BOING!

A spring is a simple but tricky object. When it comes to animation you can quickly get into trouble. You want the spring to contract/expand and bend at the same time, but you don't want the springmaterial to squash and stretch. In this tutorial you'll learn how to make a correctly deformable spring setup using messiah's flex effect. I assume that you have a basic knowledge of messiah, so I won't go into stuff like how to apply an effect, or how to create a null. If you are uncomfortable with the basics, go through the messiah documentation first ;)

To create the spring I use Lightwave's Modeler, but of course you can create it with the modeling program of your choise as long as it exports an object format that messiah supports.

Ok then, let's start!

In Modeler:

1. Create a spiral shaped spline. I used the SpringMaker lscript to build a 1440° spring.

2. In another layer create a disc at the start of the spiral and railextrude it with the spline in the background. Use "Uniform Lenghts" or "Uniform Knots" and check "Oriented". In my case I used 40 segments. Delete the caps at the ends or tranform them into tris or quads, because messiah currently does not allow to subdivide objects with polys that have more than 4 points.

3. Go back to the layer with your spline spiral and convert it to a polychain - I chose 30 Uniform Lenght segments using CurveToPolychain. The trick here is to have enough segments to create an accurate curve in messiah, while keeping the point count low, wich will determin the amount of repetable steps you'll have to do in messiah.

4. Now select the topmost point of that polychain and note it's y position (hit i on your keyboard to bring up the info panel). Divide that value by the number of segments (polys) in the polychain and note the resulting number, in my case 4 / 30 = 0.13333. You'll need this later in messiah.
Save your object with the polychain layer and the spring body layer, or save them as 2 seperate objects. That's it for the modeling part.

In messiah (studio rev9< or animate 4.0<):

5. Import your polycurve and spring body object(s).

6. Go into the Setup > Effect tab and apply Simeon Nasilowski's PointEdit effect to the polycurve (you can get the plugin here). This will create a null at each point of the polychain.

7. You can now actually delete the pedit effect, all we need here are the nulls - sorry Simeon ;) Create a Master_Null and drag-parent the points to it. Now you can also delete the polycurve.

8. Apply the Flex effect to the spring body object. With the Flex effect selected go to the Flex tab and chose Distorted (Tool Shape) in the Axis pulldown menu. Now create as many curve points as you have _PE nulls, in this case 31.

9. Drag-parent the flexcurve points to the _PE nulls in the right order, so that you get a ascending spiral curve.

We'll now create a central spine for the spring with a bone chain.

10. Create a Skeleton from the Tools tab and parent it to the Master_Null. We actually don't need the skeleton to deform anything, so we don't have to create a bone deform effect but just the tool - less cluttering :)

11. With the Skeleton selected, create a Bone by hitting + on the numeric keyboard. Give it the lenght of the value that you noted in modeler, here 0.133333. Rename the bone to Skeleton_Bone, so we won't get mixed up with the numbers later.

12. Create a XForm null under the Master_Null and rotate it -90° on pitch. This will be the parent for the bone chain, so you can leave the bone rotation at zero while make them point upwards. You can drag the Flex effect under the Master_Null, so we have everything together.

13. Drag-parent the Skeleton_Bone to the XForm null. With the Skeleton_Bone selected hit + 30 more times to create the complete spine chain. Create a Spine_End Null and parent it to the last bone.

14. Go to the Items tab (still in Setup mode) and select Parent Items in the pulldown menu and check Keep Position and Keep Alignment. Now select the first Skeleton_Bone, shift-select _PE_0 and hit the Parent button. Repeat this for Skeleton_Bone_1 and _PE_1 and so on until Skeleton_Bone_30 and _PE_30. Here it is important that you respect the right order.
For visual clarity I like to rearrange the hierarchy so that each child sits right underneath its parent, but it is not necessary. Just pay attention not to mix up the parenting if you want to do this.

15. Select the Curve and return to the Curve Options (press F3 to expand the block). Set the Vector (Bank) pulldown to Skeleton_Bone.

16. Now create a Spring_CONTROL null at the root level of the item list and move it up on y to the spring top, wich is 4m in this case. You actually can collaps the Master_Null hierarchy.

17. We've finished in the Setup tab for the moment, now go to the Command tab. Here we will create a bunch of expressions to control the spring:

First there'll be 3 variables wich will control the Skeleton_Bone's rotation:

- Call the first variable spring_heading and in the expression tab enter [Spring_CONTROL:heading] into the expression field (Note: you can automatically enter an objects selected channel into the expression field by right-clicking the empty square next to the buffer field). Go to the Channels tab and add the Skeleton_Bone bank channel.

- Create a new variable (or copy the previous one), call it spring_pitch, enter [Spring_CONTROL:zpos]/50 into the expression field and apply this to the Skeleton_Bone pitch channel.

- Call the third variable spring_bank, enter [Spring_CONTROL:xpos]/50 into the expression field and apply this to the Skeleton_Bone heading channel.

Now we'll create the variable that makes the spring expand and contract:

- Create a new variable, call it spring_scale and in the expression tab chose IKTel (note: you can hold your mouse over the menu and type "i" on the keyboard, wich will bring you closer to the function you want to select). In the first argument pulldown chose Skeleton_Bone, in the second pulldown chose Spine_End and in the third pulldown chose Spring_CONTROL. For the last two arguments enter 0 and 1.

The next variable will make the spring bend by translating the first Skeleton_Bone's rotation (wich is controlled by the Spring_CONTROL) to all the other bones in the chain using the InheritRoot function:

- name that variable spring_bend and in the expression tab chose InheritRoot from the first pulldown menu. For the arguments chose Skeleton_Bone in the first pulldown menu, in the second pulldown menu chose Skeleton_Bone_30 and in the third pulldown menu chose rotate. Enter 0 for the last two arguments. (Note: You could tie the last two values to a slider, this way you can control the damping and the curl amount of the spring. This could be of interest for a very long and flexible spring, but in this example it isn't really necessary)

Lastly we'll create a variable that will constrain the Spring_CONTROL null to the top of the bone chain, wich makes the spring more intuitive to control:

- call this variable attach_springControl and chose MoveTo from the function pulldown menu. Fill the arguments so that the expression will look like this: MoveTo(Spring_CONTROL,Skeleton_Bone_30,1)

Ok, that's almost it. We've finished with the expression part, and the spring is ready to be animated with the null. We'll however do one last thing to make the control null easier to select and the spring easier to manipulate in the world view.

18. Go to the Setup > Armatures tab. Create a New Armature, call it Spring_Armature, check Realtime Draw and add a handle by clicking in the world view somewhere near the control null. Deactivate Realtime Draw again, and with the handle selected chose Spring_CONTROL in the Controller pulldown menu. Rename the handle to Spring_Controller.

19. In the Action block add a Click > Controller Select action and a Drag > Controller Drag action. Expand the Controller Drag action by clicking the little + sign and set LMB to 1 (ypos), MMB to 2 (zpos) and RMB to 0 (xpos). Click in the middle column next to 0 (RMB) to activate the little M icon, wich actually lets you control 2 axes at once.

20. Now you can go to the Animate tab and collaps and lock all items in the list. You can set the bones display to L, wich will draw a visual line in the world view representing the spine without attracting to much attention (Note: you can use the Select Items function in the Setup > Items tab to quickly select all the skeleton bones or any other item type). Unhide the spring body and hide everything else.

That's it! By dragging the armature handle with the left mouse button you can contract/expand the spring and with the right mouse button you can bend the spring. By rotating the Spring_CONTROL on heading you can roll up or unfold the spring, wich you'll not necessarily need, but it can be fun ;)

You can download the complete setup here.

Here you can see an animated example, and get the associated file.

If you have any question, comment, suggestion: here's the place.

Have fun! :)