2 DOF with Traction Loss, harness tensioner and more to come

I didn’t write for a long time, but I worked on my sim. Not constantly, but from time to time in little steps. My plans changed over and over again.
At the moment my goal is a working 2 DOF frame mover with TL and harness tensioner. So something like 4 DOF?!

When everything is ready I will add a G-Seat.

The upper platform of my sim looks like that (old pic, it’s already a little different):


The profile with the attached u-joint can be moved forward and backward. It could be used to adapt to the weight of the driver, but I only need it for finding a sweet spot, where the motors are still fast(strong) enough (by moving backwards) but I feel as much heave as possible (by moving forward)


Before that I already tested the strength of the motors with this setup:

And on the other hand I sat in the frame with a scale in the back and looked for the right balance point… But the live test with working motors is much better

I drilled two holes through the extrusion for the wheel and attached the wheel with a plate to the frame. It’s rock solid!


I wanted to invert the pedals, but at the moment they are in F1 position:

maybe I will change it later. since the spring of the original brakemod was unusable after some hard braking maneuvers I added a custom brake mod. It’s cheap and simple (photo will be added soon). This will be refined in the future. Maybe I will just add a parabolic buffer. I like hard Brakes.

So, at the moment I have a working 2 DOF frame mover(photos will follow) Had my first ride on Monday and it was fantastic!!! Now I have to bolt everything together and tune the Software. The next step is the traction loss. After that I will add a harness tensioner. In the first place only 1 axes for both belts.
What will come after that is unsure. Maybe I will make some linear actuators as planned in the beginning. And will change the rig to a 4 DOF rig with additional TL + harness tensioner + GSeat… we’ll see.

I don’t think I will go for the steward platform in the next 5 years. Since I have lots of other hobbies it would be way too expensive.

Maybe some more info regarding the geometrical considaration of the sim.
After thinking about the influence of the geometry, I made a step by step guide for me to determine the pivot point and the rod mount points etc.
So my aim was

• as much heave (pitch axis) as possible
• position for mounting points, where the motors are least demanded

So I made up a theoretical outline how to achieve my points.
The first one is simple:
Move the u joint as far to the front as possible. The further the u-joint it away from the body, the more you have a translational motion, than a rotational.

If the u-joint is at an infinite distance away there won’t even be rotation, but just translation. Since this is not possible the u joint has to be waaaay closer to the COG. The limit here is given by the power of the motors.
If you want to have the motors as least stressed as possible (for symmetrical movements for the two motors!), than the u-joint has to be beneath the COG.

Another important consideration is the distance of the pivot point to the frame (or COG). You want to have this as close as possible. In the drawing D2 it’s 40 mm to the frame and the seat is as low as possible.

This is the first decision. The next is the determination of the rod mount points. Where to fix the rods to the frame? We have 3 dimensions for the motor position, 3 for the rod mount points and 2 angles to think about. The first I determined was the position of the rod mount.

For all values you have to find the right balance between movement and needed torque. The further you go away from the pivot point, the less movement you have and the less power is required to move the frame and vice versa.
Since I want to have as much movement as possible I tried to keep y1 (in D3) as small as possible. So the rod mount points in y-direction are as close to the seat as possible.
The next is the height of the rod mount points (RMP). If you fix them right to the bottom of the frame like this,

it's quite good for pitch, because the rod arms work tangential to the “rotation circle” almost 100 % of the force are used for pitch rotation.
BUT you have another thing to consider, the roll movement. The blue line shows the "balance area". If the COG lies on this line, the motors will consume less power for the roll rotation. So the goal is to get this line as close to the COG as possible. There are two options, the first is to move the u joint further to the front, the problem here is, that the motors will need more torque for the pitch/heave movements. So the u-joint stays where it is. The other way is to raise the RMP.

The higher, the better for the roll axis, but this isn’t the only thing to consider, it influences the ideal motor mount position. The higher the RMP, the further away the motors should be… so no need to exaggerate here. You always have to find the right balance.
The next thing to determine is the distance between the RMPs. The closer they are, the more roll you will have, but the COG will possible go out of the balance area. The motors will need torque and the motors will see different loads. For me the distance was more or less given, because of the geometry of my frame. My extrusions were cut to fit the seat and I could only add some more centimeters to this distance.
So much to the rod mount points.

Now it’s time for the motor placement. The length of motorlever (CTC lever) is just a consideration of power If the motors are strong enough, use a longer lever and you get more travel distance.

D6 shows the rotation around the pivot point in magenta. You want to have the rod arms tangential to this circle. In this drawing the motor should be further away to reach its ideal point. But I didn’t want to make myrig too big. And the applied forces are almost as much as possible. The other way would be to put the motors higher.

The distance of the motors from each other is again important for roll, not pitch/heave. And it’s the same consideration as for the rod mount points. I put i as far to the outside as possible on the frame.

Now the angles:
The angle of the motor lever is in rest position ideally perpendicular to the rod.

There is also the angle of the motor. Or better said it’s the angle between the rod and the side of the rig if you look from the top. I aligned the motor parallel to the rod, for the joints to move as less as possible.
To calculate the optimal angles and the rod mount length I made a simple excel sheet [attached]. But i didn't need it during construction. Just used it to play with simcalc, which @Tim McGuire wrote. btw: helpful application

That's a good point! The backlash of my wormgears is so annoying, that i want to switch to linear actuators asap!

So, now some info about the practical part.
First I attached the u joint to a moveable structure. It can be moved back and forth, this was important for me to determine the rotation axis. (Are the motors strong enough? ...)

Pic 3 shows a clamp which holds the two frames together…

Then I attached the motors to the bottom frame with the right angle. You see, that the rod is parallel to the motor.

Here you see the resting position of the lever.

The lever doesn't move enough to the bottom. I will fix this the next time when I work on the frame.


Now I had the proper length of the rod arms. I cut the rod arms and screwed everything together.

Now it’s mechanically “working”.

Now I can do some test to determine the mounting point for the u joint. The problem is I don’t have a clue how to tune simtools. Two hours ago I found the brandnew manual for SimTools ! So I have a lot of stuff to read

After I have a setup that I like, I will play with the u joint, determine a position and drill some holes to bold everything together.

After this stuff is ready I will put all electronics in that housing:

Two PSUs, two arduinos and two Sabertooths fit in well. Since the fan of the PSU is really loud I will use 2 or 4 120mm fans.

All cables (steering wheel, pedals) will go in this box at the end, so I just need to plug in one electricity and one usb cable to the rig. Found a nice Neutrik adapter for usb

Interesting. What engines do you use?

For the back I have 250 W 24v motors. They run @3000rpm and I have 1:60 wormgears.
For traction loss I'll use a 400W motor. For the harness tenstioner the same 250W motor.

Thanks for the mention
I'm glad my application was useful for you