Force Sensor

A spring-loaded button sensor: a switch (pressed/released) and a force gauge (0-10 newtons) in one.

What it measures

Mode	Reading
pressed	true / false
hard-pressed	true / false (above roughly 5 N)
force	0-10 N, ~0.1 N resolution

Word Blocks

<force sensor [E] [pressed]>
<force sensor [E] [hard-pressed]>
(force sensor [E] pressure %)
wait until <force sensor [E] pressed>

Example 1: press to launch

A "soft start button" for practice - the robot waits for a tap:

when program starts
set movement motors [A+E]
wait until <force sensor [E] pressed>
wait until <not <force sensor [E] pressed>>     ← wait for release, so the robot doesn't launch into your hand
move [forward] for [5] rotations

Example 2: wall contact detection

Mount the sensor on the robot's tail; back up into the wall - button pressed means firmly against it:

start moving [backward]
wait until <force sensor [E] pressed>
stop moving
reset yaw angle [0]        ← known pose against the wall: recalibrate the gyro while you're here

Python

import runloop, force_sensor
from hub import port

async def main():
    if force_sensor.pressed(port.E):
        pass
    f = force_sensor.force(port.E)   # decinewtons: 0-100 maps to 0-10 N

runloop.run(main())

Python returns decinewtons

force() returns 0-100 in decinewtons (1 N = 10 dN). A reading of 35 = 3.5 N.

FLL uses

• Confirming wall squaring: more reliable than "reverse a fixed distance" - contact is proven (see the full wall-squaring recipe in FLL Techniques).
• Debug trigger: tap to run the next test segment without touching the computer.
• Attachment end-stop: stop the arm when it presses the target, preventing overdrive.

Common pitfalls

• The button travel is a few millimeters; mount it so impact aligns with the button axis - glancing hits may not press it.
• It's a contact sensor: it must physically hit. For touch-free tasks use the distance sensor.

Next: Hub Built-in Sensors - the gyro lives there.