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

--- In oopic@yahoogroups.com, Shaggy <charrington@...> wrote:
>
>
> I'm using Rogue Robotics OOPic board, which is similar to the R, but
> configured a little differently. I also have their low cost H-Bridge
(that's
> the actual name), but I went to a different chassis from Robotics
Connection
> because I was having trouble with the Rogue Robotics ATS throwing
tracks on
> carpet. The motos on the Robotics Connection chassis are much
better, too,
> but I'm having an odd problem with driving them.
>
> To drive the wheels, I send a byte with a value from 1-127 for
forward, and
> 128 and up for reverse. This would cause different speeds using the ATS
> chassis, but I added an external power supply on the new chassis so
that the
> motors wouldn't be using the power from the OOPic board. When I send
a value
> below 100, nothing happens. In the range of about 100-120, the
motors just
> chirp. At a value of about 120-126, one wheel budges forward very
> sluggishly, while the other barely moves. However, at 127, the
wheels are
> FLYING. So I go from nothing to almost nothing to full speed ahead.
That's
> not what I was hoping for.
>
> I suspect the low cost H-bridge, which is about as simple a
component as you
> can get, is limiting things, but I'd like some input before I drop
the cash
> on a better H-bridge. Also, I'd take some recommendations if that IS
the way
> to go.
> --
> View this message in context:
http://www.nabble.com/H-Bridge-issue...maybe.-tf4867316.html#a13928519
> Sent from the OOPic mailing list archive at Nabble.com.
>

What is the voltage rating of the motor? What is the voltage of the
motor power source? Have you accounted for the internal voltage drop
of the driver chip? There will be a 4V internal drop at 1A of load.

Look at VOH and VOL here
http://www.makingthings.com/resources/datasheets/SN754410NE_slrs007b.pdf
Page 3 near top of electrical characteristics table.

Check the voltage at the motor...

Richard

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