Crankset based bicycle power measurement
The present application relates to an input torque measuring device for a drive train of a bicycle. The drive train includes a first crank arm and a second crank arm. An inboard end of each crank arm is rotatably mounted to the bicycle at a bottom bracket of the bicycle. At least one chain ring is configured to rotate a driven wheel of the bicycle. A spider is connected to the first crank arm adjacent the bottom bracket and extends out to the at least one chain ring. The spider is configured to transmit force applied to the crank arms directly to the at least one chain ring. The spider may include a plurality of sensors configured to respond to the force applied by the spider to the at least one chain ring. The sensors produce an electronic signal relative to the force transmitted by the spider to the at least one chain ring and a processor configured to receive the electronic signals from each sensor of the spider.
1. An input torque measuring device for a drive train of a bicycle having at least one chainring, comprising:
a spider directly connected to the at least one chainring, the spider configured to transmit force to the at least one chainring;
a plurality of sensors disposed on the spider, the plurality of sensors configured to respond to force applied to the spider and transmitted to the at least one chainring, the plurality of sensors configured to produce an electronic signal relative to the force transmitted by the spider, the plurality of sensors oriented to be generally parallel to a plane of the at least one chainring; and
an electronic circuit configured to receive the electronic signal and generate an output representative of the force transmitted by the spider parallel to the plane of the at least one chainring.
2. The input torque measuring device of claim 1 , wherein the spider includes one or more arms.
3. The input torque measuring device of claim 2 , wherein the plurality of sensors are distributed among the one or more arms.
4. The input torque measuring device of claim 2 , wherein each of the one or more arms includes one of the plurality of sensors.
5. The input torque measuring device of claim 2 , wherein each of the one or more arms is symmetrical about at least one axis.
6. The input torque measuring device of claim 2 , wherein the one or more arms is directly connected to the chainring.
7. The input torque measuring device of claim 2 , wherein each of the one or more arms has an outboard end, and the plurality of sensors are respectively positioned at the outboard ends.
8. The input torque measuring device of claim 2 , wherein each of the one or more arms includes an opposed pair of sensors.
9. The input torque measuring device of claim 2 , wherein each of the plurality of sensors is mounted to a shear web defined in each of the one or more arms.
10. The input torque measuring device of claim 9 , wherein each shear web includes a pair of perpendicularly arranged strain grids mounted on opposite sides of the shear web.
11. The input torque measuring device of claim 10 , wherein the shear web further includes an opening permitting electrical connection of the sensors on opposite sides of the shear web.
12. The input torque measuring device of claim 1 , wherein a majority of the plurality of sensors are oriented parallel to a plane of the at least one chainring.
13. The input torque measuring device of claim 1 , wherein all of the plurality of sensors are oriented parallel to a plane of the at least one chainring.
14. The input torque measuring device of claim 1 , wherein each of the plurality of sensors responds to a deflection of a portion of the spider when the force is transmitted from the spider to the at least one chainring.
15. The input torque measuring device of claim 1 wherein each of the plurality of sensors further comprises a pair of strain grids, the strain grids of each pair oriented perpendicular to each other.