I'm looking at buying and electric bike - at 70+ I need a bit of assistance !

I was an electronics engineer so am reasonably aware of electric motor power, and also what torque is. But can someone care to give me this further bit of mental assistance on the motors that are used in bikes. My problem is that there is a power limit in the UK of 250 watts - I believe also that they are meant to cut out above 15mph but that's a different matter. Where I am struggling is that I am being offered bikes with 40 NM motor torque and up to 80 NM. Mechanics were never my strong point, so there is probably some simple answer to this, but I am seeing radial force as being related to power in, so how can there be a 2 to 1 ration between different motors?

Thanks

On Sat, 28 May 2016 13:38:00 -0700 (PDT), Rob Graham
wrote:

I'm looking at buying and electric bike - at 70+ I need a bit of assistance !

I was an electronics engineer so am reasonably aware of electric motor power, and also what torque is. But can someone care to give me this further bit of mental assistance on the motors that are used in bikes. My problem is that there is a power limit in the UK of 250 watts - I believe also that they are meant to cut out above 15mph but that's a different matter. Where I am struggling is that I am being offered bikes with 40 NM motor torque and up to 80 NM. Mechanics were never my strong point, so there is probably some simple answer to this, but I am seeing radial force as being related to power in, so how can there be a 2 to 1 ration between different motors?

I can't really answer your question technically but assuming they are
all correctly rated at 250W then could the differences be partly down
to marketing and also efficiency / design?

If a motor was say driving the crank it would need to be slow revving
and therefore produce more torque? A motor in the wheel would be
higher revving (especially a 16" wheel) and for the same 15mph upper
limit, offer less torque (measured at the motor itself)?

I know how for the same set limits (24v, 25kg of battery and 1 hour
duration race) how a motor design can make a vast difference to the
final outcome. This was especially so when racing against someone who
developed their own motor then went on to bigger things ... ;-)

http://lynchmotors.co.uk/

Cheers, T i m

p.s. https://dl.dropboxusercontent.com/u/5772409/EV2.jpg

I think this was the one and only time anyone beat Cedric (No1)
blush.

On 5/28/2016 9:38 PM, Rob Graham wrote:
I'm looking at buying and electric bike - at 70+ I need a bit of assistance !

I was an electronics engineer so am reasonably aware of electric motor power, and also what torque is. But can someone care to give me this further bit of mental assistance on the motors that are used in bikes. My problem is that there is a power limit in the UK of 250 watts - I believe also that they are meant to cut out above 15mph but that's a different matter. Where I am struggling is that I am being offered bikes with 40 NM motor torque and up to 80 NM. Mechanics were never my strong point, so there is probably some simple answer to this, but I am seeing radial force as being related to power in, so how can there be a 2 to 1 ration between different motors?

Thanks

Power is torque multiplied by angular speed, but perhaps confusingly the
latter isn't measured in RPM but radians per second. So a 40
Newton-metre motor giving 250 watts must be going at 6.25 radians per
second, or 375 radians per minute, or near enough 60 rpm.

Similarly, a 30 rpm motor would give 80 NM torque for 250 watts.

On Saturday, May 28, 2016 at 10:13:02 PM UTC+1, T i m wrote:
On Sat, 28 May 2016 13:38:00 -0700 (PDT), Rob Graham
wrote:

I'm looking at buying and electric bike - at 70+ I need a bit of assistance !

I was an electronics engineer so am reasonably aware of electric motor power, and also what torque is. But can someone care to give me this further bit of mental assistance on the motors that are used in bikes. My problem is that there is a power limit in the UK of 250 watts - I believe also that they are meant to cut out above 15mph but that's a different matter. Where I am struggling is that I am being offered bikes with 40 NM motor torque and up to 80 NM. Mechanics were never my strong point, so there is probably some simple answer to this, but I am seeing radial force as being related to power in, so how can there be a 2 to 1 ration between different motors?

I can't really answer your question technically but assuming they are
all correctly rated at 250W then could the differences be partly down
to marketing and also efficiency / design?

If a motor was say driving the crank it would need to be slow revving
and therefore produce more torque? A motor in the wheel would be
higher revving (especially a 16" wheel) and for the same 15mph upper
limit, offer less torque (measured at the motor itself)?

I know how for the same set limits (24v, 25kg of battery and 1 hour
duration race) how a motor design can make a vast difference to the
final outcome. This was especially so when racing against someone who
developed their own motor then went on to bigger things ... ;-)

http://lynchmotors.co.uk/

Cheers, T i m

p.s. https://dl.dropboxusercontent.com/u/5772409/EV2.jpg

I think this was the one and only time anyone beat Cedric (No1)
blush.

Thanks Tim - I did wonder about the low revving torque but if you look at some electric bikes now you will see that the chain wheel is only something like 16 teeth and so revs much higher. It is actually concentric on the crankshaft with the pedals, which I imagine drive down through an enclosed epicyclic gear. I asked the cycle shop about this and didn't really take the guy's line about this being a measure to overcome chain drop on rear suspension systems - that may be a bonus but I suspect higher motor revs is the target.

Interesting to look up Lynch's website. That must have all such fun to be involved in.
Rob

On 5/28/2016 10:13 PM, newshound wrote:
On 5/28/2016 9:38 PM, Rob Graham wrote:
I'm looking at buying and electric bike - at 70+ I need a bit of
assistance !

I was an electronics engineer so am reasonably aware of electric motor
power, and also what torque is. But can someone care to give me this
further bit of mental assistance on the motors that are used in
bikes. My problem is that there is a power limit in the UK of 250
watts - I believe also that they are meant to cut out above 15mph but
that's a different matter. Where I am struggling is that I am being
offered bikes with 40 NM motor torque and up to 80 NM. Mechanics were
never my strong point, so there is probably some simple answer to
this, but I am seeing radial force as being related to power in, so
how can there be a 2 to 1 ration between different motors?

Thanks

Power is torque multiplied by angular speed, but perhaps confusingly the
latter isn't measured in RPM but radians per second. So a 40
Newton-metre motor giving 250 watts must be going at 6.25 radians per
second, or 375 radians per minute, or near enough 60 rpm.

Similarly, a 30 rpm motor would give 80 NM torque for 250 watts.

Taking it a bit further, for a 27 inch wheel, 15 mph is about 90 rpm. I
assume we are talking about hub motors here, rather than ones driving
through a belt or chain drive. So your 40 NM motor would be legal if it
drove you (unaided) at about 10 mph.

In practice, I think I would expect the motor to be governed
electronically to limit the power to the legal limit of 250 watts. They
*may* be quoting you peak torque figures; the higher the torque the
better the acceleration.

On Sat, 28 May 2016 14:26:22 -0700 (PDT), Rob Graham
wrote:

snip

Thanks Tim - I did wonder about the low revving torque but if you look at some electric bikes now you will see that the chain wheel is only something like 16 teeth and so revs much higher.

Ok. However, I was thinking anything driving the crank might be doing
so at a lower revs / higher torque than anything that wasn't geared
up.

I know on my EV I had to down gear quite a bit, even with top speeds
of only 40 mph.

https://dl.dropboxusercontent.com/u/5772409/EV1a.jpg

You might just imagine a light chain drive (under that ally cover with
the hole) where the motor had a very small gear (from the cam chain
drive / crankshaft of a small Honda motorbike) to a much larger gear I
made by hand (you can see the bottom of it under the cover). From
their a std cycle sprocket from a 7 speed block driving a fairly large
range block on the rear wheel.

It is actually concentric on the crankshaft with the pedals, which I imagine drive down through an enclosed epicyclic gear.

Ours has a powered wheel and I've not played with anything else
(production anyway).

I asked the cycle shop about this and didn't really take the guy's line about this being a measure to overcome chain drop on rear suspension systems - that may be a bonus but I suspect higher motor revs is the target.

Ok.

Interesting to look up Lynch's website. That must have all such fun to be involved in.

It was indeed. ;-)

I felt quite 'normal' (by comparison and for a change g) as most of
the others were (more) 'eccentric' to some degree, as is often the
case with 'boffin / inventive' types. Great bunch of guys though and
we raced at quite a few places that I might never have visited
otherwise (like MIRA and Oulton Park).

It was also a good opportunity to run the C5 round and many of us had
them (as one of the C5 designers also raced. In fact, he leant me one
of his earlier machines to help me get started). ;-)

Cheers, T i m

On Saturday, 28 May 2016 21:38:02 UTC+1, Rob Graham wrote:
I'm looking at buying and electric bike - at 70+ I need a bit of assistance !

I was an electronics engineer so am reasonably aware of electric motor power, and also what torque is. But can someone care to give me this further bit of mental assistance on the motors that are used in bikes. My problem is that there is a power limit in the UK of 250 watts - I believe also that they are meant to cut out above 15mph but that's a different matter. Where I am struggling is that I am being offered bikes with 40 NM motor torque and up to 80 NM. Mechanics were never my strong point, so there is probably some simple answer to this, but I am seeing radial force as being related to power in, so how can there be a 2 to 1 ration between different motors?

Thanks

Electric transport has three phase permanent magnet synchronous motors.
They have few parts, the tricky stuff is in the electronics.

Mechanical power is derived from torque times rpm.
The rpm is limited to give the top speed.
Various torques (Nm)are offered for thin people and fat gits, also if you are in a hilly area you need a higher torque to get you up the hills with less personal effort.



Most bikes only "power on" when you start pedalling. This is a a safety thing.

IFAIAA the 250 watts limit only applies if you have no motor cycle licence.
I think there are tax and insurance issues over the 250watt limit as it's then considered to be a motor cycle.

Also ask about range and battery size. (And cost of new battery)
Bear in mind the batteries gradually deteriorate over time.
And they don't like lack of use, especially if left in a discharged state.
Range is much reduced by hills.

Everyone I know with an electric bike has been very pleased with them.

Rob Graham wrote:
I'm looking at buying and electric bike - at 70+ I need a bit of assistance !

I was an electronics engineer so am reasonably aware of electric motor
power, and also what torque is. But can someone care to give me this further
bit of mental assistance on the motors that are used in bikes. My problem
is that there is a power limit in the UK of 250 watts - I believe also
that they are meant to cut out above 15mph but that's a different matter.
Where I am struggling is that I am being offered bikes with 40 NM motor
torque and up to 80 NM. Mechanics were never my strong point, so there
is probably some simple answer to this, but I am seeing radial force as
being related to power in, so how can there be a 2 to 1 ration between
different motors?

The power is directly related to torque * rpm.

The torque by itself is meaningless, you can get any amount of torque
you like by gearing, it's the speed at which the wheel is rotating
when a given torque is produced that matters.

--
Chris Green
·

Many thanks guys

Harry - that's good to know the user satisfaction. The bikes I was trying yesterday fortunately had a steep hill within a mile or so of the shop, and it was interesting to find that I was using the steps in the motor power much like I would use the selection of chain wheel; that did answer my question as to how with ~9 gears the e-bike matched a bike with the low ratios of a 27 gear set. The nice thing was that the added ratio effect came on instantaneously.

Newshound - if you are saying that the effect of higher torque is only on acceleration, then for me as an elderly cyclist there is no point in me paying the extra. I just want some assistance to get up the hills and combat the wind.

And Chris - that's a good question and one that I suspect will trip up the salesman. It still does raise the question that for the same RPM, can any one motor produce twice to torque of another for the same power input?
Rob

On 29/05/16 11:06, Rob Graham wrote:

It still does raise the question that for the same
RPM, can any one motor produce twice to torque of another for the
same power input? Rob


Absolutely, if its twice as efficient, and the other one is a complete dog.

However the power *output* will be twice as much.




--
€œBut what a weak barrier is truth when it stands in the way of an
hypothesis!€�

Mary Wollstonecraft

On 29/05/2016 11:06, Rob Graham wrote:


And Chris - that's a good question and one that I suspect will trip up the salesman. It still does raise the question that for the same RPM, can any one motor produce twice to torque of another for the same power input?
Rob



Clearly not! If those torque values applied to the same electrical power
input, they *must* have been at different rotational speeds.

As a matter of interest, how far can you go on one charge of the
battery? If you're producing 250 watts from a 12 volt battery (and you
wouldn't be using full power all the time, of course) the battery would
have to supply about 21 amps. I don't know what the battery capacity is,
but I doubt whether it's more than 21 amp-hours - which would limit you
to one hour's use at full power. Does that sound about right?
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 29/05/16 11:29, Roger Mills wrote:
On 29/05/2016 11:06, Rob Graham wrote:


And Chris - that's a good question and one that I suspect will trip up
the salesman. It still does raise the question that for the same RPM,
can any one motor produce twice to torque of another for the same
power input?
Rob



Clearly not! If those torque values applied to the same electrical power
input, they *must* have been at different rotational speeds.

input != output

As a matter of interest, how far can you go on one charge of the
battery? If you're producing 250 watts from a 12 volt battery (and you
wouldn't be using full power all the time, of course) the battery would
have to supply about 21 amps. I don't know what the battery capacity is,
but I doubt whether it's more than 21 amp-hours - which would limit you
to one hour's use at full power. Does that sound about right?


On a bike you cruise at around 15-20W

200W is for going uphill!


--
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin

Rob Graham wrote:

And Chris - that's a good question and one that I suspect will trip up
the salesman. It still does raise the question that for the same RPM, can
any one motor produce twice to torque of another for the same power input?

?? Power = torque * RPM

There's no way round that bit of basic engineering/physics.

If motor A produces 10Nm at 100 rpm and motor B produces 20Nm at
100rpm for the same 'power input' then motor B is twice as efficient.


--
Chris Green
·

In article ,
Rob Graham wrote:
I'm looking at buying and electric bike - at 70+ I need a bit of
assistance !

I was an electronics engineer so am reasonably aware of electric motor
power, and also what torque is. But can someone care to give me this
further bit of mental assistance on the motors that are used in bikes.
My problem is that there is a power limit in the UK of 250 watts - I
believe also that they are meant to cut out above 15mph but that's a
different matter. Where I am struggling is that I am being offered bikes
with 40 NM motor torque and up to 80 NM. Mechanics were never my strong
point, so there is probably some simple answer to this, but I am seeing
radial force as being related to power in, so how can there be a 2 to 1
ration between different motors?

Generally, electric motors run too fast for direct drive. So have a
gearbox to reduce that speed. So the chances are the difference is the
gearbox. So the speed at the output shaft will be approximately half that
of the one with the lower torque.

--
*Eschew obfuscation *

Dave Plowman London SW
To e-mail, change noise into sound.

On 29/05/2016 11:57, The Natural Philosopher wrote:
On 29/05/16 11:29, Roger Mills wrote:
On 29/05/2016 11:06, Rob Graham wrote:


And Chris - that's a good question and one that I suspect will trip up
the salesman. It still does raise the question that for the same RPM,
can any one motor produce twice to torque of another for the same
power input?
Rob



Clearly not! If those torque values applied to the same electrical power
input, they *must* have been at different rotational speeds.

input != output


Indeed. But it would be a bit odd if one were twice as efficient as the
other.


As a matter of interest, how far can you go on one charge of the
battery? If you're producing 250 watts from a 12 volt battery (and you
wouldn't be using full power all the time, of course) the battery would
have to supply about 21 amps. I don't know what the battery capacity is,
but I doubt whether it's more than 21 amp-hours - which would limit you
to one hour's use at full power. Does that sound about right?


On a bike you cruise at around 15-20W


So the battery should last for quite a few hours when cruising on a
level road, I assume?

200W is for going uphill!


I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 29/05/16 14:59, Roger Mills wrote:
On 29/05/2016 11:57, The Natural Philosopher wrote:
On 29/05/16 11:29, Roger Mills wrote:
On 29/05/2016 11:06, Rob Graham wrote:


And Chris - that's a good question and one that I suspect will trip up
the salesman. It still does raise the question that for the same RPM,
can any one motor produce twice to torque of another for the same
power input?
Rob



Clearly not! If those torque values applied to the same electrical power
input, they *must* have been at different rotational speeds.

input != output


Indeed. But it would be a bit odd if one were twice as efficient as the
other.

Actually, in my game - model aircraft - 40%-80% is about the range from
the worst to the best.

Ok that is pushing the point, but its not that far fetched.



As a matter of interest, how far can you go on one charge of the
battery? If you're producing 250 watts from a 12 volt battery (and you
wouldn't be using full power all the time, of course) the battery would
have to supply about 21 amps. I don't know what the battery capacity is,
but I doubt whether it's more than 21 amp-hours - which would limit you
to one hour's use at full power. Does that sound about right?


On a bike you cruise at around 15-20W


So the battery should last for quite a few hours when cruising on a
level road, I assume?

200W is for going uphill!


I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max



--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx

On 29/05/2016 11:06, Rob Graham wrote:


And Chris - that's a good question and one that I suspect will trip up
the salesman. It still does raise the question that for the same RPM,
can any one motor produce twice to torque of another for the same
power input?
Rob



Clearly not! If those torque values applied to the same electrical power
input, they *must* have been at different rotational speeds.

input != output


Indeed. But it would be a bit odd if one were twice as efficient as the
other.

Actually, in my game - model aircraft - 40%-80% is about the range from
the worst to the best.


If I can pop back in again on the point of "worst to best", this introduces another interesting element; the two bikes referenced in the original post are from the same manufacturer using a Bosch system - it may well be that Bosch do have several 'systems' but there is something in the engineering then that is allowing Bosch to make this claim.

On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Sunday, 29 May 2016 13:02:52 UTC+1, Dave Plowman (News) wrote:
In article ,
Rob Graham wrote:
I'm looking at buying and electric bike - at 70+ I need a bit of
assistance !

I was an electronics engineer so am reasonably aware of electric motor
power, and also what torque is. But can someone care to give me this
further bit of mental assistance on the motors that are used in bikes.
My problem is that there is a power limit in the UK of 250 watts - I
believe also that they are meant to cut out above 15mph but that's a
different matter. Where I am struggling is that I am being offered bikes
with 40 NM motor torque and up to 80 NM. Mechanics were never my strong
point, so there is probably some simple answer to this, but I am seeing
radial force as being related to power in, so how can there be a 2 to 1
ration between different motors?

Generally, electric motors run too fast for direct drive. So have a
gearbox to reduce that speed. So the chances are the difference is the
gearbox. So the speed at the output shaft will be approximately half that
of the one with the lower torque.

--
*Eschew obfuscation *

Dave Plowman London SW
To e-mail, change noise into sound.

Not these days with permanent magnet AC motors.
You can have lots of magnets, so obviating gearboxes and belt/chain drives.
Hence "Direct Drive" washing machines.

On 29/05/16 18:04, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

4-5mph *max*.



According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

I cant get up a 15% slope at 3.6mph...

--
Outside of a dog, a book is a man's best friend. Inside of a dog it's
too dark to read.

Groucho Marx

On 5/29/2016 11:06 AM, Rob Graham wrote:
Many thanks guys

Harry - that's good to know the user satisfaction. The bikes I was trying yesterday fortunately had a steep hill within a mile or so of the shop, and it was interesting to find that I was using the steps in the motor power much like I would use the selection of chain wheel; that did answer my question as to how with ~9 gears the e-bike matched a bike with the low ratios of a 27 gear set. The nice thing was that the added ratio effect came on instantaneously.

Newshound - if you are saying that the effect of higher torque is only on acceleration, then for me as an elderly cyclist there is no point in me paying the extra. I just want some assistance to get up the hills and combat the wind.

Ultimately, it's the power which decides how fast you can get up a hill,
or how fast you can go on the level (and that will depend on the wind).
I *don't* think you should pay too much attention to claimed torque
values. I think you need to try them all and decide which one feels most
suitable. I'd have thought the other key parameter was range, a good
indicator of that would be the amp-hours of the battery (bearing in mind
that it also depends on voltage: a 12 volt battery with 10 amp hours
contains the same amount of energy (hence the same range) as a 6 volt
one with 20 amp hours.

There are of course other factors like electrical losses in the motor,
wiring, connectors, etc. and frictional losses in bearings, and rolling
resistance. Both bicycle and electric motor technology are fairly mature
and the ways of controlling losses are well understood. Although you can
reduce losses up to a point by throwing money at them.


And Chris - that's a good question and one that I suspect will trip up the salesman. It still does raise the question that for the same RPM, can any one motor produce twice to torque of another for the same power input?
Rob

"Roger Mills" wrote in message
...
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get up
a 15% slope at 3.6 mph - and that's ignoring rolling resistance and wind
drag (not that there'll much of the latter at that speed!). If the bike is
limited to 250 watts of *input* power, the mechanical power generated will
be less than 250 - and the speed will be even lower.

Are thee things actually useful?

Of course they are if that obese ****er can't get up that hill without
it and there arent too many of them where it wants to go.

On Sunday, 29 May 2016 18:01:54 UTC+1, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

The cyclist is also putting in power.
It's only an assist device.
In practice the power output will be limited by the battery charge state.

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

On 30/05/2016 12:40, newshound wrote:
A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

3.6MPH up a nearly 1 in 6 hill?

AIUI Tour de France riders put out about 400W. Mere mortals plus 250W
from the battery should be able to get close to that - at least for a
while - which would be a great help.

Andy

On Mon, 30 May 2016 12:40:18 +0100, newshound wrote:

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

This made me finally look up the conversion between the old "1 in 4" road
signs and the more modern "25%" style.

I had assumed that 1 in 4 was equivalent to 25% and 100% would be straight
up.
Not so, apparently.

http://www.engineeringtoolbox.com/sl...radient-grade-
d_1562.html

Interesting reading, and one of the times where you can have more than
100% without getting into sporting speak of the "I want all my players to
give 110%" variety.

According to the table, 15% is roughly "1 in 6" or around 9 degrees which
doesn't seem that steep (at least for a short distance).

Now hunting down a route profiler to check how steep the diddly little
hills I ride up really are.

Cheers

Dave R

--
Windows 8.1 on PCSpecialist box

On 31/05/16 12:48, David wrote:
On Mon, 30 May 2016 12:40:18 +0100, newshound wrote:

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

This made me finally look up the conversion between the old "1 in 4" road
signs and the more modern "25%" style.

I had assumed that 1 in 4 was equivalent to 25% and 100% would be straight
up.
Not so, apparently.

http://www.engineeringtoolbox.com/sl...radient-grade-
d_1562.html

Interesting reading, and one of the times where you can have more than
100% without getting into sporting speak of the "I want all my players to
give 110%" variety.

According to the table, 15% is roughly "1 in 6" or around 9 degrees which
doesn't seem that steep (at least for a short distance).

Now hunting down a route profiler to check how steep the diddly little
hills I ride up really are.

Cheers

Dave R

I have climbed, with ropes, a 45 degree rockface.

which is 100% by their token

Its also IIRC the slope of the great pyramid at Chichen Itza, which I
have also climbed, with a rope hand hold. (and a 25kg camera bag) They
wont let you do that any more

15 degrees (1:4)(25%) is about as steep as ANY road gets. The infamous
porlock hill is that.




--
Truth welcomes investigation because truth knows investigation will lead
to converts. It is deception that uses all the other techniques.

Going back to my original enquiry, a bit of googling does a little repair to my memories of this area of mechanics.

It may well be that my 'ergo' is not correct though and I'm more than happy to be corrected.

If we apply power to something, that is energy per time and we measure that in Joules.

For torque as a rotational force - measured in Newton Metres - for one complete rotation the distance is 2 pi x the radius.

Thus 1 Nm = 2 x 3.14 joules / rev.

Also 1 joule = 1 watt-sec.

Now is it a coincidence that for a drive system producing "40 newtons of Torque" with a motor input power of 250W, that 40 x 6.28 ~= 250w ?

I suspect that this is just chance as the inference would be that the 80Nm system would then require 500 W of electrical power which is double the UK allowed power.

Without knowing very much about modern electric motor design, could the source of double the torque be related to much more powerful permanent magnets in the 'up-market' system. Or is it that in some way the electronics for the less powerful system just 'chips' the power down?

On 31/05/16 15:41, Rob Graham wrote:
Going back to my original enquiry, a bit of googling does a little repair to my memories of this area of mechanics.

It may well be that my 'ergo' is not correct though and I'm more than happy to be corrected.

If we apply power to something, that is energy per time and we measure that in Joules.

For torque as a rotational force - measured in Newton Metres - for one complete rotation the distance is 2 pi x the radius.

Thus 1 Nm = 2 x 3.14 joules / rev.

Also 1 joule = 1 watt-sec.

Now is it a coincidence that for a drive system producing "40 newtons of Torque" with a motor input power of 250W, that 40 x 6.28 ~= 250w ?

I suspect that this is just chance as the inference would be that the 80Nm system would then require 500 W of electrical power which is double the UK allowed power.

Without knowing very much about modern electric motor design, could the source of double the torque be related to much more powerful permanent magnets in the 'up-market' system. Or is it that in some way the electronics for the less powerful system just 'chips' the power down?

Neither.

Basically what 'powerful magnets' do for you is allow a better power to
weight ratio. BY and large on a small DC motor the dominant losses are
(resistive) copper losses, which you can avoid by simply having 'more
copper'

Or by having more magnetic fields, you can get away with less copper.,

For the same torque.

In terms of constant power, the output powers should be constant. If its
double the torque its delivered at half the RPM which may suit a
differently geared bike. I don't know how these things are used.




--
If I had all the money I've spent on drink...
...I'd spend it on drink.

Sir Henry (at Rawlinson's End)

In article ,
Rob Graham wrote:
I suspect that this is just chance as the inference would be that the
80Nm system would then require 500 W of electrical power which is double
the UK allowed power.

Torque doesn't include speed of any sort. Only if you know the RPM at
which it is being measured at would the power input be of note.

Torque is used to set the tightness of a bolt etc. Very little movement
there and at a very low speed. It is simply the product of weight and the
distance from the fulcrum. If you use lb.ft. it would be one pound of
weight on a 1 ft long spanner to give you 1 ft.lb

Without knowing very much about modern electric motor design, could the
source of double the torque be related to much more powerful permanent
magnets in the 'up-market' system. Or is it that in some way the
electronics for the less powerful system just 'chips' the power down?

There is bound to be some spread of efficiency with motors. However, I'd
be surprised if two designed for the same job were so much different. ie,
one producing twice the torque at the same output shaft RPM and power
input than the other. The low efficiency one would get very hot since
there's nowhere else for that power to go.

--
*A hangover is the wrath of grapes.

Dave Plowman London SW
To e-mail, change noise into sound.

I have climbed, with ropes, a 45 degree rockface.

which is 100% by their token

Its also IIRC the slope of the great pyramid at Chichen Itza, which I
have also climbed, with a rope hand hold. (and a 25kg camera bag) They
wont let you do that any more

15 degrees (1:4)(25%) is about as steep as ANY road gets. The infamous
porlock hill is that.


Wrynose pass is 1 in 3 in places.
You want to try descending tHAT in a Minor 1000

On Tue, 31 May 2016 08:28:48 -0700 (PDT), harry wrote:


I have climbed, with ropes, a 45 degree rockface.

which is 100% by their token

Its also IIRC the slope of the great pyramid at Chichen Itza, which I
have also climbed, with a rope hand hold. (and a 25kg camera bag) They
wont let you do that any more

15 degrees (1:4)(25%) is about as steep as ANY road gets. The infamous
porlock hill is that.


Wrynose pass is 1 in 3 in places.
You want to try descending tHAT in a Minor 1000

Are you sure that it's 1 i 3? I've cycled up it several times and, although
steep, is nowhere near as bad (good) as Robin Hood's Bay or Rosedale
Chimney.
--
Peter.
The gods will stay away
whilst religions hold sway

On 31 May 2016 11:48:05 GMT, David wrote:

On Mon, 30 May 2016 12:40:18 +0100, newshound wrote:

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

This made me finally look up the conversion between the old "1 in 4" road
signs and the more modern "25%" style.

I had assumed that 1 in 4 was equivalent to 25% and 100% would be straight
up.
Not so, apparently.

http://www.engineeringtoolbox.com/sl...radient-grade-
d_1562.html

Interesting reading, and one of the times where you can have more than
100% without getting into sporting speak of the "I want all my players to
give 110%" variety.

According to the table, 15% is roughly "1 in 6" or around 9 degrees which
doesn't seem that steep (at least for a short distance).

Now hunting down a route profiler to check how steep the diddly little
hills I ride up really are.

Cheers

Dave R

It's the Tangent of the angle - gets nasty over 45 deg.
Same with drive-side spokes: the tension is proportional to the tan. In the
days of early 6-speed blocks and 125mm rear ends I applied much cunning and
brute force to gain a few mm on the drive side. With a 531 frame, it was
possible to get 5mm preferentially on the drive side by standing on the LHS
chain stay near the bridge and heaving. Then simply build the wheel with a
longer axle and dis it across to the LHS.
Not good with gas-pipe frames as they tended to bend rather too easily.
--
Peter.
The gods will stay away
whilst religions hold sway

On 31/05/2016 16:58, PeterC wrote:
On Tue, 31 May 2016 08:28:48 -0700 (PDT), harry wrote:


I have climbed, with ropes, a 45 degree rockface.

which is 100% by their token

Its also IIRC the slope of the great pyramid at Chichen Itza, which I
have also climbed, with a rope hand hold. (and a 25kg camera bag) They
wont let you do that any more

15 degrees (1:4)(25%) is about as steep as ANY road gets. The infamous
porlock hill is that.


Wrynose pass is 1 in 3 in places.
You want to try descending tHAT in a Minor 1000

Are you sure that it's 1 i 3? I've cycled up it several times and, although
steep, is nowhere near as bad (good) as Robin Hood's Bay or Rosedale
Chimney.

It's marked 1:3 on one of the sides I think. It's easier from the west.
IMO Hardknott is harder. But Harlech has the steepest - marked as 40%.
That was hard.

In article , David
writes
On Mon, 30 May 2016 12:40:18 +0100, newshound wrote:

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

This made me finally look up the conversion between the old "1 in 4" road
signs and the more modern "25%" style.

I had assumed that 1 in 4 was equivalent to 25% and 100% would be straight
up.
Not so, apparently.

http://www.engineeringtoolbox.com/sl...radient-grade-
d_1562.html

Interesting reading, and one of the times where you can have more than
100% without getting into sporting speak of the "I want all my players to
give 110%" variety.

According to the table, 15% is roughly "1 in 6" or around 9 degrees which
doesn't seem that steep (at least for a short distance).

Now hunting down a route profiler to check how steep the diddly little
hills I ride up really are.

Cheers

Dave R

I don't think that is correct
The 1 in 4 notation measure the sine of the angle not the tangent.
It's a rise of 1 foot for each 4 feet you travel up the gradient.
--
bert

On 31/05/16 17:05, PeterC wrote:
Same with drive-side spokes: the tension is proportional to the tan. In the
days of early 6-speed blocks and 125mm rear ends I applied much cunning and
brute force to gain a few mm on the drive side. With a 531 frame, it was
possible to get 5mm preferentially on the drive side by standing on the LHS
chain stay near the bridge and heaving. Then simply build the wheel with a
longer axle and dis it across to the LHS.
Not good with gas-pipe frames as they tended to bend rather too easily.


WTF are you on about?


--
"Women actually are capable of being far more than the feminists will
let them."

On Tue, 31 May 2016 21:07:06 +0100, The Natural Philosopher
wrote:

On 31/05/16 17:05, PeterC wrote:
Same with drive-side spokes: the tension is proportional to the tan. In the
days of early 6-speed blocks and 125mm rear ends I applied much cunning and
brute force to gain a few mm on the drive side. With a 531 frame, it was
possible to get 5mm preferentially on the drive side by standing on the LHS
chain stay near the bridge and heaving. Then simply build the wheel with a
longer axle and dis it across to the LHS.
Not good with gas-pipe frames as they tended to bend rather too easily.


WTF are you on about?

Really?

Bicycle wheel and frame design / modifications. Derailleur driven
cycles generally have an offset 'dish' to them to accommodate the
drive sprocket that is on one side.

HTH

Cheers, T i m

On Tue, 31 May 2016 19:59:12 +0100, bert wrote:

In article , David
writes
On Mon, 30 May 2016 12:40:18 +0100, newshound wrote:

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

This made me finally look up the conversion between the old "1 in 4" road
signs and the more modern "25%" style.

I had assumed that 1 in 4 was equivalent to 25% and 100% would be straight
up.
Not so, apparently.

http://www.engineeringtoolbox.com/sl...radient-grade-
d_1562.html

Interesting reading, and one of the times where you can have more than
100% without getting into sporting speak of the "I want all my players to
give 110%" variety.

According to the table, 15% is roughly "1 in 6" or around 9 degrees which
doesn't seem that steep (at least for a short distance).

Now hunting down a route profiler to check how steep the diddly little
hills I ride up really are.

Cheers

Dave R

I don't think that is correct
The 1 in 4 notation measure the sine of the angle not the tangent.
It's a rise of 1 foot for each 4 feet you travel up the gradient.

um, now not sure. If the gradient is 1:1 (100%) at 45 deg., that suggests
tan. The diagram showed, IIRC, Opp/Adj which I think is Tan.
--
Peter.
The gods will stay away
whilst religions hold sway

On 01/06/16 09:21, PeterC wrote:
On Tue, 31 May 2016 19:59:12 +0100, bert wrote:

In article , David
writes
On Mon, 30 May 2016 12:40:18 +0100, newshound wrote:

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

This made me finally look up the conversion between the old "1 in 4" road
signs and the more modern "25%" style.

I had assumed that 1 in 4 was equivalent to 25% and 100% would be straight
up.
Not so, apparently.

http://www.engineeringtoolbox.com/sl...radient-grade-
d_1562.html

Interesting reading, and one of the times where you can have more than
100% without getting into sporting speak of the "I want all my players to
give 110%" variety.

According to the table, 15% is roughly "1 in 6" or around 9 degrees which
doesn't seem that steep (at least for a short distance).

Now hunting down a route profiler to check how steep the diddly little
hills I ride up really are.

Cheers

Dave R

I don't think that is correct
The 1 in 4 notation measure the sine of the angle not the tangent.
It's a rise of 1 foot for each 4 feet you travel up the gradient.

um, now not sure. If the gradient is 1:1 (100%) at 45 deg., that suggests
tan. The diagram showed, IIRC, Opp/Adj which I think is Tan.

yes . I always thought it referred to distance along teh map and height
above sea level, which is tan.

Then at some point someone else assured me it was sine, and now we are
back to tan.

The page linked to seems pretty definite that its tan so I'll go with
that for now


--
€œBut what a weak barrier is truth when it stands in the way of an
hypothesis!€�

Mary Wollstonecraft

In article , The Natural Philosopher
writes
On 01/06/16 09:21, PeterC wrote:
On Tue, 31 May 2016 19:59:12 +0100, bert wrote:

In article , David
writes
On Mon, 30 May 2016 12:40:18 +0100, newshound wrote:

On 5/29/2016 6:04 PM, Roger Mills wrote:
On 29/05/2016 15:18, The Natural Philosopher wrote:
On 29/05/16 14:59, Roger Mills wrote:

I'm sure I could work it out - but at what speed would it be able to
propel a 12 stone person up a 15% gradient (say)?

If you can work it you, you do it. Im fed up with being other peopels
pocket calculators.

But my guess is about 4-5mph max


OK, I've worked it out, and your 4-5 mph is a bit optimistic.

According to my calculations, a person weighing 168 lb plus a (typical)
bike weighing 62 lb would require 250 watts of mechanical power to get
up a 15% slope at 3.6 mph - and that's ignoring rolling resistance and
wind drag (not that there'll much of the latter at that speed!). If the
bike is limited to 250 watts of *input* power, the mechanical power
generated will be less than 250 - and the speed will be even lower.

Are thee things actually useful?

A continuous 15% gradient is actually pretty steep, in the context of
things like wheelchairs and mobility scooters. And 3.6 mph is a good
walking pace on a slope.

This made me finally look up the conversion between the old "1 in 4" road
signs and the more modern "25%" style.

I had assumed that 1 in 4 was equivalent to 25% and 100% would be straight
up.
Not so, apparently.

http://www.engineeringtoolbox.com/sl...radient-grade-
d_1562.html

Interesting reading, and one of the times where you can have more than
100% without getting into sporting speak of the "I want all my players to
give 110%" variety.

According to the table, 15% is roughly "1 in 6" or around 9 degrees which
doesn't seem that steep (at least for a short distance).

Now hunting down a route profiler to check how steep the diddly little
hills I ride up really are.

Cheers

Dave R

I don't think that is correct
The 1 in 4 notation measure the sine of the angle not the tangent.
It's a rise of 1 foot for each 4 feet you travel up the gradient.

um, now not sure. If the gradient is 1:1 (100%) at 45 deg., that suggests
tan. The diagram showed, IIRC, Opp/Adj which I think is Tan.

yes . I always thought it referred to distance along teh map and height
above sea level, which is tan.

Then at some point someone else assured me it was sine, and now we are
back to tan.

The page linked to seems pretty definite that its tan so I'll go with
that for now


I always thought that the 1in 4 style notation was in fact sine, i.e.
opposite over hypotenuse

--
bert