Newsgroups: comp.robotics
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From: roger034@gold.tc.umn.edu (Brynn Rogers)
Subject: Re: Piggy-backing motor chips on 6270 board
Message-ID: <Cp5EC6.L9A@news.cis.umn.edu>
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Organization: University of Minnesota
References: <9404302145591.DLITE.j85@delphi.com>
Date: Sun, 1 May 1994 23:50:46 GMT
Lines: 57

In article <9404302145591.DLITE.j85@delphi.com>,
Jeffrey Graham <j85@delphi.com> wrote:
>
>From: J85   
>To:   robot-board@oberon.com                                                    
>                                                                                
                                                                        
Botists:
>
>Talk recenlty on motor control chips concerning the L293 and the
>possibility of putting 3 atop each other, like this?
>
>            SGS L293B                    SGS L293B
>            SGS L293B            OR      SGS L293B
>            SGS L293D                    TI SN754410
>        --------------------        --------------------
>
>Is this right?
>
>
>What about using three TI chips on top of each other to get 3A?
>Would that work with my 9.6Volts from 8 AA batteries?  
>
>Thanks  
>


Stacking power components is  Bad Idea.   Call fire marshal Bob.

If you want to push that much power, each of the 3 stacked chips wants to
have good heat sinking (maybe only to the ground plane of a PC board) and
good ventalation.  Stacking these parts is a sure way to overheat them.

If you really need that much current, you need to go to a package that can
dissapate more heat.  Or go to discrete components that can handle a ton
more power  (but your parts count just went way up).

   I have found that the Allegro chopper drivers to be a lot better than
the L293 (which we use in an older design).  The UCN2954 is a part we use
in a newer design and it has given us no problems, while the L293 has
given us so many that we are redoing that board and software and putting
in a 2954.

   In a chopped current driver,  you would use a 6 volt stepper with a 12v or
24v  (or even 40v) supply.  You select current sense resistors so that the
2954 will never put more than what you want into your motor.   With a
chopped current drive circuit like this you get more torque and better
response from your stepper.  You may not have noticed, but in the Vexta
(Oriental Motors) step motor data sheets, all the specs for torque:
pull-in torque, pull-out torque, and steps per second are given for a
motor that is driven by a chopped current driver.  Chopped current drivers
are the only way I know of to get the maximum performance from a step motor.

Brynn        Varitronic Systems, Inc  (612) 536-6444
--
Brynn Rogers     roger034@gold.tc.umn.edu

