At 07:50 PM 19/08/2002 -0500, you wrote:
>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 ?

It might be that the saturation voltage of the L293 is causing
less than 6V to be applied to the motor. Have you measured it?
The L293 sucks pretty badly when you only have a low battery
voltage to start with as the saturation (drop across output drivers)
voltage is quite a high percentage of the available supply.
Roman suggested some better H-Bridge drivers some time back.
Regards...
___________________________________________
David Duffy        Audio Visual Devices P/L
U8, 9-11 Trade St, Cleveland 4163 Australia
Ph: +61 7 38210362   Fax: +61 7 38210281
New Web: www.audiovisualdevices.com.au
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