Thread: Discussion Motor formulas
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Old Feb 01, 2009, 09:46 AM
KreAture is offline
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Oslo Fornebu, Norway
Joined Jun 2003
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Hey! I just realized there is a formula missing.

Kt = T * L * D^2
Where T is a torque-constant for the motor reliant mostly on the magnet strength and airgap. L is the length of the stator stack and D is the diameter of the stack.

There is another Kt formula based on the actual values instead of just a constant.
Kt = 1/Kv
but depending on the Kv units it may become:
Kt = 60/(2*pi*Kv)
This turns a rpm/volts Kv into a radians/second/volts so that Kt becomes Nm/A.

An interesting thing about the first formula is it shows that, as mentioned, The relationship between Kt and Kv is inverse proportional and that length of stack has a linear relationship with Kt and Kv. What it also shows is that the diameter has a squared relationship! This is important if you need more torque. For a in-wheel motor, maximizing diameter will increase torque by D^2 while increasing width only adds L.
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