Originally Posted by
donhuff
The biggest difference between regular TPs and the CM/SVM series, is that the cm/svm have a one piece cylindrical magnet. Not glued on and wrapped segmented magnets. That cylinder magnet is why the cm/svm have a higher "MECHANICAL" rpm redline, which is the rpm max that most manufacturers put on their motors. There is probably a little "cushion" rpm there I'm sure. It's not like if you go over that line by 10 rpm it will let go, but if you go 5-10,000 over, then you should expect the rotor to sling it's self apart. That's what the carbon fiber and kevlar wrap is there for. To up that rpm redline before damage occurs.
That cylinder magnet usually has been ground or cast, with very shallow peaks and valleys. They are hard to see but easy to feel. The peaks are where the POLES are located. You'll find 2 pole and 4 pole rotors in the TPs. No idea as to why??
I have received for repair several of the CM/SVM types and all I can do is rewind it, they are usually burned up when the rotor dies. Those rotor are very easy to kill with not much heat. I had one die on me while holding it in my hand and running it to test a new rewind. It was a really high kv (7600kv) TP 4040 for a 2S saw attempt. I ran it up to full rpm around 60,000 rpm, and it ran good. I tried it a second time, and it was dead. I disassembled it and found that the rotor and stator had touched in one tiny spot. Since that one I have seen that same damage in 4 or 5 customer motors.
This must have happened a lot in the CMs, because the SVMs have a .020" bigger diameter hole in the stator. And the SVMs have a groove cut down the middle in each stator tooth, and again I have no idea what it's for.
The cylinder magnet rotors are very slightly larger diameter. But strip off the carbon wrap to get an accurate measure of the magnets and that difference is more meaningful. Seems like around .010" to .020". That still doesn't seem like a lot but small increases in the diameter of the rotor have a huge affect on the torque of a motor. It also increases the "rotor displacement", much like boring a car engine for bigger pistons and more displacement. This might be why the cm/svm have a little higher max watts (HP) rating.
I have given up on the cm/svm series for my record boats, and use regular rotor in my motors now. I adjust the kv to get the rpm right at, or just slightly above the recommended rpm max. Because when in the water, the rpm will be much lower and well into the "safe" region.
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