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This sort of electrical/pedalling hybrid is an interesting space, but one where legislation is often a real downer. I’m currently planning to build a velomobil

This sort of electrical/pedalling hybrid is an interesting space, but one where legislation is often a real downer. I’m currently planning to build a velomobile that I can live out of while cycling round Australia for a year. A trailer too, designed around a digital piano and some sort of fridge (either a production model or one constructed manually from a compressor). It’ll end up heavy enough¹ that I’ll want to put a motor in it, so that for local journeys I can get from Point A to Point B more quickly and more confidently dispose of my car, and because otherwise when touring there will be some hills that I simply can’t climb, and that 200–250W² should make it possible (though probably still not easy). So then I figured, how about a fully electrical drivetrain? Even with the best components, it’ll still be a bit less efficient than a well-maintained chain³, but getting the chain and front chainrings out of the way would be great, making the decision of how to facilitate sleep much easier: go quadricycle (rather than tadpole trike, which is two wheels at the front and one at the back), then to sleep tilt the seat back flat, and shift the pedals/generator a bit out of the way, and there’s no chain to worry about so you’re ready to sleep in the vehicle.⁴ Unfortunately, the legislation is drafted in such a way as to forbid such vehicles. Excerpt from Victoria’s Road Safety Road Rules 2017 <https://content.legislation.vic.gov.au/sites/default/files/2021-04/17-41sra011%20authorised.pdf#page=521 https://content.legislation.vic.gov.au/sites/default/files/2...>: > bicycle means a vehicle with 2 or more wheels that is built to be propelled partly or wholly by human power through a belt, chain or gears (whether or not it has an auxiliary motor) The way they keep talking about power assistance as the use of an auxiliary motor is troublesome, and this potentially doesn’t even allow things like hydraulic, shaft or electrical drives. But then, what is an electrical wire but a belt for electrons? — ¹ Though nowhere near the the two-seater Twike’s unladen-save-batteries 246kg. I’m aiming for a this-is-my-home practical loaded long-term touring weight of 125kg, including things like 50kg of vehicle and trailer (including all vehicle electronics), 12kg of piano, 12kg of fridge, 12kg of battery and 5kg of solar panels. ² Broadly speaking, Australia currently has two classifications: 200W with no speed limit, and the pedelec 250W but limited to 25km/h. Finer details vary by state. Not sure if you could legally get away with producing 250W if pedalling and under 25km/h, or 200W if over 25km/h (and pedalling, in some states); “an auxiliary motor capable of generating a power output over 200 watts” hangs quite a bit on the interpretation of the word “capable”. ³ An electrical drivetrain could easily be better than a poorly-maintained chain. ⁴ The main alternatives I’m considering include making the vehicle expandable in a way vaguely reminiscent of a pop-top van, and a larger and/or expandable trailer and sleep in that. But I don’t want to be messing around with tents every day.

SigmundA 5y ago
In all my research mechanical -> electrical -> mechanical double conversion is significantly less efficient than a direct mechanical drivetrain. It seems to come down to about 80% for the best electrical vs >95% for mechanical [1][2]. Also there is a weight issue the generator is at least as heavy as the motor and thats a big problem on bikes. Trains do it because they need precise traction control and have little concern for the weight. They sacrifice running efficiency for it but everything else makes them very efficient at running (low rolling resistance and low aerodynamic drag). Also the unsprung weight of hub motors causes various issues as well especially if you have suspension for ride comfort. Most electric bikes are moving to mid drives anyway which is going to have a chain or belt. 1. https://pages.jh.edu/news_info/news/home99/aug99/bike.html https://pages.jh.edu/news_info/news/home99/aug99/bike.html 2. http://large.stanford.edu/courses/2010/ph240/veltman2/ http://large.stanford.edu/courses/2010/ph240/veltman2/
- chrismorgan 5y ago
  Your 80% figure seems rather spurious, coming I think from extrapolating a gross simplification of some 2009 figures for much bigger motors. My vague understanding is that smaller motors are hard to get as efficient. Some things I was looking at last year suggested things keep improving and that in excess of 90% was in theory quite attainable now for such motor sizes, though in practice you probably won’t find it on the market. But I did find components that should combine to something like 85–87%. (I don’t think I wrote my findings down, or if I did it was on a device I don’t have access to at present. But a quick search shows https://outriderusa.com/pages/electric-bike-efficiency https://outriderusa.com/pages/electric-bike-efficiency claiming a motor efficiency of 93%, which if paired with a generator of similar efficiency would yield 86.5%, assuming no transmission loss which is of course unreasonable, and assuming the efficiency stays the same at lower power levels, which is likely screamingly wrong.) >95% for chain systems assumes good components excellently-maintained. In practice chain drives are generally somewhat less efficient, commonly more like 85–90% is what I think I read, with poorly-maintained ones often more like 65–75%. This is where an electrical drivetrain could really shine: it’ll require roughly no maintenance while maintaining its not-best-in-class-but-still-pretty-good efficiency. These figures are all rather nebulous, and get muddied a lot further once you’re putting a battery into the mix too, trying to take the power from your feet and augment it with another 200W of power from a battery (but preferably without feeding your foot-power through the battery). Then I go from being an amateur that knows just enough to be dangerous to a rank ignoramus. For my purposes, an electric drivetrain would probably be markedly less efficient, but if it can be enough more convenient, it could be worthwhile anyway. I also have a pet scheme in mind where you simulate 100% efficiency by adding a little more power from the battery to compensate for known losses. I feel that could fit within the intent of legislation, if only that legislation allowed electric drivetrains in the first place.

SigmundA 5y ago

In all my research mechanical -> electrical -> mechanical double conversion is significantly less efficient than a direct mechanical drivetrain. It seems to come down to about 80% for the best electrical vs >95% for mechanical [1][2]. Also there is a weight issue the generator is at least as heavy as the motor and thats a big problem on bikes. Trains do it because they need precise traction control and have little concern for the weight. They sacrifice running efficiency for it but everything else makes them very efficient at running (low rolling resistance and low aerodynamic drag). Also the unsprung weight of hub motors causes various issues as well especially if you have suspension for ride comfort. Most electric bikes are moving to mid drives anyway which is going to have a chain or belt. 1. https://pages.jh.edu/news_info/news/home99/aug99/bike.html https://pages.jh.edu/news_info/news/home99/aug99/bike.html 2. http://large.stanford.edu/courses/2010/ph240/veltman2/ http://large.stanford.edu/courses/2010/ph240/veltman2/

chrismorgan 5y ago
Your 80% figure seems rather spurious, coming I think from extrapolating a gross simplification of some 2009 figures for much bigger motors. My vague understanding is that smaller motors are hard to get as efficient. Some things I was looking at last year suggested things keep improving and that in excess of 90% was in theory quite attainable now for such motor sizes, though in practice you probably won’t find it on the market. But I did find components that should combine to something like 85–87%. (I don’t think I wrote my findings down, or if I did it was on a device I don’t have access to at present. But a quick search shows https://outriderusa.com/pages/electric-bike-efficiency https://outriderusa.com/pages/electric-bike-efficiency claiming a motor efficiency of 93%, which if paired with a generator of similar efficiency would yield 86.5%, assuming no transmission loss which is of course unreasonable, and assuming the efficiency stays the same at lower power levels, which is likely screamingly wrong.) >95% for chain systems assumes good components excellently-maintained. In practice chain drives are generally somewhat less efficient, commonly more like 85–90% is what I think I read, with poorly-maintained ones often more like 65–75%. This is where an electrical drivetrain could really shine: it’ll require roughly no maintenance while maintaining its not-best-in-class-but-still-pretty-good efficiency. These figures are all rather nebulous, and get muddied a lot further once you’re putting a battery into the mix too, trying to take the power from your feet and augment it with another 200W of power from a battery (but preferably without feeding your foot-power through the battery). Then I go from being an amateur that knows just enough to be dangerous to a rank ignoramus. For my purposes, an electric drivetrain would probably be markedly less efficient, but if it can be enough more convenient, it could be worthwhile anyway. I also have a pet scheme in mind where you simulate 100% efficiency by adding a little more power from the battery to compensate for known losses. I feel that could fit within the intent of legislation, if only that legislation allowed electric drivetrains in the first place.