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Force and motion Question
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Posted by: lrome48

10/04/2006, 14:26:42

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I am pivoting (raising) a staircase (mass of 200lbs) at one end, the stair is 6' long. I am having trouble determining the force required to rotate the stair, speed is 5" per second. Any help is appreciated.







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Re: Force and motion
Re: Force and motion -- lrome48 Post Reply Top of thread Forum
Posted by: swearingen

10/04/2006, 14:56:47

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I assume the force you are referring to is the torque required to raise the staircase. The torque will actually vary because the moment arm of the load changes as the stair rises. The max would be 200lb x 1/2 of the stair length, or 600 lbft.

As for the speed, where is it measured? At the outboard tip of the stair? If so, you could easily gear an electric motor to do this.








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Re: Re: Force and motion Question
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Posted by: lrome48

10/05/2006, 12:19:01

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Thanks for the information. I understand the force will change as the stair is raised, but the greatest torque will be from point of lift off, and decrease when past horizontal correct? Also, the speed is measured at the tip. Another variable is that the stair currently is raised with gas springs, one on each stringer, and each exerting ~250lbs/f. If I leave the gas springs in place as the lifting device, than I have to overcome the spring force to lower the stair. From the tip the lever arm allows me to latch the stair reasonably easily. A 140lb wieght on the tip (My wife standing on the lowest tread, or first step) will almost bring the stair down to latch. If I apply the torque at the upper pivot point, what will I need for torque to overcome the resistance of the springs? Would it be 500lbs x 1/2 the stair length, or 1500lb/ft?







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Posted by: lrome48

10/05/2006, 12:35:36

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Would I want to base my torque requirement on an overhung load, and assume the stair is bieng lifted worst case from vertical, then size the gearmotor accordingly?







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Posted by: zekeman

10/05/2006, 09:42:55

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200x1/2=100
No problem lifting w/ 2 people.







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