SoftSense started as the innovation project for Lebob, the FLL team I captain, and finished as a prize winner in July 2026. The repository holds the whole record: parametric CAD, the FEA campaigns, print profiles, the ESP32 firmware and the Orange Pi controllers.
One shaft, two fingers
The gripper has a single degree of freedom. Rotate the input shaft and both fingers open and close as a mirrored pair, splaying outward as they open.
Two equal spur gears mesh on the centreline. A 90° straight bevel pair drives the left one: a 12-tooth bevel gear sits on its top face, driven by a 6-tooth bevel pinion on a vertical Ø15 input shaft. The ratio is 2.0, at module 1.8 and 25° pressure angle. Those teeth are coarse and thick on purpose, sized from a gear-strength FEA pass rather than from a table. Because the drive enters from below, the fingers point up and the shaft stays clear of the work.
Each gear then acts as the crank of a non-parallelogram four-bar linkage, which is where the splay comes from. The bottom of the input shaft carries a female Feetech 25T spline socket, so a Feetech STS3250 bus servo presses straight in with no adapter horn between them.
The sensing idea
There is no dedicated force sensor anywhere in the gripper. The actuator does that job: motor current gives torque, and torque gives tip force through the calibrated kinematic chain.
Removing the sensor removes a part that has to be waterproofed, wired and calibrated against drift. The printed drivetrain sets the structural ceiling, and the motor's own current limit protects it. Two numbers bound the design instead of a sensor spec sheet.
Fingers that give
The jaws are Fin Ray-style compliant fingers, printed in TPU with a crosshatch micro-post grip texture. A rigid jaw meets an object at one point and pushes it away. A Fin Ray finger bends toward the contact and wraps the object, so the grip holds without a control loop chasing it.
Built to be flooded
The gear and linkage housing floods on purpose. Drain holes let water through rather than trapping it, and the material choices assume salt water rather than a bench. Sealing a housing against pressure means fighting the water. Letting it in means the design has to survive being wet, which is a smaller problem to solve.
Inside the repository
- Parametric CAD in build123d, so the gear module, spline fit and finger geometry regenerate from constants at the top of the file.
- FEA campaigns covering gear-tooth strength and voxel contact studies across the grip texture.
- Print profiles and a spline fit coupon, because the 25T socket needs caliper checking before anyone commits a full print.
- Firmware for the ESP32, and the controller code that runs on an Orange Pi.