I came running back!

[oakchas]

Whoa!

 

So, I'm in the midst of doing the piston tutorial. Everything is going along swimmingly. The tutorial works. I can make a piston go up and down while the crankshaft turns. Exactly as advertised. Well, except for those inbetween keyframes where you have to make more keyframes to get the "shaft" bone to line up correctly with the crankshaft pin... Then it's "close enough," but it really isn't.

 

Somewhere (early on) in the tute is mentioned the fact that we're going to "brute force" this animation without relationships, etc. Great, I can handle that, as long as it works. But, it really doesn't. Well, not accurately enough. It will look fine as it's moving, but somebody's gonna step through it and see that the shaft (con rod) is not actually lined up with the center of the crank pin.

 

So great, I'll try a relationship. Look that up in the tech ref... I get lots of references to expressions... So, I look at the recent discussion on expressions... man they do a lot, but I got scared in there... 'as easy as calculus" Colin said... Well, Chinese would be easier for me (maybe).

 

Okay, so back to the tech ref. Bones... 100 instances of... you say "oiler", I say "you ler" and how great that is at working the constraints of a bone in a mechanical model but not so hot at human stuff... okay bingo, that's what I want.. this is a piston; mechanical as can be.

 

But I want the center of the con rod (shaft) hole to always center on the crank pin. I can do that by making each frame a key frame. But is there another way? Easier? Aren't alot of keyframes "bad"(unnecessary)?"

 

Anyway all that math and calculus stuff scared me back here to newbie status...

 

Here are 2 questions as a result of the piston tutorial.

 

1. is there a way to make the con rod hole always line up with the crank pin without all those keyframes?

 

2. The action in the piston tute is 20 frames long but only needs to be animated for 19 to make one full revolution (then loop). If I want to animate over alonger period... how do I get the hitch out of the TDC position of the piston...? Eliminate a keyframe (#20)?

 

You can explain here or just point me to something in TAO A:M or a tute I can follow to understand. I'm feeling intimidated over something simple. (which is making me feel very old).

 

Crochety old technophobe....

[BrainLock]

Where is the piston tutorial?

[oakchas]

Where is the piston tutorial?

 

It's on the V14 extras DVD but that one is incomplete... here's the link to the original: piston tute

 

Now I'm going back to the topic because I noticed that Johnl3d did a project with relationships.

[BrainLock]

Thanks. I'll check it out.

[R Reynolds]

You realize, of course, that in the time it's taken to try to understand and work through relationships optimized for character animation, you could have set up 72 key frames (one every 5 deg.) to produce a completely convincing one_rev.act that would serve all your purposes.

 

I like brute force. Your patience is rewarded with a result that's straightforward and can't fail. I have no access to the tutorial you mentioned but as shown in the attached image of a test I did for the valve gear of a steam locomotive, to ease the alignment of the components I put in multi-spline partial circles to transcribe the paths they are going to follow. Sometimes a graphical solution is the better solution.

[oakchas]

You realize, of course, that in the time it's taken to try to understand and work through relationships optimized for character animation, you could have set up 72 key frames (one every 5 deg.) to produce a completely convincing one_rev.act that would serve all your purposes.

 

Bingo! Of course! I agree Rodger... The brute force method works and in the time I try to look at relationships I could have done the whole thing by hand! Sometimes trying to understand all the features is unnecessary if there is a work around (especially one that works as well or better).

 

I like brute force. Your patience is rewarded with a result that's straightforward and can't fail. I have no access to the tutorial you mentioned but as shown in the attached image of a test I did for the valve gear of a steam locomotive, to ease the alignment of the components I put in multi-spline partial circles to transcribe the paths they are going to follow. Sometimes a graphical solution is the better solution.

 

While I am not doing anything as complex as a steam loco, I can easily visualize what has to occur for this mechanical model to function. You do have access to the tute as it is online as well as on the DVD the link is above.

 

Now the remaining question is... in order to have the action loop without hesitation at TDC... I can eliminate the last frame (in the ACTION only) and repeat the action in the chor (as there are other actions occuring over a time where the piston cycles several revolutions)... yes? Is that correct?

 

Thanks for your input rodger, it really helps to not think I HAVE to work all the bells and whistles, when all one needs to do (to get from point a to point b ) is sit in the drivers seat and drive the darned car... Stereo and cruise control are nice to have but you don't NEED them.

[R Reynolds]

...in order to have the action loop without hesitation at TDC... I can eliminate the last frame (in the ACTION only) and repeat the action in the chor (as there are other actions occuring over a time where the piston cycles several revolutions)...

 

I don't believe that's true, but I could be wrong. It's been a good long time since I've experimented with this kind of looped animation but I seem to remember (at least many versions ago) a check box that would automatically do what you've just described. I think it was related to stride length.