What fast linear actuator would you use?

Guise. An actuator is a DC motor configured as rack-and-pinion with a shaft. You can understand why I'd mistrust opinions from people who haven't tried both options.

Anyway, pretty clear that this thread is done now. Thanks for your input.

@Antidamage , this not the wrong place to ask things or suggest new ideas at all, we welcome it. If you have new ideas, the best thing is to put them into practice and show us all.
However, unless you have more substantial proof from having or using an actual a working simulator, then I would say you are assuming from information and videos (and the one you originally linked is SCN actuators, not from a bed or hospital).
Simulation on a DIY scale is a mind trick, we are not in a position to re-create actual g-forces. Even I am surprised at what my mind thinks is going on with motion and whats happening on my screen, and thats with my "bump" simulator.
The discussion between "seat shaker - bump" simulators and 6 DOF has gotten very heated with assumptions being thrown back and forth in the past.
Again you are welcome to suggest ideas, however as seen from other peoples replies, kindly step carefully, because unless you can say you have had 100 or so people of ages from about 5 to 88 and 10 professional drivers actually use a seat mover simulator and they have stated, it feels immersive and they get the feeling of g-forces, then your assumptions and suggestions are nothing more than leaves in the wind.
Cheers, David.
P.S. I use actuators on my current ride, however, the DC motors we use have proven themselves to be excellent in motion use and quieter , and faster than my actuators sound like a wood saw going mad. Mind you, I got the actuators for free and had to re-motor them myself and even though they are a lowly 250mm per second, I might as well use them.
Actuators

DC motors

"Kindly step carefully"? That's some thug life shit. I do not care to validate my standing in your community before expressing what I want to do and if I have to, enjoy your very elite little group. Also I don't think your actuators are doing anything in that first video. Compare yours to the video I initially posted. That guy's setup could toss someone out of the seat if it wanted to.

So getting back to the point: one of the first replies to this thread is some waffler trying to show how smart he is and how dumb I am. Almost all the rest are along the lines of "you don't know what you're talking about, we haven't tried it but it's stupid". I know I don't know what I'm talking about - that's why I came here to ask questions. But what I got in return was general spite and snobbishness. I didn't come here to make a worm drive rig and all I get back is "why aren't you making a work drive rig?" You guys are unworkable.

Thanks to those of you that helped and sorry you're being tarred with the same brush as the rest of them.

Well, I'm building a Sim with actuators - all be it DIY - quick? 375mm Sec ... http://www.xsimulator.net/community/threads/seattimes-6dof-dc-build.6106/page-14. For similar specified commercial actuators, it really can get expensive .

This is a community, you explained your theory and we gave our thought on it, but nobody is stopping you to prove us wrong. I tried different approaches (always with actuators, SCN5 are 400mm/s with no load and SCN6, 40kg and 200mm/s) but the best it's what you call "bump simulator". In a 2DOF it's impossible to do it, just because the simulator can't move up. It's a complicated topic anyway, when I try to explain to my friends I can see a lot of confusion and they ask me a lot of question. It's complicated due to the quadruple model (virtual world, virtual car, real world, simulated car) and the interaction between them. Even the cable simulator you posted it's flawed, what is going to do when it have to simulate an infinite acceleration in one direction? Does it have an infinite space to travel? That's why most simulators use leaning, if you sit on a chair with the chair's leg glued to a wall, your vestibular system tells your brain you are accelerating up in 1g, cover your eyes with a VR visor and your brain tells you are accelerating in the direction you watching to 1g. That's maximum leaning (90°) but this isn't achievable because of all the transition problem, it would be very hard to quickly switch between leaning direction. Luckily, comes to help us, as a matter of fact, our brain is capable to adapt the feeling of simulated acceleration to basically any leaning angle. It doesn't matter if you leaning 10° or 20°, once you get used to a certain degrees, the trick works just as good of any other leaning angle. I know it might seems counterintuitive, but that's my experience. The first time my seat moved (a little), I was scared to fall on the ground, for the very same reason, my brain wasn't used to a moving seat, and it felt an unexpected acceleration, which made me believe to fall. Our brain is very adaptable and we have to use this ability to get the most out of our simulators. I hope this post can help you.

This isn't the first time we've had a user come through the doors with your attitude, and It wont be the last....

@Antidamage There are lots of us who like large movements, there is really nothing wrong with either type; it depends on your preference. Keep plugging away and find what you enjoy using. Please do continue to ask questions, experiment, and hopefully you can introduce something new to the hobby. And a belated welcome to the forums.

Opinions are like an asshole.

Everyone has one and only yours doesn't stink.

Yup. I'm from Auckland, North Shore.

I have a rift also and you are welcome to come over and have a blast on my motion simulator.

It would be cool to share tips on the rift because I have only had mine for a few weeks.