My dumb noobie questions

If it is OK I will post all my dumb Q's here in 1 thread adding more as they come to mind. I have a few but will just post them slowly 1 at a time.

At this point in time I am planning to make a 2 DOF with the view to the 3, 4 and maybe the 5th axis later. It will be all moving not just a desk style, very laid back more along the lines of an F1 car to keep the boss happy.
Drive motors will probably be the worm drives from Motion Dynamics as so many others have used with great success.

I keep reading that it is preferential to mount the tie rod, for want of a better description, high on the seat back.
My logic would suggest that it is the distance from the uni to the mounting point and not the height of the connection that matters. I realise that the longer the lever the more mechanical advantage that the motor has but then the motor needs a longer lever to get the required travel. The only reason that this would be better would be to reduce the shock loads on the drive motor bearings. Is my logic sound or have i missed something?

I lied, I have 2 q's this time

I see mention of the amount of throws used in various setups but this will vary depending on the distance from the tie rod mount to the uni. Can anyone translate that into angles of movement instead then i can vary my travels to suit my lever points.

Thanks
Mike

P.S. I will be back with some more q's soon

Either you can increase the distance from the ujoint or reduce the length of the lever to reduce the load on the motor. Height will also increase the distance from the u joint. Optimal load your motor can take will depend on your h bridge, power supply, motor ratings, cooling system and maximum user weight.

@MikeG , ive done that in the past
http://www.xsimulator.net/community...im-updated-photos-19-11-2013.3822/#post-47764
Motors were about 700mm from pivot to motors, and I made an extra bit of frame to reach up near bottom of seat level. It helps to get the motors up a tad higher like I did.
The only thing I did wrong was to mount the motors narrow. they are 450mm apart. so more like 225mm to pivot from motors that way. Well, not exactly wrong. I was keeping it under 600mm total width to get it in the front door of the house.
Angles of actual swing were about 7 deg total angle on surge and about 18 deg angle on sway. A profile adjustment helped it from swinging too far from side to side. And the surge was excellent. Once I had profile sorted, the immersion was great.
Motors are from Motion Dynamics in Sydney and controllers the JRKs.
Oh and also the lever was 45mm CTC.

@bsft- thanks for the angles. Hopefully they are fairly typical.
@noorbeast - yes it is along the lines of the play seat.

I have the sketch done but it is in my mind and not on paper till it is past the beta stage. I am the type that needs to understand the relationships of the system before i can make a decision on direction.

Part of what prompted my first q leads into the next one. Sorry
I imagine that as the motors are both aft of the pivot point then as one lengthens and one reduces, for sway, that would impart a degree of rotation to the seat as well. Is this movement desirable or an unavoidable consequence of the geometry ? Its a bit hard to tell from the vids as there is so much motion going on all the time it is hard to separate the motions in my mind.
My reaction to that would be to place one motor to the side, for sway, and one on the center-line ahead of the uni joint for surge. Both would be under the seat which results in a much cleaner, and shorter, appearance. With the laid back position saving length will be most important.

that in theory might work, however, I can see issues of the motors not holding properly even under power. They are 12v motors, maybe 240 v would hold it like that, but not 12v.
best you draw something up on paper for us to see.
Back to angles, the idea would be to try to keep them as similar as possible, but with different designs gives different angles.
My desk racer is 17 deg total angle surge and 7 deg total angle sway, because of motor placement.

@bsft
Your 2 DOF big motor foot placement sim seems to be close to what i was thinking. Thanks for that link.
Sorry , when i said under the seat it was not quite what i meant, my brain was visualizing more that configuration rather than high on the back. Get the long lever arm at the front under the seat rather than height at the back.

It seems to perform fine from the vids. Having that to look at gives me enough to now think further on how to incorporate surge and traction loss.
What motors are you using. They look like the Motion Dynamics Worm Drive Motor 12V/24V 200W, 180 RPM, 20Nm Torque
With that placement of motors i don't think there would be a lot of yaw superimposed on the sway.

While i have been mulling over angles and lengths of the motor arms i got fed up with diverting my attention to work out each combination so i drew up a little graph to make it easier. Hopefully others may find it somewhat helpful. Print it out at 300 DPI and it should come out the correct size.
Easy to get the third component from the other 2 variables. eg if the angle of movement and the length of the arm is know then just measure from the intersection of the angle and the radius to the same point in the bottom quadrant.

Hi
you can use google sketchup in 1:1 scale, then if you want you can print the lever arm and push rod details at full scale, save messing around with
calculating angles, xnd throws, also to get max sensitivity the seat push rod needs to be at 90 deg. to the moyor crank arm at mid position

regards Terry

When i get my thoughts a lot more organized i will probably draw it up in Solid Works although it has been quite a few years since i did any major models with it..
This was just meant to used at the stage of having many ideas and quickly seeing what a combination will need or what combination is required for an idea. A lot faster than drawing up each idea. Its pretty easy to do a quick comparison of different motors and gearboxes for resultant speed and torque for the different angles and arms required.

Good info fellas.

Have been mulling over ideas in between other projects. I have to make a diversion which will put the sim back a fair while, Mate broke my small CNC router so am going to build a lot bigger and far stronger one. Design is done and the table is under construction. Most of the gear is on order and will start putting it together after i get back from Indonesia in late January.

If i don't change my ideas about the sim the bigger machine will come in very handy for the sim construction.

This is only 1 idea for a possible machine, i have more
Warning. This idea is a little off the planet so don't spill your coffee when you look
I fly so a sim that could double as a flight sim drives a few of the ideas. My terms are more related to an aircraft so may differ from some of the terms used here to describe an axis. To me for and aft tilt is pitch and roll is termed here as sway.
This thing has +- 27 degrees of roll in .6 sec and +- 20 degrees of pitch in .33 sec. If the motors lack power then there is always bigger motors There would be roller bearings between the curved beam and seat of course and more rollers to stop the seat coming off the base.
The for aft travel, surge, i have as +- 150mm but ez to make longer if people think it needs more.
Sway for traction loss is not drawn yet.
Don't worry about strength or stiffness to much yet. Give me a bucket of epoxy and a big spool of carbon tow and i can make it plenty strong and stiff while pretty light and besides i can't weld for shit.

You mean something like this?
http://www.flightgear.org/Projects/RayChair/chair.jpg

bsft
That one is interesting but i can't see how they do the roll axis. The yaw axis must have a serious bearing at the bottom as it seems so small.
It sure does fix a couple of potential problems i can see in my version.

I want the loss of traction but that needs quite a different pivot point than Yaw for a flight sim needs so makes it difficult to decide which to have but most likely the driving sim will win out. Having both would become quite unwieldy i think.

Time for another sketch

Another feature i would like is to have 2 neutral positions for the seat. One laid back for F1 and one more upright for a normal car or flight. EZ on my version, different tie rod lengths, but will need to sketch up some axis points from the one you posted to see how that will work out.

yep, maybe do another sketch so we can get a better idea
You have the right idea with the design, but will need very powerful motors or even actuators to move it.
Just like the rock n ride. It is compact but needs a lot of power to move it. It was originally designed with air actuators.
If you have the skills, build these http://bffsimulation.com/linear-act.php
I was building some, but I ended up sending the parts to a friend and when he gets time he will finish them.
I didnt have the tools needed to tap out a 10mm thread hole.

Lots of supposition follows, lets see how stupid everybody thinks I am.

Maybe I am wrong but I think the power to shift an axis is dependent on the on the position of CG relative to the pivot point and the amount of movement and speed is desired. For a sim we need to consider the 3 dimensional position of the CG and with the pivots at the 3d CG point the power required is as small as possible.. The length of the arms is a function of the desired movement and distance from the pivot point to the attachment point.

My sketches attempt to get the pivot as close to the 3D CG as possible which is about the belly button when taking a huge guess as to the added weight of the pedals and wheel though this will vary depending on the reclined position of the victim in the seat. The usual seat mover has its pivot at the CG in a 2D plane but not the vertical CG position which must increase the power required. This , i think, would require a lot more power . Get the apparent pivot up higher and that should reduce. This would reduce the movement of the head a fair bit and i have no idea if this would be better or reduce the effect of the simulation or not.

bsft - I have a few ideas circulating in the grey matter after seeing that link you posted, another sketch is certainly coming.

You are not stupid, only creative and willing to ask questions and learn.
Lets see, like a RNR frame, but the pitch frame also swivels from side to side.
Feasible yes, you would need a ferking strong frame with built in rollers to hold it together, not to mention the force needed to overcome that weight i suspect.
Is it possible to do a "normal" RNR style and stick the whole thing on a rotating base?

Heres the link I was looking for, a commercial company makes them, but no reason why you could not copy it
http://www.accelid.co.at/index.php?id=1

bsft - not sure what a RNR style means. And thanks for not thinking I am too stupid, mad though maybe .
That last one is a variation of the first one you posted but is only 2 dof.
These are both along the lines of what i was thinking. Decent roller bearings should make it pretty free to move.
I can see how EZ it would be to add surge and yaw but traction loss gets more difficult to keep it compact.

In your opinion what impact would the reduced head movement have on the effect of the simulation. moving the pivot from below the seat to about the belly button would reduce head movement by about 50%.

A quick sketch for version2 .
The roll bearing mount is 100mm diam by 200 so sure i can fit something good enough in that. I haven't drawn the tuning fork arm, that would be EZ to make i'm sure.
Belt drive for the roll axis with 2.4:1 ratio gives 120 degree rotation for the motor and 50 degrees for the chair.
The pivot point for pitch is the white dot in the human figure

It seems many people use the Motion Dynamics 200W 160 RPM motors or similar with arms that move over a range of about 120 degrees.
This gives me thought, it seems everything does that to me .
At 160 RPM it takes .125 seconds to move 120 degrees. Allow some for acceleration under load so maybe .2 seconds, seems a pretty violent action.
Watching the various videos here some rigs seem quite violent so maybe this is correct and the slower rigs use a higher ratio hence slower.

While on the subject of motors i noticed that Motion Dynamics has 2 appropriate motors. One is 200W and weighs 2.7kg the next one up is 320W and 5.7 kg. So more than twice the price and weight but only 60% more power and it has a solid shaft that to me makes it less flexible. My thought is if i need more power is to use 2 of the 200W motors with the shaft going through both rather than a single 320W. More power lighter and cheaper .