The ThunderVolt® motive drive subsystem is based on an 'ELFA" dual motor and controller set manufactured by Siemens AG. In 2002, ISE signed an agreement with Siemens establishing ISE as Siemens' preferred distributor and integrator of ELFA products for U.S. transit buses. The ELFA drive configuration includes two motors and a combining gearbox providing a flange for a driveshaft to the differential (shown below).

The motors and the inverter module that controls them are both operated on the same water-glycol cooling loop. The dual motor/controller set has a power rating of 170 kW continuous and 288 kW peak. The combined weight of the two drive motors and combining gearbox is approximately 300 kg. Each inverter module weighs 72 kg. Buses up to 30 feet in length can be operated with a single inverter module (shown below), while 40-foot buses and large trucks typically require two inverters. For very heavy vehicles, a new configuration is available that combines three Siemens motors.

Regenerative braking is a capability built into all ThunderVolt® drive systems. In this process, the kinetic energy of the moving vehicle is recaptured by the motors and inverters during braking - a process that improves overall energy efficiency by as much as 25% while reducing brake wear by as much as 90%. The system is capable (with a discharged energy storage system) of meeting or exceeding most bus acceleration and gradability specifications.Siemens' ELFA motors and inverters have been used in more than 600 buses in Europe and have accumulated more than 30 million miles of revenue service. ISE's hybrid drive system therefore uses the most proven motive drive components in the world. No U.S. transit bus using the ISE drive system has ever experienced a road call or extended down time due to a motive drive system failure.