The goal is to design voxel force sensing modules to receive: (a) force data while building structures (load data allows for adaptively placed voxels) and (b) force feedback in the robots (force sensors on feet, closed-loop control).

(flex-PCB approach) The board is a flex board, designed to measure force along each of its four edges. The overall board dimensions are 50 mm x 50 mm, with compatible joints to be used with existing voxel boards. The ATtiny412, two IO pins for reading the Wheatstone bridge, and UPDI programming attachment holes are uesd. Each flexure is 0.9 mm away from the next. All inner corners are rounded. Traces are 4 mils wide, pushing the resolution of JLCPCB (which can achieve a minimum of 0.08 mm, ~3 mil traces). Versions have been made with 0.3 mm and 0.6 mm flexures, but I will first use an expanded version to test whether resistive sensing strain gauge can detect significant and fine enough changes in resistance to demonstrate accurate force measurement.

(LIG approach) Force sensors are fabricated using LIG with a resistive sensing mechanism. Using a polyamide sheet, a graphene layer with thin traces induced by a CO2 laser is generated. The sensor is then encapsulated with a thin elastomeric layer (such as PDMS, a silicone elastomer) to function fully as a strain gauge.