6Dof Design for Dynamic Aircraft.

Dear fellow simulator enthusiasts,

I'm starting to buy the parts for my 6DoF rig. I've had a look at some of the amazing projects that the people on this site have built and am feeling pretty inspired .

The rig I'll be building will be for a computer game that I'm writing. The aircraft that I'll be simulating is highly dynamic. Think fast min helicopter.

So my first question is about the type of actuators that would best simulate highly dynamic flight.
What are the most important considerations: stroke length, speed, force?

I've had a look at a fair few projects on this site and have seen so much amazing work, but most of the projects have been for car simulators or larger aircraft, and so I'm concerned about copying the designs. Ideally, I would build something like @zigzag49 which is both beautiful and compact. Do people think that sort of design would be suitable for my application? If not, I would be grateful if somebody could point me towards the right sort of design.

Many thanks in advance to anybody who takes the time to answer these questions. I hope I haven't wasted anybodys time .

Thank you very much @noorbeast,

I'm not totally opposed to building my own actuators if I have to, but I would rather not. I would be willing to spend up to £500 (870$Australian) per actuator and have been looking around for actuators in that price range. The supplier I hear mentioned most often is Frex, who do have some actuators in my price range but they either have a relatively short stroke 100mm https://bit.ly/2Mye4B1 , or they have a low max load (https://bit.ly/2MXbfqq). I've read that for a Stewart platform each actuator should be able to carry pretty much the full weight (Is this true?).

Considering my application (agile small aircraft), is it possible to get suitable actuators of the shelf in my price range, or am i going to need to build them my self (something I will do if necessary).

I've been trying to understand the actuator requirements for my project for a bit of time now and have been really surprised by the steepness of the learning curve (who thought there was so much to know). My greatest fear is that I buy some really expensive equipment and then find out that it's just not good enough. It seems like there are 4 considerations when buying actuators:

Stroke length, I imagine I'll need a large stroke (at least 150mm) because the vehicle I'm simulating is very agile.

Stroke speed, I've heard this should be over 150mm/s.

Maximum Force, It should be able to produce as much force as the weight of the upper platform and pilot.

Duty Cycle, Actuators with low duty cycles will not last for very long (need high duty cycle).

IF ANY OF THE ABOVE ASSUMPTIONS ARE INCORRECT, PLEASE TELL ME!

As stated previously, I am extremely grateful to anybody who takes the time to answer my questions.

Thank you in advance.

Yep, purchasing or even building quality actuators + controllers/drivers and powers supplies/batteries etc to drive a reactive/agile Stewart Platform is expensive. I'm going to be a bit controversial here and put the question - do you really need a 6DOF stewart plateform? If I was to build a simulator from scratch today - I'm not too sure that I would think it necessary. A full G seat + harness and a highly dynamic pitch/roll rig would be pretty hard to beat for performance and price. Don't get me wrong I'm not about to pull my 6DOF apart - but is it really necessary - from what I now know I don't think so. Sorry for confusing you even more ....

Something like this perhaps?

Thanks for all the answers everybody.

@SeatTime, I think you're probably right: I could get away with just a G-seat and a roll and pitch platform, in fact, I'm going to take that idea seriously and change my course of action. This should massively reduce the platforms cost and build time .

I'll get back to all of you when I have something to report, but the meantime will be busy sourcing materials.

You'd really sacrifice heave? Admittedly my gseat isn't doing heave very well at the moment but even if it did surely it won't give that genuine sensation of movement - i'd like to simulate the feel of a light aircraft being thrown around in turbulent air.

When I say a 'full' G seat I am including a heave function in it . Still have pitch and roll, so plenty of throwing around happening for a aircraft - and with the harness and G seat - much better then any 6DOF by itself. When I run my system with just the 6DOF and the G systems turn off - it feels 'dead' - especially for aircraft. I'm sure the members with G seats/harnesses will back me up - it is that good - a quantum leap for simulation. Although I am spoilt rotten with my G Vest.

FI - My current design for a commercial G seat is to use three moving panels for both under and behind the passenger - this allows good independent heave and surge motion, as well as decent side pressures.

How will you be applying heave on your G seat when it's not on a rig that heaves too? If you go up then heave will quickly max out just like a motion rig does so it's not a G seat type sustained pressure. If you go down it would be similar to a sustained force holding you down in the seat but the pressures felt will be all wrong. In my mind I would want a rig that heaves up while my g-seat moves down. While this would initially somewhat cancel out each other's motion I think it would feel good having the feeling of being compressed in the seat just prior to heaving upwards.

Or maybe you have something more exotic in mind besides a single heave flap.

Yep, your right that's why it does not work in quite that way. Your not seeing it , but that's OK - early days...

Aw shucks

Over the last week, I have been keeping my self busy putting the G seat together. I'm actuating 4 paddles using these 20kgcm actuators from Amazon.
https://goo.gl/fH3sQQ
The actuators are connected to the paddles through a cam, the shape of which can be altered to change the force produced by the actuator.

For the roll and pitch, I have opted to use these 500kgcm motors.
https://goo.gl/Z4tist
I was hoping somebody on here would be kind enough to have a look at the links for these motors and tell me if they think the motors will be good enough for my purpose (small dynamic aircraft).

Every thing is going well and thanks for the help so far!

@MarkusB uses those 500kgcm motors on his g-seat I think. You weren’t planning to use them to move a 2dof platform were you?

The other ones I have never heard of before. They might be ok on the backrest but I doubt they’d work for the base of a g-seat.

Thanks, @RiftFlyer,

Yes, I had been planning on using the 500 kgcm motors for the 2 dof platform. I anticipated that it might not be good enough so only ordered one allowing me to test it out. 500 kgcm seems like a lot of force to me, but I suppose I should try and find something else.

Thanks .

I have no idea if they’d be powerful or fast enough to be honest. Are you just moving the seat or controls and pedals etc as well? I haven’t built a 2dof yet as I use a rift and there is no solution for motion cancellation available yet. I just have the GSeat so far. I’m sure others will guide you.

@RiftFlyer is right, I am using these 500kgcm servos for parts of my g-seat.
I doubt that they are suited for the 2DOF. They are quite slow and not very accurate in their positioning, and I think they are not constructed for such a permanent load.
I have posted some information about these servos here.

About your 20kgcm servos: How many of them do you plan to use for each flap? Not just one, right?

Note that the torque value on servos is the stall torque, i. e. the torque at which the motor is not anymore able to move the load. The torque you should use for your calculations is much less.

Thank you very much @MarkusB ,
I was being naive when selecting my motors. As you advise I will no longer be using the 500kgcm for the 2dof platform, instead opting for the worm gear motors that I have seen so many people on this forum use. Should I be looking at the nominal torque value instead of the max torque? and if so what kind of nominal torque should I use?
This looks good to me, and at a reasonable price, what do you think? https://goo.gl/p49SHP.

In term of the flaps, the ones under the pilot will each will be powered by 4 20 kgcm servos, and the ones in the back of the seat will probably only need 3.

thanks.

I don't have any torque values at hand. Maybe some other members can help here.
About the motor in your link: They mention two torque values and I am not sure which is the relevant one: 20 Nm sounds ok, but 3 Nm is not really much. Maybe 3Nm is the torque at the motor axis and 20 Nm the torque at the gear axis?

I am using second hand wheelchair motors, which are perfect for me. Got them from ebay.

And since you are located in England, you could have a look at there motors, which are used by several member builds:
https://www.motioncontrolproducts.co.uk/products/8/167/dc-brushed-geared-motor-90zyt155mcp4/
The 50 Nm type should be strong enough even for a compact design.