> Sent from the OOPic mailing list archive at Nabble.com.
>
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