When is that new power-measuring device arriving?



P

Paul Kossa

Guest
At last fall's bike show I heard that there is a new power device
coming out -- I thought they said in March, but apparently not --
that, while it only works on indoor trainers, it has the big advantage
of only costing $50 - $60. Anyone know about this?
 
In article <[email protected]>,
[email protected] (Paul Kossa) wrote:

> At last fall's bike show I heard that there is a new power device
> coming out -- I thought they said in March, but apparently not --
> that, while it only works on indoor trainers, it has the big advantage
> of only costing $50 - $60. Anyone know about this?

No, but a power measurer that costs about a tenth of current systems
would be huge news. If you hear anything, let us know.

Right now, I think the sweet spot in cycling equipment would be to do a
logging HRM-cyclecomputer (like the Polar 520) for less than the couple
hundred dollars the Polar costs.

The current best deal in cycle computers that I know of is the Filzer
dB4LWc. I can't find any mention of it online yet, note even on Filzer's
site, but MEC had this computer, complete with wireless speed and wired
cadence sensing, for C$25.

--
Ryan Cousineau, [email protected] http://www.wiredcola.com
Verus de parvis; verus de magnis.
 
>Right now, I think the sweet spot in cycling equipment would be to do a
>logging HRM-cyclecomputer (like the Polar 520) for less than the couple
>hundred dollars the Polar costs.

The feedback I've seen from power meter users is that the Polar system
(which measures chain tension) is rather finicky.

Most seem to favor either hub based systems such as the Powertap or crank
based systems such as the SRM.

Unfortunately both are more $$$.


Chris Neary
[email protected]

"Science, freedom, beauty, adventure: what more could
you ask of life? Bicycling combined all the elements I
loved" - Adapted from a quotation by Charles Lindbergh
 
In article <[email protected]>,
Chris Neary <[email protected] > wrote:

> >Right now, I think the sweet spot in cycling equipment would be to do a
> >logging HRM-cyclecomputer (like the Polar 520) for less than the couple
> >hundred dollars the Polar costs.
>
> The feedback I've seen from power meter users is that the Polar system
> (which measures chain tension) is rather finicky.

I sorta changed the subject there: the Polar 7xx is the one with the
power meter option. Power measurement is a great option, but you can do
a lot with just heart rate logging. It just takes the burden off the
rider to try to get a handle on their performance while in the middle of
such distractions like racing.

> Most seem to favor either hub based systems such as the Powertap or crank
> based systems such as the SRM.
>
> Unfortunately both are more $$$.

What surprises me is that there doesn't seem to be much competition in
the logging computer market. Basically, if you want to download data
from your bike to your computer, the choices are Polar, SRM, or
Powertap. This despite the availability of sub-$100 HR cyclocomputers
and the aforementioned $25 cadence computer.

Maybe I'm naive about the costing, but it seems to me that adding a USB
interface chip and enough memory to hold a couple of hours of data to a
cheap HRM should be possible for $150 or less. I think I'll send an
e-mail to Filzer and Cateye....

--
Ryan Cousineau, [email protected] http://www.wiredcola.com
Verus de parvis; verus de magnis.
 
Ryan Cousineau wrote:
> In article <[email protected]>,
> Chris Neary <[email protected] > wrote:
>
>
>>>Right now, I think the sweet spot in cycling equipment would be to do a
>>>logging HRM-cyclecomputer (like the Polar 520) for less than the couple
>>>hundred dollars the Polar costs.
>>
>>The feedback I've seen from power meter users is that the Polar system
>>(which measures chain tension) is rather finicky.
>
>
> I sorta changed the subject there: the Polar 7xx is the one with the
> power meter option. Power measurement is a great option, but you can do
> a lot with just heart rate logging. It just takes the burden off the
> rider to try to get a handle on their performance while in the middle of
> such distractions like racing.
>
>
>>Most seem to favor either hub based systems such as the Powertap or crank
>>based systems such as the SRM.
>>
>>Unfortunately both are more $$$.
>
>
> What surprises me is that there doesn't seem to be much competition in
> the logging computer market. Basically, if you want to download data
> from your bike to your computer, the choices are Polar, SRM, or
> Powertap. This despite the availability of sub-$100 HR cyclocomputers
> and the aforementioned $25 cadence computer.
>
> Maybe I'm naive about the costing, but it seems to me that adding a USB
> interface chip and enough memory to hold a couple of hours of data to a
> cheap HRM should be possible for $150 or less. I think I'll send an
> e-mail to Filzer and Cateye....
>
I haven't seen enough of this to know for sure what has been tried but
power is going to work out to 2 things that can be measured. Linear
chain speed times tension averaged out over at least 10 seconds, so that
it would not matter what gear you were using or cadence. Coast pedaling
would show little or no power gain but could track RPM. The 10 second
average gets rid of the stroke by stroke nature of pedaling. The math
works but measuring the chain tension without power loss is a bit
tricky. Memory for logging is not a problem if you have looked at
digital camera memory lately. 512MB is under $100.00 so nearly free
compared to other such 'goodies'.
Bill Baka
 
Paul Kossa writes:

> At last fall's bike show I heard that there is a new power device
> coming out -- I thought they said in March, but apparently not --
> that, while it only works on indoor trainers, it has the big
> advantage of only costing $50 - $60. Anyone know about this?

Measuring power is a simple concept that is more illusive than it fist
appears. All it takes is a torsional strain gauge and tachometer in
the rear hub. The trouble is that driving torque varies widely during
each pedal stroke and varies in magnitude over such a wide range that
a sensor is difficult to build.

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.

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.

[email protected]
 
> 512MB is under $100.00 so nearly free compared to other such 'goodies'.

This is a very conservative statement. 512MB secure digital flash cards are
readily available for under $50.


Chris Neary
[email protected]

"Science, freedom, beauty, adventure: what more could
you ask of life? Bicycling combined all the elements I
loved" - Adapted from a quotation by Charles Lindbergh
 
Jobst 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.

This has been recently tried - see web site at -

http://www.ergomo-usa.com/sensor.html

My lbs guy Steve writes reviews of gear for a local bike magazine and says
the optical sensor in the bb is a clever idea but it only measures torsion
in one crank, and attempts to infer the power going into the other crank,
leaving the output readings open to question.

The Powertap hub is a bit heavy for use in a race. the Polar system is
fiddly and not always reliable. which leaves the SRM system the only
reasonably accurate on the bike power measurement at present - and as with
all unregulated monopolies, SRM price their system accordingly.

My reason for enquiring about this is that I recently re-built my ergo which
uses blades attached to the spokes of the driven wheel and a 7 sp Nexus
internally geared hub for resistance - in the re-building I asked Steve
about including some form of power measurement and we went through the
alternatives, all of which cost a lot for something you can get a rough
sense of from a simple cadence counter on the crank and recording how big a
gear you can push for an effort at a constant cadence. If you keep to a
given cadence, presumably reaching for a bigger gear indicates the training
is going well - and vice versa.

From the set up I describe would it be possible to calculate watts delivered
to the driven wheel ?

best, Andrew (remove the .x1 to reply)
 
Chris Neary wrote:
>>512MB is under $100.00 so nearly free compared to other such 'goodies'.
>
>
> This is a very conservative statement. 512MB secure digital flash cards are
> readily available for under $50.
>
>
> Chris Neary
> [email protected]
>
> "Science, freedom, beauty, adventure: what more could
> you ask of life? Bicycling combined all the elements I
> loved" - Adapted from a quotation by Charles Lindbergh

For once I am trying not to start a flame war of some sort because some
people might be happy to pay 100 and others can get lucky and find one
for maybe 25 dollars. Either way that is a lot of data to keep for a
bike ride, so you could keep your heart rate from pulse to pulse, speed,
power, wind, temp, and whatever else you can think of.

Happy Days,
Bill Baka
 
[email protected] wrote:
> Paul Kossa writes:
>
>
>>At last fall's bike show I heard that there is a new power device
>>coming out -- I thought they said in March, but apparently not --
>>that, while it only works on indoor trainers, it has the big
>>advantage of only costing $50 - $60. Anyone know about this?
>
>
> Measuring power is a simple concept that is more illusive than it fist
> appears. All it takes is a torsional strain gauge and tachometer in
> the rear hub.

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. Power at the wheel usually equals speed.

The trouble is that driving torque varies widely during
> each pedal stroke and varies in magnitude over such a wide range that
> a sensor is difficult to build.

That is where I came in with the multiple measurements averaged over a
reasonable time period, sort of like RMS power off of a 60 Hz power line
or arbitrary waveform. The math is not that different for electronics or
mechanical bicycles.
>
> 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.
>
> 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.
>
> [email protected]

I think it still boils down to chain speed times tension averaged out
with the RMS calculation. Even a passive speed/tension sensor would take
some efficiency out of the pedaling though due to having to run the
chain through a 3 wheeled guide/tension sensor. It would measure power
but at some cost in power so would it be accepted as a training only
device? Strain gages have a place but on a bike they would need signal
conditioning and probably a bit of DSP added to that, but they would
most likely pick up on other flexing phenomenon, making road noise into
power noise. Simple can work but may not please everyone and fancy can
work but to work really well fancy will cost a lot since this is not
high volume production.
KISS principle.
I hate that one, but it does prove to be true.
Bill Baka
 
Paul Kossa wrote:

> At last fall's bike show I heard that there is a new power device
> coming out -- I thought they said in March, but apparently not --
> that, while it only works on indoor trainers, it has the big advantage
> of only costing $50 - $60. Anyone know about this?

Well, putting it on a trainer would be a lot easier than on a bike. So I'm not
surprised if someone has come out with a cheap trainer unit.

Matt O.
 
Leo Lichtman writes:

> If you want to have any hope of measuring power on a bicycle, why
> not use the accepted method for automobiles--a dynamometer. Even on
> cars, where the space and weight restrictions are much looser, I
> have never heard of a power meter that can be read from the driver's
> seat on a car in a race.

That's because it does not matter. The engine got tested on a
dynamometer before installation in the car and not being humanly frail
and emotional, it will develop that same power at the same RPM in a
race. The bicyclist, in contrast, has an unpredictable power output
that varies with many parameters and durations. Besides, in a car,
power is easily measured at the output shaft of the engine during a
race if there were any merit to the concept.

> It seems to me that a stationary exercise bike setup could be fairly
> easily converted to measure power. You need to measure torque and
> RPM at the roller. By riding a stationary bike/dynamometer setup,
> you could find a relationship for YOURSELF, of heart rate vs power.
> This might vary, even for an individual, from day to day, and also
> for different states of fatigue. Still, that's a lot more than we
> know now.

As I mentioned, that isn't what the rider wants to know. Interesting
would be the power output in different gears on a hillclimb, since
torque and RPM don't have a fixed relationship for a human, especially
with a different duty cycle as occurs in a flat TT or a variable grade
hillclimb.

> Has this has ever been done?

Although this may reveal at what percentage of full power one is
riding, actual power is a derivative and not accurately determined by
heart rate.

[email protected]
 
bbaka wrote:

> I haven't seen enough of this to know for sure what has been tried but
> power is going to work out to 2 things that can be measured. Linear
> chain speed times tension

This is how the Polar S710 power unit measures it.
 
[email protected] wrote:
> 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
 
Andrew Price wrote:
> The Powertap hub is a bit heavy for use in a race. the Polar system is
> fiddly and not always reliable. which leaves the SRM system the only
> reasonably accurate on the bike power measurement at present

The Power Tap appears to be about as accurate as the SRM Pro model, and
more accurate than the SRM Amateur.

http://mywebpage.netscape.com/rechung/wattage
 
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

> Power at the wheel usually equals speed.

No.
 
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 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.

[email protected]
 
[email protected] wrote:
> 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 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.
>
> [email protected]

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
 
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