Psst.. wanna buy a cheap power meter?

[Rocket Man]

@ bob: The plan seems to be just replacing the spider' date=' so the chain alignment & Q-factor will stay the same as the original crankset's[/quote']

 

Actually, it's simpler than that. Leave the spider alone. Take the rings off. Bolt the power adaptor piece onto the spider. There is a new set of holes in the adaptor (rotated from the spider holes) onto which the rings are bolted. The ring alignment stays exactly the same so no adjustment is necessary to the chain.

[shade]

 

Names so far:

cyclowatt - jeremyd

Power Hubber - RM

SpiderHub- Shade

shade2008-04-24 05:36:14

[Christie]

@bob: You're right! bolting a disk onto the spider will stuff up the chainline & front deraileur's shifting, wont work!

 

I was thinking the product would more along the lines of something like the Quark, also a replacement spider. Did not read properly

[widget]

I was lost a long time ago on page one.

 

.............but just for interest, if you intend production runs, you will need tooling, and thats hideously expensive.

 

I recently had a tool made in China for a plastic componant with our name on it, around $5000.00 per tooling.

 

SA quote - R60,000.00 for the same thing, - obviously it depends on the work, but tooling costs are still a substantial investment.

 

[bob_the_builder]

 

a plastic componant with our name on it' date='

 

[/quote']

 

Come on! You didn't seriously make a widget with widget written on it

 

[widget]

a plastic componant with our name on it' date='

 

[/quote']

Come on! You didn't seriously make a widget with widget written on it

 

 - sharp today eh?

[Rocket Man]

Easy gang. Let's just assume that money is no problem for now. I estimate that it would take between R200k and R500k to go into proper production so don't even worry about it.

 

On the picture below the black area is where the power adaptor sits (but in between all the arms of the spider). The red arrow shows how you rotate the rings into the new hole positions.

 

[bob_the_builder]

Cool, RM, I'm with you now. I still like the idea.

[The Hawk CT]

For the non-believers out there I'll tell you how it works - I believe in open source!

 

There are two elements to a power meter - the power sensor and the display. The hard part is the power sensor. The display is more about graphic design than cutting edge technology.

 

The power sensor itself has two critical components:

1. A mechanical device that bends or distorts when loaded.

2. A measuring device that determines how much bending has taken place.

 

For the first component' date=' the SRM uses metal beams that bend when you push on the cranks. This bending is measured by strain guages glued onto the beams.

 

In the proposed design the mechanical system will also use bending beams but engineered in a rather unusual configuration so that it fits onto a standard spider.

 

The measuring device that detects the bending of the beams will use technology derived from the magnetic media used to store data on a hard drive. Simply put, as the beam bends two magnetic pickups will read different data streams coming from two circular "tracks" attached to the bending parts. For those with some electronics knowledge, the "beat pattern" from the data stream changes phase as load is applied.

 

Simple ne?

[/quote']

 

you make it sound like you can make it really cheaply...??? R3k for teh hubbers with a life maitanace contract???

[The Hawk CT]

Names so far:

cyclowatt - jeremyd

Power Hubber - RM
SpiderHub- Shade

PowerRoc   ... from RocMan - DaHawk

The Hawk CT2008-04-24 11:56:49

[mrmed]

I'll machine the sample parts you need, if you make the drawings / solid models.

[PEEZ@]

Do we have any idea on price yet?

[Slowbee]

 feeling ignoramus .. would love to help but dont know how ...

 

i'll buy the coffee?

[bruce]

For the non-believers out there I'll tell you how it works - I believe in open source!

 

There are two elements to a power meter - the power sensor and the display. The hard part is the power sensor. The display is more about graphic design than cutting edge technology.

 

The power sensor itself has two critical components:

1. A mechanical device that bends or distorts when loaded.

2. A measuring device that determines how much bending has taken place.

 

For the first component' date=' the SRM uses metal beams that bend when you push on the cranks. This bending is measured by strain guages glued onto the beams.

 

In the proposed design the mechanical system will also use bending beams but engineered in a rather unusual configuration so that it fits onto a standard spider.

 

The measuring device that detects the bending of the beams will use technology derived from the magnetic media used to store data on a hard drive. Simply put, as the beam bends two magnetic pickups will read different data streams coming from two circular "tracks" attached to the bending parts. For those with some electronics knowledge, the "beat pattern" from the data stream changes phase as load is applied.

 

Simple ne?

[/quote']

 

This is fundamentally the same way that the Ergomo works, except the Ergomo uses perforated light disc's on each side of the BB axle to measure the distortion of the axle due to torque applies by the left leg.  The phase difference between the signals from the two discs is used to calculate the torsion of the axle.

 

One thing to note, whatever technology you use, you must provide the feature to set the zero torque point because temperature changes will cause the zero offset to change.

 

So, there is no doubt that your idea can fundamentally work.  Knowing a little bit about what is going on in the power meter world, I'd recommend integrating the Ant+ system then you don't have to worry about a CPU for the unit.  Even if you don't want to use a Garmin or some such as the CPU and want to build a cheap CPU, using Ant+ is still a good idea because there is a market for a cheap CPU for Ant+ power sensors (not everybody wants all the functionality of a Garmin/Qranium), plus you get speed sensor and HR sensors as part of the system and don't have to worry about those issues as well.

 

One of the benefits of this design is that you could build a sensor for shimano, campag, MTB, and compact and then not have the problem that SRM and Quarq have with BB compatibility - particularly new BB systems like on the Trek and the Scott.

 

Some featured that would be useful in the CPU:

USB I/O plus charging.

SD memory, or whatever popular format.  But it is important to be able to take data off the device without downloading to a computer for multi day rides etc.

BTW, physiologists have been desperate for a power meter that provides access to a detailed pedal stroke pattern of torque application.  There is much debate as to whether a smoother pedal stroke is actually more efficient.  Your PM still won't be able to accurately show left/right leg imbalances and torque patterns because it is measure the net torque applied and not the individual torque applied by each leg.

bruce2008-04-24 12:37:21

[101%]

I still believe research should try move away from the cranks and bottom bracket and start looking into developing some sort of meter that would either fit into the pedal or the cleat

That would be the most accurate way of measuring power in each leg individually

 

my 2C.

 

 

[bruce]

I still believe research should try move away from the cranks and bottom bracket and start looking into developing some sort of meter that would either fit into the pedal or the cleat

That would be the most accurate way of measuring power in each leg individually

 

my 2C.

 

 

 

Like this one: http://www.freepatentsonline.com/y2007/0245835.html

 

Patent was filed in 2006.