Strain gage based dyno numbers

[Daniel R Burk]

Michael:

Here at Michigan Scientific where I work, the guys have calibrated their
axle torque sensors by literally strapping the rear bumper of the truck 
to a tree.  They then bring up the revs until just before the tires 
break, (or the tree roots give out!!) and measure the amount of linear 
tension on the cable.  They then can assume that the bulk of the tension 
results from the torque of the wheels as applied to the pavement at the 
contact patch.  Measure the wheel radius from contact patch to center of 
the axle, and viola!  --- Rear wheel torque.

If you are careful with your tansducer design, and insure there is no 
significant bending of your spring (aka surface to which you bond your 
strain gages)  then you can assume that the applied force is linear until 
your theoretical full scale cal value.  You can then measure torque much 
higher than that which you applied to your hapless Boxelder tree.  ;)