Quote:
Originally Posted by GriffinRU
Monday-Monday - it is Friday :)
Patrick you are:- talking about spindle motors...
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- No, I'm not... talking about motors in general - - applicable whether using spindle motors, linear motors, axial or radial flux, etc.
Quote:
Originally Posted by GriffinRU
- miss the fact that we would like to have hybrid system (or based your opinion)
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Nope, didn't miss that either. Didn't say I wouldn't make a hybrid system either... just that the halls are useless in most situations. 
Quote:
Originally Posted by GriffinRU
- sensors imbalance is fixed (constant for given motor) and can be offset (I am not even going into phase shift with RPM business)
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So -- Why would I want to take my high accuracy sensorless position and use it to correct an inaccurate sensor? Why? To what end? To lower my position accuracy? To lower efficiency?
That's like saying -- "Lets measure this distance with a tape measure, and then I'll count how many steps the distance is. Then we'll correct the number of steps using the measured distance, because we know the number of steps in inaccurate." -- Doesn't make any sense to correct an inaccurate measurement using an accurate measurement in the first place. There is no additional information that the hall sensors add to the system. Only noise -- which I don't want to add to the system.
Quote:
Originally Posted by GriffinRU
- optical sensors are rock-solid
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SLOW, same imbalance problems as halls...
Quote:
Originally Posted by GriffinRU
- motor windings are even worse in terms of matching, not even considering that load on the motor shaft is not constant in car-applications
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Phase imbalance is compensated for in sensorless -- so it doesn't matter. Not compensated for with sensors... another sensor drawback...
Quote:
Originally Posted by GriffinRU
- once motor spinning use sensoreless feedback, it is free no hardware to add
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That doesn't even make any sense. Sensorless isn't free -- it requires a lot of hardware... 
Adding sensor support on top of that adds cost.
Quote:
Originally Posted by GriffinRU
- braking, pulling and holding that is what you can do great with precise rotor position feedback
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Holding torque is better sensored. But not really important in this hobby except MAYBE for rock crawling. I don't understand where braking would be different - - same positioning algorithm as running the motor, just different FETs being turned on.
Quote:
Originally Posted by GriffinRU
- for $$$ you can add encoder and it can be single wire, or even wireless
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Throw more money at something that doesn't work well in the first place? No thanks... :)
Quote:
Originally Posted by GriffinRU
20% PWM at stall is not high current if you matched with magnet pole and motor is rated for the load.
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Incorrect -- remember there is no back-EMF at stall, and most (hobby type and high performance) motors don't have enough inductance to enter that into the equation -- So the only thing sure to limit current at stall is phase resistance. There is a non-linear (1/x) relationship to current draw vrs RPM at a given PWM level.
Quote:
Originally Posted by GriffinRU
Hall sensors are cheap and sensitive to all kind of things, including magnets or screwdrivers in their proximity, but can be shielded or replaced with opto...
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Exactly -- so why spend money trying to fix something that doesn't work well to start with?
Don't think I don't hear you -- I'm being purposefully obtuse to make my point
... -- there are situations where a hybrid would be nice to have. I just don't think that 95% of people need (or would benefit from) a hybrid system, and the reliability and efficiency issues outweigh the usefulness.