Direct-drive mechanism

The main benefits of a direct-drive system are increased efficiency (due to reduced power losses from the drivetrain components) and being a simpler design with fewer moving parts.

The main drawback is that a special type of electric motor is often needed to provide high torque outputs at low rpm. Compared with a multi-speed transmission, the motor is usually operating in its optimal power band for a smaller range of output speeds for the system (e.g., road speeds in the case of a motor vehicle).

Direct-drive mechanisms also need a more precise control mechanism. High-speed motors with speed reduction have relatively high inertia, which helps smooth the output motion. Most motors exhibit positional torque ripple known as cogging torque. In high-speed motors, this effect is usually negligible, as the frequency at which it occurs is too high to significantly affect system performance; direct-drive units will suffer more from this phenomenon unless additional inertia is added (i.e. by a flywheel) or the system uses feedback to actively counter the effect.

Direct-drive mechanisms are used in applications ranging from low speed operation (such as phonographs, telescope mounts and ski lifts, video game racing wheels and gearless wind turbines)[4][5][6] to high speeds (such as fans, computer hard drives, VCR heads, sewing machines, CNC machines and washing machines.

Some electric railway locomotives have used direct-drive mechanisms, such as the 1919 Milwaukee Road class EP-2 and the 2007 East Japan Railway Company E331. Several cars from the late 19th century used direct-drive wheel hub motors, as did some concept cars in the early 2000s; however, most modern electric cars use inboard motor(s), where drive is transferred to the wheels, via the axles.

• Belt-drive
• Chain-drive
• Drive shaft
• Hubless wheel
• Linear motor