GMAX Annimation Issues

[Tako_Kichi]

I recently decided to get off my butt and build a working aircraft (I have previously built lots scenery objects (including aircraft) in GMAX and Blender) and things have been going well until I hit an issue with animations. Obviously animations are new to me but I have lost over a week now going through numerous tutorials for both simple animation and bone animation and I still cannot get it to work in my project. It's now got to the point where I am so confused I hardly know my left hand from my right and nothing I try gives me the results I am trying to achieve. I think part of my problem lies in the fact that some parts are aligned to the world axis and some are aligned to their 'local' axes and the two things are not playing nicely together.

I have attached a couple of screens below to try and show my problem....

SHAFT_A is the main drive shaft for the gear and is aligned parallel to the world axis. It is attached to LINK_A and LINK_A can swivel on the end of the shaft.

LINK_A is connected to SHAFT_A and LINK_B via JOINT_A. The joint connection needs to be constrained so that it can only rotate in one plane (not on the world axis) but it also needs to be able to move along the radial track created by the end of LINK_A when SHAFT_A rotates.

LINK_B is connected to LINK_A via JOINT_A and also connected at the other end to the gear leg. It also rotates at the point where it is connected to the gear leg.

The gear leg (and all parts linked to it) rotate on SHAFT_B which is not aligned on the world axis but on it's own local axis.

The problem I have is that I cannot find a way of successfully tying the two link arms together at JOINT_A. If I rotate SHAFT_A then LINK_A rotates with it correctly. If I rotate SHAFT_B the gear leg (and everything linked to it including LINK_B) rotate correctly. What I need is to be able to rotate SHAFT_A and have the LINK_A, JOINT_A and LINK_B assembly work in unison to pull up the gear leg and make it rotate on SHAFT_B. The assembly should work much like the hinge on a folding pocket knife where the handle would be LINK_A (fixed at one end to SHAFT_A) and the blade would be LINK_B with the blade tip attached to the gear leg.

As I stated earlier I have tried using simple animation with dummies (although all the constraints and 'look to' features have me totally confused now) and tried a bone animation on the link assembly but that didn't work either.

Can anyone see what I am doing wrong and perhaps suggest a way of achieving my goal as at this point I am totally confused and ready to tear my hair out after spending a full week or more on this problem and getting nowhere.

Thanks for looking.

 

[hairyspin]

Only a week? This sort of problem took me more than a month to crack!

A few points to start with:

You must ensure the pivots are appropriately aligned for each part, then you can animate using the Local reference coordinate system and the parts will behave the way you want.

However you build the animation, using whatever constraints or solvers, you must reduce the finished animation to keyframes before exporting. The exception to this, afaik, is the Limb Solver used in animating jetways in FSX. All other MS sims use keyframes only.

Bones are properly used to animate skinned mesh and I got nowhere with them for this problem: IK animations didn't help either.

I finally got the results I wanted with Look At constraints. With the constraints in place, you have to decide which moving part controls the rest of the animation - in this case Shaft A. Set up its animation with keyframes in say steps of 10.

With Animate on, step through this animation in Key Mode and manually rotate Shaft B to get Links A and B to line up properly at each step - the Look At constraints will keep them pointing the right way, you just have to get them to match end positions.

Once you've got this working properly, you have to collapse the resulting animations on Links A and B to keyframes, then review the results to see if it's good enough for your model. Be prepared to do this several times until you're happy with the results

More information here, and don't be put off by the CFS3 bias, it works just fine in FS9 too:- http://www.sim-outhouse.com/sohforums/showthread.php?t=7288

Just one caveat, don't delete the dummy objects when you're done - you'll mangle the hierarchy...

 

[lionheart]

Nice work Larry! Great to see you over here.

Good job on the fancy animation.



Bill

 

[Tako_Kichi]

Thanks for the tips Hairyspin, I guess I will have to keep plugging away at it until I get it sorted. I have been able to set key frames and move things that way but I was hoping that I could get everything working as a single 'unit'. The joint between LINK_A and LINK_B is a nightmare for me at the moment. I just can't seem to find a way to 'lock' the two parts together so that they swivel as they should.

Bill I have been lurking for a while over here.

No doubt I will have lots more questions over the next few months.

 

[lionheart]

Roger that.

Just remember, landing gear is about the most difficult thing to animate, besides pilots with all different types of moving parts. Those little gear pieces may take you a long time, just be patient. Getting them exact will really make the model all the more better. People can always spot something slightly off.

Note that you can 'move' or slide KF's around, so if its not working at a certain point, you can slide it over, instead of re-animating sections.

I have had times where I had like 15 or 20 KF's on a landing gear part, because it was doing these wierd hops and over-extensions. Drove me nuts trying to get them to work, but it eventually worked.

 

[hairyspin]

Like Bill says, this is one of those fiddling jobs which takes a lot of trial and error. I never did find a way to 'lock' two parts together as you say, so here's some screenies on the Look At method:-


This is the landing gear in the animated .GIF above, plus the hierarchy. The entire gear set is parented by a dummy (arrowed) for my own reasons.

There's also a ball link at the end of StrutArm: this will play a big part in building the animation:-

First, align the pivot for l_gear_7 along its length, pointing to BallLink:-

Next apply a Look At constraint to l_gear_7:-

and click on BallLink to have l_gear_7 'look at' it:-

or use the Pick List to select BallLink:-

and the whole lot goes pear-shaped: the wrong axis is pointing towards BallLink:-

Panic not, just select the correct axis for the Look At constraint:-

The geometry has also been inadvertedly rotated and needs corrected: you can't do this in the normal way as the geometry is rigidly locked to the pivot via the constraint.
Rotate the pivot instead:-

That's it set up to build the animation, so here in very rough steps is what you then do.
The gear is fully extended and this set was built for CFS3, so Keyframe 50 corresponds to this. In FS9 and FSX this will be Keyframe 100. I've already animated ucCrank, so I can step through the animation one frame at a time, using the < and > keys, or I can drag the time slider.

Pulling the slider back from 50 to 33, the mechanism separates, but the Look At constraint keeps l_gear_7 pointing at BallLink:-

Click on Animate and rotate l_gear_4 on its y-axis (using Local reference coordinate system) until the mechanism is properly joined again:-

Step the animation slider back to 25 and again the mechanism separates:-

Again rotate l_gear_4 on its y-axis until it's properly joined again:-

You now have the general idea. Of course you'll have to set the correct positions for the gear when fully retracted, which is all part of the fun of undercarriage animating - I have the luxury of having already done this!

Once it's all working correctly, Collapse the animations for all objects that use Look At constraints as per the linked post above. Don't forget!

Hope this helps.
Tom.

 

[Tako_Kichi]

Thanks for that info Tom, I appreciate it.

I was looking at the issue earlier and then realized there were some 'interference' problems with the arms/levers so I need to sort that out before I animate them. Of course with only 3-views and photos to work from all dimensions are pure guesswork but I did email the aircraft owners group today to see if anyone can help with a couple of physical dimensions. I really need to get the lever lengths correct as parts are sticking through the wing when it's folded at the moment.