A transmission assembly (100, 200), comprising: a ring gear configured to receive an input torque from a power source; a carrier assembly coupled to the ring gear, the carrier assembly configured to rotate about a first axis and comprising: a housing; and a spider gear rotatably coupled to the housing; a carrier outlet shaft (150, 150') comprising a carrier outlet gear in meshed engagement with the spider gear, wherein the carrier outlet shaft is configured to transmit an output torque to a driveshaft; a control shaft comprising a control gear in meshed engagement with the spider gear; and a load applicator coupled to the control shaft, wherein the load applicator is configured to provide a resistive torque to the control shaft to resist rotation of the control shaft and vary a gear ratio between the driveshaft and an input shaft; a torque applicator configured to controllably apply torque to the carrier outlet shaft (150, 150'); a hydraulic circuit coupled to the load applicator and to a load controller configured to control the amount of resistive torque applied to the control shaft from the load applicator; wherein the load applicator comprises a pump fluidly coupled to the hydraulic circuit; wherein the torque applicator comprises a motor fluidly coupled to the hydraulic circuit and is configured to convert pressure of hydraulic fluid in the hydraulic circuit into rotational torque; characterised in that the transmission assembly (100, 200) further includes: a bypass circuit fluidly coupled to the hydraulic circuit; and a bypass valve fluidly coupled to the bypass circuit and configured to permit a fluid flow in the hydraulic circuit to bypass the torque applicator when the bypass valve is in an open position. a ring gear configured to receive an input torque from a power source; a carrier assembly coupled to the ring gear, the carrier assembly configured to rotate about a first axis and comprising: a housing; and a spider gear rotatably coupled to the housing; a housing; and a spider gear rotatably coupled to the housing; a carrier outlet shaft (150, 150') comprising a carrier outlet gear in meshed engagement with the spider gear, wherein the carrier outlet shaft is configured to transmit an output torque to a driveshaft; a control shaft comprising a control gear in meshed engagement with the spider gear; and a load applicator coupled to the control shaft, wherein the load applicator is configured to provide a resistive torque to the control shaft to resist rotation of the control shaft and vary a gear ratio between the driveshaft and an input shaft; a torque applicator configured to controllably apply torque to the carrier outlet shaft (150, 150'); a hydraulic circuit coupled to the load applicator and to a load controller configured to control the amount of resistive torque applied to the control shaft from the load applicator; wherein the load applicator comprises a pump fluidly coupled to the hydraulic circuit; wherein the torque applicator comprises a motor fluidly coupled to the hydraulic circuit and is configured to convert pressure of hydraulic fluid in the hydraulic circuit into rotational torque; characterised in that the transmission assembly (100, 200) further includes: a bypass circuit fluidly coupled to the hydraulic circuit; and a bypass valve fluidly coupled to the bypass circuit and configured to permit a fluid flow in the hydraulic circuit to bypass the torque applicator when the bypass valve is in an open position. a bypass circuit fluidly coupled to the hydraulic circuit; and a bypass valve fluidly coupled to the bypass circuit and configured to permit a fluid flow in the hydraulic circuit to bypass the torque applicator when the bypass valve is in an open position.