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Old 05-08-2010, 12:33 PM   #6 (permalink)
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Right, make a control board with 2 separate mosfet drivers. Each of the 2 pwm channels from the microcontroller goes through its own hcpl-4504 (or 4506) optocoupler, which goes to the input of its own mosfet driver. Write your software such that the pwm of each is what you want it to be. For example, when just taking off, perhaps it's OK to have the field voltage be very high (so high pwm duty). Keep track of how long it was at a high voltage, and force the field pwm to throttle back at a certain point. For higher rpm, you can weaken the field (lower pwm duty). There are software ways to sense the approximate motor rpm on DC motors. The dsPIC30F family has 6 pwm channels, which gives a LOT of options. They have the humble and basic dsPIC30F2010, which can come in a 28 pin DIP, all the way up to the dsPIC 30f6011 (or maybe higher, I don't know! hahaha) which has like 60 pins. They are all functionally equivalent, but the higher pin micros just have more of the same stuff (and also has CAN bus and multiple UARTs).
kits and boards
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