Driving | Hardware | Analysis

Seat Belt Tensioner

The harness tensioner allows for a limited budget to make the negative Gs (braking, ABS, shifting) credibly felt. It works with Simhub.

IMPORTANT : The harness tensioner can be dangerous. At full power, it is very stressfull around the collarbones. It is therefore necessary to provide an emergency stop button.

Make all the connections with the power off.

Do all electronic tests without any parts on the shaft.

Once the tests have been carried out, and the belt installed, carry out the tests in 10% power increments.

v2.0 beta:

  • electronics has been fixed.
  • The plastic part now integrates the cable.
  • A two-piece system ensures reliable clamping on the axis.
  • The motor support allows the tensioner to be mounted on standard profiles.To be improved :
  • Plastic processing can be improved (delicate printing, difficult cable passage).
  • The electronics can perhaps be improved.
  • It remains to make a hook support to make the link between the cable and the belt.


Final rendering :

Frankly very nice. At the first braking, we say to ourselves “Well, maybe it wasn’t worth the trouble…”. After a few laps we forget it. Then it’s when the belt doesn’t work anymore (yes because at the beginning, there were some tests…unsuccessful ^^) we can’t do without it anymore… we have again the feeling to play a video game, and not to drive a race car…

The system is quite precise, it engages immediately, and you can feel the braking difference between an F1 and a base car, you can also feel the activation of the ABS.

It’s probably not precise enough to use the information to dose the brake, like “ah it’s not working for me, I can brake more”.

NOTA BENE :  The harness tensioner can be dangerous. At full power, it is very stressfull around the clavicles. Therefore, an emergency stop button must be installed.

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Summary :

  1. Presentation
  2. Caracteristics
  3. Shopping list
  4. Building instructions


1) Presentation

The harness tensioner consists of a harness (4 or 5 points), an electric motor, an electric motor driver, and an arduino board connected to Simhub.

2) Caracteristics

The motor pulls the belt backwards, it gives the impression of being thrown forward, especially in VR.

3) Shopping list

Electronics :

  1. A 350W electric motor.(Amazon, Aliexpress, Ebay)
  2. 24V  15A 360W Power supply. It can good a good idea to add an emergency stop (Amazon, Aliexpress, Ebay)
  3. Motor driver 60A (AmazonAliexpress)
  4. Arduino Uno. Any clone will do. However, clones do not necessarily have the same dimensions, and therefore do not necessarily fit in the cases. (AmazonAliexpress)

Mecanics :

  1. A 5-point harness. 4 points do the trick (that’s what I use). When the motor pulls, the buckle goes up, but once everything is under tension, you can feel the effort in your shoulders, so no worries.(Amazon, Aliexpress, Ebay)
  2. 0,1kg PLA (Amazon)to print the rewinder. I would like to add a mechanical preload system to make the belt lightly preloaded at rest.
  3. Bicycle brake cable (Aliexpress).

Screws :

  1. 3x M4x20 (for the locker). This Amazon kit contains the two screws and many others that will be useful for other projects.
  2. 4x M6x10 to mount the motor on the mount mount.
  3. 4x M8 to mount the motor mount on aluminium extrusions

4) Building instructions

The belt drum is mounted on the motor shaft. Caution, the motor shaft is in left-hand pitch, so do not lose the nut.

The connection of the power supply and the motor to the driver is indicated on the PCB.

A. Preparation of the driver :

  1. Unscrew the two screws
  2. Using a cutter, cut the track above the 8-pin transistor (ne555p). Still using the cutter, scrape the pcb in order to clear the yellow coloured track, then solder a wire to it, to be connected to pin 10 of the Arduino.
  3. Close the driver with the two screws. Connect the mass of the driver (Power -) to one the Arduino (GND) pins.

    binary comment

  4. Link “Power -” to “-” of the power supply
  5. Link “Power +” to “+” of the power supply
  6. Link “Motor +” to “+” of the motor
  7. Link “Motor -” to “-” of the motor.

B. Setting up the Arduino card on Simhub :

  1. On Simhub: We flashe an arduino with the PWM signal function (which is generally used to drive fans to make a wind simulator) and the deceleration function is associated with it.
  2. Our motor is associated with the deceleration function in the “motor output” tab of ShakeIt Motors :
  3. The deceleration effect is set as follows. To be on the safe side, the power will be increased in 10% steps. Attention, when you test your settings in simulation, use a car with a high braking capacity (single-seater, F1…).

C. Installation of the drum

  1. Install the left-hand threaded nut between the locker and the drum using the three M4x20 screws. The fourth hole is an extractor, used only for removing the locker. Install the cable.
  2. Install the drum on the motor. After the first few turns, use Simhub’s test function at low power while holding the drum to finalize tightening.