A direct-drive simulator steering wheel (sometimes abbreviated "DD") is a simulator steering wheel with a direct-drive mechanism between the drive and output, i.e. without gearing (as opposed to simulator steering wheels with reduction gearing via gears or belts), and is used similarly as with other simulator steering wheels for providing torque feedback (often called ""force" feedback") so that the driver, through movement in the steering wheel, gets an interface for sensing what is happening to the car in the simulator. It is an example of human-machine interaction in driving simulators, racing simulators and racing video games, and is an example of haptic technology
Direct-drive steering wheels typically differ from geared or belted sim racing wheels by being stronger (having more torque), and being able to more accurately reproduce details from the simulator. They are typically constructed using a 3-phase brushless AC servomotor (on more expensive models), or sometimes a hybrid stepper-servomotor, or only a stepper motor (on very affordable models).
History
Direct-drive mechanisms for use in industrial arms began to be possible in the 1980s, with the use of rare-earth magnetic materials, of which today the most commonly used are neodymium magnets.
Before the 1980s, servo motors were not powerful enough (did not have enough torque) to be used directly, and therefore reduction gears or mechanical belts were added to the motor to leverage and multiply its power. Higher power motors were not feasible due to the expensive rare-earth materials needed to build them. This problem was surpassed in the 1980s, with the development of less expensive high power magnets.
In 2013, direct-drive sim steering wheels were introduced in large scale to the consumer mass market as a more advanced alternative to gear- and belt-driven steering wheels. The first commercially broadly available direct-drive wheel base was released in 2013 by the UK-based Leo Bodnar Electronics, after having been retailing to racing teams and professional centers since 2008. It was followed in 2015 by the US-based SimXperience AccuForce V1, and by the first do it yourself open-source hardware OpenSimwheel or "OSW" kits for users with good technical knowledge.
In 2015, a preliminary comparison of gear-driven and direct drive wheels in the 0–30 Hz frequency range, for a study on hard real-time multibody simulation and high-fidelity steering wheel force feedback, concluded that direct drive wheels are preferable.
Simucube was one of the manufacturers who previously provided Open Sim Wheel kits, and is a brand name owned by the Finnish manufacturer Granite Devices, which also supplies driver electronics for controlling servomotors and stepper motors, both for sim racing and industrial use. Granite Devices started as a hobby project by the Finn Kontkanen Tero when he was building a CNC milling machine, and realised that there was many alternating current servomotors of high quality on the market, but that driver electronics for controlling such motors was expensive or hard to come by. He investigated the operation of AC servos, and realized that it was possible to make usable control electronics with a handful of the latest electronic components and some real-time algorithms. The development of the controller then took around a year. The electronics are based on an IONI motherboard and STM32F4, and a proprietary firmware called MMos. An open source version of this software has been planned for release, but has not yet been released as of 2022.
Performance metrics
Issues, quality and performance indicators of direct-drive wheels, and of sim racing wheels in general, include detail and fidelity of force feedback, smooth torque transmission, nearly-zero backlash, rotary encoder resolution, clipping, dynamic range, torque ripple, cogging torque, drivers and digital signal processing with control electronics, signal filtering, backdrive friction, low inertia, damping, fast response, precise positioning, electromagnetic interference, and latency.
Construction
Motors
The Leo Bodnar, OSW kits, Sim-pli.city and VRS systems are based on industrial servo motors (typically MiGE, Lenze, or Kollmorgen motors), while SimXperience's AccuForce, Frex, Simucube (which initially used a MiGE motor), Fanatec, and Simagic use custom-made motors. The types of motors used vary between high-end 3-phase brushless servomotors and lower budget hybrid stepper-servo motors.