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# Calculating my DC motor Answered

Volts- 9V

Current- 0.096A

Speed-112.4rpm

Force-?

Torque-?

Power-?

Power Out -?

Efficiency- ?

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## Discussions

This is classic textbook physics, mechanics. So, if you are physics student, you are kind of a clueless one. Maybe you already knew that.

The load M pulls downward, with force F = M*g
F = (0.2334 kg)*(9.8 m*s^-2) = 2.2873 N

The torque this force puts on the pulley is tau = F*r

tau = (2.2873 N)*(5.85e-3 m) = 0.013381 N*m

Mechanical power, Pout, is tau*omega, where tau is torque and omega is angular speed, given in this problem in (revolution/min). So convert that number to (radians/second) first.

omega = (2*pi/rev)*(1 min/60s)*(112.4 rev/min) = 11.771 rad/s

Pout = tau*omega = (0.013381 N*m)*(11.771 rad/s) = 0.15750 W

Power in is electrical, Pin = V*I, voltage multiplied by current.

Pin =(9.0 V)*(0.096 A) = 0.81540 W

Efficiency is output power, divided by input power.

Eff = (Pout/Pin) = (0.15750 W)/(0.81540 W) = 0.19316 = 19%