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Old 09-26-05, 07:37 PM   #1
phantomcow2
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explain mechanical efficiency?

I have an understanding i think of what mechanical efficiency is, but it is not concrete.
FOr example I read on McMaster Carr how an Acme screw has a mechanical efficnecy of roughly 30%, versus a ballscrew with up to 90%.
Does this mean that with an ACME screw, 70 percent of the loads produced by the source (be it a motor, a human turning a handle, a water wheel or anything else) are used in moving the screw and nut? ANd 30% reaches the final outcome?
And with a ballscrew 90% of the energy reaches the final outcome? Thanks
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Old 09-27-05, 06:49 AM   #2
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stop giving me nightmares
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Old 09-27-05, 06:51 AM   #3
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That's a pretty accurate description. I like the explanation here
http://www.encyclopedia.com/html/sec...ofMachines.asp
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Old 09-27-05, 09:06 AM   #4
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http://en.wikipedia.org/wiki/Mechanical_efficiency
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Old 09-27-05, 01:03 PM   #5
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Off the top of my head, that's pretty much it. To me, it's the percentage of energy output from a system relative to the input.
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Old 09-27-05, 09:59 PM   #6
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Quote:
Originally Posted by Nicodemus
Off the top of my head, that's pretty much it. To me, it's the percentage of energy output from a system relative to the input.
Yeah, pretty much. For example, a modern internal combustion engine, like that in a car, is about 30% efficient, ie. roughly 30% of the energy (btu's) in the fuel burned actually gets converted to horsepower at the rear wheels. The rest goes out the tailpipe and cooling system as waste heat.
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Old 09-28-05, 09:46 PM   #7
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I think it's less than that...
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Old 09-28-05, 09:57 PM   #8
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Right on phantomcow. Those losses in the ACME screw are due to friction, and you'll see that manifested as heat if you use it in a high speed, continuous application.

mtnroads is correct, the efficiency of an internal combustion engine is around 30%. This actually the thermal efficiency, however, which tells you how much of the theoretical energy contained in the gasoline is available as power at the crankshaft. There is a little bit more loss from the transmission, deformation of the tires, etc, but the total mechanical efficiency, I believe is over 90%.
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