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Anonymous Poster #1

Motor and Gears = Coupled (Torque)

03/26/2018 7:41 AM

I have an Ac induction motor , 3 phase on whose shaft a 68 tooth helical gear is attached . Then there is formation of gear train , 34 tooth helical gear attached to the 68 tooth gear , and then 16 tooth gear attached with the 34 tooth gear , respectively. I am rotating the 10 hp ac induction motor @ 30 rev/sec. The Omega here is 188.45 rad / sec. .5kw is taken as heat loss and the torque of the first gear is calculated to be 37.14 Nm. I wanted to calculate the torque that will be present on the 16 tooth gear , considering the loss of power trabsmission is 15%. When I and my friend did that , we were getting sepratee answer. Also we came to know that the motor we are using is not apt for such a task . The load is taken to be 2 kg.

I am not a mechanical engineer , I search on website about it but could not find much . So :-

1) what should be the required torque at the last gear and what is the actual torque considering above scenarios.

2) if I want that the rev/ sec of the 16 tooth gear to be 120 rev/ sec then what shall be the require power of the ac induction motor , that will satisfy the need . Or indirectly what shall be the require torque for it .

3) what is the ac induction spec I should use for such a gear train .

4) I am using such a phenomena cause I am using Tesla model S transmission system and I need a gear train so that 120 rev/sec is the rotation of the last gear .

5) not a mechanical engineer so if this sounds common or too easy , pardon me .

6) what shall I use to drive my gear train @ 2 kg or 1 78 kg load @ the last gear. The torque is too low . Using the transmission power equation P =T * w I can either use higher power motor keeping the Omega of 68 tooth gear as 188.45 rad/sec. I can increase the number of poles from 2 to 4 . Although the neceesary implications I have to check .

What is your opinion? Thanks in adanvce. Any help is appericated.

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#1

Re: Motor and gears = coupled ( torque)

03/26/2018 7:53 AM

Torque is something that the load presents to the motor, and not the other way round.

  • If this number is less than the motor's maximum output, the motor will drive the load.
  • If this number is greater than the motor's maximum output, the motor will stall.

So, what is the torque/speed characteristic [i.e. the shape of the load curve graph] of the mechanical load (rhetorical question - NNTR)?

Go from there.

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#2

Re: Motor and Gears = Coupled (Torque)

03/26/2018 10:23 AM

"The load is... 2kg" is meaningless in this context.

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#3
In reply to #2

Re: Motor and Gears = Coupled (Torque)

03/26/2018 10:35 AM

Quite. The motor that rotates the restaurant at the top of the CN Tower in Toronto, for example, is in the order of 1/4hp.

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#4

Re: Motor and Gears = Coupled (Torque)

03/26/2018 10:38 AM

The available torque from an induction motor is a function of motor speed. The output torque from your gear train would be the gear ratio times the motor torque times the efficiency. As PWSlack stated, the load requires a torque that is a function of speed. Where these two curves cross is the speed and torque which will result. At a lower speed, the motor will have more torque (ΔT) than required and will speed up. At a higher speed, the motor will have less torque and will slow down.

http://www.top-ee.com/speed-control-of-induction-motor/

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Anonymous Poster #1
#7
In reply to #4

Re: Motor and Gears = Coupled (Torque)

03/27/2018 10:01 PM

Thanks , it was helpful and explained nicely .

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#5

Re: Motor and Gears = Coupled (Torque)

03/26/2018 10:43 AM

...and where the motor characteristic and the load characteristic intersect, is the "operating point".

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#6

Re: Motor and Gears = Coupled (Torque)

03/26/2018 11:41 AM

A motor is not usually geared up, but geared down....so I would start with a higher rpm motor and gear down....you want to increase the torque at lower speeds and reduce it at higher speed...

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