Psst.. wanna buy a cheap power meter?

[Rocket Man]

Nice spider from quarq but it's outside the price range that I had in mind. The strain guage technology that they use is expensive and difficult to manufacture reliably. I want to use a totally different measuring principle.

[AndreZA]

I need as much input as possible from as many people as possible - not just cyclists but everything from machinists to graphic designers to software developers to sales people. If we can get the right resources together we may be able to make a useful device. But I have no illusions about making any money from it.

 

In that case. I think the box should be red with the wording "Cheap Power Meter" in big friendly yellow letters ontop.

 

okay, got the coat. Where's my keys.

 

 

[word]

Dont forget, the Quarq ships without the computer so you either need to buy their computer (which is seriously sweet looking- http://www.quarq.us/Computers/Qranium.html) at $995 or else get an Edge 705.

 

Total cost - $2,190

[fandacious]

I've got a 705. I plan on getting the quark asap...

[Rocket Man]

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, 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?

[AndreZA]

I'm not at all interested but if you get it to work 100% and come in at about 70% of the cheapest system, not ibike or what that thing is called, you will be flooded with orders. No need for special wheels. Cannondale users can use it with their SI cranks and "al daai lekker dinge"

 

 

[Christie]

I don't know enough about the workings of PC hard drives to comment on the feasability of the idea. No commercial power meter does it this way, so if it can be made to work, you may be on to something. The structural design of the spider would be fairly simple, to do it right will cost a bit of money. 

I dont know about Aruba, but the SA market for powermeters is limited. Of the 24k odd people who ride the Argus, perhaps 2000 wonder what their power on the bike is. 1000 of those think power training is not for them, and  500 of those already have a power meter. So you are looking at 500 units in SA - it will be a challenge to make money out of 500 units (but it can be done.)

 

There may be a bigger international market, but some investment capital will be needed to patent & market the goody. To have a pro team like Barloworld use them would be ideal, but you will have to pay them some $ to use it.

[SwissVan]

 

What about a PM that uses a HRM and converts the Heart rate effort with the other variables that the HRM records into watts.

 

Q??

 

 

[bob_the_builder]

 

 

What about a PM that uses a HRM and converts the Heart rate effort with the other variables that the HRM records into watts.

 

Q??

 

 

 

Isn't that going the iBike (?) approach? Thing thingy that measures wind resistance and all, and is pretty much universally denounced as useless...

 

[Rocket Man]

The Aruba thing is just wishful thinking. I live in Jhb.

 

The display part of the powermeter is not that expensive as long as functions are limited to power specific readings - maybe a few R100 material cost. So I don't think it's necessary to compromise on the readout by trying to hook up with an existing device.

 

I was thinking of getting the mechanical parts cast in a stainless material with the right mechanical properties - can use lost wax process for small production run, high precision but inexpensive tooling.

 

ps Bob your box is full

Rocket Man2008-04-24 04:14:36

[Overlord]

Seems to me that you are on the ball here Rocket Man.

[bob_the_builder]

Cleared some space...

[jeremyd]

keep talking, we're listening

[Christie]

For small volume production, casting / forging is not cost effective.

 

CNC the spider from aluminium. Start with 6082T6.

[Rocket Man]

done some more calculations

 

It is possible to get the power meter (we need a name for this thing, ideas anyone?) to produce a "synthetic" output that does a linear conversion from power/10 to cadence - in other words, any standard cycle computer (cheap or expensive) that has a cadence input could read power but the reading would be ten times smaller than actual:

 

100W => 10rpm

1000W => 100rpm

 

a possibility...

[SwissVan]

 

What about a PM that uses a HRM and converts the Heart rate effort with the other variables that the HRM records into watts.

 

Q??

 

 

Isn't that going the iBike (?) approach? Thing thingy that measures wind resistance and all' date=' and is pretty much universally denounced as useless...
[/quote']

 

Yes the i bike thingy was a good idea but (i believe and stand to be corrected) relys on the measurement of airflow, which as we can be rather iffy.

 

What I was suggesting was not to measure airflow but to rather use the effort as recorded on a hrm and convert this to watts.

Power measurement and recording is obviously more accurate by the use of strain gauges or other mechanical devices that react in relation to the "power" appllied, but they are not cheap especially when you try to fit them onto weight concious bicycles.

 

Therefore I was wondering about a conversion factor being incorporated into a HRM software using the already vast amount of power VS heart data that has been gathered over the last few years.

 

Granted it might not be 100% accurate (how do you know for sure your current power device is 100% correct all the time), but as long as it remains consistent, this would be cheaper than the available options of power measuring devices.