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Originally Posted by Al Skierkiewicz
Whoa,
Don't go getting all excited yet. The technology behind the this discussion still has a lot of variables in place that would make this impractical for our use. There is too much production variation in the motors such that any two motors will not produce the same voltage when turned at the same speed. Add to that the resistance of the power leads and their length, temperature, connector resistance, etc. and you will see that precise speed control and distance is a going to be inaccurate. It may be possible for a theoretical controller to "learn" the circuit charachteristics, but at varying speeds and the short distances traveled I think there is still a lot of room for error. I would need a little more convincing before I would jump in on this.
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There are parameters that get tuned but I don't think this would prevent this from being a very useful feature.
Note that the guys at Charm Labs are selling robot systems right now that do just what we are talking about. Somehow they are dealing with motors variation, temperature variations, connector resistance, etc.
Also, talking to Jim Zondag of the Killer Bees (#33) about this, the auto industry has gone to this type of a system for the motors that drive the vent doors inside of HVAC units (replacing pots and/or switches for position feedback). I think this is very encouraging news.
From my point of view the most disturbing thing is that the process requires that the PWM be less than 100% In most cases that would be just fine BUT there are a lot of cases where I would want to have the motors get full power.
I am extremely hopeful.
Joe J.