A direct-drive simulator steering wheelbase (sometimes abbreviated "DD wheel") 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 beltsAsada, H., & Kanade, T. (1983) Design of direct-drive mechanical arms in Journal of Vibration, Acoustics, Stress, and Reliability in Design, Volume 105, Issue 3, pp.312-316Direct Drive vs Belt Drive vs Gear Drive, SimXperience News at simxperience.com (archived on July 5th, 2021)), and is used similarly as with other simulator steering wheels for providing torque feedback (often called ""force" feedback", or FFB) 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–computer 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 motorOpen FFBoard |Hackaday.io (on very affordable models).

In a direct drive simracing steering wheel system, the wheelbase and the wheel rim are typically separate, so that is possible to switch between rims according to the use case, for instance formula wheelrims, GT wheelrims, oval racing or truck wheel rims. The base and the rim are typically connected through a quick release system.

History

Direct-drive mechanisms for use in industrial arms began to be possible in the 1980s, with the use of rare-earth magnets, 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.Pastorino, R., Desloovere, M., Vanneste, F., Degezelle, P., Desmet, W., & Optidrive, N. V. (2015) Development, implementation and validation of a hard real-time multibody simulation for high-fidelity steering wheel force feedback, in Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics, Barcelona, Spain (Vol. 10).

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.Installing MMos firmware into SimuCUBE - Granite Devices Knowledge Wiki

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,Barnaby, G., & Roudaut, A. (2019) Mantis: A scalable, lightweight and accessible architecture to build multiform force feedback systems, in Proceedings of the 32nd Annual ACM Symposium on User Interface Software and Technology (pp. 937-948). drivers and digital signal processing with control electronics,Richard Baxter Direct drive wheels for sim racing: everything you need to know, at simracingcockpit.com, November 17, 2020Expectations vs. Reality – How To Build A Direct Drive Racing Wheel?, Alberto from boxthislap.org, July 24, 2021 signal filtering, backdrive friction, low inertia, damping,Gonzalo Bodnar V2 impressions, at boxthislap.org, October 20, 2016 fast response, precise positioning, electromagnetic interference,Jimmy Broadbent Is A Direct Drive Wheel Worth The Money?, Aug 1, 2018 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. In-runner servo motors are typically smoother and more expensive than stepper or outrunner motors. Outrunner motors typically can produce more torque than inrunner motors, but need more cooling at higher torque levels.

Control electronics Other than the motor, other parts of a complete direct-drive wheelbase include a rotary encoder (the position sensor), a controller board (that translate the FFB data from the game into steering wheel forces), and a motor driver board (servo drive), which fits into a slot of the controller board, and that controls the position, velocity and torque output of the motor.How to build a Direct Drive steering wheel - OSW Simucube, by MODIFY UP, Sep 20, 2020 Examples of encoders are the Biss-C and the SinCos encoders, an example of a controller board is the Simucube board, and some examples of motor driver boards are the IONI and the Argon ones.

The motor encoder reads the position and/or motion (torque and rotation) of the shaft. The resolution of the encoder is typically measured in PPR (pulses per revolution), but sometimes CPR (counts, or steps, per revolution) is used instead, where 1 pulse equals 4 counts. The main advantage of very high resolution encoders is the ability to implement more advanced firmware or software FFB filters to the force feedback signal; for instance, encoders with a 21-bit resolution or more (2M steps or cpr), like the SinCos encoder, allow the servo-motor electronics to handle the filters more smoothly, and also allow to have more nuances in the FFB signal.Mirko De Santis Simagic Alpha Mini review "the end of the straps!", Aug 25, 2021

One of the main purposes of FFB filters is to optimize the FFB signal for a given wheelbase and rim device.Simucube_2_User_Guide The most basic FFB filters include the reconstruction filter, damper, friction and inertia. The reconstruction filter is included even in non-directdrive wheelbases, and has the effect of interpolating and smoothing the FFB signal from the game, to reduce the noise and artifacts from the FFB signal caused by the low update rate of a racing game.Mirko De Santis I "filtri" nel simracing pro e contro , Oct 3, 2020, 6 June 2024 The wheel rim weight and size also have a significant effect on the perceived FFB signal, with lighter and smaller wheels being able to move faster and deliver more details.

More advanced FFB filters include static force reduction and slew rate reduction filter. The static force reduction filter was introduced to address a problem that emerged with high-torque DD wheelbase, due to their force output making too difficult to even turn the wheel with some cars in high-speed corners. The static force reduction filter introduced with Simucube 2 wheelbase allowed to address this issue while keeping a fully linear signal. A side-effect of this filter however is that while turning the wheel one feels a weakening of the FFB signal, which some drivers might dislike.Mirko De Santis Riprovo Simucube 1 OSW è ancora un prodotto valido nel Simracing?, Aug 4, 2020 Similarly, the slew rate reduction filter reduces or dampens sudden acceleration spikes in FFB torque, due for example to hitting kerbs or bumps. Therefore, the static force reduction and slew rate reduction filters make feasible to drive with higher maximum torque settings, which can enhance micro-details in the FFB signal.

Torque The torque says something about how "powerful" the engine is, and can be specified in two ways: Continuous torque, the greatest load of which the motor still can perform continuous movement at a continuous speed, and thus performing continuous work Stall torque, the load which will cause the motor to stop so that it can no longer move, and thus produces a holding torque, but not performing any work

The latter always gives a higher number in newton-meters, and is therefore the number that usually is communicated the most by manufacturers to consumers, but is actually a less useful specification since the steering wheel in theory does not perform any work when rotation has stopped. One must therefore be aware of the type of torque specification given when comparing two motors. The relationship between the continuous torque and stall torque can vary between motors, and can say something about the motor characteristics (responsiveness versus strength).

For comparison, usually around 7-10 Nm is experienced in a street car, and on steering wheels with very high torque (e.g. 20 Nm) it may therefore be appropriate to adjust the torque down in the software. However, the stronger motors will often have a faster slew rate (the time an amplifier takes to respond to a signal) which gives better steering response and more realism.

Steering wheel mount Similar to many real-world racing cars, sim-racing steering wheels usually come with a bolt circle of 6×70 mm, which means the wheel is mounted to the base via 6 evenly spaced out screws along a 70 mm circle on the steering wheel. Other bolt circles are sometimes used.