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- Thread starter ach2oman
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cjl

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Nugatory

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That was 3.8, not 38, and 3.8 agrees with my calculations.

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cjl

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That was 3.8, not 38, and 3.8 agrees with my calculations.

38 if you want the mass descending at 10 cm/s (I did mention that as an option as well).

As for common sense? It can prove surprisingly unreliable in situations like this. The reason such a large weight is needed is because of the low input RPM (and thus, the low velocity of the mass). Most 50-ish horsepower motors provide their power at a fairly high speed, and thus the forces involved are much smaller.

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cjl

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As I said in my first reply, it depends on how fast the weight is descending. To use non-metric units, a horsepower is equal to 550 lbf*ft/s, so a 550 pound weight descending at 1 ft/s would give 1 horsepower. Using the same math, to get 50 horsepower with an 1800 pound weight, you would need it to be descending at 15.3 feet per second (so you could only get 50hp for a very short time unless you have an extremely long distance for the weight to descend).

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256bits

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sorry but no.

You need 50hp in to get 50hp out, assuming no friction losses over you pulley system.

Gears or pulleys change the torque and angular velocity from input to ouput but not the hp.

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cjl

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You keep overlooking the fact that the weight will depend on the velocity at which the weight is descending (which is how it is related to the gear reduction). The fact that you want your output to be much faster than your input actually

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cjl

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QuantumPion

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This crane could lift it. It uses 5 diesel generators totaling 3500 hp to do so though. Also I doubt you'd be able to fit it in a room with an 8 ft ceiling :)

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russ_watters

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I think you need to slow down, read thoroughly, and absorb what is being explained to you. Three keys here:

1. You need to understand the difference between power and energy and how to calculate them. The equations are simple.

2. You need to recognize that conservation of energy applies to gears, so gearing is irrelevant to the energy/power calc.

3. But if you want to think about gearing, you need to learn that a reducing gear DECREASES the RPM. You are not dealing with a reducing gear.

We get this same question about once a month and the intuition of the poster is always very wrong.

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russ_watters

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50*550*3600/2000/8=6188 tons

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