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Question: designing a system lift a 7 kg mass gear motor...

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designing a system lift a 7 kg mass.


Gear motor  ------  Pulley(Drum) η = 100 %   ------- Mass

Two motors are being considered in this design and their data is present in Table 1. 

Motor 1 Nominal Voltage:12V        Noload                           Maximum Efficiency            Stall

Speed (rad/s)                                    4.5                                        3.8                                   -                              

Torque(N.m)                                         -                                         0.35                                1.05

Current(A)                                           0.2                                          0.81                               2.5

Motor 2 Nominal Voltage:6V        Noload                           Maximum Efficiency            Stall

Speed (rad/s)                                    6.1                                        4.6                                   -                              

Torque(N.m)                                         -                                         0.22                                0.62

Current(A)                                           0.25                                          0.77                               2.4

For  all calculations, you may assume steady-state operation.

A)For this system if a pulley with a radius of 1 cm is selected, and it is assumed to be 100% efficient, what torque will be required by the pulley to lift a 7 kg mass? Which motor can provide this torque?

C)Calculate the overall efficiency of the system when the motors are operating at peak efficiency, which motor would you select based upon these calculations?

D)If the ideal operating range for a motor is 19 – 75% of the motor’s maximum power, and the lifting power required from the system is 0.82 W, what range of maximum motor powers would be suitable for this system? Which motor would you select based on this power requirement?

E)Assume the system has been designed using motor 1 and an appropriate gear ratio and pully radius such that the motor runs at its maximum efficiency point. Under these conditions and assuming a pulley efficiency of 100%, how long will it take to lift the 7kg mass 30cm.

F)Sketch a torque-current curve for the Motor 1 using the no-load and stall data provided. Write down an equation for the curve and use it to predict the current draw of the motor when lifting a10 kg mass assuming a pully radius of 0.5 cm, assume pulley efficiency is 100%.




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