Strain Gage Placement

A project log for Human Power Output Measurement Device For Cycling

A training tool that provides real-time human power output and form feedback

valgusvalgus 08/09/2014 at 01:530 Comments

The gages are specified as having a max strain threshold of 2.5%.  I'll post some estimates for optimal placement on a 6061 Al crank arm (soon to be purchased in triplicates) given a peak applied force of 2000 N. I'll assume the typical cantilevered beam equations are adequate with an elliptical cross-section, and a factor of safety of 2. I'm a little worried this may dilute my low force readings, but I feel it is a good starting point given the risk of sensor delamination or premature failure. Worst, slow sensor drift that would give the appearance of proper function, but entirely wrong. Is that Type 1 error?

By Friday August 15 I should have these calculations done along with a more formal analysis done with NASTRAN. I'll model the cranks as soon as they arrive and run a FEA to guide my first go at sensor placement. Both estimate and analysis will hopefully corroborate each other and be a fun learning opportunity for working with NASTRAN.