Mechanics is a very interesting theme in blender as complex it is. But also it can be for amateur domain, even animate a single cube can show up an interesting animation performance. So I don't doubt at all that this tutorial -as many of experiments with ipo window- will result in a good theme for people that interests in mechanic animations.
I accept that these animations have little about scientific fundamentals for mechanics, but is an opportunity for introduce to further analysis of mechanics.
Constructing A Chain
I wanted emulate the chain of some mechanic elements through some ipo curves and easy constraints.
In front view create a pulley system with a large pulley and a one smaller, add another details if you want. Try to modify these features with Transform Properties Dialog box. Then, create a curve and adjust it to resemble the band for these pulleys.
Split whichever windows –good thought flexibility in blender- for visualize additional controls. And in the option 'Display Current Window Type' select Ipo Curve Editor.
In 3d Window select the curve you create and name it C –this will speed up some settings afterwards-. As in figure 2, in the Option 'Show IPO Type’, select Path -only available for curves-. You'll see a graph that Emo (a elephants dream movie character) wouldn’t doubt to say “there’s nothing there”. Also, the parameter 'Speed' isn't enabled.
As figure 3 shows, graph has some remarked black lines that give some physical constraints of curve C. Inside this bounds you will create the position relation for objects which will use the C curve (in 3d window) as a path through the default 100 frames given to curves. All animations start with frame 1, by default when a curve is used as a path its animation ends at frame 100. But if animation was continue a new cycle would start at frame 101. But this behaviour isn't shown in this graph because isn't activated.
Create the new behaviour in Ipo curve editor by [CONTROL + left mouse button] inside of remarked boundaries, It will create a horizontal line that runs through all visible frames.
Press N key or on Ipo header menu View>>Channel properties of Transform properties, it will appear transform properties box dialog. Set the parameters as in figure 4.1.
It looks to be a little difficult to understand behaviour through curves, but this is a cheap one.
Unfortunately, Blender doesn’t show units. But if limits are 0 and 1, automatically you think about percentage. Blue curve in figure 4 is the curve what we going to modify. Speed curve always indicates that velocity = position related to time or x(t). E. g. consider a horizontal straight curve with slope = 0; this ‘curve’ indicates just one position (%) all the time, thus, path just has a single point available to objects that use this curve as path. But if this straight curve has slope, objects will run through all positions of path with a constant velocity, if slope is small objects will run very slowly, but if slope is big, objects will run very rapidly. But if straight line is totally vertical, objects would occupy all positions at same time (infinite velocity). If slope become negative the direction changes.
Due curve C is a closed path, a cycle for constant velocity is a straight sloped line, if we want add a variable velocity we must get a curve, but in this case we just need constant velocity.
For create the next key, move the green bar to frame 101 (it can be achieved with right arrow button) and press I key to INSERT A KEY VERTICE to current frame. Next enter edit mode by press TAB key and with vertex at frame 101 selected press G key to grab up it to 1.0. Also you better can achieve this by typing 1 in ‘Vertex Y:’ field in Transform Properties Ipo dialog in edit mode. In 3d window create a empty object, then, SHIFT + select curve C and [CONTROL+P key] and will appear PARENT TYPE dialog and select follow Path. Select only empty object and [ALT+O key] to clear origin, next press [ALT+A key]. Animation starts and velocity for empty object is variable (is slower at start and at end, and slightly faster in between).
Go to Ipo window and on header menu select [Point>>Extent Mode>>Cyclic]. This will extend velocity beyond of frames we started on. With vertex at 101 frame still selected, press G key and grab horizontal through left and right, cyclic will change as you move this vertex, experiment with this behaviour and check it in 3d window, undo the changes you made to back or select a position of this by typing values in Transform Properties dialog.
Delete empty object, and in Front View add an armature object named A1, press F7 to display Object panel Select Draw Name and Axis in Draw extra settings (Draw panel), in Anim Settings set track to Y, Up to Z. Parent with curve C to follow path and clear origin again as you made with empty object.
With A1 still selected press [ALT+D key] to duplicate, name the new armature object A2. On Constraints panel, add ‘Track to’ constraint, type A1 in OB: Target Object field -A2 will track A1-. In Anim Settings panel type 1 in TimeOffset field, move frames in 3d window with Right arrow key and back to see the new offset with armature objects, adjust TimeOffset values to get a well looking chain.
Next you will create a link duplicate of A2 and name it A3. Change the name on OB name field (Constraints panel) with A2. Change the TimeOffset value for the number given to A2 and Right arrow to add *2, the result will be TimeOffset value for A3. [ALT+D key] to link duplicate A3. Change the OB name field (Object and Link panel) for the next number, Change the target name on OB name field (Constraints panel) for the precedent name, make sure this name target exists. Position the cursor inside Time Offset field and CONTROL+ left mouse click for avoid move this value and add + .(A2 TimeOffset value). Do the same for next duplicates until fill the curve. Finally add a empty object called 1 and add a ‘Copy Location’ constraint with last armature object. Select first armature object (A1) and add a ‘Track to’ constraint to this Empty object by typing 1 in target panel
The result will be a chaining mechanism that will have an excellent performance.
Add some objects and add to each of these ‘copy location’ and ‘copy rotation’ constraints to occupy location of armature objects.
Select curve C and add some Hooks by selecting a vertex or a group of vertices. In Edit mode for curve C Select vertex group for larger pulley and [CONTROL+H key], select ‘Add, to New Empty’; and add a Hook. Select vertex group for smaller pulley and add a Hook. Add others Hooks for vertices that are left. Parent curve C with a large cube object. Create 2 more cube objects for pulleys and Parent to large cube. Parent the empty object that is Hook for large pulley and parent to closest cube, The empty object for smaller pulley will parent with closest cube of vertices. Other empties belonging to this curve will parent with large cube.
So the large cube will move all mechanism, you can tweak, rotate, move parent cubes and single hooks to get a nice effect in animation and so on. The file related to this tutorial has a little animation. Camera also adds more effect
Erick Ramirez is an Industrial Engineer specialized in 3d projects. During several years he had modelling industrial models in diverse industries and handling for tutorials in National University of Mexico. Actually he is in a search for involve blender as a common knowledge among society.