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3DOF · 6DOF · Stewart · Control system
Motion platforms, 20 kg to 35 t, in four architectures.
If you already know which mechanism you are specifying, the four routes below go straight to it. If you do not, the selection tools further down settle it in about five minutes.
Six controlled axes
6DOF Motion Platform
Surge, sway, heave, roll, pitch and yaw from six coordinated legs.
Three controlled axes
3DOF Motion Platform
Heave, roll and pitch, with yaw added by a rotary stage where the range demands it.
Parallel kinematics, short stroke
Stewart Platform
Six limbs, twelve attachment coordinates, one moving frame. Stiffness-led rather than travel-led.
Platform-side control
Motion Control System
Controller, drives, cabinet, kinematics and the host interface as one work package.
If none of the four was obvious
The 5-Question Architecture Gate
Answer these in order. The first clear yes decides the mechanism; everything after that is configuration rather than architecture.
01 · Does the motion have to be reproduced in all six axes at once?
Not “would six be nice” — does the task fail if surge, sway or yaw are missing? A test standard or recorded field data usually answers this without interpretation.
Yes → 6DOF. No → keep reading.
Roll, pitch and heave cover most vessel and vehicle attitude work. Three axes you never command still cost installed power, footprint and maintenance.
Yes → 3DOF, with a rotary stage if yaw range exceeds the mechanism.
Alignment, docking and controlled pose work load the machine on stiffness and repeatability instead of travel and bandwidth. Different machine, same axis count.
Yes → Stewart platform, short stroke.
The actuators do not hold the mass, they control it through a lever equal to the centre-of-gravity height. Same mass, different height, different machine.
Yes → the load class sets the frame before the architecture does. See the table below.
A simulation host, a test controller or a PLC already in the cell fixes the command level, the coordinate convention and who owns the safety chain.
Yes → scope the control system alongside the mechanism.
More than one answered yes? That is normal — the matrix shows what each combination costs →
What each mechanism can and cannot do
The Architecture Selection Matrix
Read the last row first. Each of these is the wrong answer to some requirement, and finding out which is faster than comparing four datasheets.
| Decision line | 2DOF | 3DOF | 6DOF / Stewart |
|---|---|---|---|
| Controlled axes | Two, typically roll and pitch | Heave, roll and pitch | Surge, sway, heave, roll, pitch, yaw |
| What it reproduces | Attitude only | Attitude plus vertical motion | Full rigid-body pose |
| Mechanism | Two actuators, fixed pivot | Three actuators, constrained centre | Six actuators, 6-TPS parallel geometry |
| Governing constraint | Pivot loading and tilt angle | Actuator force against CG height | Combined-axis workspace, which shrinks as axes are commanded together |
| What it cannot do | Any translation | Surge, sway and yaw | Large yaw at large radius — the geometry runs out before the actuators do |
| When it is the wrong choice | The task has a vertical component you have been ignoring | A lateral cue is written into the standard you are testing to | You only ever command three of the six — three axes bought and maintained for nothing |
| Where to go next | Ask us — 2DOF is quoted per project | 3DOF platforms → | 6DOF → · Stewart → |
Two architectures still look viable? Send the motion profile and we will run it through both geometries →
Which constraint takes over as the load rises
The 5-Band Load Class Router
Two assemblies of the same mass do not place the same demand on a platform. The band tells you what governs the design, and that is a better starting point than a model number.
| Load class | Gross moving load | What takes over the design | Usually points to |
|---|---|---|---|
| Compact | 20 – 100 kg | The stiffness of your fixture rather than the actuators. A soft adapter plate is often the real limit on measured performance. | Stewart or 6DOF, short stroke |
| Light | 100 – 500 kg | Centre-of-gravity height starts to dominate the moment. Two builds at the same mass diverge sharply here. | 3DOF or 6DOF, by axis requirement |
| Mid | 500 – 2,000 kg | Actuator force and frame stiffness are sized together; neither can be raised alone. | 6DOF for full pose, 3DOF for attitude |
| Heavy | 2,000 – 5,000 kg | Foundation loading and installation access become hard constraints on the design. | 3DOF or 6DOF, frame designed to the load path |
| High-payload | 5,000 kg – 35 t | Site conditions turn into design inputs: crane capacity, door width, floor rating, available supply. | Project-specific frame, architecture by requirement |
Linear acceleration across the full range falls between roughly 0.1 g and 1.0 g. Where a build lands depends on the band, the centre-of-gravity height and whether axes are commanded singly or together, so the figure for a configuration is issued with its load condition attached. Which released configurations cover your band comes back with the sizing reply.
Know the mass but not the band? Start with gross moving load and CG height →
The number most specifications get wrong
Single-axis travel is not the travel you get
On any parallel platform, including ours, every axis of motion is produced by all six actuators together. Move one axis to its stated maximum and the actuators are already partly extended, so what remains for the other five is less than their own stated maxima.
On any parallel platform, including ours, every axis of motion is produced by all six actuators together. Move one axis to its stated maximum and the actuators are already partly extended, so what remains for the other five is less than their own stated maxima.
That is why an envelope quoted axis by axis is a set of separate best cases rather than a workspace. A specification that lists surge, sway, heave, roll, pitch and yaw at their individual maxima has not yet been checked as a trajectory — and checking it is the first thing our engineering does with an enquiry, because it is where mismatches surface.
It also explains a comparison that confuses buyers: two platforms can publish the same axis-by-axis figures and behave differently the moment axes are combined, because the attachment geometry differs. The honest comparison is a trajectory run through both geometries, not two tables side by side.
Axis-by-axis maxima are six best cases, not one workspace.
Have a trajectory rather than a table? Send it and we will check it against the real envelope →
The outer outline is what a datasheet lists. The inner shape is what a real trajectory can use. How much they differ depends on the attachment geometry, which is why it is issued per configuration.
Seen on most incoming specifications
Three ways a platform gets specified wrong
None of these are exotic. They are the three that cost the most time to unwind once a purchase order exists.
Specifying axis by axis
Six maxima written into one requirement, then discovered to be unreachable together at the design review.
Instead: give one representative trajectory, or the standard you are testing to, and let the envelope come out of it.
Buying axes you never command
Six axes specified because six sounds safer, then three of them stay at zero for the life of the machine — paid for, powered and maintained.
Instead: check whether the dropped axes carry information the task depends on. If they do not, three axes is the right machine.
Quoting mass without CG height
A payload figure with no centre-of-gravity height attached, so every quotation is answering a different question.
Instead: send mass and CG height together. They do more work than everything else on the sizing sheet.
Working from a specification someone else wrote? Run it through the selection sequence first →
What turns an enquiry into a configuration
The 8-Input Sizing Sheet
You do not need all eight to start. Send what you have — the gaps come back as a list, and a blank is more useful than an estimate.
01 · Gross moving load
Everything above the mounting plane: equipment, fixture, adapter, cabling.
02 · Centre-of-gravity height
From the mounting plane. Sets the moment the actuators work against.
03 · Inertia or mass properties
CAD mass properties are ideal. Rotational demand cannot come from mass alone.
04 · Axes, travel and angles
Which axes, how far, and about which reference point on the moving assembly.
05 · One motion profile
A representative trajectory, a frequency band, or the standard being tested to.
06 · Installation envelope
Footprint, ceiling height, access route, floor construction, any pit.
07 · Site supply and environment
Voltage, phases, capacity, ambient conditions, any ingress requirement.
08 · Host and acceptance
What commands it, at which command level, and how you intend to accept it.
Inputs 01 and 02 together decide more than the rest of the list combined. A 600 kg assembly with its centre of gravity 1.8 m above the mounting plane and a 600 kg assembly sitting flat are two different machines, and the difference is not marginal.
Have the first two only? Enough for a first pass — send them →
One accountable platform subsystem
What the Motion Platform Supply Package Can Include
We define the platform work package and the customer-owned system separately. That boundary keeps quotations comparable and prevents a platform project from being mistaken for complete simulator or test-system delivery.
Typical CSCMotion Scope
Included when identified in the approved project baseline.
- Motion-platform mechanical assembly
- Electric actuators and drive equipment
- Base, moving frame and agreed mounting
- Controller and electrical cabinet
- Platform-side communication interface
- Drawings and interface documentation
- Factory assembly and agreed platform FAT
- Contracted installation or commissioning support
Normally Customer / Integrator Scope
Owned by the application-system supplier unless separately reviewed.
- Cockpit, cabin, vehicle buck or DUT fixture
- Visual, audio, avionics or application equipment
- Application cueing or complete-system software
- Building work, foundation and site utilities
- Complete simulator or test-system validation
- Training-course delivery and qualification
- Regulatory certification outside contracted scope
Selection questions, answered here
Choosing a motion platform: FAQ
Which architecture do I actually need — 3DOF or 6DOF?
The deciding test is whether the task fails when surge, sway and yaw are missing. If it does, you need six axes, and tuning the remaining three cannot recover what was dropped. If it does not, a right-sized 3DOF platform reproduces the same motion with less installed power, a smaller footprint and fewer parts under maintenance. Work the five questions above in order rather than starting from an axis count.
Why is the combined travel smaller than the figures listed per axis?
Because all six actuators serve every axis. Driving one axis to its listed maximum already consumes actuator extension, so what remains for the others is smaller than their own listed maxima. This is true of every parallel platform, not just ours. It is also why we ask for a trajectory rather than a table of maxima — the trajectory is the thing that can actually be checked.
What does "20 kg to 35 t" cover, exactly?
Gross moving load: everything above the mounting plane, including your equipment, the fixture, the adapter and the cabling. Not the mass shown on the drawing. The load class table on this page is organised by that figure because the band decides which constraint governs the design long before a model number does.
Can I start with 3DOF and add the other axes later?
Not as a retrofit. The mechanism, the frame and the control geometry are different from the outset, so a three-axis platform does not become a six-axis platform by adding actuators. What is possible is planning a second machine around a shared interface and control convention so the host software carries over. If an upgrade path matters, say so at the requirement review — it changes what we design now, not what we do later.
Is the control system included, or a separate item?
Platform-side control is part of a platform supply: controller, drives, cabinet, kinematics and the platform-side interface. The separate control system page covers the cases where the scope is different — an existing host with its own command convention, a multi-platform installation, or an OEM subsystem supplied without our mechanism. If a host is already fixed, scope it alongside the mechanism rather than after it.
My requirement says 6DOF but the yaw range is large. What happens?
A hexagon runs out of geometry before it runs out of actuator force, so large yaw at large radius is a mechanism limit rather than a sizing problem. The usual answer is a rotary stage in series above a six-axis base, which reaches the yaw range without stretching the parallel geometry into a shape that performs badly everywhere else. We will propose that rather than quote a hexapod that cannot do it.
Commercial questions — lead time, warranty, acceptance, support: Those are answered in the full FAQ →
Still between two architectures?
Mass, centre-of-gravity height and one motion profile are enough for us to run your requirement through both geometries and tell you which one it actually needs.
Where each answer takes you
- Full pose, six axes commanded together → 6DOF
- Attitude and heave only → 3DOF
- Accuracy and stiffness over travel → Stewart
- Existing host, defined command set → Control system
- None of the above → Custom & OEM