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Setting the Prop Axis in GMAX

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I cannot figure out for the life of me how to set the axis for the prop in GMAX...I can get it to rotate, but unfortunately, it's rotating on the blasted y axis.One attempt had the prop rotating on a horizontal plane with about a 7' center of rotation (the prop was transecting the cabin)!TIA

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Check the blue arrow, it should be pointing down the center line of the aircraft. Also the direction of rotation will depend on if it is pointing forward or reverse, I belive. Go into your props hierarchy and rotate the axis as needed.Bob C.

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>Check the blue arrow, it should be pointing down the center >line of the aircraft. Also the direction of rotation will >depend on if it is pointing forward or reverse, I belive. Go >into your props hierarchy and rotate the axis as needed. Thanks, Bob! That did the trick. Pointing the blue arrow to the rear results in anti-clockwise rotation (when viewed from the front), so that is what I need...Now, if I can just get the darned rotation tool to be more precise!

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HI Bill,I group my blades into engine prop groups. Then, align the pivots for the groups.Usually, in Hierarchy Mode, Affect Pivot only, click Center to Object, then Align to World does the trick. YOU may then have to reverse the axis for proper rotation.MiltonThe Dash 7 Project8 Prop Groups and 4 Blurred Meshes :-)

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>Now, if I can just get the darned rotation tool to be more >precise! Bill, the transformation type-in is very useful for this (function key 12). Just type in the rotation you want and you'll get it. It's also useful for creating prop blades. Make a copy of the first blade and use the type-in to rotate the blade exactly 90 or 120 degrees.... Best regards, Chris

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Another quick way to bring the type-ins up is to right-click on the respective transformation buttons.Also, whilst in this case the type-in is probably the best answer it's worth knowing about the angle-snap tool. Towards the bottom right of the screen you'll see a magnet with a curved arrow next to it, click on this and rotate your object, it'll go in 5 degree steps - you can see how much by watching the numbers change in the boxes just above.Erm, while I'm at it I might as well mention one more thing that's useful for creating lots of symmetric objects. Towards the top of the screen you'll see a button with a circle of dots on it - this is the array tool. Click on it and you can type in the number of copies you want and how they change from copy to copy. In this case you'd type in 120 into the appropriate rotation box and 3 into the 1D count box. Click on OK and you'll get all three blades at once. With a simple thing like that any method will do, but if you were copying something more complex, or something with a lot of components then it's much faster than doing each one individually.Have funFinn

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>HI Bill, >>I group my blades into engine prop groups. Then, align the >pivots for the groups. >>Usually, in Hierarchy Mode, Affect Pivot only, click Center >to Object, then Align to World does the trick. YOU may then >have to reverse the axis for proper rotation. I have grouped the three blades and the hub spinner into prop_still...Whenever I select the group and try the steps you set out above, the whole pivot point is offset to the right side, and the 'blue axis' rotates to a positon parallel with the wing... :(But, I can manually spin the axis and get very, very close to right...Perhaps what I need to do is realign the entire aircraft to "World" first???

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You need to link the blades to the hub rather than grouping them, that way they'll take their animation from the 'prop_still...' tagged part (which would be the hub in your case).Have funFinn

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>You need to link the blades to the hub rather than grouping >them, that way they'll take their animation from the >'prop_still...' tagged part (which would be the hub in your >case). Hmmm... Well, grouping seems to be working!In fact, I now have three hubs:prop_still ==>grouped with three bladesprop_slow ==>grouped with the 'slow' elementprop_blurred ==>grouped with the 'blurred' elementBut, I'll go back and try it with 'linking' instead of grouping, to see what (if any) difference it makes.I would assume that the same technique is used to achived wheel rotation and control surface movement (assuming that I use the makemdl default animation).

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Groups may work, but the sample aircraft use the linking method. You will need three sets as you have already. I'm away for a couple of days but if you're still having problems when I get back I'll e-mail you a working file to have a look at.Have funFinn

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Finn, thanks! One of the things I like about Gmax is that there's always more to learn. But, strangely, some people don't seem to like that! Best regards, Chris

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Yep, some people look forward with zeal to change, while others would like to keep everything as it is. Now where did I lay that stone knife?Just think how much fun you could have with a full blown 3ds max!I would even buy a student version after I finish my ProE class ($150).Bob

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When see ing the airplane in front view (gmax back),the z axis must be pointing you. So it must be to the direction opposite of the aircraft's rear. Read milton't tutorial at freeflightdesign.com about props.Thanks

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> When see ing the airplane in front view (gmax back),the z >axis must be pointing you. So it must be to the direction >opposite of the aircraft's rear. Read milton't tutorial at >freeflightdesign.com about props. Well, as I've discovered, it also depends on what the "World Geometry" is also! If the "World Geometry has the Y axis pointing forward (towards the front of the aircraft, the X axis parallel with the wings, and the z axis pointing straight up, then the prop's rotational axis will then be y, not z...

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No, the prop's rotational axis will always be 'z'. I think it's probably best if I explain a little:When you are working with gMax you can use a whole range of co-ordinate systems. The basic one is the 'world' co-ordinate system - this is the coordinate system fixed in space, everything else is relative to this. The second one is the 'local' coordinate system - these are connected to the objects in your scene. The next two 'view' and 'screen' are relative to the viewports, and the final ones 'parent', 'grid' and 'pick' are basically ways of pinching the local co-ordinate system from one object and using them on another. All of these can be important depending on what you're doing, but most of the time you'll want to use world and local. It's important to be clear on this as all the documentation in the MakeMDL SDK (other than plane alignment) refers to local coordinate systems rather than world ones.Select an object (for example your prop hub) and on the top middle of the gMax window select 'local' from the list - if your prop is working you should see the pivot change to show the blue (z) axis pointing down the axis of rotation you see in FS2002. I haven't tried using groups instead of linked hierarchies yet, but in general it's the pivot of the group rather than the individual objects inside it that affects what you see in the sim.Have funFinn

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