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Technology · Choosing the actuator
Electric vs hydraulic motion platform: why six-axis platforms moved to servo electric.
For decades, large motion platforms were hydraulic because nothing else could carry the load. That reason has mostly gone. Servo electric cylinders now carry tens of tonnes, and on a six-axis platform they bring things hydraulics never could: position without drift, behaviour that does not change as oil warms up, no power unit running when the machine stands still, and no oil. This page compares the two side by side, including the jobs where hydraulic is still the right choice.
Where we stand: every platform we build is servo electric. We have also designed valve control boards for hydraulic and pneumatic platforms, so this comparison is written by people who have driven both.
A servo electric cylinder needs a power cable and an encoder cable. A hydraulic one needs a pump, a tank, valves, hoses and a cooler behind it.
Start here
How each actuator turns electricity into motion
Both end with a rod that pushes and pulls. The difference is everything that happens before the rod moves.
Servo electric cylinder
A servo motor turns a precision screw. A nut on the screw is fixed to the rod, so every turn of the motor moves the rod a known distance. An encoder on the motor counts that turn, so the controller always knows exactly where the rod is. Energy is converted once: electrical to rotary, then straight to linear through the screw.
Hydraulic cylinder
An electric motor drives a pump that pressurises oil in a power unit. A servo or proportional valve meters that oil into one side of the cylinder or the other, and the pressure pushes a piston. Position is read by a separate sensor, and holding still means the valve must hold the oil column in place. Energy is converted several times: electrical to rotary, rotary to pressure, pressure through a valve, pressure to force.
Every conversion in the hydraulic chain loses some energy as heat, and every one of them sits in oil whose behaviour changes with temperature. That is the root of most of the differences in the rest of this page.
Fewer conversions, fewer places for energy, accuracy and oil to leak away.
Servo electric vs hydraulic actuator working principles.
Want to see inside the cylinders we build? See how each cylinder is built and run in →
Everything in one table
Servo electric vs hydraulic cylinders, The 12-Line Actuator Crosswalk
Read the last column. It is what each difference means once the cylinder is one of six legs under a moving platform.
The 12-Line Actuator Crosswalk Property, servo electric, hydraulic, and what it means on a six-axis platform
| Property | Servo electric | Hydraulic | What it means on a six-axis platform |
|---|---|---|---|
| Position accuracy | Encoder on the motor, screw sets the ratio | Separate sensor, valve and oil in between | Six legs that agree with each other give a table that goes where it is told |
| Holding still | Motor holds position; held mechanically on power loss; no drift | Valve holds the oil column; leakage lets it creep | A parked platform stays exactly where it stopped |
| Temperature sensitivity | Low | Oil viscosity changes with temperature | Same behaviour at 9 a.m. and at 5 p.m.; no warm-up period |
| Stiffness | Mechanical: screw, nut, bearings | Set by oil compressibility and trapped oil volume | Hydraulic legs soften as stroke and hose volume grow |
| Force in a given size | Lower | Much higher | Hydraulic’s real advantage — see where it still wins |
| Shock and impact loads | Must be sized for them | Tolerates them well | Matters for crash and drop tests, rarely for simulators |
| Energy at rest | Small holding current only | Pump usually running | Idle hours cost almost nothing on electric |
| Noise | Motors and screws; < 70 dB(A) at 1 m at 40 mm/s on our machines | Power unit adds pump noise, often in a separate room | Electric can share a room with people and instruments |
| Infrastructure | Power supply and cabinet | Power unit, tank, cooling, piping, drip trays | Electric needs no plant room and no oil containment |
| Maintenance | Screw lubrication, bearings | Oil, filters, seals, hoses, leak checks | Fewer consumables and no oil disposal |
| Cleanliness and fire | No fluid | Leak and fire risk from oil | Suits laboratories, training centres and public venues |
| Control integration | Drives on the same fieldbus as the controller | Valve cards, pressure loops, oil conditioning | One control system from host command to motor |
Green marks the stronger option on each line. Hydraulic wins two lines, and they are real: force in a small envelope and tolerance of shock. If neither is your constraint, the other ten lines favour electric on a six-axis platform.
Comparing an electric quote against a hydraulic one? Send both and we will line them up against this table →
The argument for electric, specific to six legs
Why servo electric suits a six-axis platform better than hydraulic
On a six-axis platform no leg works alone. The table only goes where it is told if all six legs reach their commanded lengths at the same moment. Anything that makes one leg behave differently from the others shows up as an error in the table.
A six-axis platform is only as good as its worst leg. Electric makes six legs alike.
Servo electric Stewart platform with power and encoder cables.
Need figures for your own duty cycle rather than an illustration? Send the duty profile and we will return peak and average power for an electric platform →
What changed
Three claims about electric platforms that are now out of date
Each of these was once true. Each is still repeated in specifications written from habit.
Claim 1
“Electric cannot carry heavy loads”
In 2021 we built a 30-tonne all-electric six-axis platform to carry full-size aircraft cabin sections. It was designed for 25° of tilt and 1,000 mm/s, and was machined, assembled, installed and tested in 41 days. Our electric range now runs to 50 t.
Claim 2
“Electric cannot do high frequency”
Our vibration-class electric machines are specified to a system response of 20 Hz or better, and micro-vibration configurations to 25 Hz working frequency. What electric does not do is very high force and high frequency at the same time.
Claim 3
“Screws wear out; oil lasts”
A screw’s life is calculated from its load rating and your duty, before it is ordered; our cylinders are also checked by finite element analysis at three times rated load. Hydraulic seals, hoses and oil wear too — they are just replaced more often and less predictably.
A 30-tonne all-electric six-axis platform. Heavy loads stopped being a reason to choose hydraulic.
6dof motion platform for vehicle driving training and testing
Your specification says hydraulic because the load is heavy? Send the load and we will size it electric →
Beyond the purchase price
Total cost of ownership, The 8-Line Life Cost Ledger
The price of the platform is one line. The others arrive over the next ten to twenty years, and most of them lean the same way.
The 8-Line Life Cost Ledger Where money goes after the order, and which way it leans
| Cost line | Servo electric | Hydraulic | What drives the difference |
|---|---|---|---|
| Platform price | Depends on load and envelope | Depends on load and envelope | Compare two quotes for the same load case, not two catalogues |
| Plant and installation | Supply and cabinet | Power unit room, piping, cooling, oil containment | Hydraulic brings a small plant room with it |
| Energy | Mostly while moving | Pump runs through idle periods | Platforms spend much of their day stopped |
| Consumables | Screw lubrication | Oil, filters, seals, hoses | Oil also has to be disposed of |
| Scheduled maintenance | Bearings, screws, joints | All of those plus the hydraulic circuit | Fewer systems to service |
| Unplanned stops | Drive or motor fault, swapped as a unit | Leaks, contamination, valve faults | Contamination can reach every leg at once |
| Room and building | No fluid risk, lower noise | Fire and spill precautions, pump noise | Matters in offices, labs and public venues |
| Spare parts | Standard motors, drives, encoders | Valves, seals, pump parts | We buy motors, drives and encoders in standard sizes so you can too |
We do not put numbers on this ledger because they depend on your duty, your energy price and your site. What we will do is quote an electric platform against your load case and give you its peak and average power, so the energy line can be worked out rather than guessed.
Building a business case to replace hydraulic? Ask for the electric quote with power figures for your duty →
If you run a hydraulic platform today
Replacing an ageing hydraulic platform with electric
Many electric platforms we build replace a hydraulic machine that has become expensive to keep running. The replacement is sized from what the old machine actually did, not from its nameplate.
The most useful thing you can send is a recording of the old machine working: leg pressures or forces, positions and velocities over a representative session. From that, the real peak force per leg and the real duty are known, and an electric platform can be sized to them instead of to the old machine’s theoretical maximum — which is often much larger than anything it was ever asked to do.
The site usually gets simpler. The power unit, its room, its cooling and its oil go; a supply and a cabinet arrive. Floor loading and anchors still need checking against the new machine, because a different mechanism puts different loads into the slab.
Have logs or drawings from the old machine? See how a replacement platform is scoped →
What to send for a replacement
- Payload mass, centre-of-gravity height and inertia
- Recorded leg forces or pressures, and positions, from real use
- Stroke, velocity and acceleration the job actually needs
- Frequency content of the motion
- Room layout, floor construction and available power
- The host software or controller interface you want to keep
What comes back
An electric platform sized to your real duty, its peak and average power, and what changes on your site.
The decision
The 5-Question Actuator Test
Answer in order. A “yes” to any of the first four points towards hydraulic and deserves a closer look. Four “no” answers mean servo electric is the better platform for you.
Question 1
Is the force per leg extreme for the space available?
If the envelope is fixed and small and the force is very large, force density decides it.
Question 2
Will the platform take shocks or impacts?
Crash, drop or impact loading as part of normal use.
Question 3
Very heavy payload at high frequency, together?
Not one or the other — both at once, as on large structural vibration tables.
Question 4
Must you use an existing hydraulic plant?
A site with a power unit, oil handling and staff already in place, by requirement.
Question 5
Do people, instruments or a clean room share the space?
Training centres, laboratories, offices, venues, anywhere oil or pump noise is unwelcome.
Answered “not sure” to question 1 or 3? Send the load and motion; we will size it electric or tell you it is not →
Once the actuator is settled
Where to go next
Platform
6DOF motion platform
Six servo electric legs: travel per axis, load range and the jobs these machines are built for.
Decision
3DOF vs 6DOF
The other early decision: how many axes your motion actually uses, and what the missing ones cost you.
Trade-off
Payload, stroke and acceleration
How load, travel and acceleration pull against each other, and how that sizes each electric leg.
Custom
Replacing or extending a platform
Existing hydraulic machine, fixed pit, legacy host software — how a custom electric platform is scoped around them.
Asked when choosing
Electric vs hydraulic FAQ
What is the difference between a servo electric cylinder and a hydraulic cylinder?
A servo electric cylinder turns a servo motor’s rotation into straight-line motion through a screw, so the drive controls position directly. A hydraulic cylinder is pushed by oil that a pump has pressurised and a servo valve meters, so position depends on the oil, the valve, the hoses and the pump as well as the cylinder. The electric leg needs a power cable and a signal cable; the hydraulic leg needs a power unit, an oil tank, cooling, filtration and pipework.
Is servo electric strong enough for a heavy motion platform?
For the large majority of motion platforms, yes. We built an all-electric six-axis platform with a 30 t load in 2021, designed for 25° of motion and 1,000 mm/s, and our range runs from 10 kg to 50 t. Hydraulic keeps the advantage when a very large force has to fit in a very small envelope, or when very heavy payloads must be moved at high frequency together. Send the load case and we will say which side of that line it falls on.
Is an electric platform stiff enough for accurate motion?
An electric leg is a steel screw in a steel tube, with no compressible oil column inside it, so its stiffness does not change with the piston’s position. A hydraulic leg is softest near mid-stroke, where the oil volume on each side is largest. Our single-cylinder steady-state error is under 0.1 mm, and six-axis test machines are specified with no more than 1% coupling between axes, measured on each machine at acceptance.
Does an electric motion platform cost more than a hydraulic one?
The actuators themselves can cost more for the same force. What an electric platform does not need is a power unit, oil, pipework, cooling, filters, a bunded area and the service around them, and it draws power mainly when it moves rather than keeping a pump running. We do not publish prices; we compare the cost of owning the machine over its life against the same load case, which is where the difference shows.
What maintenance does a servo electric platform need?
Scheduled lubrication of the screws and joints, checks on cables and connectors, and a periodic look at the drives and their error logs. There are no oil changes, filter changes, seal leaks or hose replacements, and nothing needs draining before a move. The maintenance schedule for your machine comes with the acceptance documents.
Can you replace our existing hydraulic motion platform with an electric one?
In most cases, yes. We size the electric legs from your platform’s real duty — recorded forces or pressures and positions from normal use are the best input — and keep the host interface you already use where we can. The site usually gains floor space and loses its oil handling. If the recorded duty shows loads that only hydraulic can carry, the answer we send says so.
When is hydraulic the better choice?
When the force per leg is extreme for the space available, when the platform must absorb shocks or impacts as part of normal use, when very heavy payloads must move at high frequency together, or when a site requires the use of an existing hydraulic plant. Outside those cases, servo electric is usually the better platform.
You only build servo electric platforms. Is this page simply a sales argument?
We chose servo electric because it suits six-axis motion platforms, and the reasons are on this page with the numbers behind them. We have also designed valve control boards for hydraulic and pneumatic platforms, so we know both sides. Where hydraulic is the right answer, we say so — and in those cases we are not the supplier.
Lead time, payment terms and warranty are answered in the full FAQ.
Send the load and the motion. We will size it electric, or tell you it should not be.
Tell us what sits on the platform and how it has to move. If you are replacing a hydraulic machine, tell us that too — its recorded duty is the fastest route to a sized answer.
What comes back first
- Whether servo electric suits the load case — with the reason
- The leg force and speed the platform needs
- Peak and average power, and what the site has to supply
- The inputs still missing, if any