Low rpm bicycle motor design
- Thread starter veloman
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liveforphysics
100 TW
If you went ironless axial flux, you could reach those goals.
sackspeed
10 mW
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This aim could be reached by using an optimized design.
http://www.vde.de/de/fg/ETG/Exklusiv-Mitglieder/Antriebssysteme2004/Documents/MCMS/02_03.pdf
About 12 cm stator dia and 5 cm wide you can produce a little monster. A KV around 40 RPM/V is easy to handle
and the noise of chain/Belt is ok.
http://www.vde.de/de/fg/ETG/Exklusiv-Mitglieder/Antriebssysteme2004/Documents/MCMS/02_03.pdf
About 12 cm stator dia and 5 cm wide you can produce a little monster. A KV around 40 RPM/V is easy to handle
and the noise of chain/Belt is ok.
Miles said:Errr... no, it's a value judgement.
i would have thought (or is it hoped) that taking a detour/u-turn by gearing down to crank rpm only to turn around & simply gear it back up to wheel speed is something to be avoided at all cost.
it can never be as efficient a route as line of sight, i.e. the 'better for what?'.
i guess u have a different take on the 'for what?'?
Not "at all cost", that's all. Which way is most efficient? Driving the rear wheel directly, without multiple gears for the motor or driving the cranks and utilising the pedal gears? It depends on power available, top speed and terrain....
well when comparing fruit of the same genus, driving the rear wheel directly with multiple gearing will always be more efficient.
and not telling u anything new that with an electrix wider bandwidth 2 or 3 speeds is all u need to cover most conditions.
even safe came to realize that shifting thru a boat load of corn cob cogs was a waste of time.
and not telling u anything new that with an electrix wider bandwidth 2 or 3 speeds is all u need to cover most conditions.
even safe came to realize that shifting thru a boat load of corn cob cogs was a waste of time.
jmygann
100 kW
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http://www.bike-eu.com/news/3611/bionx-launches-hub-motor-with-integr...
FRIEDRICHSHAFEN, Germany - The component many e-Bike makers are
waiting for; a hub motor with integrated 3-speed gear hub is already
there. This new BionX IGH3 technology will be used in Trek bikes in
2010.
It wasn’t launched at Eurobike with all the glitter and glamour this
important e-Bike component should have had and maybe that’s why many
industry insiders will have missed it. But Canadian BionX, which is a
spin of company of auto parts giant Magna International that took over
car maker Opel in Germany earlier this week, presented its BionX
PL250HT motor with integrated SRAM 3-speed gear hub.
FRIEDRICHSHAFEN, Germany - The component many e-Bike makers are
waiting for; a hub motor with integrated 3-speed gear hub is already
there. This new BionX IGH3 technology will be used in Trek bikes in
2010.
It wasn’t launched at Eurobike with all the glitter and glamour this
important e-Bike component should have had and maybe that’s why many
industry insiders will have missed it. But Canadian BionX, which is a
spin of company of auto parts giant Magna International that took over
car maker Opel in Germany earlier this week, presented its BionX
PL250HT motor with integrated SRAM 3-speed gear hub.
Hillhater
100 TW
Miles said:
Ahhh well, i guess we can call that a "near miss" !
Maybe these motor designers are all electrical based , but why is it they just dont seem to see the advantage of gearing and torque multiplication for lower powered motors. ?
jmygann
100 kW
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- May 30, 2008
- Messages
- 1,069
what do they mean ....?
"The motor (not just the rider) benefits from the gearing to help you to climb steep slopes and use another gearing for higher speeds. The gearing range is 35% to 300%.
http://www.ebikeriders.com/messages/boa ... ad=7716164
"The motor (not just the rider) benefits from the gearing to help you to climb steep slopes and use another gearing for higher speeds. The gearing range is 35% to 300%.
http://www.ebikeriders.com/messages/boa ... ad=7716164
Wouldn't larger EVs be more efficient with a transmission? Apparantly not, since they have only one gear (Leaf, and I believe others). The idea is that under typical usage (steady driving at 65mph) the motor is still only at ~20% of max power, right?
So, to parallel that to ebikes, if at 25mph, I was at 20% of max power, I would be best off with only one gear? 400watts at cruise speed, 2000watts peak capability.
But since my current motor is only capable of about 750watts peak, and I have no interest in cruising at 15mph, I need gearing to compensate for the relatively underpowered motor.
But if I go to a 60volt 9c with 40amp limit, my bike would perform fine (other than climbing 15% mtns)?
Am I on the right track?
So, to parallel that to ebikes, if at 25mph, I was at 20% of max power, I would be best off with only one gear? 400watts at cruise speed, 2000watts peak capability.
But since my current motor is only capable of about 750watts peak, and I have no interest in cruising at 15mph, I need gearing to compensate for the relatively underpowered motor.
But if I go to a 60volt 9c with 40amp limit, my bike would perform fine (other than climbing 15% mtns)?
Am I on the right track?
Thud
1 MW
if your going to use the word "efficient" then the answer is Yes. They would be more efficant if there was optomised gearing for varying grades & conditions.
Just because they don't provide them doesnt mean it wouldn't be better......cost factors force us to accept the compromises.
Hillhater said:Miles said:
Ahhh well, i guess we can call that a "near miss" !
Maybe these motor designers are all electrical based , but why is it they just dont seem to see the advantage of gearing and torque multiplication for lower powered motors. ?
So are engineers at bicycle manufacturers compleat (sic) idiots? Does "conventional wisdom" on ES trump science? Now consider that a typical MTB today has 27 gears to cover (assuming a reasonably fit rider) the speed range up to 30km/h (20mph). How come a conventional car that goes 160km/h (100mph) has only 4 or 5gears, and not the predicted 160/30*27 = 144 gears?? And electric cars have even fewer or only one gear.
Consider the efficiency graph in the "Badnews thread":
http://endless-sphere.com/forums/viewtopic.php?f=2&t=19681&p=289416&hilit=badnews#p289416
On flat ground all types of conventionally available eBike motors have a very flat efficiency curve from 10km/h up to their design max speed. For most riding conditions the hills are small enough that the lower efficiency of climbing a hill does not detract appreciably from the range. For those living in hilly terrain it is cheaper to add $100 or so and buy a BMC hub instead of a DD hub like the 9C, compared to dealing with the cost and complexity of multispeed gearing of the motor. The calculations in the thread linked above are purely theoretical. Ilya at eBikesSF has found the same result purely experimentally. Experiments and science agrees; a pillar of modern though.
Hillhater
100 TW
Yes, similar argument for "fixie" track bike set ups...nice and efficient for a single purpose...but p155 poor for real every day use. !
Which ever way you cut it, a 250w dd hub motor will not haul you up a 10 -15% hill !
Efficiency is great, but if i buy a motor to assist me up hills , i want it to work and do its job.
Its not very efficient if it wont move the bike up the hill ! ( you will be down in the "0.0 km/hr" range on those graphs !)
Run that 250w through a gear set (already on the bike normally) and you stand a fighting chance
This is not science ...its common sense.
PS: ..those graphs are not very convincing....i would hope any motor is going to be a little more than 0.8% efficient at its optimum :lol:
Which ever way you cut it, a 250w dd hub motor will not haul you up a 10 -15% hill !
Efficiency is great, but if i buy a motor to assist me up hills , i want it to work and do its job.
Its not very efficient if it wont move the bike up the hill ! ( you will be down in the "0.0 km/hr" range on those graphs !)
Run that 250w through a gear set (already on the bike normally) and you stand a fighting chance
This is not science ...its common sense.
PS: ..those graphs are not very convincing....i would hope any motor is going to be a little more than 0.8% efficient at its optimum :lol:
Hillhater said:
That's not what was suggested. But it is a myth that a "drive through the bike gears" system is cost efficient or superior in terms of energy efficiency. When a low torque $200 hub motor (whether DD like the 9c or geared like the small Bafang or Cute) does not suffice, it is often wiser to plunk $3-400 into BMC (for most cases) or $400 into RC/leftside drive (for really steep hills/demanding use) than a mechanically complex drive-though-the-bike-gears. These incur inefficiencies by first gearing down the motor to pedal speed, then gearing up again, and these inefficiencies are always there, not just at peak load like the electrical inefficiency of a single gear motor at high loads. An electrical motor does not need 27 or even 8 gears. One is usually enough and two would practically always suffice.
The way manufacturers view this is that a simple low power hub motor satisfies likely 90% of people's eBike needs, (just like a small car is enough to take you to work), a higher power hub motor is likely good enough for another 9%, and the remaining 1% isn't really of interest for volume manufacturers.
That's why 9C is sold by multiple vendors here and worldwide.
BMC by a few in smaller volumes
Stokemonkey is a niche product
Cyclone likely has decent sales, but still a drop in the sea compared to all hub motors.
That is not to say that gearing is not good. A 2 stage 2 speed planetary that would match e.g. Astro motors would be nice. Could have a 5:1 first stage and an dis-engagable 2:1 or 3:1 second stage, then a chain or belt drive to a rear wheel sprocket separate from the pedaling gears. Such a setup would be much more complex and expensive than say a BMC hub motor though. One also has to think about the tradeoffs: Does the addition of cost and weight for the hear stacks make sense, when one could instead just put that money in a bigger motor. (a 2:1 selectable downgear might be 1" wide or more and weigh 1lbs. That weight and size could instead be used to double the width of the motor stator and rotor, which also gains exactly a factor 2 in torque, and additionally gains a factor 2 in power.
Hillhater
100 TW
jag said:
Not if it is a 250w motor and a 15% hill ...( unless your 2nd gear was a "granny ratio' strictly for hills.)
Hillhater
100 TW
Hillhater said:
and why this fixation on "efficiency" ?
If you were building / buying a motor bike, would you be as concerned about its efficiency ( get a Honda moped) or its performance ?
Hillhater said:
An Astro 8150 geared 70:1 takes you up a 15% hill at 5km/h with 250W, 80% efficiency. The same 250W lets you go about 25km/h unassisted on the flats, just as good as any multispeed through-the-bike-gears setup.
A good electric motor can be efficient over a very wide rpm range, e.g. 1000-10,000 rpm. That't a 10x range and the reason why electric bikes and cars don't need more than one or two gears.
By comparison, an ICE motor is usually only efficient in a more limited range, often 2000-4000rpm in volume production cars, a 2x range
And a human is only efficient in the narrow range of 60-80rpm, a 0.3x range. That's why a human can use 3-8 gears beneficially. (The 27 gears of a MTB are usually spaced in a way to not be much more useful than 8 properly spaced gears)
Hillhater said:
Give the Astro 5-10kW of input power and you'll see performance.
performance (output power) = efficiency * input power
80-90% efficiency of an Astro + left side belt drive is much better than 60-80% of typical other solutions.
See the very first post in the badnews thread linked before to see how bad performance can get with an inefficient motor at full load.
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