TACTIC · Open Hardware

Tactile Skin

A WiFi-based 22-taxel piezoresistive sensing suite for the Kinova Gen3.

Hardware files ← Project page
Whole-arm tactile sensing for the Kinova Gen3-7DoF: FlexiForce pads on 3D-printed mounts across the wrist, forearm, and half-arm links.
Fig. 1 The 22-taxel skin on the Gen3: exact-fit printed mounts carry the pads and their wireless readout boards on each link.

Overview

The skin mounts 22 Tekscan FlexiForce A502 sensors across the Gen3's links to measure pressure along the arm: thin, flexible force-sensing resistors with a 50.8 mm × 50.8 mm sensing area per pad that convert applied force into a change in electrical resistance.

The sensors are organized into four mounts: five pads on each spherical wrist joint, six on the forearm link, and six on the half-arm link. Each mount pairs with an Adafruit Feather M0 WiFi board that communicates pressure readings at 800 Hz per board; sensor and mount positions relative to the robot come from CAD model measurements. The boards run on LiPo batteries and report over WiFi, so no cables tether the robot.

Bill of Materials

Table 1 Everything purchasable, with vendor links.
VendorPartUnit costQtyCostLink
TekscanFlexiForce A502 pads$27.8722$613.14Product page
AdafruitFeather M0 WiFi$39.954$159.80Product page
Adafruit3.7 V LiPo rechargeable battery$12.504$50.00Product page
AdafruitMicro-Lipo charger$6.954$27.80Product page
Adafruit10 kΩ through-hole resistors (25-pack)$0.751$0.75Product page
McMaster-Carr302 stainless steel torsion spring$3.231$3.23Product page
AmazonGorilla clear double-sided mounting tape$11.991$11.99Product page
AmazonJST XH 2.5-2 pin battery connectors (50 set)$7.791$7.79Product page
AmazonDouble-sided Velcro$15.431$15.43Product page
Total$889.93

Printed Parts

Each mount is shaped to its link, carrying the pads on the outside and the readout board on the inside. STL and CAD files are in the hardware files folder.

CAD renders of the 3D-printed sensor mounts for the wrist, forearm, and half-arm links of the Kinova Gen3.
Fig. 2 Sensor-mount parts for each link.

Assembly

Step 1 · Wire the pads to the boards

Make up the sensor wires and connect each taxel to its link's Feather board, following the circuit below (each pad forms a voltage divider with a 10 kΩ resistor).

Circuit schematic for connecting FlexiForce taxels to the Feather M0 board through voltage dividers.
Taxel readout circuit.

Step 2 · Attach boards to the mounts

Screw each board onto its mount, then fix the tactile pads to the outside of the mount with the double-sided Gorilla tape.

A 3D-printed mount with the Feather board screwed to the inside and FlexiForce pads taped to the outside.
Board and pads on a mount.

Step 3 · Fit the mounts on the robot

The longer mounts snap into place on their links. For the smaller mounts, a small strip of Velcro on the inside holds them to the robot if needed.

The completed installation: all mounts and pads fitted to the Kinova Gen3 arm.
Fig. 3 The finished skin, fitted to the arm.
All done! The software setup guide will be linked here when the repository is released.

See also: the leader-arm teleoperation interface used alongside this skin to collect whole-arm demonstrations.