# Torque and Power

Table 1 shows a set of torque-speed measurements for a d.c. electric motor intended for use in an electric wheelchair. Data of this type is used by manufacturers to help specify motor performance.

Table1

Speed /rpm..............600..........1200......1850..........2400.......3050.........3700

Torque /Nm..............5.51..........4.53.......3.75..........2.94........2.09.........1.08

(a) Use the data in Table 1 to plot a suitable graph and obtain the five missing pieces of information, labelled (i)-(v), in the motor specification chart shown in Table 2.

Table 2

.................Stall....................No Load................Maximum Efficiency (Effic)

Operating

Volt /V.......Torque...Current....Speed.....Current...Torque....Speed...Current...Output

................./Nm....... /A.........../rpm ......./A......... /Nm....../rpm....... /A......(Effic)/%

24................(i)........140............(ii)..........5.2.........(iii).......4000.......(iv).........(v)

(b) One of the design requirements for the wheelchair states that the motor must be able to supply 40 Nm of torque at 100 rpm. Determine whether this particular motor has the power to meet that requirement.

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## SOLUTION This solution is **FREE** courtesy of BrainMass!

Speed /rpm Torque/Nm

0 6.31

600 5.51

1200 4.53

1850 3.75

2400 2.94

3050 2.09

3700 1.08

4000 0.717

slope = -0.001

y intercept 6.31

y = -.001x + 6.31

y = -.001 ( 4000) + 6.31

0.717

y= -.001 (5000) +6.31

-0.04

The torque of motor is proportional to the current

flowing through it ( T = i)

The angular velocity of motor is proportional to the voltage across it ( w = v)

The electrical power of current I and voltage is I s Pw = T X w

Pw= power

T= Torque

w = angular velocity

Angular speed =P/T

Maximum Efficiency

Operating Stall No load Current /A Torque/Nm Speed / rpmC Current/A Output power/W Efficiency/ %

Voltage Torgue/Nm Current Speed

24 i)0.144 140 ii)6350 5.2 iii) 7.53 4000 18 iv) 30120 v) 62.99

20.37 oz -inch

Speed = P/T

T * Speed = P

T = P/Speed

T = (-20.37 /6350 * speed + 20.37

T= (-20.37 /6350* 4000 +20.37

7.538503937

Power = T X angular speed

Power = 7.53 * 4000

30120

Motor must supply 40 Nm of torque at 100 rpm.

Power = T X angular speed

Power = 40Nm X 100 rpm

Power = 4000 Watt

Divide the Speed with the load with the no load speed

% Efficiency = 4000/6350 * 100%

62.99212598

Since the motor above has a total Output Power of 30120 Watts, it should be enough to meet the requirement of above

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