New 2-DOF Frame Design

The first revision 2-DOF frame has a few issues that we are working to address in our next revision:

1) Rigidity isn’t great: accelerating quickly causes the frame to bounce.
2) The frame is large and unwieldy.
3) Sometimes the frame squeaks during motion – the mounting feet rub when weight shifts around.
4) It’s difficult to climb into the simulator, because the chair sits so high.

We hope to fix these problems in our upcoming V2 frame prototype.  First, we think that some of our rigidity issues stem from how the outer yoke (roll axis) connects to the base frame.  Right now, we use two opposing angular contact bearings on a 1.5″ shaft.  The idea is sound in principle, but because we compress them together around 3″ square stock, there is a lot of room for deflection.

Here is the proposed solution:

Roll yoke bearing pack
Roll yoke bearing pack exploded view

The new bearing design utilizes a fairly large (~ 6″ OD) needle roller thrust bearing.  The assembly is held together using a 1″ shaft and a single angular contact bearing in the center to handle radial loads.  Overall, we think that this will handle the cantilevered load much more effectively than the V1 prototype does.

The main frame is also being changed.  Instead of having a large base platform with two verticals, the new version will mount to a single standalone pillar, designed to be rigid enough on its own (i.e. no angled mounting plates like we have on the V1 prototype).  The “pillar” can be bolted directly to a concrete floor, or it can be bolted to a frame of some sort, which we’ll design later.  See below:

Pillar frame design
Pillar frame design – wireframe

The interior ribs provide increased torsional rigidity.  And the pillar itself is sized so that its area moment of inertia is *significantly higher than the combined result of the two 3″ verticals used in the current design (more than 2x higher, in fact).  The new yoke bearing pack mounts at the top of the pillar, as shown.  I’m a little concerned about the rigidity of the stock at the bearing mounting point – that may need more attention.

And finally… the roll axis yoke needs to be redesigned.  It is partially finished, but still needs some work.

V2 Frame Concept – still in development

The concept is shown above, with a human model for scale.  The pillar is shorter than the original verticals on the V1 prototype, and it bolts directly to the floor. The outer yoke (no arms yet) also has internal ribs to improve torsional stability.

We’ll have this design fleshed out in more details soon.  If it looks good, we’ll get the metal parts laser-cut and start welding the new assembly together!

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