Bodies, supports and mechanisms
These tools are on the Build tab; ropes, joints and drives are on the Connect tab. Tools used less often are under More in their group. While a tool is active, Properties shows its options (sizes, mass, whether a pulley's axle is fixed …), and the status bar says what the next click does. Esc cancels a half-made shape; Backspace removes its last point.
Bodies
| Tool | Key | How |
|---|---|---|
| Circle | C | click for the default size, or drag the radius |
| Ring | a circle with a hole (a hoop, a tube, a washer): radius and rim thickness in the options. Bodies dropped in the hole stay inside and roll on the inner rim. Any circle gets a hole in Properties → Shape → Hole radius | |
| Box | B | drag a rectangle; the options have a corner radius |
| Capsule | a bar with round ends: length and radius in the options | |
| Polygon | P | click to place a regular polygon; the number of sides and its size are in the options |
| Triangle | T | right (drag along the slope: a wedge), isosceles (drag a box; ⇧ equilateral) or any (three clicks). ⇧ gives 5° steps. A right triangle's base, height and slope angle stay editable in Properties |
| Shape | S | your own outline: click the corners one by one, then click the first corner again (or press Enter) to close it. ⇧ keeps the next edge at 15° steps, Backspace takes the last corner back. The outline may be concave — an L, a hook, a cup — as long as its edges do not cross: it is one rigid body, and things fall into its hollows |
| Freehand | drag to sketch an outline; its convex hull becomes the body | |
| Shoot | a slingshot: press where the projectile starts, pull back and let go; it flies the other way, faster the further you pull. The band, its speed and angle and its path under gravity are shown while you pull. What it shoots (balls, boxes, or bullets: pointed triangles that leave nose first and, in air, keep turning their nose into their flight; size, mass, bounce), the speed per metre pulled and the top speed are in the tool's options | |
| Liquid | drag a rectangle from one corner to the other (a click puts the default pool with its surface there): a still pool of water (or sea water, oil, ethanol, glycerine, mercury) that buoys up what is in it. It has no walls or bottom: put it on a ground. Liquid and density in the options and Properties |
Liquids. A body in a pool is buoyed up by the weight of the liquid it displaces, ρ g V, at the centre of the part under the surface, so a ball lighter than water floats at its waterline and a raft let go tilted rights itself. Volumes are counted as for air drag: a circle as a sphere, a polygon as a prism as deep as its Depth (Properties → Air Resistance; by default its smaller side). Bodies in it also feel its drag and the drag on their spin; accelerating, a body also moves the liquid round it (its added mass, half the liquid it displaces), so a light ball let go under water rises firmly but does not shoot out; and a body floating at the surface is calmed by the ripples it makes (Wave damping). Whether a body floats depends on its density as a 3D body: a 100 kg ball of radius 0.5 m is 0.52 m³, 191 kg/m³, so it floats in water like a block of wood. Properties → Mass & Inertia → In a liquid says it for each body. The liquid itself does not flow, rise or make waves: it is not a fluid simulation.
A body's mass, material, friction, bounciness and colour are in Properties. Slice (Build → Modify) cuts a body along a line; the pieces share its mass by area and keep its velocity (a concave body is not sliced).
Edit Points (Build → Modify, E, or right-click a body) shows the corners of the selected polygon body as handles: drag a corner to move it, drag the + in the middle of an edge to add a corner there, and ⌥-click a corner (or click it and press Delete) to remove it. Joints and thrusters on the body stay where they are on it. An edit that would make the edges cross is taken back. Boxes, circles and rounded bodies keep their own controls in Properties.
Supports and guides
- Ground / Wall: drag the surface line at any angle. It locks to level or vertical within 4°; ⇧ snaps to 15°. The hatched side is solid; ⇧F flips it.
- Slot / Guide: drag along a channel; a slider block runs in it. Properties sets the length, the channel width, stops at the ends (closed, open or a wall), and more sliders can share one slot.
- Pin Support and Fixed Support: click on a body or a ground. A pin lets the body turn; a fixed support holds it completely. Both snap to grounds and walls. A Pin Support clicked on a body pins that body there: it snaps to the centre, a corner, the middle of a side or any point along a side (a ring shows where), the body turns about it, and the pin moves with the body when you move it by hand and goes when you delete it. Click a Fixed Support on a body's corner to put a bracket there: one leg out of the corner along its angle, with a pin at its end, fixed to the body (it moves with it). Put a pulley on that pin with the Pulley tool, as at the top of an incline.
- Sliding Support: a fixed support on rollers. Click near a ground or wall; it slides along it, keeps its angle and stops at the surface's ends. Weld a body to it and the body slides without turning; pin a body to it for a roller support.
Mechanisms
- Pulley: a wheel. In empty space it turns on a fixed axle (or is free, set in the options); on a body it is mounted on a bracket and moves with it. A cable or rope over it makes the pulley system.
- Gear: number of teeth and module (mm). Dropped next to a gear it snaps into mesh: position and tooth phase.
- Ring Gear: teeth inside a rim; a gear dropped inside meshes with it. Click on a gear's centre to put the ring round it.
- Rack: drag along it; it slides in a hidden guide, or is fixed. A gear dropped on its teeth meshes.
Drive (Connect tab):
- Gear Mesh meshes any two placed gears, a ring gear or a rack. A mesh has a pressure angle (20° by default; 14.5° and 25° in Properties): the teeth push along a line tilted by it, so besides the tangential force that turns the gears they push them apart onto their axles with F_t tan φ. Properties shows both, and the free-body diagram shows the tooth force tilted (F_g, or F_t and F_rad with components).
- Belt connects two circles or gears, drawn as a belt or a roller chain. A roller chain's slack span (the one not pulling; at rest, the lower one) is drawn sagging, as a real chain hangs.
- Thruster: press on a body and drag to set the direction of a constant thrust on it.
Motors are part of a pin: select a pin or a pinned-axle body and set its motor in Properties.
Parts
A part is a mechanism you build once and place in any scene: a pendulum on its pin, an Atwood machine, a crank and slider, a gripper, a cart with its wheels.
- New Part (Build → Parts) opens a tab for designing one: draw its bodies with Shape and the other tools, join them on the Connect tab, and press Play to try it (Stop brings the design back). The floor in that tab is a test bench: grounds and walls are never part of a part. Save Part keeps it in My Assets; after that, Save Part writes a new version of it.
- Save as Part (Build → Parts, the Edit menu, or right-click a body) in any scene: saves the selected body and everything joined to it — through pins, welds, sliders, springs, rods, cables, ropes, gears, belts, thrusters and supports — with the annotations on those bodies. Or choose everything in the scene. A joint to a ground or wall is left out: a pendulum pinned to a Pin Support keeps its support, one pinned straight onto a ground does not.
- Parts are kept in My Assets, on this device or in your account, with a picture of each. On a part's card, Place puts it in the open scene and Edit opens it in its own tab.
- Placing: click in the scene. Each click places another copy, R turns it by 15° (⇧R back), and Properties has its angle as a number. Esc finishes.
- A placed part is ordinary bodies and joints: edit, move or delete them as usual. Names that are taken get the next number (m₁ becomes m₁ 2), and one ⌘Z removes a placement.
A part taken from a running scene is saved at rest: its bodies' velocities are not kept.
Placing precisely
- Grid and Snap (View tab) snap to the grid; G toggles the grid.
- Points of ropes, cables, springs, rods, bars and dimensions snap to a body's centre, its corners and the middles of its sides.
- The arrow keys nudge the selection by 1 cm (⇧: 10 cm). Properties has every position and angle as a number.
- Tab cycles through bodies that overlap under the cursor.