# DC Motor Transfer Function units

Discussion in 'Homework Help' started by onlyvin, Feb 8, 2014.

1. ### onlyvin Thread Starter New Member

Feb 8, 2014
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omega/Vin = (Kt/LJ)/(s^2+R/Ls+Kt^2/LJ) -----> DC Motor

J = 3 lbm*ft^2
R = 5000 ohms
L = 300 H
Kt = 300 ft*lb/A

I'm not sure if I have to do a unit conversion of the elements to get the correct transfer function or if I can simply plug the numbers into the function above. I know omega is in rads/sec and Vin is in volts but I'm still not sure about the next step.

2. ### ericgibbs AAC Fanatic!

Jan 29, 2010
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3. ### onlyvin Thread Starter New Member

Feb 8, 2014
2
0
If I have to do a unit conversion of J and Kt with all other variable units correct,

J = 300 lbm*ft^2 * (1 kg/2.2046 lbm)*(1m^2/10.764 ft^2) = .1264 kg*m^2
Kt = 300 ft lbm/A * (4.4482 N/1 lbf) = 1334.46 Nm/A

Kt this doesn't seem like an accurate number. The physical parameters in the homework problem indicate Kt = 300 ft lb/A, I think it is missing meters (m)? Checking with professor on that.