Re: [oopic] Re: H-Bridge issue...maybe.

Richard,

I wouldn't worry about the oPWMS (oServo) resolution here. Most
robotics operations use "slow, medium and fast" and not much else.
Under those circumstances the 6 bit resolution of the oPWMS is perfectly
fine.

DLC

rtstofer wrote:

>--- In oopic@yahoogroups.com, Shaggy <charrington@...> wrote:
>
>
>>Then I will go with the Sabertooth.
>>
>>Thanks for the information.
>>
>>
>
>Until I read the documentation at
>http://www.dimensionengineering.com/Sabertooth2X5.htm I was concerned
>that the device would only work with R/C pulses. That would seriously
>limit resolution due to the manner in which the OOPic generates the
>pulses. The .pdf is here:
>http://dimensionengineering.com/datasheets/Sabertooth2x5.pdf
>
>But the good news is that the H-Bridge will also work in analog mode
>and you can use the oPWM objects to control the motors.
>
>You may want to deal with the issue of 2.5V being the OFF condition.
>When the OOPic first starts up, the IOLine is an input and floating.
>The motor may run away briefly. I might put a 20k resistor between the
>input and +5V and another 20k resistor between the input and Gnd in an
>attempt to bias the input to 2.5V until the oPWM object takes over.
>
>Obviously, you want to start with the oPWM at 50%, then establish the
>IOLine and finally set the operate property. Hopefully, you will get a
>bumpless transition into the stop condition.
>
>Thinking about the OOPic.Delay = 500 as the first executable statement
>(and it is HIGHLY recommended) the motor could run away for a very long
>time.
>
>If the bias idea doesn't work, put a suitable SPST relay in series with
>the motor power and control it via the OOPic and a trasistor of MOSFET.
>
>One way or the other, you need to deal with this bias situation.
>
>Oh, and read the note on filtering the PWM signal on page 10 of
>the .pdf. If you use the bias resistors, the resistor at the pin needs
>to be a lot smaller (maybe 1k or less) to allow the pin to pull the
>signal all the way up or down. The 1k resistor is working in series
>with the bias resistors and forms a voltage divider. Given that the
>resistor is much smaller, the capacitor should be much larger - say 1
>ufd (probably electrolytic).
>
>I suspect there will still be a little tinkering to do...
>
>Richard
>
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>
>

--
------------------------------------------------------
Dennis Clark ooPIC Tech Support
www.oopic.com
------------------------------------------------------

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