Bicycle crankarm having a stress/strain detector for a torque meter or a power meter, and methods for manufacturing and using the crankarm
A bicycle crankarm the bicycle transmission side that has a main body length measured along a length from a crankset's crankarm rotation axis to a pedal axis. The crankarm has at least one stress/strain detector oriented along the length direction at a fixed distance, measured from the center of the stress/strain detector to the rotation axis of the crankarm, such that the ratio of the distance and the length is in the range between 0.45-0.65.
1. A bicycle crankarm for mounting on a bicycle transmission side, comprising a main body having a length (Lp) measured along a length direction (L) from a rotation axis (X) to a pedal axis (Y 1 ) of the crankarm, said crankarm having at least one stress/strain detector for a torque meter or a power meter, oriented along the length direction (L),
wherein said at least one detector is fixed at a distance (Do), measured from a center of said at least one stress/strain detector to the rotation axis (X) of the crankarm, such that a ratio between said distance (Do) and said length (Lp) is in a range between 0.45-0.65.
2. The bicycle crankarm according to claim 1 , wherein said ratio is in the range between 0.48-0.62.
3. The bicycle crankarm according to claim 2 , wherein said ratio is in the range between 0.50-0.60.
4. The bicycle crankarm according to claim 3 , wherein said ratio is in the range between 0.52-0.58.
5. The bicycle crankarm according to claim 1 , wherein the crankarm is made at least in part of composite material comprising structural fiber incorporated in a polymeric matrix.
6. The bicycle crankarm according to claim 5 , wherein said at least one detector is integrated in said crankarm.
7. The bicycle crankarm according to claim 5 , wherein said at least one detector is positioned on a first face of the crankarm, and comprising at least one second detector arranged on a second face of the crankarm opposite said first face.
8. The bicycle crankarm according to claim 5 , further comprising at least one cavity, and said at least one detector is on an inner face of the cavity.
9. The bicycle crankarm according to claim 5 , further comprising a core, wherein said at least one detector is arranged between the core and the composite material.
10. The bicycle crankarm according to claim 9 , wherein said core has at least one recess, and said at least one detector is arranged in said at least one recess.
11. The bicycle crankarm according to claim 1 , wherein said at least one stress/strain detector is at least one strain gage and a length ratio (Lr) of a length (Le) of the at least one strain gage over the length (Lp) of the main body of the crank arm is at least 1% and no greater than 15%.
12. The bicycle crankarm according to claim 11 , wherein the length ratio (Lr) is at least 2% and no greater than 13%.
13. The bicycle crankarm according to claim 11 , wherein the length ratio (Lr) is at least 3% and no greater than 11.6%.
14. The bicycle crankarm according to claim 11 , wherein the length ratio (Lr) is at least 5.7% and no greater than 9%.
15. The bicycle crankarm according to claim 11 , wherein the length ratio (Lr) is at least 6% and no greater than 8%.
16. The bicycle crankarm according to claim 11 , wherein the length ratio (Lr) is 7%.
17. A bicycle crankset comprising a bottom bracket spindle, a first crankarm on the transmission side according to claim 1 , and a second crankarm on the side opposite to the transmission side.
18. A method for detecting pedaling torque or power applied to a crankarm of a bicycle configured for mounting on a bicycle transmission side, the method comprising the steps of:
a) providing a crankarm configured for mounting on the transmission side that has a main body with a length (Lp) measured along a length direction (L) extending from a rotation axis (X) to a pedal axis (Y 1 ) of the crankarm; and
b) fixing at least one stress/strain detector for a torque meter or a power meter at a distance (Do), measured from the center of said stress/strain detector to the rotation axis (X) of the crankarm, such that a ratio between said distance (Do) and said length (Lp) is in a range between 0.45-0.65.