Alt-BEAM Archive

Message #04516



To: beam@sgiblab.sgi.com
From: Richard Weait crs0274@inforamp.net
Date: Mon, 14 Jun 1999 22:19:25 -0400
Subject: [alt-beam] Re: MOTOR DRIVER QUESTION


At 06:17 PM 6/14/99 -0400, you wrote:
>ok, nobody answered my question so i'll ask it again.
>
>is there any preference on motor drivers?
>h-bridge, z-bridge, 74hct240 IC (miller's tutorial) ?
>

Well, Sparky,

Yes. I have a preference. That preference is a 'moving
target' though. It depends on what I'm doing.

The '240 variations can't supply much current on an ongoing
basis, so don't use them unless you are using efficient
motors.

Same thing goes for using a demux chip as a motor driver. . .
it really isn't designed for the task, but you can do it if
you can live with the limitations.

Building an H-bridge from transistors involves more parts, but
gives you more flexibility. Look at the FAQ for some of the
bridges submitted by Steve Bolt.

Another option is to use single chips that are designed to be
used as motor drivers. This can give you the low component
count and of the '240 and '139 designs and the increased current
capacity of the H-bridge. Best bet for these is to search on
the manufacturers website for the datasheet, and go through that
before you plunk down any money on them. Some can be pricey.
Others can be hard to find. I recall a big stink over getting
the correct variation of a motor driver chip on the comp.robotics
news group. The chip that had the reverse diodes was out of
stock, but the available chip required external diodes and the
PCB real estate was hard to come by. . . That too, depends on
your motors.

[snip]
>local elec supply shop wants $1.40 each for their 2N3904 transistors
>thats over $10 for two h-bridges (four "04's" each h-bridge) and the IC
>only cost $1.20 at Rat Shack.

Those prices look a bit high. Lots of mail order places should be
able to do better if you order in 10 - 25 quantities. Pool your
order so that you only pay delivery once.

Cheers,

Richard.


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