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Complete Lift Designer

Torque, speed, stability and the shaft carrying it, checked together. A lift can pass all four individually and still fail, because raising the load is what makes the robot tip.

Inputs

The lift

lb
in
lb
in
in
°

Used for the speed figure.

Power

The robot

lb
in
in
in

Results

Does it work?

—

Torque needed, worst case

—N·m

Torque available

—N·m

Of what the motors give

—%

Time to raise

—sec

CG with lift raised

—in

Tipping threshold, lift up

—g

Shaft safety factor

—

The four checks

    How this is calculated

    Each of these four is covered on its own page, and each is easy to pass in isolation. Putting them together is the point, because the trades run against each other.

    Torque and speed pull opposite ways

    More reduction gives the torque to hold the load and takes away the speed to raise it. TheRequired Lift Torque page covers this in detail, including why the worst case is always with the arm horizontal. Here it is combined with the time to sweep through the travel angle, so a lift that holds beautifully and takes six seconds to get there shows up as the problem it is.

    Stability is the one that surprises people

    Raising a load moves the whole robot's balance point upward in proportion to the share of the mass that moved. Every tipping threshold divides by CG height, so the robot that was rock solid empty can go over the moment the lift is up and the driver accelerates.

    This is why the check belongs here rather than only on thetipping page. A lift is not just a lift; it is a change to the robot's stability that happens to carry game objects.

    The shaft is where it actually breaks

    Gearing down for torque multiplies what the shaft carries. A lift geared to hold a heavy load at long reach is exactly the mechanism most likely to twist a shaft, and the numbers are not close: a standard shaft yields at about 1.24 N·m and a geared-down lift can ask for ten times that. The shaft check has the detail.

    What to change when it fails

    • Not enough torque: gear down, add a motor, or shorten the reach.
    • Too slow: gear up, which costs torque, or accept it.
    • Tips over: lower the whole mechanism, lighten what rises, or widen the track. Gearing does nothing here.
    • Twists the shaft: bigger shaft, split the load across two, or move the shaft to the fast side of the gearing.

    Note that the third one is unaffected by everything that fixes the others. That is the reason for checking all four at once.

    Sources & assumptions

    Stall torque is published for the 100 RPM cartridge andderived for the others. Shaft strengths arederived from torsion theory with assumed material properties, as described on the shaft page. The friction coefficient isestimated, since VEX publishes none.

    Models a single rigid arm about one pivot. Four bar and DR4B linkages change the geometry, though the torque peak still lands near horizontal. Ignores friction and rubber band assist, which many lifts depend on heavily: a banded lift can hold far more than this predicts. Size the bands with the Rubber Band Assist calculator and subtract what they supply.

    The speed figure assumes the motors run at free speed, which they will not under load. Treat it as a best case and expect a real lift to be slower, especially one running near its torque limit.

    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.

    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.