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Motor and torque calculations

Motor and torque calculations

Motor and torque calculations

(OP)
Hi,
I am slightly confused and hope someone can put me straight on this.

Power in W is Shaft torque in Nm * the angular velocity in rad.
So at 195Nm (44lbf) and a shaft speed of 1250rpm I am developing  25619W (25.6kW)

Now when I look at my motor curve …. 44lbf and 1250 rpm …The power curve indicates about 10HP (7.45kW)

Is my motor curve wrong or is it my interpretation of  the relationship between Torque and RPM ??

Jan ....

RE: Motor and torque calculations

I think you have to divide the product of shaft speed and torque by 5252 or multiply by its recipical 0.00019. The  answer then comes out to 10.47kW. (T*RPM)/5252.

RE: Motor and torque calculations

Did you forget to multiply by 3.28 to get ft*lbf? 195N*m=144ft*lbf

TTFN

RE: Motor and torque calculations

Sorry to be such a bore. Use SI and forget about all those constants.

1250 RPM = 1250/60 RPS (60 seconds to one minute) and there are 2*PI radians to one revolution. So your speed is 2*PI*1250/60 = 130.8 rad/s

You already have 195 Nm and shaft power is speed times torque or 130.8 * 195 = 25.5 kW, which is wrong.

The 44 lbf (poundfoot? I think poundforce, so the torque arm is missing) translates into 1.36*44 = 59.7 Nm. So your shaft power should be something like 130.8 * 59.7 = 7.81 kW, which agrees quite well with your "about 7.45 kW".

RE: Motor and torque calculations

(OP)
Thanks everyone !!
Yes my mistake was the "ft/lb" to Nm conversion I did first...

Now it all makes sence ...

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