Reinventing the Load Sensor: Innovation on a Budget

Foil strain gauges had their time. But development doesn’t always need high-priced lab gear. Sometimes, hardware-store parts and creativity are enough.

The Problem: A Pricey Sensor Market

A customer asked me to design a load sensor for a trailer hitch. Since the application could scale to hundreds of thousands—or even millions—of units, keeping costs low was critical.

Off-the-shelf strain-gauge sensors weren’t practical. They often cost several hundred dollars each and were designed for lab testing, not mass production. Even for my prototypes, the price was hard to justify, especially with the extra electronics needed to interpret micro-ohm outputs.

The Search for a Better Solution

Foil strain gauges have been around for more than 80 years, but I wanted something simpler and cheaper. After a lot of digging, I found a sensor made from layered Mylar with a conductive coating. As force increases, its resistance drops—a perfect candidate for my proof of concept.

Armed with washers, nuts, bolts, and a voltmeter, I built a quick test model. Drill a hole in the sensor, slip it over the bolt, tighten the nut, and watch the voltmeter. The resistance changed exactly as expected. It was simple, cheap, and it worked.

Figure 1  – Load sensor parts showing load sensor, washers nuts and bolts

FEA to the Rescue

The next step was figuring out where to place the sensor on the trailer hitch. That’s where finite element analysis (FEA) came in. Using ANSYS, I modeled the hitch, applied variable loads with a virtual bottle jack, and identified high-stress locations perfect for sensor placement.

Figure 3 – Trailer hitch prototype FEA model

Figure 4 – load sensor location determined by FEA model 

Building the Test Stand

To validate the setup, I built a test stand from basic materials—lumber, nails, nuts and bolts. By pumping a bottle jack, I applied real forces at one of  the hitch receivers (fig 3 red arrow)  and watched the resistance shift. The low-cost sensor proved it could do the job.

What We Learned

The prototype confirmed multiple viable mounting spots. The next step would have been integrating electronics to convert resistance into a clean voltage or current signal. The sensor manufacturer even provided a starter circuit.

Although the project stalled at the proof-of-concept stage, it demonstrated something powerful: innovation doesn’t always require expensive equipment. With a little creativity, a load sensor for pennies can compete with ones that cost hundreds of dollars.

Norman T.  Neher, P.E.
Analytical Engineering Services, Inc.
Elko New Market, MN
www.aesmn.org