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Pneumatic or Motor?

Both cost you something the rules keep short: motors spend watts, cylinders spend air. This works out whether each can do the job, and what it takes from the rest of the robot.

Inputs

The job

lb·in / lbf

Pound-inches for an arm, pounds of force for a straight push.

° or in

Degrees of swing, or inches of straight travel.

A full there-and-back counts once.

Holding a middle position, or moving at a controlled speed.

The pneumatic option

psi
psi

Below this the mechanism gets unreliable. Same figure as the air budget tool.

The motor option

W

Everything else on the robot, drivetrain included. The cap for the whole robot is 88 W.

Results

Which one can do it

—

Cylinder: can it move the load?

—

Cylinder gives

—lb·in / lbf

Cylinder: fires available

—

Motor: can it move the load?

—

Motor gives

—lb·in / lbf

Motor costs

—W

Motor takes

—s

Robot motor power if you choose the motor—

of the 88 W the rules allow

Match air used if you choose the cylinder—

of the usable air on board

How this is calculated

This is not really a question about which is stronger. Both can usually be made strong enough. It is a question about which scarce thing you would rather spend, and what the mechanism has to be able to do.

What each one costs

  • Motors cost watts, and watts are capped by rule. The whole robot gets 88 W, with at most 55 W of that on the drivetrain. Every motor you spend on a mechanism is one you cannot spend elsewhere, and the budget is the same whether the mechanism runs once a match or continuously.
  • Cylinders cost air, and the air does not come back. Two reservoirs is the limit, they are charged before the match, and nothing refills them during it. A cylinder is free in watts and finite in actuations.

The thing that usually decides it

A cylinder has two positions: all the way out, and all the way in. It has no others. If your mechanism has to stop halfway, hold a middle angle, or move at a controlled speed, the comparison is over before any of the numbers matter — that is a motor's job.

Going the other way, a cylinder holds its position with no power and no heat once it is there. A motor holding a load against gravity is drawing current and warming up the whole time, and a motor that overheats mid-match is a mechanism that stops working in the last minute of a match.

Where the cylinder's torque figure comes from

For a swinging arm there is no single answer without knowing exactly where the cylinder is anchored — except that there is an upper limit, and it depends only on the stroke:

best average torque = force × stroke ÷ sweep in radians

It comes out of the geometry: the rate the cylinder lengthens as the arm turns is the moment arm, so the total stroke is the moment arm added up across the sweep. Spend all your stroke over a small angle and you get a large moment arm; spread it over a large angle and you cannot.

So the figure here is the best any mounting could manage, not what a particular one will. Use themount finder to see whether a hole exists that gets close to it — and if this page says a cylinder can just barely do the job, that means only a perfect mounting will.

What this does not weigh

  • Weight and space. A cylinder plus tubing, valve and two reservoirs is not obviously lighter than a motor, and it takes more places on the robot.
  • Speed. Cylinders are close to instant, which is sometimes exactly what you want and sometimes how a game object gets launched across the field.
  • How much of it you have already built. The best mechanism is often the one your team can wire, program and fix at a competition without a laptop.

Save this as evidence

Collects what you entered, what came out, how it was worked out, and anything the tool flagged, with a timestamp and a version so someone else can reproduce it.

This is evidence, not a notebook entry. It deliberately does not write your problem statement, your reasoning, or your conclusion, because under RECF rules an Engineering Notebook has to be the students' own work and no tool may generate or organise its content. Take the numbers, decide what matters, and write it yourself.

Save this run, and compare

Keeps what is on screen so you can change something and see both sides of the change. Saved in this browser only, never uploaded.

Sources & assumptions

The 88 W robot cap, the 55 W drivetrain cap and the 2-reservoir limit are competition rules. Motor stall torques and reservoir volume are VEX figures.

Air is computed with the same shared function theair budget tool uses, so the two pages cannot drift apart on how many fires you get. A dual-acting cylinder is charged for a full stroke in each direction.

The cylinder torque figure is an upper bound, verified.Average torque equals force times stroke over the sweep in radians. Checked against an exhaustive search of anchor positions on four different sweeps: the best mounting found reached at least 99.5% of the bound each time and never exceeded it.