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
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