Alt-BEAM Archive

Message #13443



To: beam@sgiblab.sgi.com
From: Richard Weait beam@sgiblab.sgi.com
Date: Sat, 15 Apr 2000 08:14:47 -0400
Subject: Re: Reverser


Jef,

Your answer is not 'wrong.' Biassing the high-side switch
of an h-bridge can be an issue. The difference between your
answer and Bruce's answer is in the 'assumptions.' (and isn't
that what always causes problems?)

'BUDSCOTT's' question about a reverser for a two motor walker
does not explicitly state the starting conditions. That is; in
a two motor walker, both motors are driven by h-bridges just to
make it walk forward. (note that if the motors don't reciprocate
all you have is a 'really bad helicopter' :-) ) To make this
same two motor walker walk backwards the motors must still
reciprocate, but the relative phase changes.

So a typical reverser for a two motor, four legged walker changes
the front-to-rear phase from +90 degrees, to -90 degrees, reversing
the robot's direction.

Cheers,

Richard.

At 11:52 PM 4/14/00 -0400, 'jef' wrote:
>I am very new to the list, and this answer seems so painfully
>obvious to me that it has to be ubsurdly wrong. :-)
>
>Don't most motor reversing circuits uses H-bridge configurations?
>At small voltage levels it may be difficult to bias the switches
>properly..haven't looked at it that closely yet.
>
>Does that sound right?
>
>ok..jef
>
>On Fri, 14 Apr 2000, Bruce Robinson wrote:
>
> > BUDSCOTT@aol.com wrote:
> > >
> > > I asked this earlier, but didn't really get a clear answer to my
> > > question. How does one hook up a reverser to a two motor walker
> > > circuit ...
> >
> > Reverse the polarity to ONE motor :)
> >
> > Bruce
> >
>
>
>Jeffrey D. Spears
>University of Michigan
>College of Engineering
>
>``Double-E, can't spell gEEk without it!''
> -Captain Gerald M. Bloomfield II, USMC
> (my brother)
>
>

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