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Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

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Old 01-15-09, 12:22 AM
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Ok you laughing stock. I decided to spend few minutes thinking about possible design for cheapo power-meter.

1. I'd build it into bike pedals.
2. I'd use load sensors that are being used in digital scales. They cost peanuts while providing good accuracy.
3. Each pedal would have 2 sensors measuring pressure orthogonally so that the resulting force vector could be calculate later by cycle computer.
4. Each pedal would have built in single Ant sport unit to transmit data from sensors and a small battery to power it up.
5. I did not do any research for Ant capable head unit but since the existing ones cost about $100 retail consider this as a price ceiling.

If made nicely I think that the whole thing should be around $300-$500 retail.

Pros: Continuous measuring of force for each leg independently.
Cons. Need to manufacture own pedals.

Now rip it apart
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Old 01-15-09, 12:31 AM
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1. Someone is already working on it... I don't remember the name but it's been vaporware for a while
2. I'm not sure that would handle torque from different angles. Pulling up? Do you have any idea how much force goes through the pedal? On my ride today my max torque was 1800lb-in... that's 264lbs of force. I don't know if those kinds of sensors can handle that much load. I know my kitchen scale only goes up to a few pounds...
4. I don't think the Garmin would be able to handle to signals... I'm not sure if that means the ANT+ protocol can't handle it though. You may need to combine signals from both pedals and retransmit it. Also, power is torque x cadence so you also need something that can measure cadence.
5. 100??? What ANT head unit are you looking at that is $100?
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Old 01-15-09, 12:43 AM
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Originally Posted by umd
1. Someone is already working on it... I don't remember the name but it's been vaporware for a while
2. I'm not sure that would handle torque from different angles. Pulling up? Do you have any idea how much force goes through the pedal? On my ride today my max torque was 1800lb-in... that's 264lbs of force. I don't know if those kinds of sensors can handle that much load. I know my kitchen scale only goes up to a few pounds...
4. I don't think the Garmin would be able to handle to signals... I'm not sure if that means the ANT+ protocol can't handle it though. You may need to combine signals from both pedals and retransmit it. Also, power is torque x cadence so you also need something that can measure cadence.
5. 100??? What ANT head unit are you looking at that is $100?
Well as I said I spent few minutes (less then 5 I think) so I have no idea if someone is working on it.

2. Orthogonal is the keyword here, you measure vertical/horisontal push/pull, from that data you can extract true force vector. 264 pounds is nothing. Those can handle much higher loads.

4. Garmin will not be able to handle those directly. I was talking about having your own head unit. If one wants to use Garmin then either Garmin's firmware has to be updated, or extra ant unit with small controller has to be added to convert all signals to a single power value. It is easier I think to produce one's own head unit but yes communicating to Garmin would have great advantages since it does much more then just measure power and it looks to me that Garmin is well on it's way to become bike computer of choice for people with money.
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Old 01-15-09, 12:56 AM
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Originally Posted by umd
1. Someone is already working on it... I don't remember the name but it's been vaporware for a while
Found it Here

Applied force

This method monitors the forces applied to the pedal by the cyclist's foot. Sensors in the shoe or pedal measure the forces as the cranks rotate, and calculate the power based on the magnitude and direction of the applied force, and the angular velocity of the crank. Advantages of this technique include independent measurement of power for each leg, measurement of efficiency of pedaling style, and (depending on placement of sensors) avoiding the need to replace bike components. No commercial system using this technique is available yet for use outside a laboratory
So this could be something interesting, not for me though ...
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Old 01-15-09, 08:45 AM
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Originally Posted by kostyap
Found it Here



So this could be something interesting, not for me though ...
Isn't that exactly what you are trying to do?

btw, this and this are what I was thinking of...
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Old 01-15-09, 09:02 AM
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If Brim Brothers can make it work, it would be a great solution for multiple bikes, even tandems.

And build it into shoes, not pedals, and it's even more versatile.

Biggest problem I see is the up force, but perhaps you could compensate for that in the calculations.
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Old 01-15-09, 09:07 AM
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+1 - nothing really to add, but there are definitely people who have been experimenting. Doesn't mean there is no room to look into it further.
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Old 01-15-09, 09:32 AM
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The concepts of using the sensors in the shoe inserts (not a great concept IMHO) and in the pedals have already been patented.
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Old 01-15-09, 07:42 PM
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Originally Posted by umd
Isn't that exactly what you are trying to do?

btw, this and this are what I was thinking of...
LOL. Nice links "Not for me" part means that I just did some mental exercise but I am not really interested in making powermeters
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Old 01-15-09, 07:47 PM
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Originally Posted by umd
Isn't that exactly what you are trying to do?
and this are what I was thinking of...
"We would like to take this opportunity to thank all our customers who placed Pre-Orders"

wonder if their customers got refunds
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