https://www.pololu.com/product/4760
Add quadrature encoders to your micro metal gearmotors (extended back shaft version required) with this kit that uses a magnetic disc and Hall effect sensors...
pololumagneticencoderpairkit
https://www.pololu.com/product/5096
Add connectors to your micro metal gearmotors with these boards that feature back-entry, 2-pin male JST SH-type connectors. These boards are compatible with...
micro metal gearmotorsjst shpololustyleconnector