hub motor design & torque
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yes, come on guru Flecc spill the beans. we are getting impatientOk, now I'm really intrigued! You changed the tyres?
thanks
Jed
Now, now Jed, I know how you feel, but we'll just have to be patientJed said:yes, come on guru Flecc spill the beans. we are getting impatient
: all in good time; genius can't be rushed! Anything good in life is worth waiting for (except traffic lights of course) and I'm sure all will be revealed when the job is done & not before, and quite right too .Stuart.
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Too much to explain, it'll have to covered on site pages, and you'll need to be sitting down and have smelling salts handy!
Let's just say that amongst other things, it really goes, it really stops, and there's no judder. And now I'm just off to frighten a few more motorists like the one who respectfully followed me for over a mile and half earlier.
.
Let's just say that amongst other things, it really goes, it really stops, and there's no judder. And now I'm just off to frighten a few more motorists like the one who respectfully followed me for over a mile and half earlier.
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Now you're talking!! Q Wheelies and now turbopower... you could get something of a reputation flecc, if you've not already!flecc said:And now I'm just off to frighten a few more motorists like the one who respectfully followed me for over a mile and half earlier.
My olbas oil is to hand, now just wait for rain to keep you in & updating those web pages....
Stuart.
Jed said:apparently there has just been a news report on the BBC about an unidentified flying object near Croydon
but we know its an IFF - Identified Flying Flecc!Is that to prevent fainting from shock of the ingenuity, or the sight of grinding & bending of metalflecc said:...you'll need to be sitting down and have smelling salts handy!
Fleccs Latest Creation
Attached is a speed camera image taken in Croyden earlierJust shock at the cheek of it!
50cycles will have a fit and eZee could be even more determined never to speak to me again as they don't already.
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Attachments
moving swiftly on.... I've seen a couple more torque curves for motors with a high geared reduction ~10:1 & hence high rpm, relatively low EM torque, and they all seem to exhibit the same behaviour (mentioned previously) of low rpm loss from the max efficiency rpm, with increasing load, before point of maximum torque i.e. max torque at a relatively high rpm/speed compared to higher EM torque motors, so weakening their hill performance...
Another quick design question then: for a quality hub motor with good EM torque, to be put in a 26" wheel would you expect a difference in performance in mixed hilly/flat terrain between:
2) fairly low geared reduction to ~270-280rpm for ~ 20mph @ say 36V, with a high current limit of ~20A to give higher torque @ lower speeds
1) higher geared reduction to ~200-215rpm for good speed & torque up to ~15-16mph @ 15A current limit, with a higher voltage limit & battery e.g. 24-36V or 36-48V to enable speeds up to ~20mph?
That is, from a design point of view, is it better to choose gearing & torque of motor for 15mph, then extend top speed by "overvolting" if wanted, or to gear for 20mph while boosting lower speed torque by increased current limit?
I realise both are compromises between speed & low-speed torque with hub motors, but how well can either work i.e. how much efficiency loss & with what limitation of use to retain efficiency?
I'd have thought that for use on hills and with moderate speed use (little more than 15mph normally) ease & efficiency suggest to gear lower & overvolt for speed (lower current limit = less heating too?); whereas if you're likely to maintain higher speed, with only minor slopes at worst, higher gearing
with high current for torque might suit better, but at expense of heating risk and range reduction under load on steeeper hills?
I've seen a couple more torque curves for motors with a high geared reduction ~10:1 & hence high rpm, relatively low EM torque, and they all seem to exhibit the same behaviour (mentioned previously) of low rpm loss from the max efficiency rpm, with increasing load, before point of maximum torque i.e. max torque at a relatively high rpm/speed compared to higher EM torque motors, so weakening their hill performance...Another quick design question then: for a quality hub motor with good EM torque, to be put in a 26" wheel would you expect a difference in performance in mixed hilly/flat terrain between:
2) fairly low geared reduction to ~270-280rpm for ~ 20mph @ say 36V, with a high current limit of ~20A to give higher torque @ lower speeds
1) higher geared reduction to ~200-215rpm for good speed & torque up to ~15-16mph @ 15A current limit, with a higher voltage limit & battery e.g. 24-36V or 36-48V to enable speeds up to ~20mph?
That is, from a design point of view, is it better to choose gearing & torque of motor for 15mph, then extend top speed by "overvolting" if wanted, or to gear for 20mph while boosting lower speed torque by increased current limit?
I realise both are compromises between speed & low-speed torque with hub motors, but how well can either work i.e. how much efficiency loss & with what limitation of use to retain efficiency?
I'd have thought that for use on hills and with moderate speed use (little more than 15mph normally) ease & efficiency suggest to gear lower & overvolt for speed (lower current limit = less heating too?); whereas if you're likely to maintain higher speed, with only minor slopes at worst, higher gearing
with high current for torque might suit better, but at expense of heating risk and range reduction under load on steeeper hills?
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P.S. I forgot to say: the question isn't just theoretical, since I think one of the 2 types above has been done, but the other seems equally viable?
I just wish I had the technical skills of some here, to be able to build or shape my own bike! still, if quality hub gears, geared for 26" wheels @ 15mph, were available and didn't cost the earth or weigh a ton, I'd probably give it a go! There's still the front/rear motor issue though... and bike styling...
I just wish I had the technical skills of some here, to be able to build or shape my own bike!
still, if quality hub gears, geared for 26" wheels @ 15mph, were available and didn't cost the earth or weigh a ton, I'd probably give it a go! There's still the front/rear motor issue though... and bike styling...
Yes, I agree with your conclusion Stuart, this one is what I'd choose:
" higher geared reduction to ~200-215rpm for good speed & torque up to ~15-16mph @ 15A current limit, with a higher voltage limit & battery e.g. 24-36V or 36-48V to enable speeds up to ~20mph?"
Assuming you can obtain the appropriate voltage controller.
Where you put the motor depends on the uses for the bike to some extent.
.
" higher geared reduction to ~200-215rpm for good speed & torque up to ~15-16mph @ 15A current limit, with a higher voltage limit & battery e.g. 24-36V or 36-48V to enable speeds up to ~20mph?"
Assuming you can obtain the appropriate voltage controller.
Where you put the motor depends on the uses for the bike to some extent.
.
Yes, I think I'd choose that one too.
So, the only additional thing to design in really (other than a good quality design & build motor, with good efficiency) is to either ensure the peak torque occurs at a speed well-matched to the peak power output, or vice-versa i.e. ensure the peak power output is proportional to the speed at maximum torque, to enable good hill-climbing... which way round is that best designed, do you think? I suppose the usage is a big factor, like with the cycles maximus example! But for more usual bikes...? Is either hill-climbing or speed performance/efficiency necessarily compromised by hub motor design, or can a good balance be struck (and then used with a high capacity, fast charge Li battery for good range & ease of refuelling)?
I'll post a question about stretching frames & fitting hub motors in the T bike thread.
Stuart.
So, the only additional thing to design in really (other than a good quality design & build motor, with good efficiency) is to either ensure the peak torque occurs at a speed well-matched to the peak power output, or vice-versa i.e. ensure the peak power output is proportional to the speed at maximum torque, to enable good hill-climbing... which way round is that best designed, do you think? I suppose the usage is a big factor, like with the cycles maximus example! But for more usual bikes...? Is either hill-climbing or speed performance/efficiency necessarily compromised by hub motor design, or can a good balance be struck (and then used with a high capacity, fast charge Li battery for good range & ease of refuelling
)?I'll post a question about stretching frames & fitting hub motors in the T bike thread
.Stuart.
I think the choice is always to enable good hill climbing Stuart, given the very low powers that we're dealing with on electric bikes.
The only exception might be for a speed machine that would only be used in a flat area. (with a half blind police force. )
The only exception might be for a speed machine that would only be used in a flat area. (with a half blind police force.
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