Hi Kevin,

It looks like you are losing several volts in the bridge.  Page four of
the datasheet http://www-s.ti.com/sc/ds/sn754410.pdf  (High level output
voltage and Low level output voltage) indicates you will lose between 2
and 4 volts (depending upon load and temperature).  You could try
measuring the voltage across the motor terminals under load to verify
this.

Best regards,

Dave

"Kevin A. Benedict" wrote:
>
> Hi,
> I posted this under EE, but then found a big discussion from
> 12/2000 about the tamiya twin motor drives.  I still have the same
> question, the FA-130 motors are rated 3v@800ma stalled.
> So why can't I drive the twin motor gear box a pic and
> a sn754410 chip with 4AA batteries ?
> One note I did have it set to 58:1 ratio, I am going
> to try 203:1 next.
>
> Thanks in advance,
> Kevin
>
> >>Hi,
> >>I am driving two small DC hobby motors in a gear box assembly,
> >>that drives two tank tracks. I wanted to power the F628,
> >>SN754410 and two motors all from the same 4AA batteries.
> >>If I drive the two motors right off the 4 AA batteries,
> >>the tank tracks are powerful and can drive over a thick
> >>book.  However, when I power the pic/SN754410/2 motors,
> >>the motors are barely able to turn the tracks ?
> >>
> >>In the F628, I have port A set as digital, and set ra1, and
> >>ra0 high and low to turn on motor a, and follow the same for
> >>ra2 and ra3, for motor b (through the SN754410 of course.)
> >>The SN7554410 is just a 1 amp version of the L293D.
> >>port b is set as output and all pins low.
> >>
> >>I quess I'm just looking for a sanity check, I can't believe
> >>the F628 and H bridge chip are using up so much current
> >>that the motors can't even turn the tank tracks ?
> >>I have both enable pins on the h-bridge chip tied to the +5v
> >>supply through a 10k resistor.
> >>Any one familiar with these chips ?
> >>Any thoughs on what's happening ?
>
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