how do they actaully install a power meter in a crank arm?
09-07-20, 07:52 PM
#1
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how do they actaully install a power meter in a crank arm?
So were "discussing" the value of a power meter with the group and somebody asked how do crank arm power meters actually work? How do they actually install them? Do they cut a hole in the crank arm per say and weaken the crank to install the load cell? I don't own a crank meter but it got me wondering how they actually work. I tried to search for an install of the actual meter and I couldn't find anything so hoping somebody here can give me some insight?
might be a dumb question but just wondering how its installed to the crank
might be a dumb question but just wondering how its installed to the crank
09-08-20, 01:40 AM
#2
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Very simplified explanation:
A strain gauge is adhered to the crankarm. With a known weight on it to calibrate, the strain gauge can measure how much the crank is flexing and figure the torque.
Actually, probably two strain gauges are used to measure bending since a single one could be confused by just stretch. And there's something there to measure cadence- either an encoder or accelerometer- since power is torque times angular velocity.
So there is no drilling into the crankarm. The strain gauges are on the surface of the cranks.
A strain gauge is adhered to the crankarm. With a known weight on it to calibrate, the strain gauge can measure how much the crank is flexing and figure the torque.
Actually, probably two strain gauges are used to measure bending since a single one could be confused by just stretch. And there's something there to measure cadence- either an encoder or accelerometer- since power is torque times angular velocity.
So there is no drilling into the crankarm. The strain gauges are on the surface of the cranks.
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09-08-20, 07:19 AM
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really strong adhesive. seriously, thats it. i talked with 4iiii about their factory install. only some cranks work- they need to be smooth on the inside of the arm for there to be enough surface area to set the power meter.
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09-08-20, 08:17 AM
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thanks for the explanation! I was curious about compromising the strength of the crank epically carbon.
good to know....tech, so over my head!
good to know....tech, so over my head!
09-08-20, 08:24 AM
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One crank I was interested in (grx 600) has a groove in the back, so no joy on power meters. Workaround would be to buy a better crankarm from the power meter company. So far it's only available through factory install though
