Structure and fasteners
Understand load paths, frame stiffness, construction styles, screw selection, and joint reliability.
A 's structure carries forces between wheels, , and the ground. Its joints must preserve alignment as the robot accelerates, handles objects, and contacts its surroundings.
Load paths
A is the route a force takes through an . For a lift, trace the payload through the carriage, slide , mounting brackets, , and wheels. A strong slide mounted to a flexible bracket still produces a flexible system.
is resistance to failure. is resistance to deflection. A frame can survive a load while bending enough to disturb gear mesh or a transfer. Reinforce the joint or geometry causing movement before making every member thicker.
Use triangulation, gussets, suitable cross-members, and short unsupported spans where they help resist the expected loads. Check the extended mechanism as well as its stowed position.
Construction methods
| Style | Useful when | Main design burden |
|---|---|---|
| Kit channel or extrusion | The team needs adjustable, reusable assembly | Compatible hole patterns, brackets, and joints |
| Parallel plates and standoffs | and bearings need defined spacing | Plate alignment, cross-bracing, access to inner parts |
| Box tube | A long member needs efficient bending resistance | Accurate holes, joint design, access inside the tube |
| Tabs and slots | Cut parts need repeatable location during assembly | Process-specific fit and a joint that actually retains them |
Plate and standoff, box tube, and tab and slot are common construction methods. None is automatically rigid: a plate assembly with poorly placed connections can twist, while a carefully braced kit frame can work well.
Fastener specifications
A screw specification includes thread diameter, pitch, length, head, and material or grade where required. M4 × 0.7 describes a metric thread with a 4 mm nominal major diameter and a 0.7 mm pitch. An imperial #6-32 thread has 32 threads per inch. Similar diameter does not make metric and imperial threads compatible.
Identify the thread and size before assembly. Keep common sizes in separate labeled bins and use the correct driver to avoid rounding heads.
For most screw heads, length is measured from beneath the head; countersunk screws are measured including the head. Confirm the convention on the supplier drawing.
Clamped joints
A tightened fastener creates , a clamping force between parts. In a properly designed joint, friction between the clamped surfaces can resist motion before the screw shank bears against a hole. Loose screws lose that benefit and can let parts shift.
Select a screw long enough for the required thread engagement but short enough not to bottom out or enter a . There is no single engagement or value suitable for steel nuts, aluminum threads, printed plastic, and motor mounting holes. Use the component specification.
Washers spread load and protect softer surfaces. Thin plastic may under clamping force; a spacer or metal compression sleeve can keep a screw from crushing it. Keep rotating components out of a structural clamping stack unless their bearing or bushing arrangement is designed for it.
Use compatible removable threadlocker on suitable metal threads or appropriate locking nuts where vibration threatens retention. Check chemical compatibility before threadlocker touches plastic. Do not use locking compound as a substitute for correct screw length, alignment, or joint design.
Frame testing
With power off and the robot safely supported, apply a representative load gradually and observe where movement occurs. Mark joint positions so slipping is distinguishable from member flex. Compare diagonals and check shaft alignment after tightening.
For a repeatable exercise, measure an unloaded mounting point, apply a known test load within the assembly's safe capacity, and measure deflection. Repeat after changing one brace or joint. Record geometry and load with the result; "feels stronger" is not a transferable measurement.