Force Sensor

This force sensor uses a linear potentiometer to measure the displacement of a rod connected to a pair of springs. The displacement is related to the force applied to the rod. With known sample masses, the sensor can be calibrated to provide numerical measurements of the force on the rod.

We assume the sensor will be connected to an Arduino with a Grove shield. The linear potentiometer produces an analog value so it should be connected to an analog input. See below for how to use the sensor.

Materials

• Laser-cut 3mm acrylic parts
• Grove linear potentiometer
• 40mm Grove cable
• 6" by 1/4" precision steel rod
• Four 1.5" 1/4-20 bolts with nuts
• Two 1" 1/4-20 bolts with nuts
• Two springs
• Coupling for 0.25" shafts
• 1/4-20 eye bolt
• Two 1/4" shaft collars
• Two 1/4" innder diameter bushings
• Four M2-10mm machine screws with nuts
• Four 1/8" long nylon spacers
• About 1cm of heat shrink tubing

Note about Grove Physics Kit

If you purchased the Grove Physics Kit from Seeed Studio, you'll find that the collars do not fit onto the shaft (possibly an issue of metric/inch incompatibily). We can send you a new shaft; contact us at at kits@manylabs.org. The kit has a few other differences from what you see here; refer to the included diagram for assembly.

Assembly

Note: if your laser-cut parts have paper covering, use a knife to peel it off.

1. Attach the linear potentiometer to the acrylic piece with corresponding holes using the M2 screws and nuts. Use the small plastic spaces between the potentiometer and the acrylic. Make sure the potentiometer connector is toward the circular hole in the acrylic.

   

2. Attach the plastic part with the groove cut out onto the metal rod using the provided collars. Leave about 1.5 inches (about 38mm) of exposed rod on one side of the collars:

   

3. Place the plastic bushings into the laser-cut parts as shown:

   

4. Connect the cable to the linear potentiometer and run it throw the plastic parts as shown Press the groove onto the potentiometer. It will be a snug fit with the rubber cover on the potentiometer; use pliers if needed:

   

5. Attach this assembly to one of the large plates:

   

6. Add another spring and another bushing unit:

   

7. Add the remaining laser-cut parts:

   

8. Bolt the unit together and attach the eye hook to the end of the rod:

   

9. Place a collar and rubber washer on the long bolt as shown:

   

10. Connect the long bolt to the force probe using a wing nut:

    

11. You can use the provided clamp to attach the force probe to a ring stand (not provided):

    

Usage

The linear potentiometer produces an analog value. Connect it to one of the analog inputs on your Grove shield.

You can use the Force Approximation lesson on ManyLabs to calibrate the sensor and plot forces. We plan to add additional force sensor lessons. Contact feedback@manylabs.com if you have any requests.

A sample sketch is available that shows how to read an analog value from the force sensor. You can use the Arduino Programmer to upload the sketch to your Arduino, or you can download the sketch. This sketch depends on the WireGarden library.

If you would like to read the values directly using your own Arduino code, see the Arduino analog input tutorial.