CAD assemblies
Position parts, control their movement, and plan space for the whole robot.
A places parts together so you can check how a or fits. It can show that a collides with a bracket before either is bolted to the robot.
Parts and assemblies
In Onshape, use a to make parts and an Assembly tab to connect them. You can insert several copies of a part into an assembly without drawing it again. Each placed copy is an instance.
Start a practice assembly and insert the mounting plate from Your first CAD part. Fix this first instance in position. Fix holds a part still so the assembly has a stable reference. Without that reference, the whole group can move when you drag a part.
Add a simple spacer or a second plate to practise making a connection. A spacer holds parts a set distance apart. You can model one by sketching two concentric circles, circles with the same centre, and extruding the ring-shaped region between them.
Use mates to connect parts
A describes how two parts are allowed to move relative to each other. Degrees of freedom are the independent movements still available, such as sliding along one direction or turning around an axis.
| Mate | What remains possible | Example |
|---|---|---|
| Fastened | No relative movement | A bracket bolted firmly to a frame. |
| Revolute | Rotation around one axis | A wheel turning on a . |
| Slider | Translation along one axis | A carriage moving along a rail. |
Translation means movement without rotation. An axis is an imaginary line that a part can move along or rotate around.
Onshape uses mate connectors to define the position and orientation of a connection. Select suitable geometry, such as the centre of a hole, and check the connector preview. Use a Fastened mate to place the spacer against the plate with its hole aligned to a plate hole.
If the spacer appears on the wrong side or points the wrong way, adjust the mate's alignment or flip its direction. Do not add extra mates to fight a wrongly aligned first mate. Drag the part afterward: a fastened spacer should stay still relative to the plate.
Mates describe intended movement. They do not prove that a real screw is tight, a shaft is supported, or a part can carry the load.
Insert purchased parts
A parts library is a collection of existing CAD models. Use the libraries linked by Onshape and models supplied by your actual vendors. A part is a commercial off-the-shelf part: something you buy ready-made.
Check the exact part number and revision. Similar motors may have different shafts or mounting holes. Do not redraw a standard part from a photograph when an accurate vendor model is available.
Keep the source document and part number with the design. If an inserted part uses a link to another Onshape document, pay attention to its version. Review an update before accepting it into an assembly your team is manufacturing from.
Plan the robot's space
Make a rough robot layout before modelling every bracket. Space planning means reserving room for the main systems. Simple boxes can stand in for a battery, controller, , and lift while you compare arrangements.
Include the parts people often forget: battery mount, main switch, wire connectors, cable bends, game objects, and the tools needed to reach a screw. Reserve the space a mechanism sweeps through as it moves. Check the current starting-size and expansion limits with a correctly sized reference shape.
Share the layout with everyone designing a subsystem. A subsystem is one part of the robot with a particular job, such as the intake. Agree where it mounts and how much space it may use. If that changes, tell the other designers before their parts are made.
Make a parts list
A (BOM) is the list of parts and quantities in the design. Onshape can generate one from an assembly, but useful names, part numbers, and descriptions must be entered first.
Compare the BOM with the team's inventory before ordering. Include screws, nuts, washers, and , not just the large visible parts. Create a named version when the assembly is ready to build, and keep the physical robot and model in agreement as you make changes.