Cable Robot Simulator [video] | Hacker News Reader

Cable Robot Simulator [video]

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261 pointsalex_marchant70 comments

This seems like a poor fit for VR motion simulation - actual movement through space is generally unnecessary, you just need to gimbal the platform to simulate accelerations. Actual linear acceleration is of limited value in simulation because you can't maintain that acceleration indefinitely - you run out of room and have to apply an opposite acceleration, which can conflict with the simulation needs.

On the other hand this looks more useful for something like movie making, to throw actors around in front of a greenscreen.

I agree that rotation should be enough for VR purposes, and linear translation of the subject is not strictly necessary.

Any acceleration up to g = 9.81 m / s^2 can be easily simulated, and it can be maintained indefinitely. All you need to do is to rotate the subject so that the perceived acceleration is aligned with g, or keep it at an angle, to get a fraction of g. Interestingly, for VR you don't need to simulate velocity, as it cannot be perceived by the body.

Flight simulators have been using this approach for decades now, and it works really well: http://arabiansupplychain.com//pictures/300x200/CAE-simulato...

But this system looks to have the advantage of being able to simulate accelerations above g.

PS: Is gimbal a verb now?

Not up to 1g acceleration, exactly 1g aceleration only (if the platform only rotates), with varying direction.

You can't do brief periods of weightlessness with rotations on a gimbal, or periods of larger than 1 g.

Gimbals are limited to ||acceleration||=1g. I guess there are some elements you miss from that, like when a roller coaster starts to fall (you experience <1g), or when a car takes off (you experience >1g). Here you can provide a bit of both and also gimbal action. There's also rotation effects (which I don't know if are felt) that can be mitigated too and better jerk simulation (not only acceleration, but variation of acceleration).

Actually if your whole simulation has ||aceleration||>1g you should be able to do it perfectly (save for jerk/rotation effects) with some large centrifuge: the rate of rotation of the large centrifuge dictates the "perceived gravity" and gimbals dictate the "perceived direction". In this sense it would be perfect if you could get a centrifuge with a gimbaled end in a 0g environment.

Hey NASA, I have this one little idea for the ISS... :)

I've been working with full motion simulators for the past two years (I even rode that simulator last week at MPI) and I must say that this is plain wrong. This is actually a great fit for VR simulation (see below):

> Actual linear acceleration is of limited value in simulation because...

Linear acceleration is immensely useful for sudden accelerations. Image a sudden linear acceleration (e.g. a racing car accelerating). You cannot recreate this acceleration by suddenly rotating. The angular accelerations would ruin the experience. Rather, you make a linear movement, and THEN you rotate the simulator (if you need to sustain the acceleration).

> you run out of room and have to apply an opposite acceleration, which can conflict with the simulation needs.

wrong again. If you move the simulator at slow speed, you can actually come back to the optimal position and the subject does not notice it (washout filter [1])

[1] https://en.wikipedia.org/wiki/Motion_simulator#Implementatio...

Would adding rotation to the seat allow for sustaining the acceleration?

The way I understand what he said (see quote below), yes it would.

> you make a linear movement, and THEN you rotate the simulator (if you need to sustain the acceleration).

I have zero experience with this though, I'm merely interpreting and copying what ghgr said.

That's right, and this system seems perfectly capable of that.

> Rather, you make a linear movement, and THEN you rotate the simulator (if you need to sustain the acceleration).

Am I understanding this wrong or are you saying long accelerations can be achieved by accelerating, turn, accelerating, .... etc? Wouldn't the person wearing VR headset feel the turn?

I think hes saying you accelerate forward then tilt back to let gravity help out.

Let's say I want to simulate acceleration going forward. First, there's the burst of forward motion provided by the cable rig, and that can be > 1G. By also gradually flipping the person onto their back you can simulate continued acceleration of 1G because lying on your back feels the same as 1G of acceleration forward. The VR rig would still show you accelerating forward. I am guessing that if the rig also slowly moved back to its original starting point the user wouldn't notice.

This is really neat! I'm really curious what the motion would look like from outside the room, and what the limits of a simulation would be using this technique...

It seems like the sort of fun project that would be cool to simulate in a graphic engine -- pairing the playing of certain games with a 3D model of the simulation room :)

Thanks for explaining, I kind of understand it now, but what if the acceleration is > 2G, then gravity won't be enough to simulate it, and I'm still a little skeptical that the user won't feel the rotating and "slowly move back" to original position, but I've never used a VR headset so I might be completely wrong here

Your body's not that good at measuring acceleration. Sure, it'll be hard to convince your brain that blood's pooling in your feet, but being leaned way back will provide a pretty convincing >1g forward acceleration feeling if the visuals are right.

Another way of saying this: we're good at sensing the delta of acceleration, not the absolute acceleration. Also, we tend not to notice small DC values of either acceleration or rotation, so you can manipulate the user's perception.

Someone published a similar hack for full-room VR, showing you can 'bend' someone's trajectory, to create the false sense that they're walking straight when in fact they're curving. In a large enough space you could simulate an infinite hallway (by having the user walk in a circle).

Sorry, I tried but can't dig up the link right now... but it's out there somewhere.

http://cb.nowan.net/blog/2008/12/02/redirected-walking-playi...

I think you were searching for that. It seems it also comes from the Max Plank institute.

That's the one. YourGoogleFu >> myGoogleFu.

Funny, I think Star Trek TNG described how the holodeck works by saying that it tricks the user not to walk into the walls. The visual feedback of slowly rotating hallway would definitely overdrive the inner ear. Too much, though, and you're going to get sick from it.

That's fair; turning motion into lean gives you best of both worlds - and there is, at least, with this the possibility of up/down accelerations, which are the hardest to pull off convincingly.

NASA seems to think different. http://www.aviationsystemsdivision.arc.nasa.gov/facilities/v... https://www.youtube.com/watch?v=fhu_UldlP_E (in motion...)

Yes, NASA Ames has had their huge Vertical Motion Simulator for many years. That has about 20 meters of travel in each axis. It used to have a Space Shuttle cockpit mounted; now it's mostly used with a helicopter cockpit. NASA's is a much heavier system, because it has to lug the whole cockpit around.

For flight, the problem is that the only acceleration that really matters is variation in vertical acceleration. Linear acceleration can briefly simulate that, but it can't be sustained. That's a fundamental problem that can only be dealt with by creating that kind of massive vertical acceleration environment - even that will be limited in terms of how long it can simulate sustained > or < 1g. You can create sustained accelerations by spinning something round on the end of an arm, but there's always that pesky downward gravity vector that keeps getting added to everything, unless you build your simulator in orbit.

If you like this, lookup "6DOF platform" - there's an active scene of people who tinker with home-made motion platforms, primarily for simulator games. Some very impressive stuff there, e.g. http://motionsim.blogspot.ch

I would love to see one of these platforms that's capable enough to feel right when playing Descent.

[0] https://youtu.be/rrUF8Dz84rE?t=329

The concern I have is that failures in the control software or mechanical failure would have grave consequences. Maybe that's a solved problem and the cable capstans have mechanical arrestors that kick in, etc but the setup looks inherently unstable unless under active computer control (due largely to the crossed cable attach points).

This is quite a bit different than a more typical hydraulic setup where an unpowered/uncommanded state simply leads to the platform settling in a stable configuration.

Having said that: I still want one. :D

You could make the floor foam blocks or a trampoline, but in concept it's very similar to the Skycam used for NFL games and they are very reliable. I've never heard of one coming down (and they have a lot more travel).

https://en.wikipedia.org/wiki/Skycam

There's certainly been instances of cameras coming down and having near misses with players and referees. Those cams weigh a lot and are moving at high speed as well.

edit: quick search returns https://www.youtube.com/watch?v=GPPJ6rg_TTA

Around 25 seconds into the video you can see how thick the cable is. I would guess probably an inch thick. With regular wire rope, the breaking strength of that diameter would be in the neighborhood of 80,000lbs[1] with the safe load strength closer to 16,000lbs. I'm guessing with regular maintenance and checking, it would be exceedingly rare to have a mechanical failure.

Additionally, the occupant is harnessed into the chair, bolted into what is essentially a spherical roll cage. Even with failure, I'm guessing there would be a crash but no serious injuries.

[1] - http://www.engineeringtoolbox.com/wire-rope-strength-d_1518....

It's more about how the cable is managed in terms of slack, keeping the cage from flipping over, etc. I agree with you, the cable itself is an unlikely point of failure.

Massive wires each under 1.4 tons of tension would make for quite a show if one did break

I'm surprised they have the computers right next to it... and people standing there. I wonder how they mitigate the possibility of unintentional (error driven) movement?

Cable Robots are generally a very interesting technology. I wrote a bit about them (eg. for 3D printing, as a crane, etc) a while back: http://www.hizook.com/blog/2014/07/15/stadium-sized-3d-print...

I purchased a commercial motion simulator as part of research for a vr tech we're working on and while you can immediately see the potential, it's not quite there yet.

Some resources to share

If you buy a simulator - offsetting to the chair with the rift is a work in progress https://forums.oculus.com/viewtopic.php?t=7933 - and not currently supported in the Oculus SDK. I can't find the thread but Oculus has said that's a "future tech" goal.

Excellent thread on currently available options / configurations - https://forums.oculus.com/viewtopic.php?t=1673

A great resource with a community of enthusiasts that have tried nearly every sim on the market (racing specific, but still the best) is here - http://www.isrtv.com/forums/

Multiple computer-controlled winch systems have been used for movie special effects for years. Here's a 2010 system test for a flying taxi, which shows the controller as well as the taxi.[1] Disney's Aladdin at Tuacahn Amphitheater has a magic carpet which flies out over the audience with two performers on it. That's done with four computer-controlled winches.

The robot simulator looks like it's using the same winches Kirby's AFX uses for theatrical work. That's not surprising; few companies make high speed precision-controllable winches rated for human safety.

[1] https://www.youtube.com/watch?v=VkjM9leyQPc

Somehow it reminds me of this: http://www.youtube.com/watch?v=G-N3XDc-3QQ

Looks a lot like University of Iowa's National Advanced Driving Simulator NADS-1 [1]. NADS-1 has an entire dome on tracks, hydraulics and a bunch of other cool stuff going on. I guess it's used mostly for research.

[1] https://www.nads-sc.uiowa.edu/sim_nads1.php

Here's the press release from the Max Planck Institute:

http://www.ipa.fraunhofer.de/en/cable-driven_parallel_robots...

I didn't see any Yaw motion in this video. (Rotation about the Y axis.)

Does it support it? Is it not necessary for the motions they're trying to induce? Would you have to make the seat rotate on the platform?

I believe with that cable configuration, Yaw motion isn't really possible. I'm sure it would help with motion programming with the VR, but perhaps true Yaw wouldn't be entirely necessary. Good questions though.

For your last question, I do think that's the way they would need to add Yaw if desired. Otherwise more cables and/or a different configuration would be needed.

As an example, check out the robocrane design from NIST: http://www.nist.gov/el/isd/gantry-2.cfm

It says "freely programmable trajectory in six dimensions", and there are indeed six cables, so yes it's supported. But any rotation of that object is going to be limited of course.

A motor under the platform that swivels the user, chair, and floor inside the cage would do it. But I agree with the other commenters that the video does not seem to demonstrate a yaw capability.

I want one. I'll replace the walls/stairs in my house with this and just zoom exactly where I need to go. Think of the space savings; I could mount my computer 6" from the ceiling!

This would actually be dope for flight training. As a student pilot there are some things like unusual attitudes training, that rely on motion to fool the senses.

I'd like to know more about the winches, since they aren't made for constant use. They have planetary gears with very high gear ratios, which can overheat if used too long. I believe many linear actuators (with high gear ratios, used to lift beds/tvs) have ~20% duty cycle (use for 2 minutes requires 8 minutes of cool down).

it looks really cool, however with cables wouldn't this limit the amount of "instant Gs" you can generate? it seems motion simulators based on pistons would be able to simulate better things like driving on a bumpy road and sudden changes of direction as there isn't the slack of the cable to take into account or the inertia of a large suspended mass (cables are heavy too)

Still given enough space and light enough cables that support enough tension (to minimize slack) it seems this could be scaled up very cost effectively compared to other technologies to enable longer sustained accelerations

> slack

why cables are loaded at 1.5tons. Electric motors have incredible torque and those looked like some honking big motors.

Hopefully not a completely ridiculous question, is there any chance cable technology like this could be used as public transportation in the future similar to in Pixar's Robots?

Come visit beautiful San Francisco! https://en.wikipedia.org/wiki/San_Francisco_cable_car_system

I think the wires would get in each other's way if you had pods in the same volume.

Ah of course, that was silly of me. I guess I meant suspended cable travel.

Sure: https://en.wikipedia.org/wiki/Ski_lift or https://en.wikipedia.org/wiki/Gondola_lift

You are right! But it is now apparent that the question I had in mind is completely different from the one I actually asked. nbadg caught on to what I meant which was more along the lines of: could suspended cable transportation be a feasible mode of public transportation in cities?

Yes. The biggest benefit is very low ground footprint and highly predictable traffic flow. A few articles discuss it as a reasonable form of mass transit.

http://urbanland.uli.org/infrastructure-transit/public-trans...

http://www.seattletimes.com/seattle-news/commute-by-gondola-...

This is really cool. Thank you for sharing!

Two quick answers:

1. Could it?

Depends what you mean by "cable technology like this". I haven't seen Robots, but this kind of constrained, multiple-degree-of-freedom movement would not be possible in an "open world" -- you have to have existing infrastructure, and for something like cables (which "operate" in tension only), that infrastructure has to surround the entire "vehicle". And cables have an effective practical length limit before you run into a number of physics barriers. Now, you could have something that operates by a cable pulling a car along a predefined route, but it would be a simple linear movement. Not only can you, we already do this: most ski lifts work this way. So do, for example, the SF cable cars.

2. Even if you could, should you?

The tl;dr here is that in the vast majority of modern cases, other technology is better. If you're going to expend a whole bunch of money on infrastructure, which is necessary for public transportation in general, why not make it something higher capacity? Lightrail, or high-speed bus, or really almost any other form of public transportation is more effective. Where the ski lift approach shines is in low-volume, low-speed transport across terrain that would be very, very difficult (read: expensive) to lay tracks or road across, like mountains. Similarly, the cable car approach shines in situations where rails offer questionable traction in adverse conditions, and a positive connection with something is hugely beneficial (like a very steep hill). There are always niche applications, but I wouldn't hold my breath for widespread use.

"Robots" is not a Pixar movie.

Ouch, my mistake. 20th Century Fox's Robots.

Cool, it's the same concept as the NFL skycam! I wonder if there are any practical uses for it, say military or civilian training?

Do you get sick from driving a car or riding a bus though? Because I guess you could make the experience to be exactly like that. It's supposed to feel like a normal, natural motion.

Very fascinating, but I also feel left out. I get sick just by riding a Ferris wheel.

This could make for an interesting Disney ride!

Anyone knows scalable it would be? To start, everyone would need a VR headset, not that amusement parks are short on cash

with those same cables, they would probably be able to carry hundreds of people at the same time... just make the platform a bit bigger and maybe upgrade the winches.

It _is_ a Disney ride! I've ridden on it—tons of fun.

https://en.wikipedia.org/wiki/Star_Tours

The technical description:

> Star Tours utilizes hydraulic motion base cabins featuring six degrees of freedom, including the ability to move 35 degrees in the X-Y-Z plane. The simulator was patented as Advanced Technology Leisure Application Simulator (ATLAS), originally designed by Rediffusion Simulation[8] in Sussex, England, now owned by Thomson-CSF. The Rediffusion 'Leisure' simulator was originally developed for a much simpler show in Canada called "Tour of the Universe", where it featured a single entrance/exit door in the rear of the cabin and a video projector. The film is front-projected onto the screen from a 70 mm film projector located beneath the cockpit barrier. The Disneyland original has four simulators, while the shows in Tokyo Disneyland, Disneyland Paris, and WDW Disney's Hollywood Studio each have six motion bases.

looks like we are getting close to VR with some (unreal) experience

It's a holodeck!

All well and good with the standard little girl model, but what does this look like with ten fat disney tourists? What would the machinery look like to swing 10 or 50 times the weight? (Same question if this is to be used for flight simulators.) Is there a point at which linear hydraulic actuators are easier?

> All well and good with the standard little girl model

"The software developer Maria Lächele from the 8-person developers team at the Max-Planck Institute is seen amongst others as a passenger of the robot."

Reading a bit too literally and presuming the worst intent behind the statement. It leads to better discussions when people assume the best possible intent unless the person later clarifies their intent. I don't think they meant "model" as in "attractive fashion model".

"Standard model" is a thing among products. For example, they give out 3D glasses at the movie theater I visit. One-size-fits-all is the "standard model" but they have two sizes of booster seats. They have the "children model" and the "adult model".

So let's throw the complete statement that you removed back in:

>but what does this look like with ten fat disney tourists?

So the standard model ("little girl" [sic] sized) works great. How does the "jumbo model" work for an obese population?

I'll agree with the implicit sexism and infantilization behind the use of "little girl". Though I also refuse to ascribe sexist intent behind the word choice and I'm someone who cares about intent and not interpretation. One can always interpret the worst possible intent and find evil in everyone and every statement. Also yes, I'm aware that bad deeds can sometimes have good intentions.

They were highlighting a physical trait (smallness). "Small woman" and "little woman" are awkward to say and imply dwarfism. "Woman" as a standalone fails to highlight the smallness. I'd personally use "petite woman" but that becomes awkward in conversation because I'm seemingly the only person who uses the word "petite" in adult context without referring to porn actresses or nude models.

TL;DR:

It works fine for the 105 lb~ model. How about the 350~ lb model?

So? She could be the chief engineer, but in the video she is the model, the stand-in, the demonstration person. Call it sexist if you want, but it is standard marketing practice to use young women/girls in promotional vids. Where movement is involved, models with long hair are also preferred as it shows the motion, something that again tends towards young girls. Smaller people also make products seem larger. Where the product involves a seat (cars, air travel etc) a really tiny person makes things look much roomier and more comfortable. Where the action is recorded at a distance people with clear skin but darker lips and larger eyes are more expressive, again trending towards females. Where there is any sort of perceived physical danger you pick models that, rightly or wrongly, are perceived delicate. Use a 250lb Army grunt with massive muscles (of any sex) and viewers might think they also need to be tough to enjoy the product. So this vid is following standard marketing practices in selecting a very standard model.

My point still stands. What would rigging for several non-small people on this thing involve? Looking at the angles on those cables, a 10-fold increase in payload might need a 20 or 30-fold increase in cable strength ... adding weight ... needing stronger cables.

After watching it a couple times more, I'm also interested in how it would handle asymmetric loads. How much before it tips into a cats cradle of wire? Is there any feedback into the system to detect such situations?

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