Odometry Error Simulator
How far your tracking estimate wanders from where the robot really is, along your own path, from error sizes you measure. See which error costs you most before you spend a day chasing it.
Inputs
Your route, one leg a row: drive this far, then turn this much. Copy it from your autonomous. The robot starts at 0, 0 facing along the field.
Each error below is measured on your robot. The simulation won’t run until every one is filled in: type 0 for an error you’ve measured as none.
Push the robot 100 in along a tape measure and read what the tracking says. (Reported − 100) is the percent. Negative if it reads short. The Odometry Calibration tool works this out from several pushes.
Repeat that 100 in push five times. The standard deviation of the readings, as a percent of 100, is the scatter. The Descriptive Statistics tool gives the standard deviation.
Spin the robot 10 full turns in place and read the heading. (Reported − 3600) ÷ 3600 × 100 is the percent. Negative if it reads small.
How fast the heading wanders while the robot sits still. The IMU Drift tool measures it.
Time a long straight drive in your routine and divide the distance by the time. Used to turn drift per minute into drift per inch.
Time a 360° turn in your routine and divide 360 by the seconds.
Slip is random. The same seed always gives the same answer; change it to see another set of runs.
Results
95% of runs end within
—in
Of where the tracking thinks the robot is.
Average error at the end
—in
Error at the end, the run drawn
—in
Largest error along the way, the run drawn
—in
Runs simulated
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Show the numbers behind this chart
The true and estimated position at the end of each leg, for the run drawn.
How this is calculated
The robot drives the path exactly. The tracking adds up what it measures: each bit of distance a little long, each turn a little big, and the heading creeping by the drift for as long as the move takes. The gap between the two is the error.
measured step = true step × (1 + distance error) × (1 + slip) measured turn = true turn × (1 + turn error) + drift × time turning heading while driving creeps by drift × (step ÷ driving speed)With your numbers
Why it runs 200 times
Slip is different on every run, so one run tells you little. The page runs the path 200 times with random slip the size you measured, and reports the average and the distance 95% of runs stay inside. The seed fixes the random numbers, so the answer only changes when you change an input.
What this doesn’t cover
Each error is treated as steady: a wheel that reads long does so by the same percent all the way. Real slip bunches up in hard starts, stops and collisions, which this spreads evenly. Sideways skid in a turn isn’t modeled. Use it to compare errors against each other, then check the biggest one on the robot.
Make a notebook page
Turns this calculation into a dated engineering notebook page: the setup, data, results, figures, working and sources, numbered and cited. You add the goal, the decision and the reflection in your own words, plus photos and sketches. Print it, paste it into Google Docs, or download a Word file or slides.
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
No VEX figures are used. Every error, speed and leg is yours, measured on your robot. The drift is simulated from them with the steps above, the same tracking arithmetic the other odometry tools use.
Where this goes next
Explore further on the full mapWhere the answers on this page can be used, and which tools could have given you the numbers it asks for.
Comes after
IMU Driftfills in your heading drift hereAutonomous Consistencygives you your position errorYou are here
Odometry Error Simulator
a number carries across the next question it raises