Hybrid seat shaker/full frame?

Greetings all, newbie here with a bit of an interest in 'maybe one day' building something

Going through some of the FAQs and looking at some builds and descriptions though, I had a thought and was wondering if it had occurred to others as well and if anyone had tried it out & could give feedback.

I've noted some people referring to the relative motion between body and limbs as providing some additional feedback, and there was another one I'd looked at (apologies for the lack of specifics here) where someone was working on a 'pseudo surge' control by putting the pedals and wheel/sticks on linear bearings and moving just them.

I was wondering if you couldn't 'go half way' between a seat shaker and full frame.. basically a seat shaker with an independent frame for the hand and foot controls, which could move slightly separately from the seat.

Simple option would be to build a seat shaker and then 'loosely' attach the hand/feet frame... pivot it off the seat and support it with springs and dampers to let it 'lag' a bit behind movements. Actually, I'd think the reverse would probably be more effective, so the changes hit your hands and feet first.. but that's the opposite effect of a seat shaker..

Other possibility is to make the frame separately - build a 'ring' universal joint around the outside of the main support with its pivot point aligned, and attach it off the same control arms, just at a different 'throw' off the motor, so it gets the same movements as the seat, just at a different rate Attach the control rods a little closer in to the motor axis and it doesn't move quite as much.. move it further out and it's amplified. You could probably rig something something up on threaded rod and have that quite easily adjustable to tune it.. Being independent from the chair and user means that assembly need only be quite lightweight and wouldn't put too much inertial strain on things to throw about.


I'm kinda curious as to how it would go..

Oh.. another thought.. If using a four (/five) point harness, attaching it to the base rather than the moving assembly, just with springs/bungee cord. That would emphasize the feel of the seat movements as well, giving extra pressure or releasing it as you move?

Aaah yeah, yours was the one Very inspirational design, I'll certainly have to study it more if and when I go down the path of doing my own..

Sadly I'm not really in position to sketch anything out right at the moment, but if you think of the "diy universal joint" of a bit of box section and some rod ends, then expand that box section out so it's big enough to allow the whole thing to surround a second universal joint, then you have two independent but coaxial attachment points. The inner universal extends up a little higher to the seat, the outer stays low and has the pedal/wheel subframe attached.

In that way, both chair and limbs can move separately to each other (I'm just talking a standard 2DOF setup, here). The control arm coming off each motor can then have two separate connecting rods attached to it, going separately to seat and subframe. If those connecting rods are attached at different lengths down the control arm, they'll move at different rates, like a pantograph. That means the seat moves more than the hands and feet, adding some of that feedback in to hands and feet. Things would be pivoting from the same point, but as you note - there's a bit of an arc there if they're not moving the same amount..the distances will change, but the angles would shift around a little as well.. maybe playing with the position of that subframe universal could change the feel of it. Could be worth setting that up on some sort of adjustable track (threaded rod?) to allow some tuning of it?

You could perhaps also use springs/bungees to connect subframe to seat, which would let it 'lag' a bit.. and/or further attach that subframe to the base as well to let it again move in proportion to the seat, though that would also be effectively attaching the seat to the base with springs as well, increasing the resistance the motors would need to overcome.

Ok, went off and learned sketchyphysics and simtools and how to get them both working (which seems ok, though it does also seem to lag a little..), drew up this sketch. Not sure I got the "proper" universal joint (in green) done properly, it seems like it can still twist.. I'm probably not doing that right.

Basically, the green section is the basis of a "standard" 2DOF seat shaker design.. mounted on a central universal, with connecting rods hooked up to control arms on two motors.

Where the 'hybrid' bit comes in is the separate subframe for attaching the 'hands and feet' bits, rather than mounting them directly to the seat. There's what amounts to a "ring" universal joint built around the outside of that existing universal (the blue structure), the lighter blue box area in the middle being hinged on opposite sides and connected to base and then the subframe that would hold the pedals and hand controls. The white control arms hanging off the motors have the standard 2DOF connecting rods to the platform which would hold the seat, but then also connected (but closer to the motors, hence with a shorter throw) are a second set which connects the subframe.



End result is that chair and subframe both move separately, but are tied by the control arms and while they make the same movements, do so at different rates - the subframe moves slightly less (depending on the difference between connection points on the control arms) than the seat.

I'll also attach the model if anyone wants to check it out - should work on the same basic settings that the sample "Wackelstuhl" model does (though without the 3rd axis)

interesting!
I would appreciate to see a video (as I haven't installed Sketchup)

Hrm.. ok, it's only subtle, and I still haven't got some of the joints right since there's some rotation in there that shouldn't be, but this should be enough to give you the idea.. I think.

Did a bit more work on it, fleshing the model out a little. Have also saved it in sketchup 6 format for anyone using older software builds who wants a peek.

With the seat pitched back, distance from the seat back to wheel, as well as seat base to pedals is extended. This should further emphasize the 'pushed back in the seat' feel as the controls move away from you. Coming forward, the effect is reversed, 'pushing you forward' into the wheel and pedals under brakes or diving..





I haven't really 'dimensioned' anything properly as such, it's all just eyeballing in there, (including rescaling the downloaded seat/wheel/pedals), so don't get too caught up in things not sitting right, it's really just proof-of-concept, there.

Oh, I should also note that things get a bit screwy at the extremes of movement. Again, I think it's down to that main universal not working right as far as sketchyphysics is concerned.. No matter how I try to mess with that and re-do things, it's not behaving as I figure it should..