Rigs and constraints
Rules that do part of the posing: connectors, weighted joints, Smart Stretch and Angle lock, and which one to use.
A rig is a figure with rules that do part of the posing for you: a carriage that stays on its rail, a piston that stays in its cylinder, a head that stays level, panels that slide out together. This page shows the four kinds of rules, what each is for, and how to add them.
- Rules live in Build → Properties → Rig: Connect, Weighted, Smart Stretch and Angle lock.
- You animate a few controls; the rules work out the rest on every frame.
- New to rigs? Open Library → ⋯ → Rig examples… and take one apart.
See rigs in action
Pick an example above the editor and drag its red control. Each one is moved by a single control; Properties shows the one value you would animate.
- Sliding carriage: drag the red slider along the rail.
- Piston: turn the crank. The rod stays attached.
- Telescoping panels: hold Ctrl and drag to stretch.
The four kinds of rules
A connector between two joints of the figure, with a slider that travels from 0% to 100% along it. For carriages, pistons, zips. Connectors
A joint that follows a mix of up to 16 other joints. For a detail between two controls, like a cheek between jaw and eye.
A driver whose length stretches the parts below it. Each part can stretch, stay rigid or stop it. Smart Stretch
A part that keeps one angle while what it hangs from turns: a head that stays level, a tray that stays flat.
Which rule do I need?
| You want… | Use | Then you animate |
|---|---|---|
| A prop that follows a hand, as its own figure | Join | The hand. (This is a scene link, not a Build rule.) |
| A point that travels between two joints | Connector | The slider’s Position, or the anchor bones. |
| A section that squashes and carries its details along | Smart Stretch | Ctrl-drag the driver, or its Length. |
| A detail that stays level while its support turns | Angle lock | The support. |
| A detail that blends several joints’ movement | Weighted joint | The joints it follows. |
| A hand that reaches while the elbow bends by itself | IK | The hand. |
Rules don’t replace keys: on every frame they work out the figure from the controls you posed. Put IK on the bones that drive a rule, not on joints a rule controls.
Add a rule and test it
- Open the figure in Build. Finish its shape first: name the controls, set the origin, split the parts you need.
- Click the joint of the part that should own the rule. In Properties, open Rig: click Connect or Weighted, turn on Smart Stretch, or choose an Angle lock.
- Select the parts attached below it and set what they do (their Stretch response, or an Angle lock).
- Click Test rig in the top band. Try the rest pose, both extremes and something in between. Reset puts the preview back; nothing you do there changes the figure.
- Click Done: Update figure changes every copy; Import as new figure keeps the old one.
In Test rig, the Joint list can reach controls you can’t see, its value is Length for a bone (Slide for a connector), and Angle is greyed out when a rule owns the angle.
Smart Stretch in short
In Animate, Ctrl-drag the driver to stretch it. The full guide is Smart Stretch.
Angle lock
Select an attached part and choose a mode in Rig → Angle lock. When you turn it on, the part’s current angle is kept; change it with Angle.
| Mode | The angle follows | Example |
|---|---|---|
| Off | Normal posing. | A forearm you pose freely. |
| Figure | The whole figure’s rotation, but not the turns of what it hangs from. | A sign that stays upright with the character, not with the arm holding it. |
| Movable parent | The nearest parent that can move, times Rotation. | A gear that turns the other way from the one driving it (Rotation −1). |
| World | A fixed direction on the canvas. | A platform that stays level while its support swings. |
Rotation (Movable parent only) goes from −10 to 10: 1 follows the parent’s turn, 0 ignores it, −1 turns the opposite way. Applies chooses After stretch (the visible angle is locked) or Before stretch (a stretch can still change it). With Movable parent, Second rotation can add another joint’s turn: set its Joint, Rotation and Rest angle (Joint 0 turns it off). A connector can’t be locked, because its anchors decide its angle; lock a part attached to it instead.
Weighted joints
- In Build, select the driving part and click Rig → Weighted. A new joint is added.
- In its Weighted joint section, choose the Origin joint, how many Anchors, and each anchor’s joint and Weight.
- Attach the detail to the new joint, then pose the anchors in Test rig.
The joint sits at the origin joint plus each anchor’s offset times its weight. Weights are not shared out for you: two anchors at 0.5 put it halfway between them; two at 1 add both offsets and push it further. A negative weight pulls the other way. You can use 1 to 16 anchors, weights from −100 to 100; joint 0 is the figure’s origin. You move a weighted joint by posing its anchors, not by dragging it.
Attachments and older rigs
The Attachment section of a part shows its Stretch driver and Orientation (Follow connector or Keep authored angle). Older rigs can show Legacy influence on a stretch binding, or an Angle-driven path that moves a joint along a path as another joint turns. Leave them as they are unless you mean to change how the rig moves.
Rig examples
StykAnimate comes with small ready-made rigs to learn from, like counter-rotating gears, a folding fan and an accordion screen. Open Library → ⋯ → Rig examples… (or + → Examples → Rig examples…), try one, then Add to Animate. In Build, the figure’s Examples quick action opens them too.
Build in the right order
- Put the origin where it belongs (right-click a joint → Set as origin).
- Split parts into all the joints you need.
- Only then add connectors, stretch and locks. A part with rules can’t be split any more.
- Check with Test rig before you click Done.
Good to know
- You can’t delete a joint that a rule still uses. Remove or change the rule first.
- Pivot files (.piv, .stk) can’t keep connectors, rules or one-sided fills. Save as .styk or .stkz.
Troubleshooting
The rule changed every copy of the figure.
Rules belong to the design that all copies share; poses stay per copy. Finish Build with Import as new figure to keep the old design.
I can’t find a control: it has no line.
Use the Structure panel or the Joint list in Test rig. An invisible control can still drive what you see.
A rule is refused as depending on itself.
The driver, anchor or reference would depend on what it controls. Pick a joint outside that branch; your rig is left as it was.
Split or delete is refused.
Rules use that joint. Finish the shape before adding rules, or remove the rule first.
IK and a rule fight.
Turn off IK on the joint the rule controls and keep IK on the bones that drive the rule.
A locked part won’t turn when I drag it.
That is the lock working. Change its Angle, choose Off, or Ctrl-drag to change its length.
It works at rest but breaks when squashed flat.
Check the Minimum, the rigid and stop parts and the width. Test small lengths before zero.
Keep going
Still stuck?
Ask the community, or tell us what’s missing from the docs.