When is that new power-measuring device arriving?

[Robert Chung]

[email protected] wrote:

>>> Placing it in the BB seems even more difficult, the rotation rate
>>> being even slower and forces greater with no more space than in a
>>> rear hub.
>
>> $1299. http://ergomo-usa.com
>
> This design does not generate much confidence or me. There is no
> clear explanation how and where the optical sensors are located or
> protected, although their need for careful protection is mentioned
> almost as a warning to not use this under anything but the most ideal
> conditions. As was mentioned, torque from the right crank (that
> appears on the left in the web blurb) goes directly into the chain and
> is never "seen" by the sensor.
>
> Not too good! but expensive.

http://mywebpage.netscape.com/rechung/wattage/ergomo/ergomo-pt.html

 

[Brian Huntley]

Maggie wrote:
> [email protected] wrote:
>>[snip]
> Are you a walking encyclopedia of bicycle knowledge?
>

Rolling.

 

[[email protected]]

Robert Chung writes:

>> Ideally there would be a torsion bar (equipped with a strain gauge)
>> between the gear cluster and body of the hub. Such a torque sensor
>> would need a limit stop because rider output on standing starts can
>> exceed any reasonable torque for which the sensor is designed.
>> Such a mechanism is hard to build inside a hub. Then, because the
>> load varies widely during each wheel rotation, an averaging method
>> must be employed to reduce data to some usable form, for instance
>> average torque per wheel rotation, and then this data must get out
>> of the wheel somehow. That requires a transmitter and power. This
>> hub is getting larger all the time... and expensive. I believe
>> that this is more expensive and difficult than it first appears and
>> will probably stay that way.

> $700. http://www.cycle-ops.com/products/powertap.htm

>> Placing it in the BB seems even more difficult, the rotation rate
>> being even slower and forces greater with no more space than in a
>> rear hub.

> $1299. http://ergomo-usa.com

This design does not generate much confidence for me. There is no
clear explanation how and where the optical sensors are located or
protected, although their need for careful protection is mentioned
almost as a warning to not use this under anything but the most ideal
conditions. As was mentioned, torque from the right crank (that
appears on the left in the web blurb) goes directly into the chain and
is never "seen" by the sensor.

Not too good! but expensive.

[email protected]

 

[[email protected]]

Robert Chung writes:

>>>> Placing it in the BB seems even more difficult, the rotation rate
>>>> being even slower and forces greater with no more space than in a
>>>> rear hub.

>>> $1299. http://ergomo-usa.com

>> This design does not generate much confidence for me. There is no
>> clear explanation how and where the optical sensors are located or
>> protected, although their need for careful protection is mentioned
>> almost as a warning to not use this under anything but the most
>> ideal conditions. As was mentioned, torque from the right crank
>> (that appears on the left in the web blurb) goes directly into the
>> chain and is never "seen" by the sensor.

>> Not too good! but expensive.

> http://mywebpage.netscape.com/rechung/wattage/ergomo/ergomo-pt.html

I'm still not convinced the mechanism is reliable and will not get
contaminated by dry dirt, aside from rain and road splash. For singe
riders, this is a technically manageable measurement task but where it
might do more good is on tandems where balancing effort is one of the
difficulties in such riding. For tandem riders, quantified power is
not so much a problem as is effort. The two riders, not in competition
with anyone cannot easily determine how much effort each is exerting.

The measure could easily be determined by riding at maximum output and
speed and normalizing that effort as 100% and then having a percentage
readout of both riders on each handlebar to help assess what ones fair
share of effort should be. I believe this would be a boon to tandem
riders who currently have only indirect ways of knowing which of the
two is propelling the bicycle. This is a more complicated task than
power meters on a single bicycle but it would have a long term
practical value.

[email protected]

 

[Blair P. Houghton]

I'm still waiting for the Cateye CC-TR100, which, until I
*****ed at xmastime, still said it's be avaliable in early
Summer of 2004...

--Blair
"Who knows what my heart
rate looks like..."

 

[Blair P. Houghton]

<[email protected]> wrote:
>As I mentioned, that isn't what the rider wants to know. Interesting

I want the power meter installed in my muscle cells so I
can tell how much power I'm actually expending.

--Blair
"My finish time will tell
me how efficient it is."

 

[Robert Chung]

[email protected] wrote:

> I'm still not convinced the mechanism is reliable and will not get
> contaminated by dry dirt, aside from rain and road splash.

Ergomo units have been on the market in the US for about 18 months now and
some riders have thus used it through two winters. I've heard several
complaints about the Ergomo (incuding the fact that replacing a worn-out
bottom bracket now becomes a several hundred dollar job) but water damage
doesn't appear to be one of them. Early versions of the Power Tap were
notorious for being unusable in anything worse than a heavy dew--current
versions are much better but get data dropouts whenever you pass by a high
voltage line. Calibration of the SRM Amateur (which only has two strain
gages) appears to depend on the orientation of the crank (i.e., whether
the crank was horizontal or vertical when you test it). Some SRM Pro
models got sent out with bad epoxy that resulted in calibration changing
over time. The Polar S710 chain speed-and-tension system is sensitive to
chainring-cog combinations (see
http://mywebpage.netscape.com/rechung/wattage/testing/testprotocol.html
for an especially bad example).

 

[Mike Kruger]

"Maggie" <[email protected]> wrote in message
news:[email protected]...
>
> [email protected] wrote:
<< a bunch of stuff >>
>
> Are you a walking encyclopedia of bicycle knowledge?
> Come mantenete tutto il questo nella vostra esplosione capa
del
> withoug?
> Going to Italia next year...gotta practice.
> Maggie
>
Jobst is more like a pedaling encyclopedia.
For lots more info, see the FAQ's to the bicycle newsgroups
which he wrote:
http://www.sheldonbrown.com/brandt/

 

[Weisse Luft]

"Fiddly" describing the Polar might be due to the wide scope of bicycle frames which affect its application. On my Cannondale, it has provided great data save the times I have accidently disturbed the ream mounted speed sensor. The last time was during a flat fix and the sensor was too close to the wheel, making the speed read twice actual.

Measuring torque on the rear wheel seems even more "fiddly" to me due to the rotation. What would be better would be reaction torque or the compression of the right chain stay. Bending would have to be accounted but accurate compression measurement would indicate chain tension. Knowing chain speed via a Polar type sensor or crank speed and chainring position is easily done.

 

[bbaka]

Robert Chung wrote:
> bbaka wrote:
>
>
>>That would get you the power to the rear wheel, which may not be what
>>someone wants to measure. Personal power before bike losses would be my
>>idea for training information.
>
>
> Drivetrain losses aren't all that high. Here's a comparison of the SRM and
> Power Tap (and the Polar) on the same bike:
>
> http://mywebpage.netscape.com/rechung/wattage/rosetta/rosetta.html

That link is broken, at least for now.
>
>
>>Power at the wheel usually equals speed.
>
>
> No.
>
>
Really? So you are implying that more power reduces your speed? I think
we were talking about level ground road biking with no wind. More power
equals more speed in this universe. Negative power is possible with the
brakes and that makes heat, which, again, is power.

Please qualify your blanket 'No.'

Bill Baka

 

[bbaka]

Weisse Luft wrote:
> "Fiddly" describing the Polar might be due to the wide scope of bicycle
> frames which affect its application. On my Cannondale, it has provided
> great data save the times I have accidently disturbed the ream mounted
> speed sensor. The last time was during a flat fix and the sensor was
> too close to the wheel, making the speed read twice actual.

That is most likely a magneto-electric effect causing the sensor to be
over stimulated and to have a 'return to zero' rebound and the echo is
picked up as a signal. A minimal correction of the programming ( a few
lines of code) would fix that but that is just my electronics background
talking.
>
> Measuring torque on the rear wheel seems even more "fiddly" to me due
> to the rotation. What would be better would be reaction torque or the
> compression of the right chain stay. Bending would have to be
> accounted but accurate compression measurement would indicate chain
> tension. Knowing chain speed via a Polar type sensor or crank speed
> and chainring position is easily done.
>
>
Chain speed is the easy one and can be done optically for non contact.
Torque must be corrected to know what gear you are in and frame flex is
not the best way to go here what with bump flex, road noise, and many
more variables which add up. Just moving your weight from sitting up and
going 'no hands' would make a fairly big variable.

Bill Baka

 

[bbaka]

[email protected] wrote:
> Robert Chung writes:
>
>>http://mywebpage.netscape.com/rechung/wattage/ergomo/ergomo-pt.html
>
>
I looked at the graph shown and it looks more like a scatter plot than a
power plot of any sort. It is sure not something I would base my
training on, were I training. All that it is labeled to show up is
variance, but from what?

> I'm still not convinced the mechanism is reliable and will not get
> contaminated by dry dirt, aside from rain and road splash. For singe
> riders, this is a technically manageable measurement task but where it
> might do more good is on tandems where balancing effort is one of the
> difficulties in such riding. For tandem riders, quantified power is
> not so much a problem as is effort. The two riders, not in competition
> with anyone cannot easily determine how much effort each is exerting.
>
> The measure could easily be determined by riding at maximum output and
> speed and normalizing that effort as 100% and then having a percentage
> readout of both riders on each handlebar to help assess what ones fair
> share of effort should be. I believe this would be a boon to tandem
> riders who currently have only indirect ways of knowing which of the
> two is propelling the bicycle. This is a more complicated task than
> power meters on a single bicycle but it would have a long term
> practical value.
>
> [email protected]

Regarding tandems, the only use I have seen mentioned here is when the
stronger spouse wants to take her husband along on a 50 mile ride and
she carries the load when he is winded. Organized tandem racing might
have an application for the above logic, but in marital rides it might
cause more disharmony than intended. Scientific evaluation is good but
not healthy to put between a man and wife, especially if the wife shows
70% of the average power for a ride or vice versa. Some of the graphs I
have seen do show that a human is good for more than a horsepower but
only for a short burst.
Happy riding.
Bill Baka

 

[Robert Chung]

bbaka wrote:
> Robert Chung wrote:

>> Drivetrain losses aren't all that high. Here's a comparison of the SRM
>> and Power Tap (and the Polar) on the same bike:
>>
>> http://mywebpage.netscape.com/rechung/wattage/rosetta/rosetta.html
>
> That link is broken, at least for now.

Sigh. Nope, the link's not broken; yes, it's for one of those freebie
sites that's (ahem) underpowered. Usually, but not always, when you get a
"page not found" you can hit the reload current page button and it will
appear.

>>> Power at the wheel usually equals speed.
>>
>> No.
>>
> Really? So you are implying that more power reduces your speed? I think
> we were talking about level ground road biking with no wind. More power
> equals more speed in this universe. Negative power is possible with the
> brakes and that makes heat, which, again, is power.
>
> Please qualify your blanket 'No.'

In my universe, but perhaps not yours, roads aren't flat, the winds do
blow, speeds aren't constant, and position changes. We're talking about
on-bike power measuring devices. Why would you need such a thing if power
equals speed? All you'd need is a speedometer.

 

[Robert Chung]

bbaka wrote:
> Torque must be corrected to know what gear you are in

Not if you have wheel speed.

 

[Robert Chung]

bbaka wrote:
> [email protected] wrote:
>> Robert Chung writes:
>>
>>> http://mywebpage.netscape.com/rechung/wattage/ergomo/ergomo-pt.html
>>
> I looked at the graph shown and it looks more like a scatter plot than a
> power plot of any sort. It is sure not something I would base my
> training on, were I training. All that it is labeled to show up is
> variance, but from what?

That page compares measurement variation between the Ergomo and the PT so
it addresses Jobst's scepticism about data quality from a BB-based system.
The Ergomo and the PT produce pretty similar power numbers so if you think
that one system is suitable for power-based training, you might think the
other would be, too--at least, from a data quality perspective. These
comparisons don't take into account reliability, usability, features, or
cost; they only look at comparative data quality.

 

[bbaka]

Robert Chung wrote:
> bbaka wrote:
>
>>Robert Chung wrote:
>
>
>>>Drivetrain losses aren't all that high. Here's a comparison of the SRM
>>>and Power Tap (and the Polar) on the same bike:
>>>
>>>http://mywebpage.netscape.com/rechung/wattage/rosetta/rosetta.html
>>
>>That link is broken, at least for now.
>
>
> Sigh. Nope, the link's not broken; yes, it's for one of those freebie
> sites that's (ahem) underpowered. Usually, but not always, when you get a
> "page not found" you can hit the reload current page button and it will
> appear.
>
>
>>>>Power at the wheel usually equals speed.
>>>
>>>No.
>>>
>>
>>Really? So you are implying that more power reduces your speed? I think
>>we were talking about level ground road biking with no wind. More power
>>equals more speed in this universe. Negative power is possible with the
>>brakes and that makes heat, which, again, is power.
>>
>>Please qualify your blanket 'No.'
>
>
> In my universe, but perhaps not yours, roads aren't flat, the winds do
> blow, speeds aren't constant, and position changes. We're talking about
> on-bike power measuring devices. Why would you need such a thing if power
> equals speed? All you'd need is a speedometer.
>
>
I haven't seen a mention that this was just for indoor use and have seen
a graph of power over a trip, so we need to be all talking about indoor
or outdoor. Indoor is simple to put on a trainer so if that is the
direction of the discussion, what is the big deal? How many people train
indoors anyway???
Bill Baka

 

[bbaka]

Robert Chung wrote:
> bbaka wrote:
>
>>Torque must be corrected to know what gear you are in
>
>
> Not if you have wheel speed.
>
>
Even that has to be corrected according to the gear you are in unless
you are talking a single speed. This is not as simple as some would like
and this thread could go on for a while due to that.
Bill Baka

 

[Robert Chung]

bbaka wrote:
> Robert Chung wrote:
>> bbaka wrote:
>>
>>> Torque must be corrected to know what gear you are in
>>
>> Not if you have wheel speed.
>>
> Even that has to be corrected according to the gear you are in unless
> you are talking a single speed. This is not as simple as some would like
> and this thread could go on for a while due to that.

The Power Tap calculates power by using torque and angular velocity at the
rear hub. The SRM uses torque and angular velocity at the crank. The Polar
uses chainspeed and chain tension. None of these devices needs to know
gear ratios.

 

[Robert Chung]

Robert Chung wrote:
> bbaka wrote:
>> Robert Chung wrote:
>>> bbaka wrote:
>>>
>>>> Torque must be corrected to know what gear you are in
>>>
>>> Not if you have wheel speed.
>>>
>> Even that has to be corrected according to the gear you are in unless
>> you are talking a single speed. This is not as simple as some would
>> like and this thread could go on for a while due to that.
>
> The Power Tap calculates power by using torque and angular velocity at
> the rear hub. The SRM uses torque and angular velocity at the crank.
> The Polar uses chainspeed and chain tension. None of these devices
> needs to know gear ratios.

The Ergomo uses torque and angular velocity at the bottom bracket. It
doesn't need to know gear ratio either.

 

[Ryan Cousineau]

In article <[email protected]>, bbaka <[email protected]>
wrote:

> Robert Chung wrote:
> > bbaka wrote:
> >
> >>Robert Chung wrote:
> >
> >
> >>>Drivetrain losses aren't all that high. Here's a comparison of the SRM
> >>>and Power Tap (and the Polar) on the same bike:
> >>>
> >>>http://mywebpage.netscape.com/rechung/wattage/rosetta/rosetta.html
> >>
> >>That link is broken, at least for now.
> >
> >
> > Sigh. Nope, the link's not broken; yes, it's for one of those freebie
> > sites that's (ahem) underpowered. Usually, but not always, when you get a
> > "page not found" you can hit the reload current page button and it will
> > appear.
> >
> >
> >>>>Power at the wheel usually equals speed.
> >>>
> >>>No.
> >>>
> >>
> >>Really? So you are implying that more power reduces your speed? I think
> >>we were talking about level ground road biking with no wind. More power
> >>equals more speed in this universe. Negative power is possible with the
> >>brakes and that makes heat, which, again, is power.
> >>
> >>Please qualify your blanket 'No.'
> >
> >
> > In my universe, but perhaps not yours, roads aren't flat, the winds do
> > blow, speeds aren't constant, and position changes. We're talking about
> > on-bike power measuring devices. Why would you need such a thing if power
> > equals speed? All you'd need is a speedometer.
> >
> >
> I haven't seen a mention that this was just for indoor use and have seen
> a graph of power over a trip, so we need to be all talking about indoor
> or outdoor. Indoor is simple to put on a trainer so if that is the
> direction of the discussion, what is the big deal? How many people train
> indoors anyway???
> Bill Baka

Bill, I think you've now argued both sides of the argument. What Robert
is saying is that power, while a useful measure of a rider's ability, is
by no means the only factor in performance. Remember how we were talking
about the importance of aerodynamics? There are many cases where a rider
with superior power output over a TT has been beaten by a rider with
inferior power and better aerodynamics (through some combo of
positioning, equipment, and morphology).

Similarly, power to weight mattes more than power once the road turns
uphill, but even there aero matters more than you might think.

--
Ryan Cousineau, [email protected] http://www.wiredcola.com
Verus de parvis; verus de magnis.