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Stewart platform · Hexapod · 6DOF parallel mechanism
Stewart platform on Stewart geometry, built for the pose you have to hold.
Two jobs share this mechanism: holding a commanded pose against a load, and reproducing a recorded motion. They are specified differently and they fail differently, and which one you need decides the geometry before it decides the payload.
Comparing us against a precision positioner? Start with where we stop — the class line is stated on this page rather than discovered at the acceptance test.
A pose is only a claim until something measures it. The target on the moving platform is what turns one into the other.
0.01 mm
Typical repeatability, laser tracker at the acceptance load
Pose by pose
Resolution and stiffness stated where you work, not at the best point
All-electric
Servo electric cylinders; we do not build hydraulic hexapods
12 months
Warranty, with the identification and acceptance records shipped alongside
Three words, one mechanism
Stewart platform, hexapod and 6DOF platform describe the same six legs
The name changes with the industry rather than with the machine. A ship-motion group says Stewart platform, a photonics group says hexapod, a simulator group says 6DOF platform, and all three are describing six actuators between a fixed base and a moving frame. The word tells you who is asking. It does not tell you what the machine can do.
The Three-Vocabulary Crosswalk Same mechanism, three industries
| The term you will see | Where it comes from | What the speaker usually means | What the word still does not tell you |
|---|---|---|---|
| Stewart platform | Gough's tyre-test rig of the 1950s and Stewart's 1965 paper on a six-legged motion base | The mechanism itself, in its published form | Actuator type, stroke, payload or precision class |
| Hexapod | Precision positioning and photonics | A six-legged positioner commanded in pose, more often holding than moving | The precision class — the same word covers nanometre stages and tonne-class frames |
| 6DOF platform | Simulation and vehicle testing | Six axes of motion available at the same time | Whether the six figures can be reached together, which is the question that decides a build |
| Hexapod positioner · motion base | Supplier catalogues | Duty rather than mechanism: a positioner holds, a motion base moves | Anything about geometry, which is what sets the workspace |
Our four platform pages are split by what you are buying rather than by vocabulary. This page covers hexapod geometry, joints and pose-holding duty. The 6DOF motion platform page covers motion reproduction, the motion reference point and acceptance under combined motion. The 3DOF page covers heave, roll and pitch on a serial mechanism.
The word is a dialect. The geometry is the specification.
Holding two quotations that use different words? Send both and we will line the figures up on one sheet →
The question that comes before payload
Holding a pose and reproducing a motion are two different machines
A hexapod asked to sit at a commanded pose and hold it against a load is judged on where it actually is. The same mechanism asked to reproduce a recorded motion is judged on what it does between poses. The mechanism is identical. Almost nothing else is.
Sizing follows the judgement. A positioning duty pushes stiffness, joint clearance and thermal drift to the front, because each of them shows up as a pose error that does not tune out. A motion duty pushes actuator force, cooling and continuous rating to the front, because the platform never settles long enough for a static error to matter.
Buying the wrong one of these fails quietly. The machine meets its datasheet and still misses the job, because the datasheet was written for the other duty.
Not sure which duty your requirement is? Send the pose set or the profile, whichever you have →
6DOF Stewart platform for precision positioning and dynamic motion control
The 2-Duty Hexapod Split Which column your requirement sits in
| What you are actually asking for | Positioning duty | Motion duty |
|---|---|---|
| The figure that decides the build | Pose repeatability at your working pose | Combined-axis travel and acceleration at your load |
| What the design is driven by | Stiffness, joint clearance and drift | Actuator force and thermal margin over a continuous profile |
| What acceptance measures | Where the platform actually sits, by laser | What the platform does through a commanded trajectory |
| What goes wrong when it is under-specified | Settling and drift that no amount of tuning removes | Travel that shrinks the moment two axes are commanded together |
| Typically bought for | Pointing, alignment, test fixtures, compensation | Simulators, durability rigs, motion cueing |
A build can serve both, and several do. What it cannot do is be specified for both at once and accepted against whichever column is convenient afterwards — so the duty is written into the proposal before the frame is sized.
Where the numbers on this page come from
The joints decide the repeatability the legs can only promise
An actuator that resolves to a micrometre is worth nothing if the joint at its end has play. On a parallel mechanism the errors do not average out — six leg errors combine into one pose error, and clearance in a single joint moves the platform in a direction no encoder on that leg can see.
Machined on our own line
- Servo cylinder bodies, rods and rod ends
- Base and moving frames, and the attachment pattern itself
- Joint housings and their mounting interfaces
- Controller boards, designed and populated here
Bought on purpose
- Motors, drives and encoders from catalogue suppliers
- Screws, bearings and joint bearings in standard sizes
- Chosen so a maintenance team anywhere can source a replacement
- Nothing on the load path is a part only we can supply
Recorded for every leg
- Zero length and measured stroke
- Joint preload torque, as set
- Backlash reading, taken with an indicator
- The platform serial number the leg belongs to
Preload is where a batch is won or lost. Too little and the joint carries clearance the controller cannot see; too much and the joint runs warm, and the friction comes back as a settling error rather than as a position error. It is set against a value that belongs to the joint size, confirmed with an indicator, and written on the sheet that ships inside the crate.
None of this is visible in a finished machine, which is exactly why it is written down. A hexapod that has been assembled well and one that has not look the same from the outside and read the same on a datasheet.
Rod-end joints and actuator housings are integrated into the leg assembly, keeping the critical connection between each actuator and the moving frame mechanically controlled and consistent from leg to leg.
Actuator housings, lower joint mounts and base attachment points are assembled as one controlled geometry, helping minimize unwanted play and maintain consistent leg alignment across the platform.
Auditing how a supplier controls joint clearance? Ask for a sample leg record sheet →
Why one accuracy number is not enough
Resolution and stiffness move with pose, so we state where
On a serial stage, encoder resolution and axis resolution are close relatives. On a hexapod they are not. Six leg lengths map to one pose through a relationship that changes as the platform moves, so the same encoder produces different platform-level resolution at different poses and in different directions.
Stiffness behaves the same way. Near neutral height, with the legs steeply inclined, a hexapod is stiff vertically and softer laterally; tilt it towards a workspace edge and that ratio shifts. Neither figure is wrong where it was measured. Neither survives being quoted as one number for the whole workspace.
So the figure we issue is tied to a pose. Tell us where you actually work — the neutral pose, the extreme you reach occasionally, or the small region you spend the shift in — and the number is stated there, with the load on.
A pose accuracy figure without its pose is a best case, not a spec.
Need the figure at your working pose rather than at neutral? Send the pose and the load and we will state it there →
The 5-Row Pose Statement How each figure is written on a proposal
| Quantity | How it is stated on our proposals | Why a single number misleads |
|---|---|---|
| Pose repeatability | At a named pose, at the acceptance load, by laser tracker | Repeatability at neutral is the best case anywhere in the workspace |
| Platform resolution | Per axis, at a named pose | The leg-to-pose relationship changes across the workspace |
| Stiffness | Vertical and lateral, at a named pose | Leg inclination sets the ratio between the two, and inclination changes |
| Settling | Time to a stated band after a stated step | A band with no step size behind it is not a measurement |
| Angular resolution at a payload height | Referred to a stated point on your assembly | The same angle at a higher point is a larger linear motion for the legs to produce |
The last row is where hexapod specifications most often part company with reality. An angular tolerance measured at the sensor, not at the platform surface, is a different requirement — and on a parallel mechanism it is the legs that pay for the difference. The 6DOF page works through that geometry in full.
Measured motion · completed builds
Stewart platforms in motion and across configurations
The videos show one platform under external measurement and another demonstrating coordinated six-axis motion. The photographs present three completed builds with different footprints, moving plates and actuator layouts. Compare the architecture here; project-specific payload, workspace, accuracy and duty still depend on the load, CG and required pose set.
Laser-tracker verification. This completed 6DOF Stewart platform is operated with the external measurement setup visible, showing how platform motion can be checked independently of the controller’s internal position data.
Coordinated six-axis motion. A compact Stewart platform moves through combined positions and orientations, making the relationship between actuator extension and moving-plate motion easy to see.
Raised-interface custom build. A compact six-actuator layout supports a circular moving plate above a purpose-built base, showing how platform height and mounting geometry can be adapted to the surrounding structure.
Compact circular configuration. Six electric actuators connect the round base and drilled moving plate in a close-packed layout, clearly showing the working geometry of the Stewart mechanism.
Larger-format Stewart geometry. A broad base, larger moving plate and spaced actuator arrangement show how frame proportions change with the required mounting interface, pose set and load case.
Want the clip that matches your duty? Tell us whether you are holding or moving →
WHERE SIX-AXIS MOTION ADDS VALUE
Stewart Platform Applications
This application range focuses on CSCMotion Stewart platforms configured for payloads typically between 10 and 100 kg. They are best suited to test articles, instruments and OEM equipment that require coordinated six-axis motion, controlled pose or disturbance compensation. Final configuration depends on payload, center of gravity, inertia, workspace and motion profile.
Compensation
Motion Compensation and Stabilization
Use measured base motion as an input to command corrective six-axis movement and help keep a camera, sensor or instrument within a defined orientation or working envelope. The compensation strategy is configured around the disturbance, payload and required response.
Testing
Multi-Axis Component Testing
Mount components, instruments or assemblies on a controlled six-axis base to reproduce defined trajectories or measured motion profiles under laboratory conditions. This supports functional, durability and disturbance-response testing within the approved payload and motion configuration.
Research
Laboratory and Control Research
Configure a programmable six-axis motion base for robotics, control development, kinematics, sensor evaluation and repeatable pose or trajectory work. The mechanical setup and motion profile are defined around the experiment.
Pointing
Sensor, Camera and Antenna Positioning
Move cameras, optical instruments, antennas or other sensors through commanded positions and orientations. This fits applications where controlled multi-axis pointing or scanning is more important than large linear travel.
ALIGNMENT
Calibration and Equipment Alignment
Present an instrument, test object or assembly at defined poses for calibration, alignment or measurement-system verification. Automate position-and-orientation sequences within the approved workspace and payload condition.
Discuss calibration and alignment →
OEM INTEGRATION
Motion Integration for OEM Equipment
Integrate coordinated six-axis motion into inspection equipment, laboratory instruments or custom machinery. CSCMotion can coordinate the mechanism, mounting, controller and host interface around the equipment, payload and required motion.
Explore custom OEM systems →
Not sure whether your application fits? Send the payload, center of gravity, motion envelope and required motion profile for an engineering review →
Where we stop
The precision class we build, and the one we do not
Hexapod covers an enormous range of machines under one word. At one end are piezo and flexure stages resolving in nanometres inside a vacuum chamber. At the other are tonne-class frames carrying cabins. We build one of these, and the distance between them is not a matter of tuning.
What we build
- Servo electric hexapods on screw-driven cylinders
- Repeatability in hundredths of a millimetre, by laser tracker at the acceptance load
- Gross moving load from 10 kg reference frames upward, project-specific above 100 kg
- Indoor industrial environments; IP55 and other ratings on request
What we do not build
- Piezo, flexure or voice-coil driven hexapods
- Sub-micrometre or nanometre positioning
- Vacuum-compatible or cleanroom-class hexapods
- Calibration certified as metrology to a national standard
Worth a conversation first
- A few hundredths of a millimetre held across a whole shift
- A small workspace with an unusually high stiffness requirement
- Continuous duty at a high load factor
- Outdoor, humid or elevated-temperature installations
Where it is exactly right
- A pose held against a real load rather than in free air
- Six axes needed together rather than stacked as stages
- Loads measured in hundreds of kilograms and upward
- Geometry that has to be drawn around a structure that already exists
If your specification is written in micrometres or nanometres, that is a different class of machine, and you will hear so in the first reply rather than in the third meeting. There is no version of our mechanism that gets there, and saying otherwise would only move the disappointment to the acceptance test.
Not sure which side of the line your tolerance sits on? Send the tolerance and how it was arrived at →
What happens at the edge
A hexapod's limits are not six numbers, and the controller has to know it
A commanded pose can be unreachable for reasons that belong to no single axis. A leg would run past its stroke, a joint would exceed its angle, or the mechanism would pass near a configuration where a small leg motion produces a large platform motion and the force needed climbs sharply.
So a requested pose is tested against all of those before anything moves, and one that fails is refused with a reason returned to the host. A positioner that quietly clips a commanded pose is worse than one that declines it, because the first failure mode is invisible until something downstream is out of alignment.
The same check runs on the path between two poses, not only on the endpoints. Both ends of a move can be legal while the straight line between them is not, and on a parallel mechanism that is a common case rather than an exotic one.
Host link is TCP/UDP, serial or Modbus, with EtherCAT or CANopen below it. Command set, coordinate convention and pose order are fixed at the interface freeze and signed before manufacturing; the control system page carries the full stack.
Integrating into a host that already drives a positioner? Send its pose convention and we will state what changes →
A refusal that names the leg and the limit is a diagnostic. A move that stops halfway is a fault report somebody has to write.
Two ways this gets built
A reference frame, or a hexagon drawn around your load
Most enquiries can be answered by configuring a frame we have already built, and a minority cannot. The honest answer usually depends on one thing: whether the mounting envelope is yours to choose or already fixed by a structure that exists.
The Reference-or-Custom Gate Which route your envelope takes
| The question | Reference frame | Geometry drawn for the project |
|---|---|---|
| Your mounting envelope | Fits the released footprint and neutral height | Fixed by a structure, a vehicle or a room that already exists |
| Your workspace requirement | Inside the reference envelope at your load and CG height | Needs rotation or reach the released layout does not have |
| What we change | Stroke within the frame, interface plate, controller configuration | Attachment points, radius ratio, leg inclination, joint size |
| What it does to the schedule | Shorter, because the frame is a known build | Longer, because geometry, structural analysis and drawings come first |
The difference between the two routes is engineering weeks rather than build quality. Both are identified and accepted the same way, and both carry the same records — a custom hexagon is not a prototype, it is a layout we have not built before.
Have an envelope drawing but no geometry yet? Send the drawing and we will say which route it takes →
What a hexapod quotation needs
Six inputs a hexapod quote needs that a motion quote does not
Mass and stroke are enough to start a conversation about a motion platform. They are not enough to size a positioner, because on a hexapod the same mass at a different place in the workspace is a different machine.
The 6-Input Hexapod Quote Sheet What a positioner needs beyond mass and stroke
| The input | What it changes in the design | What happens if you leave it blank |
|---|---|---|
| The pose set, or the region you work in | Every accuracy and stiffness figure is stated at a pose | We state at neutral, which flatters the machine and may not describe your job |
| Where the load sits relative to the platform centre | An off-centre load sizes the worst leg rather than the average one | We size to a centred load and the worst leg comes out under-rated |
| Required resolution, and how the figure was arrived at | It sets the precision class, and whether we are the right supplier at all | We assume the industrial class and may quote the wrong machine entirely |
| Settling requirement: the band and the step | Stiffness target and control tuning both follow from it | We quote a stiffness that satisfies no stated settling requirement |
| Duty cycle across a working day | Thermal margin and continuous rating of the actuators | We size for intermittent duty and the machine runs warm in service |
| The structure it will be bolted to | A hexapod is no stiffer than its foundation | It is measured on our floor and behaves differently on yours |
Send what you have and mark the rest unknown. An unknown we can see is an engineering question; an unknown filled in with a guess becomes a specification, and specifications are what acceptance is run against.
Only have the tolerance and the load so far? Those two are enough to start →
From the hexapod line
Stewart platform and hexapod engineering notes
Four pieces buyers ask for once a hexapod requirement is on the table: the layout, the mathematics, the trade-off and the vocabulary.
Layout
Stewart platform design and attachment layout
Base and platform radii, leg inclination, 6-6 and 6-3 arrangements, and how each one moves the reachable set.
Mathematics
Inverse and forward kinematics, and why the forward answer is not unique
Why leg lengths from a pose is arithmetic, pose from leg lengths is not, and what the controller does about it.
Trade-off
Payload, stroke and acceleration, and how they buy each other
What raising one of the three does to the other two on a parallel mechanism, before cost enters the conversation.
Vocabulary
Motion platform and hexapod glossary
Gross moving load, motion reference point, combined-axis travel, singularity — defined once, used the same way across the site.
Asked before a specification is written
Hexapod and Stewart platform FAQ
Is a hexapod the same thing as a Stewart platform?
In practice, yes. Both describe six actuators connecting a fixed base to a moving frame, and the six leg lengths together set the platform's position and orientation. Precision positioning suppliers tend to say hexapod, simulation suppliers tend to say Stewart platform or 6DOF platform, and the mechanism underneath is the same. What differs between machines is geometry, actuator technology and precision class — none of which is carried by the name.
What accuracy can you actually hold, and how is it measured?
Typical repeatability is around 0.01 mm, measured with a laser tracker on the assembled platform at the acceptance load rather than read from encoder feedback. The figure belongs to a pose: it is best near neutral and degrades towards the workspace edges, so the number on your proposal is stated at the pose you told us you work at. If you need it at more than one pose, acceptance samples more than one pose.
Can you build a hexapod for micrometre or nanometre positioning?
No. That class of machine is piezo, flexure or voice-coil driven, usually in vacuum or a cleanroom, and it is a different discipline rather than a smaller version of ours. Our mechanism resolves in hundredths of a millimetre and there is no configuration of it that reaches micrometres. If your tolerance is written in µm or nm you will hear this on the first reply, because finding out later costs you a project schedule.
Why is your quotation higher than a supplier offering the same stroke?
Compare what each figure is attached to before comparing prices. Ask whether the travel is single-axis or combined, whether repeatability was measured by instrument or reported by encoder, at which pose and at what load, and whether the joints carry a recorded preload and backlash figure. Two hexapods can publish identical stroke and differ by a factor in what they hold under an off-centre load. Where a competing quotation genuinely covers the same conditions and costs less, that is worth knowing and we would rather you tell us.
Can one hexapod do both positioning and motion reproduction?
Often, and several of our builds do both. The condition is that the harder of the two duties is what the machine is sized and accepted against. A frame sized for a motion profile and then asked to hold a pose to a tight band usually fails on stiffness or settling rather than on force. So both duties go into the proposal, the governing one is named, and acceptance is run against that.
Do you supply the kinematics and the API, or is the controller a black box?
The controller and its boards are ours, so the command set, the coordinate convention and the level you command at are configuration decisions rather than fixed features. You can command pose and let the platform solve the kinematics, or command leg lengths directly if your host already runs its own solution. What we do not hand over is the compensated parameter set as an editable file, because it belongs to one machine and an edited copy would invalidate the acceptance record it was measured against.
What happens if I need a pose outside the workspace after installation?
The controller refuses it and reports which limit was hit — a leg stroke, a joint angle, or proximity to a singular configuration. Whether the pose can be added afterwards depends on which limit: a controller-side software limit can be reviewed and changed with our engineering, a leg stroke or a joint angle cannot be changed without new hardware. This is the argument for sending the pose set rather than an axis envelope at the enquiry stage.
Commercial questions — lead time, payment terms, spares, on-site support — are answered in the full FAQ.
Send the pose and the load. We will tell you if the geometry holds it.
A pose set, the load with its offset from centre, and the tolerance you have to meet are enough for a first pass. If a reference frame already covers it, that is what you will hear back, and if the tolerance belongs to a different class of machine you will hear that instead.