If I may put in my 2 cents (first a disclaimer, I'm new at this stuff, on my first build,and very knowledgable) that said-- this is what my opinion is..a motor controlled to RPM...is a big mistake, what if prop fouls or a bearing seizes? won't this send massive amps to the motor and burn it out? Controlling for torque seems to be more about tires on pavement. Think of your prop in water as a fluid transmission torque converter. So, Unless you are trying to impress girls by popping your bow up in a wheelie at the marina..forget torque.
I just bought a dandy little PWM controller 3000watt for $15.00.(chinese/e-bay) it works like a charm, I added a digital read out meter that reports Amps/volts/watts, refreshing every few seconds($18. missouri wind/e-bay). I set the potentometer to the WATTAGE I wish to expend. I can troll along on at a whisper <1kt using less than 100 watts, or I can set it any where up to over 2000 watts where I approach my max hull speed for my 21 ft sailboat hull. The bonus by setting it for a given KW target is that you can compute your battery life in amp/hrs for a given round trip.
I am adding a temp gauge/sensor in the motor, and an RPM gauge on drive shaft, just to know what thrust I'm using and approx speed I'm traveling at, (estimating wind/weight/current losses or gains)
One could send temperature or rpm info to the board of a more complex controller circuit board, for auto limiting....But I'm just keeping an eye on the gauges and learning my boat, trying to find the "sweet range" of maximum speed for a reasonable battery life, whilst running the motor cool.
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Posted by: billhopen@yahoo.com
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