Question Heave Concepts

Hi folks, I'm currently in the planning phase of a DIY motion simulator with 3 DOF - pitch, roll and heave.

I took looks at a lot of rigs presented in this forum and noticed that most 3DOFs with heave utilize a concept where the gearboxes have output shafts on both sides, and both levers are then connected to a quite massive structure that is shaped like an inverted U, with some form of U-joint on top, that connects it to the platform. It's tough to describe geometry using words, so take a look at the attached picture.



These rigs usually utilize a heim joint / rose joint / ball joint / rod end bearing (whatever it is called in your flavor of the english language) to connect the inverted U-shape with the platform. I've spent some time looking but I can only find such joints with angular motion ranges of about +/-14 degrees. I found versions with about 17 degrees but those were massive, like 20+ mm diameter of the holes. I want to stay in the 8...12 mm ballpark.

Currently I am aiming for a rig that can do +/-20 degrees, so the commonly used rod ends don't seem to work for me. Or can you folks show me where to find a rod end with a wider range of motion?

Maybe I should use a different heave concept for my rig?

I found a few people using a single central U-joint like in a 2 DOF, but it's movable in the vertical direction. The motors are also connected like in a 2 DOF (of course, there are 3 motors for the 3 DOF) , with a single thin push rod connecting the motor levers with the top platform. I also attached a picture showing this concept.



This concept uses a standard U-joint which easily can achieve a wide range of motion. It's also quite simple do a assisted heave system this way, just put a spring under the U-joint.

However, I'm struggeling a little transforming the idea of making the central U-joint movable into an actual construction. Should I use cylindrical rods that move through cylindrical plain bearing bushing, like in the attached picture? Or should I use linear guide rails? I'm afraid to miss out on a easy and good solution just because I don't know about what hardware exists out there.

I have not found many implementations of this heave concept to inspire me. I know of noorbeast's DX rig, but I don't want to utilize this office chair mechanism, although it's a clever way to do it. Do you folks know of more rigs that implement heave via central U-joint?

Best regards
Sebastian

Question is the y style ctc possible if the motor have shaft only in one side?

I think it would be hard to create a mechanism that has the necessary stiffness. The common double shaft inverted y structure is quite stiff against forces directed parallel to the motor shaft. I think you would need to have quite a long single shaft and special motor levers to even get close to that stiffness.

So I go with u joint mounted on linear rail guide.

I am wondering why they using 4 instead of 1 or 2 for example. I need only stabile not heave assist. Because I will use gas damper.

Again, it's about stiffness on the horizontal plane. 4 vertical guide rails, spaced somewhat apart and interconnected with a stiff mounting, will be stiffer than one single guide rail, even if it was 4 times the weight.

Also, 2 columns would provide more stiffness in one direction that in the other, which would not make much sense. 3 could to the trick but you would need triangular mounting plates on both ends. Rectangular mounting plates for 4 guide rails might be easier to make. After all, the cost disadvantage of 4 vs. 3 guide rails is marginal, compared to total cost of the rig.

I will go with four rails.