I’m animating what would be a very heavy object … free falling … from about 7 stories high. Since I flunked physics I need some help trying to get a somewhat realistic fall in terms of velocity / speed ect.
The object is dropping about 85’ to the ground
Its an elevator (pretend like the cables broke) so it is very heavy.
I can’t use rigid bodies, I need to keyframe by hand.
Currently I have it keyframed just using 2 keyframes set to constant. Of course this is not the way it should be .
Here are my questions
I’m Trying to get a good guess on the number of seconds it would take for it to hit the ground from the distance noted above(85’)
I’m really not sure how the graph would look to represent increasing velocity as it falls? I would like to try and represent the fall similar to what they are saying here
Are there any F curve modifier presets I could use, or possibly a special type of easing, that would represent a free falling object?
Any help would be appreciated…
And a super special bonus question…
If I want to have the object have a little wiggle as its falling, are there any f modifiers I can use for that?
Recall that gravity is a force of acceleration. As the diagram at the end of the above page shows, for each second that goes by, the velocity of the object (“so many meters per second (m/s)”) increases. So, acceleration is “so many meters per second per second. (m/s/s)”
We also know, from Mr. Galileo’s famous experiment, that the weight of the object does not influence how fast it falls. A rock and a cannonball, and an elevator, will hit the ground at the same time.
You could start with simple keyframing and maybe that will be good enough. As each second goes by, the distance travelled by the object increases, the increase representing the acceleration force. (Keyframes are placed once per second, say.)
Now, you can also use a real Blender physics engine. Or, you can “do the math” and set your keyframe-Y’s accordingly.
It will also be important to consider how you intend to film the event. For instance, I daresay you’re not going to have a fixed camera … unless you’re doing a boring physics lesson. You’ll have cut-aways among several dramatic camera shots. You might have the camera falling just-ahead of the elevator as pieces start ripping off of it (somehow) in the air-stream. Go rent an action-movie and watch similar scenes; deconstruct them.
In other words, a piece of action that you will need to choreograph, and experiment with using OpenGL Preview renders. It may be that the sense of urgency and speed is created more by “shorter and shorter cuts” between increasingly-exciting cameras. Choreography and cinematography may prove to be far more important than physics-correctness.
@sundial I was able to figure out the time it takes to hit the ground is roughly 2.3 seconds. So I made 2 keyframes spaced out around 55 frames (24 frames/sec). I selected the 2 keyframes and choose key… interpolation… exponential. This gave me a nice accelerating curve. My problem now is it seems like there are no adjustment handles available to tweek it some. It seems like it is too slow at the beginning. But I can’t seem to access the handle to make adjustments. Maybe when you use these presets it locks it in, or more likely I’m doing something wrong.
There will only be a locked down camera, because I have already rendered the backplate (the elevator shaft). My biggest problem is I have not used the graph editor much at all.
Using a calculator (http://keisan.casio.com/exec/system/1224852055) you’ll find out it would take 2.3 seconds for the elevator to hit the ground. So, it would be approximately 24+24+8=56 frames if you’re animating in 24fps.
The link you posted has some distance values for the free fall, 4.9 meters after 1 second, 19.6 meters after 2 seconds, so you can change the scene settings in Blender to metric to make this easier.
An easy way to see how much your object has moved is to first position it in object mode so it’s on the ground plane, then do Cursor to Center and Origin to 3d Cursor. Then move it up into the air to where it’s supposed to fall from, then do Apply Object Transform with location selected. Then when it’s falling you can see the current distance in the Z axis transforms.
Insert the first keyframe at the top, then the second keyframe at the bottom after 56 frames. In the graph editor change the interpolation type to bezier and the handle type for the second keyframe to free, then move the handle itself all the way to the right so it’s a straight vertical line. Then you can adjust the handles of both keyframes to make sure it has moved 4.9 meters at frame 24, and 19.6 meters at frame 48. This should make the motion realistic.
For the wiggle you can try using a built in function generator (sine wave).
@Cyaoeu Thank you very much for taking the time to put the blend file example together and for your suggestions. I want to study it a bit later tonight… but one quick question on sine wave… I experimented really quickly with it, Is there anyway to tell it to just move in two directions…
Imagine my camera is looking straight up the elevator shaft from the ground… My position key frames have the elevator free falling on the z axis. so I want the wiggling to occur just on x and y axis. Because it should never wiggle up and down if it is free falling due to gravity. I’m not sure this is possible with the sine generator.
Yes, you have to add the sine wave to every transform, so you would add it to the X and Y location (one modifier each) and the Z would stay unaffected.
