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Originally Posted by P-hack
... maybe if you have a lead on 2 or 4 small motors that are just enough power for your needs (leads have to be the same length) and are on a tight budget.
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Fitting the available motors into the engine bay with the transmission, etc is sometimes a challenge. The Siemens motors that are surplus from Azure dynamics, for example.
With a small single-speed gearbox per motor, you may open up some options on different builds, or make the builds possible.
IMHO cost is always a factor, but not necessarily the over-riding factor. If something will do the job (safely, power is OK, etc) why not use it?
Why do the motor leads have to be the same length? At my day job, we are running 4 motors in parallel, each with a gearbox, for 4 wheel drive. There are separate overloads and contactors on the output side of the controller for each motor. Leads vary from 16 feet to the nearest motor to about 60 feet for the furthest motor on the opposite side. They've been running (intermittent duty) since 2006. They are only 3 HP, and the big iron thing they are moving (called a tripper) only moves 200 feet per minute ... but that's how fast it's supposed to move
There's not much access (to the motors), and my boss won't let me run tests on them. The controller is in V/Hz, no encoders or feedback to the controller. A DCS gets an encoder feedback from one wheel, so it can send out the stop and start commands.
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But if you have 4 regular motors, you are going to need so much battery that the extra power sections aren't gonna be noticed in the budget (and your controllers might need a controller, conceptually anyway, if you are trying to do stuff like traction control).
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If there are 4 motors, I won't need full power from any of them (I don't drag race). It would be nice to have one controller, but complexity COSTS MONEY in development time and troubleshooting PITA.
Multiple power stages on one controller would allow for separate control and be a bit more complicated in the one controller. Multiple controllers would need, in my opinion, to exchange a bunch of data to keep things running smoothly, perhaps with an overall controller as you suggest. But it sounds complicated.
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You have multiple rotor positions here (using current sensors),
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How do you do position sensing using current? That would be useful. As I understand it the commercial products use Back-EMF (voltage)
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if you want FOC on multiple motors, you need multiple switches (IGBTs) and signals at a minimum so that the stator coils fire at just the right angle for each motor (though you still need some slip with FOC, I think it is mostly when changing speeds that it targets the highest torque vector).
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Darn - I was hoping you had thought of a way to do FOC on multiple motors. Oh well.
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But a slip algorithm can also set slip for max torque, just not on the very first pulse.
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Not sure I understand that one. Slip for the motor, to generate torque in the ACIM, or slip between tires on multiple outputs?