They use a custom plug system that doesn't use the standard brick shape as contacts. https://www.lego.com/en-us/themes/powered-up https://www.lego.com/en-us/th

They use a custom plug system that doesn't use the standard brick shape as contacts. https://www.lego.com/en-us/themes/powered-up https://www.lego.com/en-us/themes/powered-up shows some examples of the connector and socket. There's also the discontinued "Powered Functions" connection scheme, which can be seen on this model: https://www.lego.com/en-us/product/power-functions-motor-set-8293 https://www.lego.com/en-us/product/power-functions-motor-set... . It appears to be post-brick contacts and pre-"powered up" connectors. There have been many electrical connection schemes over the course of lego's history.