On 29 Dec 2012 at 11:23, Bill Alburty wrote:
We need a controller which will work on all types of DC motors;
namely, series wound, shunt wound, compound wound, and all the other
combinations.
I'm not an engineer, but my impression is that this is a pretty tall order.
Pairing a motor and controller is not a trivial process.
In particular, separately excited motors need a customized field current
profile, different for each motor. You may be able to find a compromise
that will work with several similar motors from the same manufacturer (the
Alltrax ET controller works OK with most ET wound-field drive motors,
AFAIK). But I think that once you get into more dissimilar motors, the
controller's designer has to consider each motor's behavior separately.
Series motors seem to be more forgiving, but you can still run into
compatibilty problems, even beyond whether the controller can handle enough
current to run the motor in its intended use.
For example, certain Curtis controllers need more inductance than some
Advanced DC motors provide. Their current limiting doesn't work right with
those motors unless you add a series inductor. This is why more recent
Curtis road EV controllers reduce their chopping frequency to the audible
range at low duty cycles - it gives the current limiting circuitry more
time
to respond.
Someone with more chops may blast me out of the water on this one, but I
wonder if it might be possible to design a microprocessor controlled
controller for which the firmware was user-uploadable. Then all the
manufacturer would have to do is develop a new field map or control
algorithm for each motor the users wanted.
However (here I am attacking my own idea), doing somethng like this in a
timely manner - so you weren't waiting months or years for your firmware -
would, again, be a nontrivial process. It'd require a long term commitment
from the designers. And at engineers' salaries, I don't think it would be
too compatible with a price that most of us would want to pay.
It would be great to have someone design such a controller as a volunteer,
but would he want to support it long term, generating yet another profile
for yet another user for years to come? I think the best chance for such
an
enterprise would be if we could find a large community of qualified
developers to work on the project, something like some of the Linux
variants
have. Maybe with open specs, we could develop a user community to support
such a controller.
I question whether we have enough EEs in the ET world to make such a
project
fly. Ffor this to work, I think the controller would have to also be
applicable to other machines more common than the ET. Maybe golf cars?
NEVs? What else?
The market size is an ongoing problem with ETs, just as it is with hobbyist
road EVs. I suspect that the reason we have the Alltrax ET controller at
all is that Steve Richardson owned an ET, worked for Alltrax, and wanted a
modern, customized controller for his tractor. Given the market size, I
can't imagine Damon making it a priority otherwise.
While it would be great to have a DIY / open source option, I would be very
impressed if a controller of any kind, DIY or otherwise, could be made to
support "all types of DC motors" - especially while costing in the hundreds
rather than the thousands of dollars.
David Roden - Akron, Ohio, USA
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