Strain gages on the drive shaft for torque measurement

[Daniel R Burk]

In regards to the message about placing strain gages on the drive shaft:

There exist slip ring assemblies that allow one to gage up a drive shaft.
There is a spinning amplifier that is placed on the driveshaft to boost
the gain from the wheatstone bridge configuration strain gages. The slip
ring has remarkably low noise: Witness the fact that they are still 
widely used in automotive testing to gather wheel loading information.

Another method used to determine torque (as well as payload in trucks)
is to gage up the axle assembly.  The gages are placed on the axle 
housing where they measure the deformation caused by either truck 
payload, or torque from the engine.  I have heard engineers at my firm 
say that readings within 10 ft-lbs are possible.  

Don't just rule out slip rings by saying they are "complicated".  Most
modern slip rings use brushes on gold contacts, where the contacts 
are mounted on a spindle of only a quarter inch diameter.  The angular 
velocity is therefore very low.  Hence, brush noise is minimal.

--- Cheers,

		--Daniel Burk
['84 Trans Am WS6/L69]
	Instrumentation engineer at Michigan Scientific Corp.