Re: (ET) motor ratings

["David Roden" <etpost drmm net>]

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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