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Technology · Choosing the number of axes
3DOF vs 6DOF motion platform
A 3DOF platform is not half a 6DOF platform. It is a different machine that makes three of the six possible motions and fakes some of the others with tilt. Whether that is enough depends on one thing: whether your application needs the motions it cannot make, or only the ones it can. This page shows the difference axis by axis, then gives you five questions that settle it.
Short version: if your job needs a sudden push forward or sideways, or has to reproduce a recorded six-axis motion, choose 6DOF. If it needs up-and-down plus tilt, a 3DOF machine often does the job for less.
3DOF and 6DOF electric motion platforms side by side
Start here
Six ways a body can move, and which three a 3DOF platform keeps
Anything rigid can move in six independent ways: slide in three directions and rotate about three axes. A 6DOF platform can do all six, alone or in any combination. A 3DOF platform can do three of them.
Which three depends on the design. The most common 3DOF machine — and the one this page compares against — keeps heave (up and down), roll (tilt side to side) and pitch (tilt nose up or down). It gives up surge (forward and back), sway (side to side) and yaw (turn left and right).
Other 3DOF layouts exist: a roll, pitch and yaw machine for attitude work, or a surge, sway and yaw table for planar motion. The reasoning on this page applies to them too — just swap in the axes your machine keeps and loses.
The 6-Motion Availability Table What each motion feels like, and which machine can make it
| Motion | What a person or payload experiences | 3DOF | 6DOF | Typical need |
|---|---|---|---|---|
| Heave | Bumps, road texture, turbulence, a lift or drop | Yes | Yes | Almost every application |
| Roll | Banking, a vehicle leaning in a corner, a ship rolling | Yes | Yes | Almost every application |
| Pitch | Nose up or down, climbing, braking dive, a ship pitching | Yes | Yes | Almost every application |
| Surge | The first jolt of acceleration or braking | No — faked by pitch | Yes | Driving, flight take-off and landing, test profiles |
| Sway | The first push of a lane change, a side gust, a skid | No — faked by roll | Yes | Driving, rotorcraft, ship sway, test profiles |
| Yaw | Turning, spinning out, heading changes | No | Yes, limited range | Driving and flight; unlimited yaw needs a turntable |
“Faked by pitch” means the platform tilts slowly so that gravity pushes the occupant back into the seat, which the body reads as sustained forward acceleration. It works for sustained cues. It does not work for the first half-second, which is the part the next two sections are about.
Know which motions your job uses but not which machine that means? Go to the five-question test →
Why the difference is physical, not software
Three legs or six: the mechanism sets the limit, not the controller
It is tempting to think a 3DOF machine could be upgraded to 6DOF in software. It cannot. The number of independent motions a platform can make is fixed by how its legs are arranged.
A heave-roll-pitch 3DOF platform stands on three near-vertical actuators, sometimes four, with the table constrained so it cannot slide or turn. Lengthen all three legs together and the table rises. Lengthen one side and it tilts. There is no combination of leg lengths that moves the table forward, because the geometry does not allow it.
A 6DOF platform — usually a Stewart platform, or hexapod — stands on six inclined legs that cross between the base and the table. Because the legs lean, changing their lengths in different combinations can push the table in any direction and rotate it about any axis. Six legs, six independent motions.
The same geometry decides where rotation happens. On a 3DOF machine the table tilts about a point the mechanism fixes, usually near the table. On a 6DOF machine the controller can rotate about any point in the workspace — including the occupant’s head — by adding a small slide to every tilt. That capability matters more than most buyers expect, and the next section shows why.
An axis the legs cannot make is an axis no software can add.
Six inclined legs crossing between base and table. The lean is what lets a Stewart platform slide as well as tilt.
Want the geometry in detail? Read Stewart platform design →
The difference you can feel
Where 3DOF genuinely falls short: the first second of a push
Both machines can make you feel a sustained forward acceleration by tilting you back. Only one of them can make you feel it start. For simulators that is usually the deciding difference, and it can be worked out with a calculator.
A braking or launch cue, worked
To make a seated person feel 0.2 g of forward acceleration by tilt alone, the platform has to lean back far enough that gravity supplies it: about 11.3°, because the angle follows the ratio of acceleration to gravity.
That tilt cannot happen quickly. Rotate faster than roughly 3° per second and the occupant notices the rotation itself and reads it as tilting, not accelerating. At that rate, 11.3° takes about 3.8 seconds. So a 3DOF platform delivers a 0.2 g push that builds slowly over nearly four seconds — while the event it is meant to represent was a jolt.
A 6DOF platform supplies the jolt with surge: the table slides forward briefly, the occupant feels the onset at once, and tilt takes over the sustained part while the slide quietly returns to centre. The feeling of “now” comes from translation; the feeling of “still” comes from tilt. A 3DOF machine only has the second.
The same problem shows up at the head
A 3DOF platform tilts about a point near its table. The occupant’s head sits perhaps a metre above that point, so every tilt also moves the head. A 5° pitch shifts it about 87 mm fore or aft — a translation that was never commanded and that the body feels. A 6DOF controller cancels it by rotating about the head instead. A 3DOF machine has no axis to cancel it with.
3DOF can tell you that you are accelerating. 6DOF can tell you when you started.
Simplified: real cueing filters shape both curves, but the gap at the start is the physics, not the tuning.
When this does not matter. If the payload is an instrument rather than a person, or the motion is slow and sustained — a ship rolling, a platform tilting to set an angle, a seat reacting to bumps — onset cues are irrelevant and the argument above disappears. That is exactly where 3DOF machines earn their place.
Building a driving or flight simulator? See how cueing is specified for simulators →
Everything in one table
3DOF vs 6DOF side by side, The 12-Line Axis Crosswalk
The last column is the one to read. It turns each technical difference into what it changes for your project.
The 12-Line Axis Crosswalk Property, 3DOF, 6DOF, and what it means for you
| Property | 3DOF (heave, roll, pitch) | 6DOF (Stewart platform) | What it means for you |
|---|---|---|---|
| Independent motions | 3 | 6 | Any motion your job needs outside the three is either faked or missing |
| Actuators | 3, sometimes 4 | 6 | Fewer drives, cables and joints to buy, wire and maintain on 3DOF |
| Sustained forward or side cue | By tilt | By tilt | No difference for long, steady accelerations |
| Onset of a push or jolt | Not available | By surge and sway | The main perceptual difference in driving and flight simulation |
| Turning (yaw) | Not available | Limited angle | Unlimited turning on either needs an added yaw stage |
| Rotation point | Fixed by the mechanism | Placed anywhere in software | 6DOF can rotate about a head, a sensor or a workpiece; 3DOF cannot |
| Reproducing a recorded six-axis motion | Not possible | Yes, within the workspace | Decisive for test rigs that replay measured vehicle, ship or aircraft data |
| Cross-coupling between axes | Low, few axes to couple | Controlled by kinematics; about 1 % or less on our six-axis test machines | Ask any supplier for this figure and how it was measured |
| Height at rest | Usually lower | Higher for the same stroke, legs lean | Matters under low ceilings and for step-in access |
| Control and calibration | Simpler | Full kinematic model, more set-up | Both are delivered calibrated; 6DOF takes longer to commission |
| Price | Lower | Higher, but not twice | Actuators double; structure, cabinet, controller and testing do not |
| Upgrade path | Cannot become 6DOF | Can be commanded on three axes only | If unsure and the budget allows, 6DOF keeps the option open |
Row eight quotes the cross-coupling figure specified for our six-axis test machines in the 2024 product manual. It is a machine-class figure, not a promise for every configuration; for your machine it is measured and recorded at acceptance.
Comparing two supplier specs that use different axis counts? Send both and we will line them up against this table →
The decision
The 5-Question Axis Test
Answer these in order. One “yes” in the first three is usually enough to settle on 6DOF. If all five are “no”, a 3DOF machine is very likely the better buy.
Question 1
Does a person need to feel the start of a push?
Braking, launching, a lane change, a touchdown. If the first half-second matters to your training or research outcome, you need surge and sway.
Question 2
Do you have to replay recorded motion?
Measured vehicle, ship or aircraft data with six channels. A 3DOF machine can only replay three of them, and the result is no longer the recording.
Question 3
Must rotation happen about a specific point?
A pilot’s head, a sensor aperture, a point on a workpiece above the table. Only 6DOF can move its rotation point there.
Question 4
Do you need turning or heading change?
If yes, you need yaw. 6DOF gives a limited angle; a 3DOF machine with an added yaw stage (4DOF) may be cheaper if yaw is the only missing axis.
Question 5
Is the job mostly bumps, tilt and slow motion?
Seat and cabin effects, ship roll and pitch, attitude setting, a tilt test. These are what a heave-roll-pitch machine was built for.
Choose 3DOF when
- The motion is heave, roll and pitch, and nothing else
- The payload is an instrument, not a person judging onset
- Ceiling height or budget is tight
- You need many identical seats or cabins and simplicity scales
Choose 6DOF when
- A person must feel pushes start, not only persist
- You replay six-channel recorded data
- Rotation must happen about a head, sensor or workpiece
- The application may change and you want the option open
Neither, on its own, when
- You need unlimited turning — add a yaw stage
- You need large travel on one axis — add a rail or use a dedicated long-stroke axis
- You need hydraulic-class force in a small envelope — we build servo electric only
Answered “not sure” to one of them? Send the job in two sentences and an engineer answers the question for you →
What is usually chosen, and why
3DOF or 6DOF by application
These are typical choices, not rules. The right-hand column is where projects cross over.
The 7-Application Axis Map Usual choice, reason, and the exception
| Application | Usual choice | Why | When the other one wins |
|---|---|---|---|
| Flight training | 6DOF | Onset cues and rotation about the pilot’s head are part of how devices are assessed | Introductory or familiarisation trainers, where 3DOF is common |
| Driving research | 6DOF | Braking and lane-change onset are the cues studies measure | Fatigue or distraction studies where motion is secondary |
| Entertainment seats | 3DOF | Bumps and tilt carry most of the effect, and cost scales with seat count | Premium single-seat rides that need yaw or sharp jolts |
| Industrial testing | Depends on the profile | Six-channel recorded data needs 6DOF; a tilt or roll test does not | Single-axis vibration, where a shaker is the right tool |
| Motion compensation | Often 3DOF | Ship roll, pitch and heave dominate the disturbance | When surge, sway or yaw at the payload also has to be removed |
| Laboratory research | 6DOF | Experiments change; six axes keep future studies possible | A funded single study with a known, limited motion |
| Attitude and tilt tables | 3DOF or 2DOF | Setting and holding an angle needs rotation, not translation | When the rotation point must sit above the table |
Your application is not on the list? Open the applications column →
The honest version
The cost difference is real, but it is not twice
A 6DOF machine has twice the actuators and drives of a three-legged 3DOF machine. It does not have twice everything else.
The table and base structure, the control cabinet, the controller and its software, calibration, the loaded acceptance test, packing and installation all exist on both machines, and several of them grow only a little with the axis count. So the price step from 3DOF to 6DOF is noticeable and smaller than the axis count suggests. The running cost gap follows the same logic: three fewer actuators and drives to service.
We do not publish prices, because on these machines the load case sets the price more than the axis count does. The fair way to compare is to ask for both architectures quoted against the same load, stroke and acceleration — and when the job allows either, we quote both.
Compare two quotations for the same load case, not two catalogue prices.
Want to see what the extra three axes cost for your load? Ask for both architectures quoted side by side →
The visible difference: three cylinders and drives against six. The structure, cabinet and controller around them are not doubled.
Between and beyond
What about 2DOF, 4DOF and 7DOF?
3DOF and 6DOF are the common choices, not the only ones. We build single-axis rotation, two-axis, three-axis with an added rotation, three-axis on four actuators, six-axis and seven-axis machines, so these options are real ones.
2DOF
Usually roll and pitch. Enough for a tilt table, a simple seat or a sensor swing test. The lowest cost and height, with the narrowest set of cues.
4DOF (3DOF + yaw)
A heave-roll-pitch machine on a yaw turntable. Adds turning without adding surge or sway. Useful when turning is the one missing axis.
7DOF (6DOF + yaw)
A six-axis platform on a yaw stage in series, so heading can change far beyond what the hexapod alone allows. Each of the seven axes runs its own control loop.
Need one axis with far more travel than the rest? See what can be changed on a custom platform →
What goes wrong
Four common mistakes in the 3DOF vs 6DOF decision
Buying 6DOF “to be safe”
If the job is bumps and tilt, three of the six axes will never be commanded. That is cost and maintenance with no return.
Buying 3DOF for a driving study
If the study measures braking or lane-change reactions, the missing onset cue is the measurement. No tuning fixes it.
Counting axes instead of checking travel
A 6DOF machine with too little stroke on the axis you need is worse than a 3DOF machine with enough. Check each axis against your motion.
Forgetting the rotation point
Tilting about the table when the occupant or sensor sits a metre above it adds motion nobody commanded. Say where rotation must happen.
Once you know which one
Where to go next
Platform
3DOF motion platform
Heave, roll and pitch machines: envelopes, loads and the jobs they are built for.
Platform
6DOF motion platform
Six-axis Stewart machines: travel per axis, loads and where the extra axes pay off.
Trade-off
Payload, stroke and acceleration
The next decision after the axis count: how far and how fast, at your load.
Custom
When neither fits as built
Longer stroke on one axis, an added yaw stage, a lower machine — how a custom platform is scoped.
Asked when choosing
3DOF vs 6DOF FAQ
What is the difference between a 3DOF and a 6DOF motion platform?
A 6DOF platform can move in all six independent ways a rigid body can: forward and back (surge), side to side (sway), up and down (heave), and rotate in roll, pitch and yaw. A common 3DOF platform makes three of them — heave, roll and pitch — and imitates sustained forward or sideways acceleration by tilting. The practical difference is that 3DOF cannot produce the sudden start of a push, cannot turn, cannot replay six-channel recorded motion, and rotates about a point fixed by its mechanism rather than one you choose.
Is 6DOF always better than 3DOF?
No. For bumps, tilt, slow motion and instrument payloads, a 3DOF machine does the same job with fewer actuators, lower height and lower cost. The extra axes of a 6DOF platform only pay off when your application uses them: onset cues for a person, recorded six-axis motion, rotation about a specific point, or turning. Buying axes that will never be commanded is cost without benefit.
Can a 3DOF platform be upgraded to 6DOF later?
Not in software, and not in any practical way in hardware. The number of motions a platform can make is set by how its legs are arranged, so a three-legged machine would need a new mechanism. The reverse works: a 6DOF platform can be commanded on only three axes. If the application may change and the budget allows, 6DOF keeps that option open.
Is 3DOF enough for a driving simulator?
For entertainment or for studies where motion is secondary, often yes. For research that measures braking, acceleration or lane-change behaviour, usually not, because those studies depend on the onset of a push that only surge and sway can produce. Building a 0.2 g forward cue by tilt alone takes nearly four seconds at a tilt rate the driver will not notice, which is much slower than the event itself.
How much more does a 6DOF platform cost than a 3DOF one?
Noticeably more, but not twice. The actuators and drives double; the structure, cabinet, controller, calibration, acceptance testing and installation do not. We do not publish prices, because the load, stroke and acceleration you need drive the price more than the axis count. Where either architecture could do the job, we quote both against the same load case so the difference is visible.
Does a 3DOF platform carry more payload than a 6DOF one?
Not as a rule. Payload depends on actuator size, leg geometry, the centre-of-gravity height of the load and the accelerations you need, and both architectures are built across a wide load range. The right comparison is two machines sized for the same load case, not two catalogue figures.
Why do you not simply recommend 6DOF, since it sells for more?
Because a machine that does more than the job needs is harder to justify internally, costs more to run, and makes the next project harder to win. We build two-, three-, six- and seven-axis machines, so recommending the smaller one costs us nothing we cannot make back on the next order.
Lead time, payment terms and warranty are answered in the full FAQ.
Send the motion, not the axis count. We will tell you which one.
Describe what the platform has to do and what sits on it. The reply says whether 3DOF will do the job, and if it will not, which missing axis is the reason.
What comes back first
- 3DOF, 6DOF, or a variant such as 3DOF plus yaw — with the reason
- Which axes your motion actually uses, and how far
- Whether both architectures are worth quoting side by side
- The inputs still missing, if any