FSR 402 force sensor
A polymer pad whose resistance drops as you press it. Crude, hysteretic, but it costs eight dollars and it stops your gripper from crushing an egg.
The role it plays
Sensors split into proprioception — encoders, IMUs, joint torque, motor current — which tells the robot about itself, and exteroception — LiDAR, depth, force, GNSS — which tells it about the world. Build proprioception first. A robot that does not know where its own joints are cannot use a good world model anyway.
Typical use: Gripper contact detection, bump sensing, foot contact.
What the numbers actually mean
The headline figure is 0.1 – 10 N (force range), with Resistance, ~∞ → ~1 kΩ as the next most load-bearing number (output). At $8 in the sensors tier it sits cheap enough to prototype with and replace without regret, which is the correct way to learn a new subsystem.
How it compares
Same subsystem, closest alternatives. The primary spec column is usually the one that decides it.
| Part | Price | Primary spec | Second spec |
|---|---|---|---|
| FSR 402 force sensorForce-sensitive resistor | $8 | 0.1 – 10 N | Resistance, ~∞ → ~1 kΩ |
| AS5600 magnetic encoderAbsolute rotary encoder | $3 | 12-bit (4096 counts/rev) | I²C (also analog / PWM out) |
| AS5047P magnetic encoderAbsolute rotary encoder | $10 | 14-bit (16384 counts/rev) | SPI + ABI quadrature + UVW |
| CUI AMT102-VCapacitive incremental encoder | $25 | up to 2048 PPR (configurable) | Quadrature A/B/Z |
| BNO085 9-DOF IMUIMU with onboard fusion | $25 | 3-axis accel + gyro + magnetometer | Quaternion / Euler / rotation vector, plus raw |
Where it shows up
It is a component-level choice rather than a defining part of a named platform — pick it for the subsystem it serves, not to match a reference build.