Strain Gage Load Cell for Thrust Measurement

Posted on Feb 5, 2014

This web page presents details regarding the design of a strain gage based load cell that can be used, in conjunction with an electronic data acquisition (DAQ) system, for static thrust measurement of a rocket motor. The load cell described here is meant to be relatively simple to make, versatile to design with regard to load capacity, sufficientl

Strain Gage Load Cell for Thrust Measurement
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y accurate for its intended use, and inexpensive. The cost of a basic (single-gage) load cell made by this method would typically be no more than $10-20 USD. For a more precise four-gage loadcell made by this method, the cost would be about double this amount. Of course, the underlying reason for constructing a load cell isn`t measured in "dollars and sense", but is part of the fundamental premise of Amateur Experimental Rocketry - the challenge to fabricate, whatever is practical, from scratch. I have made a number of loadcells using the method described here, and have utilized them extensively for thrust measurements of my motors, with excellent results. Even for those who prefer to utilize a commercial load cell for thrust measurement, the load cell described here can be of great benefit as a "dispensible" tool for static testing of new designs (or modified designs) which inherently have a greater likelihood of catastrophic failure. With this inexpensive load cell, thrust data can be obtained on maiden firings of motors, saving the commercial unit for proven designs. The type of load cell that is being presented is basically similar to a bending beam type. When a force is applied to the load cell, the beam (or bridge) onto which the strain gage is mounted, is subjected to combined bending and axial compressive stresses. The bending stress is by far the dominant component, hence the term "bending beam". Importantly, the...

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