Investigation of the effect of continuously variable transmissions on ground robot powertrain efficiency

Explosive ordinance disposal (EOD) robots are limited in endurance and range by the amount of energy available in the batteries used to power them. Continuously variable transmission (CVT) technology has developed quickly in recent years in the automotive field and is now being applied to smaller vehicles such as bicycles and electric scooters. This paper will discuss simulations investigating the feasibility of adding CVT transmissions to robot powertrains in order to improve the overall efficiency of the drive system. The equations used to calculate the power required to move a robot at varying speeds will be described, as well as the equations used to model CVT and direct-drive transmissions, DC motors, and power discharge from a battery. The results of a constant mass simulation, where the added CVT mass was offset by a loss in battery mass, showed that adding CVTs is not a feasible option due to the mass of the CVTs. In an added mass scenario, where the mass of the CVTs was added to the overall robot mass, the benefits of a CVT depended strongly on the speeds at which the robot was expected to perform. A robot expected to operate at low speeds most of the time would benefit more from a CVT than a robot expected to operate near maximum speed most of the time.