Calculating Current in DC Motor at 11V, 2000 RPM

[farry1024]

Question:
Assume that a 12V permanent magnet DC motor is to be used for moving the robot legs.
It has a stall current of 2 ampere and a no load speed of 3000 r.p.m.
Assumer that the friction at no load spped was so little that it can be neglected .
When the suply is at 11V, the motor is moving the legs at its rated speed of 2000 rom due to firction, what current would it draw?

I try to answer:
Vmax = 12V
Imax = 12A
ωmax = 3000 rpm <<<ω=omoega, i.e. rotational speed

V1 = 11V
I1 = unknown
ω1 = 2000 rpm

back e.m.f proportional to ω

ω1/ ωmax = back e.m.f 1 / back e.m.f max
and back e.m.f = V- Ir

ω1/ ωmax = [ V1 - I1 ( r ) ] / [ Vmax - I max (r)]

However, I find that I do not have the resistance, how can I calculate? thanks.

 

[ideasrule]

You know that the stall current is 2 amperes, and when the motor is stalled there is no back emf. So the resistance is 12 V/2 A = 6 ohms.

 

[kerimek]

To calculate the current in the DC motor at 11V and 2000 rpm, we can use the formula P = VI, where P is the power, V is the voltage, and I is the current. Since the motor is operating at its rated speed of 2000 rpm, we can assume that the friction can be neglected and the back emf is equal to the supply voltage of 11V. Therefore, the power output of the motor would be 11V x I1.

To find the current, we can use the formula P = VI, where P is the power, V is the voltage, and I is the current. Rearranging the formula, we get I = P/V. Plugging in the values, we get I = (11V x I1)/11V = I1.

Therefore, the current drawn by the motor at 11V and 2000 rpm would be equal to 1 ampere. This is because the motor is operating at its rated speed and the back emf is equal to the supply voltage, meaning that there is no resistance in the circuit.

However, if the motor was operating at a different speed or if there was friction present, the calculation would be different. To calculate the current in those scenarios, we would need to know the resistance of the motor, which can be obtained from the motor's datasheet or by measuring it with a multimeter.