Robot joint parts: housings, bearing carriers, shafts and adapters
Joint hardware is the structure that holds a robot joint together: the housing, the bearing carrier that locates the output bearing, the shafts that carry torque, and the adapters that connect motor, reducer, encoder and link.
Pico supplies these robot joint parts to your design: a prototype or pilot batch first, then repeat supply, as loose parts or kitted with the custom gears and purchased bearings for the same joint.
At a glance
| Part | What it does | Design points to settle |
|---|---|---|
| Housing | Holds the reducer and output bearing, and ties the joint to the link | Wall stiffness, heat path from the motor, sealing, mounting pattern |
| Bearing carrier | Locates and clamps the output bearing | Bearing seat fits, preload method, alignment to the housing bore |
| Shafts | Carry torque between motor, reducer and output | Keys, splines or flats, bearing journals, hollow bore for cables |
| Adapters and motor mounts | Connect motor, reducer, encoder and link | Pilot diameters, concentricity, bolt patterns, face flatness |
What hardware does a robot joint need besides the gears?
The reducer sets the ratio and the torque. The hardware around it decides whether the gear mesh stays aligned under load, how the output bearing carries the link's moments, and whether motor, encoder and reducer share one axis. For the reducer itself, see robot joint gearboxes and reducers and custom planetary gearboxes.
Most of these parts are specific to one joint. Pico supplies them as one set, so the parts are reviewed against each other instead of quoted by separate shops.
How do housings and bearing carriers affect joint stiffness?
Tilting stiffness at the joint output depends on the output bearing type (and, for a bearing pair, their spacing), the rigidity of the carrier and housing walls around it, and the fits and preload that hold it. A stiff bearing in a thin carrier still tilts, because the carrier deflects first.
Alignment is a tolerance stack: motor pilot to adapter, adapter to housing, housing to reducer and output bearing. Each interface adds position and angle error, which shows up as a misaligned gear mesh, uneven tooth loading, noise and a change in backlash. Common ways to keep the stack short:
- Dimension bearing seats and pilots from one datum axis, usually the main housing bore.
- Machine features that must stay concentric in one setup where the part allows it.
- Call out runout between bearing seats, not only their diameters.
- Locate with pilots or dowel pins, and let the bolts clamp.
- Combine the reducer housing and the joint housing into one part where the design allows; one interface drops out.
Which output bearings do robot joints use?
- Crossed roller bearings: rollers alternate at right angles in a single row, so one bearing carries radial, axial and tilting loads in a short axial length. Common at robot joint outputs and in strain wave reducers.
- Thin-section angular contact bearings: usually a preloaded pair, mounted back to back for moment stiffness. The carrier and spacers set the preload, so their dimensions matter as much as the bearings.
- Four-point contact bearings: one row that carries radial load, axial load in both directions and tilting load in a thin section, where axial space is tight.
Pico works around purchased bearings and does not make bearings. The bearing maker's mounting guidance sets seat fits, shoulder dimensions and ring clamping, and the drawing should follow it. Name the bearing you have chosen in the inquiry, or the loads if the choice is still open.
Which materials and finishes are common for joint hardware?
| Part | Common materials | Common finishes |
|---|---|---|
| Housings and covers | Aluminum alloys, for low weight and easy machining | Anodizing; hard anodizing on wear surfaces |
| Bearing carriers | Aluminum for light loads; steel where the seat must stay stiff | Anodizing on aluminum; black oxide or plating on steel |
| Shafts | Alloy or stainless steels, hardened at journals and splines where needed | Black oxide, plating or passivation |
| Adapters and motor mounts | Aluminum or steel, by stiffness and weight | Anodizing, black oxide or plating |
Aluminum expands roughly twice as much as steel with temperature, so a steel bearing in an aluminum seat changes its fit as the joint warms up. Some designs add a steel insert or carrier for that reason.
Material, finish and route are settled per part in the engineering review. Finishes such as anodizing and plating may come from outside suppliers; the scope states where each step happens, and a US manufacturing requirement can be marked in the inquiry.
What do we need to quote joint hardware?
| Item | Why it matters |
|---|---|
| Drawings or CAD | A 3D model plus a toleranced 2D drawing; a sketch is enough to start |
| Critical tolerances and fits | Bearing seats, pilots, runout and flatness decide how each part is made and inspected |
| Material and finish | Or the loads and environment, if the choice is open |
| Quantities | First build and expected annual volume |
| Inspection needs | Which features are measured, and the records you need |
| Timing and country of origin | When parts are needed, and whether US manufacturing is required or preferred |
Partial information is fine; we will ask for what is missing. If the parts should arrive as a kit or an inspected gearbox subassembly, say so, and start a project with what you have today.
Questions
Do you supply the bearings?
Pico does not make bearings. Purchased bearings can be included in a kit or subassembly when the scope calls for it, and the scope names the bearing and its source.
Can you work to our tolerances and fits?
Send the drawing with its tolerances and fits. The engineering review confirms how each feature will be made and inspected before anything is quoted as final.
Can joint hardware come as a kit with fasteners and bearings?
Yes, mechanical kits are one of the ways we supply parts. A kit lists every part, its revision and its source, and can be delivered unassembled or as an inspected subassembly.
Can you build joint hardware around a reducer we already buy?
That can be scoped as a joint hardware project based on the reducer maker's interface drawings. Name the unit in the inquiry.
Send your joint drawings
Share the drawings you have, with quantities, timing and any country-of-origin requirement. Partial information is fine.
Start a project