3D Printer Tension Belt Roller (v2)

7 min readJan 17, 2022

If you are into sim-racing, and have decided to get a belt tensioner system, chances are that you will want to add a “roller” onto your system, so that the belt pulls you “backwards” and not “down”, which is what happens if you use the belt holes in the seat but your shoulders are higher than said seat holes (as is my case).

There are a number of solutions, much better than this one, which include building a structure with aluminum profiles, and much more. Instead, I decided to go as minimalistic as possible, and design a “snap in” roller that I can place into the seat hole and be done with it.

Update March 9, 2022 — clamp style NRG PRISMA

With the help of Jeff Weaver, we’ve completed the version of the clamp-style rollers for the NRG PRISMA seat. You can find the STL files here. Pictures of the finished and installed clamps are shown below.

Update Jan 29, 2022 — clamp style NRG FRP-301

Based on some other simracers’ ideas, I decided to modify the design to reduce the flex (which was the only real issue the snap-in version has). I still did not want to drill holes in the seat, so I came up with a two-halved clamp style, and bought M4 30mm bolts/nuts, as well as one OD=25mm and one OD=20mm M4 washers, and designed the following:

Still no drilling of the seat. The big washer on the bottom, the smaller on the top. The head of the bolt on the side where your shoulders are, the nut on the back. Pretty easy. A couple of finished pics below.

Flex is completely reduced. If the roller flexes, it’s because the seat flexes. Getting the belt knuckle through the printed pieces was a challenge, but patience did the trick. My NRG-FRP301 seat has very small holes for the belt, to begin with. Most other seats would have no issues. The washers do not look great, I know, and perhaps that’s something that could be improved (painting them somehow?) — Still, it is completely functional.

I have remixed the original design and posted the updated files to Thingiverse here. Enjoy

Original post follows….

The end result is something like what the picture above shows. I initially designed a hole in the snap-in roller so I can bolt it to the seat, but after testing (see video below) I decided that bolting it is probably not needed, so I spared the seat from another puncture.

Of course, this design is (has to be) bespoke to the specific model of seat I have, as the roller has to “snap in” and be held in place. I have an NRG FRP-301 seat if it helps. This one: https://getnrg.com/collections/seats/products/frp-301

If you happen to have the same seat, then all you need to do is to download the STL files and print them. If not, some design work will be needed, and you need to keep reading. You can download everything you need from here: https://www.thingiverse.com/thing:5205065

If your seat is not the NRG-FRP-301

In this case, you need to edit the model for your own seat. You will need Fusion360 software, or something similar. In addition, you will need to measure your seat as the picture below shows:

Note that strictly speaking, you do not need #2 and #3, but you need everything else. Calipers and millimeters are your friends btw, as you need to be somewhat precise.

Before going much further, I want to disclose that I am not a Fusion360 expert, and thus much of what you will read below is probably not optimal, and perhaps even wrong. It works for me because I don’t know of a better way of doing it. However, if you do, let me know, as I would love to learn :-)

With the above disclaimer out of the way, once you open the .f3d file you should see something like this:

I have labeled all the bodies that matter, as well as the mirror plane.

Update SnapIn to your seat

To begin with, you will be modifying “BeltRoller-SnapInLeft” first. The stuff you print is composed of two parts, the snapin part, and the roller part, as you can see below.

If you want to get fancy, you can of course modify “SeatRimLeft” as well as “Seat”, but strictly speaking, you do not need it.

Thus, you need to hide everybody except the BeltRoller-SnapInLeft one and modify that one. In the picture below, I have the SeatRimLeft body shown, only for illustration purposes. In theory, you’d have your own metrics and the idea is to make your edits so that in the end, the snap-in part fits in on the rim of your seat.

On the backside, the body of the snap-in follows the inside of the hole (as you outlined in the measurements).

In a left-side view, you can see the body extending 1mm to each side.

In the view below you can see the snap-in design in relations to the measurements you took earlier.

I would suggest you outline your seat-hole, and print a 2mm high outline so you can triple-check that your measurements are correct. Once that is done, you can do everything above.

Rotate If Needed

Once you have the body of the snap-in worked out, we need to make sure we take care of the angle the hole is at in relation to the center plane (the plane parallel to the center monitor, for example). For my seat, and embodied in the downloaded file, the sides went in 26 degrees, as you can see in the picture below.

Then, if your #1 measurement is different than 26 degrees, you need to rotate the SnapInLeft body appropriately. Please rotate the SnapInLeft element, and not the other one.

Rotating snap-in example

As an example only, suppose that your seat was at 35 degrees (unrealistic, but only for illustration purposes), you would do something like the following.

Select “Move”, “Bodies” (A), then the body to move (A), then “rotate” icon (C), and for the axis select the edge shown (D)in the picture above.

Then, for the degrees of rotation, you enter the difference between 26 degrees (that comes with the file) and the #1 measurement. In this example, the #1 measurement is 35 degrees, and thus the difference is 9 degrees.

After you rotate, then you need to “fill the gap”. You can attach the newly extruded volume to either of the bodies (the snap-in one, or the roller one) but don’t combine everything yet.

Tidying things up

Once you have it, tidy things up (add fillets wherever you want, etc) and then you are ready for the final step. Keep in mind that you can always unhide the other bodies to make sure that the modeled belt is at the center of the hole, and at the appropriate height, and that everything looks roughly correct.

Combining and Mirroring for Printing

The final step is to combine the two halves and then mirror everything for the right side. First, combine the two halves, as seen below.

Then, you need to mirror around MirrorPlane to create the right half. As seen below, first make MirrorPlane visible, then CREATE →Mirror, then in “Bodies” select the one you just created by combining the two halves, and for Mirror Plane select the mirror plane, of course :-)