Low Cost PowerMeter for cycling trainers

[George]

Design of low cost powermeter required for cyclers. I need some help
on ideas of various methods to measure power output from a cycler on a
bicycle. The current power meters in the market are Power-Tap, SRM,
Polar and CompuTrainer etc. These however are too expensive in the
market and I'm required to design a similar device (powermeter).
Current methods are measuring deformation force of crank, Measurements
of tension in chain and rotation of hub. I'm thinking of measuring
force exerted on both peddles but I don't know if this would be the
best idea. Ps. Precision also needs to be taken into consideration.

 

[JeffM]

ideas...to measure power output from a cycler on a bicycle.

George

http://www.google.com/images?q=prony-brake+tpub

 

[Bob Monsen]

Design of low cost powermeter required for cyclers. I need some help
on ideas of various methods to measure power output from a cycler on a
bicycle. The current power meters in the market are Power-Tap, SRM,
Polar and CompuTrainer etc. These however are too expensive in the
market and I'm required to design a similar device (powermeter).
Current methods are measuring deformation force of crank, Measurements
of tension in chain and rotation of hub. I'm thinking of measuring
force exerted on both peddles but I don't know if this would be the
best idea. Ps. Precision also needs to be taken into consideration.

What about when somebody stands on the pedals? Pedal force isn't going
to be such a good measure.

I've seen altimeters for bikes; seems like you could do a simple power
meter based on work, by adding the actual power on the system (ie, mass
times change in height) to a factor that adds in drag from wind, road,
and mechanical linkages (which is probably close to linear with
velocity.) Using GPS might make it a bit more accurate than pressure
altitude, since you only care about differences, not absolute altitudes.

However, calibration will be required, such as entering total mass, drag
coefficients, and that sort of thing. It might be possible to auto
configure the main drag coefficients using terminal velocity on a glide.
At terminal velocity, the power going into drag equals the power being
obtained by a decrease in altitude.

--
Regards,
Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
Thomas Henry Huxley, 1877

 

[Adrian Jansen]

What about when somebody stands on the pedals? Pedal force isn't going
to be such a good measure.

I've seen altimeters for bikes; seems like you could do a simple power
meter based on work, by adding the actual power on the system (ie, mass
times change in height) to a factor that adds in drag from wind, road,
and mechanical linkages (which is probably close to linear with
velocity.) Using GPS might make it a bit more accurate than pressure
altitude, since you only care about differences, not absolute altitudes.

However, calibration will be required, such as entering total mass, drag
coefficients, and that sort of thing. It might be possible to auto
configure the main drag coefficients using terminal velocity on a glide.
At terminal velocity, the power going into drag equals the power being
obtained by a decrease in altitude.

Measuring the real force is going to be a *lot* better than trying to
estimate aerodynamic drag. Drag is approximately a * v^2 + b*v + c
where a,b,c are set by the geometry. But on a bike the geometry is
nowhere near constant - standing up / sitting upright / bent over in
full racing position / clothing all make a huge difference. To say
nothing of trying to estimate the wind effects on the actual velocity.


--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.

 

[Rich Grise]

What about when somebody stands on the pedals? Pedal force isn't going
to be such a good measure.

I've seen altimeters for bikes; seems like you could do a simple power
meter based on work, by adding the actual power on the system (ie, mass
times change in height) to a factor that adds in drag from wind, road,
and mechanical linkages (which is probably close to linear with
velocity.) Using GPS might make it a bit more accurate than pressure
altitude, since you only care about differences, not absolute altitudes.

However, calibration will be required, such as entering total mass, drag
coefficients, and that sort of thing. It might be possible to auto
configure the main drag coefficients using terminal velocity on a glide.
At terminal velocity, the power going into drag equals the power being
obtained by a decrease in altitude.

Isn't there some kind of transducer that can measure the torque being
applied to a shaft? X ft-lb * S mph = power, or something like that,
isn't it? Just put one of those on the hub, at the sprocket. Measuring
RPM is trivial.

Thanks,
Rich

 

[dalai lamah]

Un bel giorno Bob Monsen digitò:

What about when somebody stands on the pedals? Pedal force isn't going
to be such a good measure.

Why? I don't see the difference.