Accuracy Ergomo power meter

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Hi,

I've been looking into some power meters lately,
and came across the Ergomo power meter. Looks
great at first (accurate, low price,...) but:
With brute calculation power I'm sure that the measured
torque is within 1.5% accuracy, but this does not
necessarily mean that's it has anything relation to your
power output.
The SRM measures torque between the crank
and bracket (via chainring), but the Ergomo measures
torque within the bracket axle which is the difference in force between your left crank and the right crank/chainring combination. Imagine this:
when only using your left leg, the torque within the axle
represents the torque between crank and bracket
on the right side, but as soon as you start using
your right leg (push or pull), it will change the torque
(hence power) even though your left leg is
doing the same amount of work.

I sure hope somebody can convince me that my theory
is wrong, otherwise the Ergomo is completely
useless as a power meter.

Thanks,
Jos.

Jos,
Have you seen the this page?

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

And Robert Chung did a bang-up job in his report on this page

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


Thought you might be interested.
H


Originally posted by josd
Hi,

I've been looking into some power meters lately,
and came across the Ergomo power meter. Looks
great at first (accurate, low price,...) but:
With brute calculation power I'm sure that the measured
torque is within 1.5% accuracy, but this does not
necessarily mean that's it has anything relation to your
power output.
The SRM measures torque between the crank
and bracket (via chainring), but the Ergomo measures
torque within the bracket axle which is the difference in force between your left crank and the right crank/chainring combination. Imagine this:
when only using your left leg, the torque within the axle
represents the torque between crank and bracket
on the right side, but as soon as you start using
your right leg (push or pull), it will change the torque
(hence power) even though your left leg is
doing the same amount of work.

I sure hope somebody can convince me that my theory
is wrong, otherwise the Ergomo is completely
useless as a power meter.

Thanks,
Jos.

Originally posted by josd
Hi,

I've been looking into some power meters lately,
and came across the Ergomo power meter. Looks
great at first (accurate, low price,...) but:
With brute calculation power I'm sure that the measured
torque is within 1.5% accuracy, but this does not
necessarily mean that's it has anything relation to your
power output.
The SRM measures torque between the crank
and bracket (via chainring), but the Ergomo measures
torque within the bracket axle which is the difference in force between your left crank and the right crank/chainring combination. Imagine this:
when only using your left leg, the torque within the axle
represents the torque between crank and bracket
on the right side, but as soon as you start using
your right leg (push or pull), it will change the torque
(hence power) even though your left leg is
doing the same amount of work.

I sure hope somebody can convince me that my theory
is wrong, otherwise the Ergomo is completely
useless as a power meter.

Thanks,
Jos.

Hello josd,

first I'm sorry for my bad englisch.
The ergomo power system was developed by a single engineer in Germany.
I have worked as an engineer for 2 years by this developer, it was my job to test the ergomo system under scientific aspects.

The problem of the ergomo is:

It' only possible to meassure your left!! side. The use of your right leg has absolut no effect to the ergomo meassurement system! (your right leg makes no torque!). This means, only your left leg is meassured.
If you use only your right leg, ergomo will shows 0W of power!!!
So, persons with different strong legs maybe have a problem!

I hope this could help you a little.

For further questions you can contact me.

Greetings from Germany,
Rübe.
;)

why the ergomo powermeter measure the power output only to the left side ?





Hello josd,

first I'm sorry for my bad englisch.
The ergomo power system was developed by a single engineer in Germany.
I have worked as an engineer for 2 years by this developer, it was my job to test the ergomo system under scientific aspects.

The problem of the ergomo is:

It' only possible to meassure your left!! side. The use of your right leg has absolut no effect to the ergomo meassurement system! (your right leg makes no torque!). This means, only your left leg is meassured.
If you use only your right leg, ergomo will shows 0W of power!!!
So, persons with different strong legs maybe have a problem!

I hope this could help you a little.

For further questions you can contact me.

Greetings from Germany,
Rübe.
;)

why the ergomo powermeter measure the power output only to the left side ?

because of the way that it's designed.

i think someone mentioned why above

ric

why the ergomo powermeter measure the power output only to the left side ?

The Ergomo measures the distortion or twisting of the BB spindle. To do this, the deflected, measured component must be between where you apply the force, i.e., the left pedal and crank arm, and the load which is resisting the force, i.e., the chain ring which is connected to the rear wheel. When you apply pressure to the right pedal/crank arm, there is no twisting moment imparted to the BB spindle. The twisting moment is only between the loaded left crank arm and the Chainring.

I have found the Ergomo to be quite repeatable, which I believe is of more importance to your training than accuracy. Having said that, it also shows good coorelation with tests that I have taken on CompuTrainers, and matches well with climbing numbers derived from Analytical Cycling.

Hope this has helped more than confused.

George