This a torque meter for indoor free flight models. It's design is based largely on the Flite-Tork meter that was originally developed by Bill Gowen. This meter reads torque in inch/ounces.
UPDATED 11/24/17 I've refined a few of the parts, and added a version of the collar that works with 1/8" RC airplane wheel collars that you can find at a hobby shop.
To build the meter you need 1 of each printed part plus a second collar. You will also need the following components:
2 - M3 x 20 screws (mounting load cell)
3 - 1/8" stop collars (McMaster P/N 6432K17) or 1/8" RC airplane wheel collars
2 - 6-32 x 3/16" set screws (4-40 x 3/16 set screws if you're using wheel collars)
1 - 6-32 x 1-1/16" piece of threaded rod (4-40 if you're using wheel collars)
2 - 6-32 nuts (4-40 if you're using wheel collars)
1 - M4 fender washer (or washer of approximate 7/16" diameter)
1 - 2xAAA battery holder (McMaster P/N 7712K16)
1 - TBBSC 200g scale (Amazon)
1 - 1.75" long piece of 1/8" music wire or shaft (McMaster P/N 1257K83)
1 - Piece of music wire for hook
1 piece of 1/4" OD Rulon J bearing sliced in half (McMaster P/N 6377K48) or 1/4" OD x 1/8" ID Teflon tube
See this thread for details on assembly. The second torque meter in the thread details assembly of the current version.