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Mechanical Efficiency
I have been looking all over the Internet to find comparisons of mechanical efficiency and haven't found anything that isn't covered in different units of measure that require multiple iterations of conversions.
Can anyone here compare the efficiency of: A very long chain drive as used in a recumbent A hydraulic drive system and A electric motor And perhaps there's something I missed? |
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Mechanical Efficiency
On 4/19/2017 3:23 PM, Martin Borsje wrote:
expressed precisely : I have been looking all over the Internet to find comparisons of mechanical efficiency and haven't found anything that isn't covered in different units of measure that require multiple iterations of conversions. Can anyone here compare the efficiency of: A very long chain drive as used in a recumbent A hydraulic drive system and A electric motor And perhaps there's something I missed? You start here comparing the efficiency of the transmission (chain or hydraulic pmp/motor/tubing combination) with that of the drive (e-motor). Something with apples and pears. Please be more clear on this. As Martin says, the electric motor is the answer to "One of these things is not like the others..." But electric motors vary widely in efficiency. The trend, very logically, is that big ones are made more efficient than tiny ones. My guess (TM) would be approaching 95% for really huge ones, down to 70% for tiny shaded pole motors driving timers, clocks, etc. I'd expect a motor as used in a motorized bike to be around 80% efficient. Roller chains are very efficient. Over 90% is not at all unusual, and they can get into the high 90s under the right conditions. Hydraulic drives typically consist of a pump, valves, hoses and a hydraulic motor. This site gives roughly 85% for a fairly simple pump: http://machinerylubrication.com/Read...rs-maintenance A hydraulic motor of similar technology would be similar. And you'd have losses in valves and piping. You'd need to compound all those efficiencies to get the total. I'd guess overall efficiency of less than 70%. -- - Frank Krygowski |
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Mechanical Efficiency
On Wednesday, April 19, 2017 at 7:52:24 PM UTC-7, John B Slocomb wrote:
On Wed, 19 Apr 2017 12:10:33 -0700 (PDT), wrote: I have been looking all over the Internet to find comparisons of mechanical efficiency and haven't found anything that isn't covered in different units of measure that require multiple iterations of conversions. Can anyone here compare the efficiency of: A very long chain drive as used in a recumbent A hydraulic drive system and A electric motor And perhaps there's something I missed? I can't quantify it but I've known a number of people that had a hydraulic drive in a sailing yacht. Every one hated it. I remember a guy had sailed from Australia to Singapore and when I met him he was industrially re-engining his 35 ft. boat to use a direct drive (propeller shaft and gear box). Due to hull design and shape installing an auxiliary motor is difficult in some sail boats and a hydraulic pump on the engine and a hydraulic motor driving the prop seems like a good idea. Until one tries it. On the other hand an electrical drive seems to work great. At least on a boat :-) It might be considered that a chain drive probably has the lowest losses of any drive system :-) Thanks for everyone's input. While going through all of the literature I got the idea that with electric or hydraulic you couldn't really expect much more than a total of 60% at best but I wanted to make sure. High speed recumbents have the problem of not being able to get high enough gears and end up having multiple large and small wheels to get pure wheel speed. The best I saw was an internally geared wheel that gave a 1:4 ratio but you can't buy those sorts of components and would have to build them yourself. Straight cut gears are the most efficient losing only around 2-3%, chain drives in perfect condition are something like 90% but rapidly lose that unless fully enclosed and often serviced. |
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On 4/20/2017 10:20 AM, wrote:
On Wednesday, April 19, 2017 at 7:52:24 PM UTC-7, John B Slocomb wrote: On Wed, 19 Apr 2017 12:10:33 -0700 (PDT), wrote: I have been looking all over the Internet to find comparisons of mechanical efficiency and haven't found anything that isn't covered in different units of measure that require multiple iterations of conversions. Can anyone here compare the efficiency of: A very long chain drive as used in a recumbent A hydraulic drive system and A electric motor And perhaps there's something I missed? I can't quantify it but I've known a number of people that had a hydraulic drive in a sailing yacht. Every one hated it. I remember a guy had sailed from Australia to Singapore and when I met him he was industrially re-engining his 35 ft. boat to use a direct drive (propeller shaft and gear box). Due to hull design and shape installing an auxiliary motor is difficult in some sail boats and a hydraulic pump on the engine and a hydraulic motor driving the prop seems like a good idea. Until one tries it. On the other hand an electrical drive seems to work great. At least on a boat :-) It might be considered that a chain drive probably has the lowest losses of any drive system :-) Thanks for everyone's input. While going through all of the literature I got the idea that with electric or hydraulic you couldn't really expect much more than a total of 60% at best but I wanted to make sure. High speed recumbents have the problem of not being able to get high enough gears and end up having multiple large and small wheels to get pure wheel speed. The best I saw was an internally geared wheel that gave a 1:4 ratio but you can't buy those sorts of components and would have to build them yourself. Straight cut gears are the most efficient losing only around 2-3%, chain drives in perfect condition are something like 90% but rapidly lose that unless fully enclosed and often serviced. But you already have a meat engine as cargo so any additional energy source (electric) will increase total mass and any degradation of efficiency in transfer (hydraulic) will waste energy. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
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On Wed, 19 Apr 2017 12:10:33 -0700 (PDT), wrote:
I have been looking all over the Internet to find comparisons of mechanical efficiency and haven't found anything that isn't covered in different units of measure that require multiple iterations of conversions. https://en.wikipedia.org/wiki/Bicycle_drivetrain_systems I also couldn't find anything that is instantly useful. There's probably a reason why nobody has made such a general study. My guess(tm) is it's because it wouldn't apply to most useful situations, power levels, rotational speeds, and other design limitations. A realistic comparison would include a range of acceptable power transmission levels, weight limits, and possibly some operational considerations. On a bicycle, the book "Bicycling Science" by David Gordon Wilson 2nd and 3rd editions (they're somewhat different) http://www.alibris.com/Bicycling-Science-David-Gordon-Wilson/book/17828968 https://books.google.com/books?id=0JJo6DlF9iMC is a good reference of work for such surveys. The section on power transmission includes Berg cable drives, toothed belt drives, drive shafts, etc. Can anyone here compare the efficiency of: A very long chain drive as used in a recumbent Might be something in he http://www.cyclingpowerlab.com/drivetrainefficiency.aspx http://www.bikeradar.com/us/news/article/friction-facts-measuring-drivetrain-efficiency-35694/ A hydraulic drive system and The weight penalty of dragging a plumbing nightmare around might make this a losing proposition even if it were 100% efficient. A electric motor I'm going to assume you're only interested in a human powered transmition, not building a battery or wind powered bicycle or hybrid. An electric generator and motor transmission is the mostly the product of the generator and motor efficiencies, going from kinetic energy to electric energy and then back to kinetic. A small (1-2HP) permanent magnet electric generator is probably about 75% efficient while a similar sized motor is about 70%. There are power/rpm curves for both that can be used to determine the most efficient operating point, or the efficiency at some particular power and RPM level. Using my guess(tm) numbers, that's: 0.75 * 0.70 = 53% efficiency. In other words, an all electric drive system sucks. On Pg 337 of the "Bicycling Science" book, the author does a better job of estimating the electrical system efficiency. He has the following in series: 70% - Pedals driving gears with short chain to generator. 98% - Generator 95% - Controller 80% - Motor driving short chain to wheel Multiplying these together yields 52% efficiency. There's also a short section on hydrostatic drives (as in earth movers), which the author claims maxes out at 80% efficiency and is therefor useless. And perhaps there's something I missed? Well, I would suggest you disclose what you are trying to accomplish so that I don't need to guess(tm) so much. You also missed other transmission systems: 1. Perforated metal tape instead of a chain 2. Cable (Snek) drive 3. Berg cable and plastic chain: http://802.11junk.com/jeffl/pics/Berg/ 4. Toothed rubber belt 5. Direct gear drive using lots of spur gears. 6. Drive Shaft 7. Direct drive (Penny Farthing) 8. Ratchet drive 9. Various eccentric gear drives (elliptical crank, reciprocating pedals, rolling exercise machines, etc). http://www.elliptigo.com https://www.streetstrider.com 10. Rowing motion drive https://rowingbike.com 11. Front wheel pedal drive with hub transmission. 12. Whatever else I forgot. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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