Sim Racing Seatbelt Tensioner

This project is going to get an option to work with the Moza pedals. I need to get some testing done before I will have this done. Hopefully it will be just a software change.

This is NOT a simple project! If you are not electronically AND mechanically proficient, this project may be over your head.

This has been the most complex project since retiring a few years ago. As an engineer for over 50 years I had worked on lots of interesting projects and also was a project nut at home. It was fun and challenging! 

This system has been a nice improvement to my DOF Reality H3 which started off as an H2 and then was upgraded to the SFU gear system and then upgraded to the H3 version.

I had modded my brake pedal (Thrustmaster T300) to a load cell sensor (10KG) for better “feel” during braking (https://www.youtube.com/watch?v=KIldeuIU-jM). I decided to use that signal source to control a stepper motor connected to a worm drive transmission to pull on the seatbelts simulating negative G's (braking). Commercial devices are sold but they are very expensive so I looked around at what I had and decided to make my own. I'm guessing that you could do this for around $300USD. YMMV…..

The Arduino software is in a text file so you will need to type or import it in. It is pretty simple and is well commented along with lots of print statements for troubleshooting. I'm NOT a programmer so don't laugh too hard at my code. It at least works.

Theory of Operation:

A load cell signal (~0 to +3VDC) is read by analog input A0. This is divided by a number to reduce A/D reading uncertainty (reducing noise). This value is compared to the previous value to drive the stepper motor either CW or CCW by the amount of difference from where it was. As you press on the brake pedal the signal value increases to a max of around 3VDC. This pulls tension on the seatbelts to simulate braking. The seatbelts need to be a five point type to keep the tension correct.

The Calibration switch tells the controller to turn the stepper motor so that the tension arm hits the Cal microswitch which then tells the stepper to backup to “HOME” position (no tension).

The LIMIT switch is there in case the system goes nuts and drives to the limit in which the software shuts the system down. At that point you must do a reset and cal. I adjusted the TB6600 stepper driver to limit the motor drive to 2 amps. This gives a pretty good tension and if you really press hard on the brakes it will stall the motor. No harm in doing this.

The RESET switch is simply wired to the Arduino UNO reset.

The GAIN control is a 20K pot that allows you to adjust the power of the tensioner. A MX5 Cup car does not brake like a F1 car! Adjust to your liking.

Cal should be done after adjusting the Gain control. Remember that the stepper drive limiter will override too high of a gain setting. It is adjustable and so far I have done about ten hours of practicing at Brands Hatch with the MX5 Cup car and no problems. The seat belt tensioner gives you a MUCH better feel of your braking. 

All parts were printed on my MK4 and XL printers in PLA except the stepper motor to worm drive coupler. It was printed with PRUSA PETG at 100% infill @ 50% print speed. So far it has held up to over ten hours of hard use now.

The schematic has been added. It is pretty simple if you have been working with stepper motors and Arduino SW.