Force Sensor
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Out of Stock    Force       $24.00                 

Using this sensor with NXT requires a Lego NXT conversion cable (W770323).

Measure how hard you are pushing or squeezing.

A force sensor lets your Lego Mindstorms RCX measure how hard something is pushing or squeezing. You can build a scale to see how much things weigh, or see how hard your robot can push or pull. The Force Sensor measures force applied to the blue button in the middle of the sensor top. It measures force between one to 15 Newtons . A mass of 1 Kg (2.2 pounds) has a weight (force due to gravity) of 10 Newtons.

This sensor is not very accurate or repeatable. It is not intended for laboratory measurement. It is intended to provide a rough indication of force in a working robot. The sensor is NOT capable of measuring force between zero and one Newton. The sensor is best programmed as an unpowered sensor in RAW mode. Maximum force is limited to4 Newtons when programmed as a light sensor in the standard RCX icon language.

Relay brick for Mindstorms

Force Sensor for Lego Mindstorms.


The Force Sensor is an unpowered sensor. It may be programmed as either a powered or an unpowered sensor. If you are using Robolab, use the generic unpowered sensor icons. If you are using NQC or similar text languages, program the sensor as a passive (unpowered) sensor in the RAW mode. If you are using the standard Lego icon language, you can program it as a light sensor. When programmed as a light sensor, the measurable range is about 1 to 4 Newtons . If you are using NXT G-code, program it as a temperature sensor and use the RAW output as shown below.

Using the G-code temperature sensor icon to read an unpowered sensor in raw mode.

Typical RCX values for unpowered RAW mode.

Typical RCX values when read as a light sensor.

Time delay

It takes some time for the foam rubber to be squeezed down after a force is applied. The graphs below show how the RCX value varies over time, for two different amounts of force. The graphs were created with Robolab Investigator using the generic unpowered sensor icon.

                           2 Newtons                                                                        5 Newtons


Example: Scale

The scale below provides a stable mechanical platform on top of the force sensor.

Connector for Mindstorms relay control

Simple Scale using Force sensor.

Short shaft (black) pushes blue button on sensor.


•  Brick Size: 2 bumps by 2 bumps.  Height is one and one thirds bricks.  (one brick plus one flat plate). Overall size: 16 x 16 x 15 mm. (.625 x 0.625 x .575 inch)

•  Mindstorms black electric connector on 6 inch (10 cm) cable.

•  4 mm (.15 inch) blue button actuator

•  Passive (unpowered) sensor.

•  Resistance 500K with no force, 500 ohms at 15 Newtons..

Technical Description

The force sensor contains a piece of foam rubber that has carbon dust mixed in the rubber. Carbon lets the rubber conduct electricity.. Electricity flowing through the foam must follow a long path, going around all the air pockets. As you push on the blue button, the foam rubber gets squeezed together. The air gets squeezed out, and electricity has a shorter path. A shorter path means lower electrical resistance. Your RCX measures the electrical resistance.