aarondc's nDOF rig

Hey there

I am starting this thread to track the development of my sim / rig. I saw some videos of the DBox in action and thought it looked really simple - a good sign of something well engineered. I thought it looked so simple I could probably build one, and went about looking for linear actuators with similar specs to the ones they provide with the different models of actuator units.

I have some in mind, but once I saw this forum, and the different methods employed for nDOF movement, I am cooling on the idea of the linear actuators to some extent, and looking to gain significantly more knowledge and understanding on the principles of nDOF movement and its implementation.

I probably prefer flight games and FPS games to driving games, but to be honest I prefer writing software and building things more than playing games.

First question category: Degrees of freedom

I see lots of 2DOF and then a leap to the 6DOF in the FAQ section, and have seen 3DOF mentioned also. Is there a good explanation of what they (2 vs 3 vs 6) are anywhere? I found the list of roll, pitch yaw, heave, etc, but which 2 are used for 2DOF, which for 3? I am googling / do google - definitely not asking you to do the heavy lifting. But if you know a good explanation immediately, that's helpful and avoids me reading about depth of field and manufacturer-specific marketing bs.

When it comes to flight sim, what's the minimum required to get by - or, given the answer is probably 2DOF, how much better is 3DOF? And is 4DOF nonsensical? And if not, how much better than 2 or 3DOF is it? And how much better is 6DOF than the others?

This is fundamental to the design I will pursue, so your assistance in understanding this concept would be much appreciated.

Good 6DOF explanation here: https://en.wikipedia.org/wiki/Six_degrees_of_freedom

Pictures help - I am very visually oriented.

Specifically:

So the chair I am sitting on can:

swivel left and right = (yaw)
adjust for height = (heave)
adjust forward angle, like a rocking chair = (pitch)

So my chair has 3 degrees of freedom yeah?

And translation is the whole object, rotation is fixing one part of the object and moving the rest. 3rd year 3D graphics unit from Comp Sci and all those matrix calculation memories are flooding back.

Hi aarondc

Good choice!

With your second post I think you've found a good starting point.

• 2DOF is of course the easiest. If you balance your platform nicely (i.e. the rotation axes cross the centre of gravity) there is not a lot of force needed to move the platform → that's the reason why many people here have built simulators with relatively weak windscreen wiper motors.

• The next step is 3DOF. The budget you have to assume is about 5x the one for a 2DOF because of the additional hardware requirements.
While you can balance a 2DOF so that you only need to overcome the inertia (→ wiper motors) a 3DOF must lift the full weight of the platform including you. So we're talking of moving/lifting 100 - 200 kg.

• Then comes the 6DOF. This is obviously the best for simulation. Here the challenge is not only in the hardware but also in the software. Like with the 3DOF you have to lift the full weight of the platform and you have to develop a sophisticated control software that steers the motors and tricks the mind. Because you have a restricted movement range with a Stewart platform, you have to quickly return the platform back to the initial position after a movement – but in such a manner that the user this time doesn't realise the movement.

Yes, you got it :thbup:
Remember though that yaw and pitch are rotations, while heave is a translation. See difference above.

Great! So you are in a good position for the software and we can come back to you when we need help on vector algebra. :hi:

G'day value1

Hah! I finished that degree before most people here were born. I can certainly try, at any rate.

Top quality answer, value1, much appreciated.

I think it was the first time I ever saw a Stuart platform in operation that I started dreaming of building a simulator rig.

The few posts I have seen here and youtube videos have demonstrated the balancing strategy quite well. It's actually helped me rethink another non-sim (kinda) project I have on the boil, so it's been doubly helpful here.

Thanks again.

So then, the choice seems to be..
2DOF, 3 DOF, 4 DOF or 6 DOF.

And purely my own experience , I played on the VRX 4DOF Dbox race sims in town. I was not impressed at the slow motion.
People whom have played on these units have had the chance to play on my big motor 2DOF and they agree, its a far better motion for race compared to a $40,000 sim.

Depending on what you plan to use the sim for, even a 2 DOF with a good motion profile, after a while, your brain thinks you are on more DOFs, so to speak.

Up to you of course ;D

I will have to investigate some arcade places with these machines to try them out.

bsft, what do you think makes the difference in your 2DOF sim vs the 4DOF sim - is it just the motion profile, or are there other contributing factors? If the VRX increased their speed (can they?) would that make it better? Is it possible people see the VRX and their expectations are raised, only to be unimpressed? Form over function seems to be the way for a lot of things these days.

I am definitively in the function over form camp, although have a lot of ideas for making the sim look good once it's fully operational.

Can you point me to the thread where you discuss / demo your sim? Would like to check it out.

jfc, this unit was $20k new. wtf!?

It looks pretty quick, but the range of movement is far less than the 2DOF scn5 sims I have seen demoed here.

http://www.youtube.com/watch?v=5tdoQCUrtgs

Does range of movement play much impact in realism?

Right then. I've made my choice. Just need to find some window wiper motors...

http://www.youtube.com/watch?v=QCGcWOwV8Qs

bsft is motiondave? sounds similar

Ok dude, heres my thread on the motor sim I have.
2-dof-big-motor-foot-placement-sim-t3822.html
Videos to look at are on the page.

Heres a video of an earlier frame with the same big motors, I was only using a single turn pot for feedback so the fine resolution was a bit less than what it is now. But you can get an idea of the movement of the motors on a different frame. http://www.youtube.com/watch?v=ZbN8XF027lc

AS for 2DOF to 4DOF, I am not really qualified as I have only sims I have built for experience. a good 4DOF would work well for sure.
I only have done 2DOF for cost reasons.
The dbox sim place had the motion turned down as most people whom go in there havent played on a motion sim, so even for them , its nasty. I just wasnt impressed on the units in town, thats all.
I was going to try the 3DOF unit you show a video of, but at $150 per hour, minimum 3 hour.......get stuffed.... or $15 for 10 mins if I can get to a show they are at. Then theres entry cost, etc. In town it cost me $30 for 15 mins. Plus travel costs , etc.
SCN5 sims are snappy, however, the scn5 actuators tend to snap the pin inside after a while.
SCN6 are stronger, but more costly.
Range of movement could impact on realism, but not sure how much.
Car racing is fun with BIG movements, but would take some getting used to. Whens the last time you saw a car lift more than 150mm off the line at a race, exception of a drag race car.
Rally on the other hand :brows:
It took me a while to get used to motion and fiddle with values to get the right feel, that and many different designs to find a decent compact simulator.
Others here have WAY more experience than me, but I will endeavor to help.
Motion simulators is about tricking the brain as to actual throwing you around.

thats me, different name on a different forum, of which i was banned from for false reasons.

Beware wipers are only good for seatmovers, any other way they tear the gear apart, very quickly.
Plus you have to open them up and modify the wiring, and risk it not working after you put it back together again, for me they we just headaches, $100 winchs and still going 4 years later.

Sorry mate, I posted a link to a $M++ robot arm sim, and said where's me wipers - it was a bit of a tongue in cheek joke.

Do you mind providing a bit more info on the winch motors you are using? Which ones, their stats, etc?

Do your motors allow you to provide fine-grained feedback (like shuddering?) or are transducers better placed for providing that low level feedback?

I found some $100 winches on Ebay: http://www.ebay.com.au/itm/12V-3000lbs- ... 0457328300

but bsft seems to think they are not the right ones.

I will let Rob answer further on this

Sounds mysterious?

http://www.ebay.com.au/itm/NEW-12V-2000 ... 109&_uhb=1
found it!

Yep they are the ones.

http://www.x-simulator.de/forum/gallery/image_page.php?album_id=92&image_id=354

With covers off and modified with 5 turn pot for fine feedback results