Re: Sparrow and programming (was: For you, AC drive fans ...)

["Eric Chang" <walkabout179@email.com>]

Hi David.  Sorry I did not get the message
across more clearly, but perhaps it was
intentionally worded so that it could go both
ways (so I would not polarize myself on any one
side of the war; but I guess it is also
inadvisable to cycle back and forth on the
issue either :-)).

Your take on the meaning is what I intended to
say.  Yes, the DC system was the final choice
(at least for now), but the AC system is like
the continually crashing program.  Even though
it contunually crashes, its bugs are of a very
different nature than the ones in the DC
system, as you pointed out.  The ones in the
DC system are, in a sense, inherent ones, which
are quite difficult to solve.  The AC issues,
on the other hand, are more like small bugs
that, once fixed, will produce a more advanced
system in the end.  Specifically, one can point
to the case of the fireballing.  This is a very
difficult problem to solve for a DC system,
since the readily available motor is not
available with arc suppression poles/windings,
and there is no mechanical reverse.  Such
matters are non-existent in an AC system, and
instead we have a stability problem, for which
it is well known that a solution is available
from control theory, becoming, as Otmar would
put it, a SMOP (small matter of programming).

The stability issue, however, rendered the AC
system unusable in the short run, and look what
we ended up with.

So, I do read my own posts :-).

-----Original Message-----
From: "David Roden (Akron OH USA)" <roden@ald.net>
Date: Mon, 14 Jan 2002 11:19:05 -0500
To: ev@listproc.sjsu.edu
Subject: Sparrow and programming (was: For you, AC drive fans ...)


> On 14 Jan 2002 at 3:46, Eric Chang wrote:
> 
> > Despite all the shortcomings, the DC system was better
> > than the alternative.  
> 
> I'm not sure it's fair to say "better."  More useful for a production 
> vehicle, perhaps.  But reread your own post:  your comparison of the 
> program that crashes versus the program that's slow could apply here.  
> You suggest that fireballing a motor is like crashing the program; I see 
> it quite differently.  The series motor and controller is the old, slow 
> program; the BLDC and AC systems Corbin tried are the new program that 
> keeps crashing.
> 
> I think Corbin used the series motor -- conservative technology -- in 
> part because production was already behind schedule, and he couldn't get 
> any BLDC or AC (SL-MTI?  Denso?) system working right.  Money was 
> gurgling down the drain, with no vehicles yet being sold.  
> 
> The first Sparrow prototype used 48 volts and a series motor.  He really 
> wanted to use a BLDC motor in the production vehicle, but instead of 
> working with companies with an established road EV track record, he chose 
> SL-MTI (I think that was the name).  He even invested in that company.  
> When they couldn't pass muster, he turned to Denso.  Months went by, and 
> the bugs still were crawling all over that system, too.
> 
> If he'd been able to spend more time and dollars working on either of the 
> alternate systems he would have had a new EV design, instead of enhanced 
> forklift technology -- and he might not be having some of the problems he 
> has now.  
> 
> Another answer, somewhere between the conservative and progressive 
> choices above, would have been to go with a company with more EV 
> experience.  Drive systems from such companies as Siemens, Brusa, and 
> Solectria have proven track records.  But that might have driven the 
> vehicle cost even higher, and I think he knew what the market would bear.
> 
> Of course I'm not privy to the decision process at Corbin, and I may be 
> way off with my speculation.  Still, I don't think you can really argue 
> that Corbin's falling back on a series DC motor and, what, 3 or 4 
> different DC controllers he's tried now?  -- is a progressive choice.
> 
> 

-- 

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