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Odometry Ticks per Inch

Turns your drive geometry into the numbers autonomous code needs: encoder ticks per inch, plus the ticks for a given distance or turn.

Inputs

Diameter across the wheel. Mecanum and flex wheels share a diameter with the plain ones, so pick by name rather than by size. Anything not listed can be typed in.

in

Needed for the turn figures. Left wheel center to right wheel center.

in
°

Results

Ticks per inch

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Ticks per wheel turn

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Inches per tick

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Ticks for your distance

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Ticks per side for your turn

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Point turn, wheels opposing.

Ticks per tile

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24 inches.

Motor degrees per inch

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When you would use this

  1. Our autonomous drives the wrong distance.

    Ticks per inch is the number your code converts with. Work it out here from your real gearing and wheel size rather than trusting a figure copied from another team, whose drive is not yours.

  2. We changed our wheels and everything broke.

    Wheel size changes ticks per inch directly. Run it again with the new wheel and update the constant. This is the single most common reason a working autonomous stops working.

  3. Our turns are close but never exact.

    Enter the angle and your track width to get the distance each side has to travel. If your code turns by driving one side, that is the number it needs.

  4. We want more precision without buying anything.

    Gearing down multiplies ticks per inch. Try a taller reduction here and see how much resolution it buys, before deciding whether tracking wheels are worth it.

How this is calculated

The encoder is inside the motor, not on the wheel. So the first job is working out how many motor turns make one wheel turn, which is exactly the gear ratio:

ticks per wheel turn = ticks per motor turn × (driven ÷ driving) ticks per inch = ticks per wheel turn ÷ (π × wheel diameter)

Gearing down multiplies your resolution. A drive geared 5:1 gives five times as many ticks per inch as a direct drive with the same cartridge, because the motor spins five times for each wheel rotation.

Cartridges change resolution too

The three cartridges report different tick counts per output turn: 1800, 900 and 300 for the 100, 200 and 600 RPM cartridges. That is the internal gearing showing through: the same encoder on the same motor shaft, divided by a different reduction.

So a red cartridge gives six times the positional resolution of a blue one at the same wheel. If a mechanism needs to stop precisely, that matters more than the speed does.

Turning

In a point turn each side drives a circle of radius half the track width, so the distance each side travels for a given angle is:

distance per side = (angle ÷ 360) × π × track width

Turn figures drift more than straight-line ones, because turning scrubs the wheels sideways across the tiles by design. Almost every reliable autonomous uses a gyro or inertial sensor for angles and saves the encoder for distances. Treat the turn number here as a fallback, not a plan.

If you have tracking wheels

Unpowered tracking wheels sidestep most of this. They carry no torque so they barely slip, and their encoder sits on the wheel itself, so there is no gear ratio in the sum at all, and ticks per inch is simply the encoder resolution divided by the wheel circumference.

Sources & assumptions

Encoder resolutions of 1800, 900 and 300 ticks per output revolution for the 100, 200 and 600 RPM cartridges are published figures, as are the cartridge ratios and wheel diameters. Circumference is computed as π × diameter rather than VEX's rounded travel figures.

Assumes rolling without slip and a wheel at its nominal diameter, neither of which holds exactly, which is why the calibration note above matters more than the arithmetic.

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.