Calibration strip

Three printed sheets and a tape measure on any table about 1.2 m long, to check how far the robot really drives and how far it really turns. Run the same short programs in FLL Practice (pick Calibration strip in the table menu) and on the real robot, then compare.

The 2 sheets to print (PDF) Print this page (with the results sheet)

Top view, to scale. The robot (red dashed outline) starts with the middle of its wheels on sheet 1's black line. Every line on sheet 2 starts at that point, so whatever turn the robot makes there, a short drive afterwards puts its front on the line for the angle it really turned to. Sheet 3 has a line for every cm from the start line, from 70 to 87, to read where the wheels stopped after a long drive.

What you need

The 3 sheets from the PDF, printed on US letter paper (black and white is fine).
A tape measure in cm, at least 1 m (a metal one stays straight best), masking tape and a ruler.
A table at least 1.2 m long. No cutting or joining.

Set it up (5 minutes)

Print the PDF at 100% / Actual size, not "Fit to page". Check the 10 cm bar on sheet 1 with a ruler.
Tape sheet 1 near one end of the table, the robot driving "up the page" along the table.
Lay the tape measure along sheet 1's right edge, with its 0 at the start line (the "tape measure 0 here" mark). Pull it out to 1 m, straight along the table, and tape it down at the start, the middle and the end.
Put sheet 2 with its near edge at 28 cm and its right edge touching the tape measure. Tape it down flat.
Put sheet 3 with its near edge at 68 cm the same way. Check: its 70 line is at 70 cm on the tape measure.

All three sheets touch the tape measure, so they are in line without measuring sideways. In FLL Practice, Reset position puts the robot on the start line, and the box at the top right of the 3D view shows the same readings: where the wheels are (in cm from the start line) and which fan line the front is on.

The tests

Use the same robot build in the simulator as on the table. Write each program once in FLL Practice, run it there, then export it (Save .llsp3) and run the same file on the real robot. Do every real test 3 times: the real robot changes a little from run to run. Start every run with the middle of the wheels on the start line and the robot's middle on the dashed line, and put any arm in the same place each time.

1Distance

move forward 80 cm (speed 50)

Look at the robot from the side and read the line on sheet 3 beside the middle of the wheels (the hubs). Each line is 1 cm; the little marks at the edges are millimetres. Then try speed 30 and speed 100, and 75 and 85 cm. For short moves (20 and 40 cm), read the tape measure beside the hubs instead: they show how the robot starts and stops.

2Straight

move forward 30 cm

Read the fan line under the middle of the robot's front. It should be 0. This is your baseline: a robot that reads 1° right here will read 1° right in every turn test too.

3Small turns

set yaw angle to 0 start moving with steering 100 (speed 20) wait until yaw > 9 stop moving move forward 30 cm

It should read 10° right. Try 10° left (steering -100, wait until yaw < -9) and speed 50: faster turns overshoot more.

4Quarter turns

four times: set yaw angle to 0 start moving with steering 100 (speed 30) wait until yaw > 89 stop moving then move forward 30 cm

Four quarter turns make a full turn, so it should read 0. Whatever it reads, divided by 4, is how far off each quarter turn is. Try two half turns (wait until yaw > 179) the same way.

5Turns by wheel rotations

move with steering 100 for N rotations (four times) move forward 30 cm

In the simulator, find the N that makes each one a quarter turn (four of them read 0). Run the same N on the real robot. Real tires slip in a spin, so it usually turns less: the reading divided by 4 is how much per turn.

What to change when they differ

Distance: if the real robot went 78 cm instead of 80, change the set 1 motor rotation to … cm moved block in its program: new value = old value × 78 ÷ 80. Then test 1 again.
Straight: a robot that drifts needs its tires checked (same tires, pushed on all the way) before anything else.
Gyro turns: if each quarter turn goes 2° too far, wait until yaw > 87 instead of 89, or turn slower. Use the real robot's number in programs for the real robot.
Wheel-rotation turns: use the real robot's N, not the simulator's, or switch to gyro turns for turns that matter.

Results sheet

Robot build: ______________________ Batteries charged? ☐ Date: __________

Test	Simulator	Real 1	Real 2	Real 3	Difference
1. 80 cm at speed 50: wheels at (sheet 3)
1. 80 cm at speed 30: wheels at
1. 80 cm at speed 100: wheels at
1. 20 cm and 40 cm: wheels at (tape)
2. Straight 30 cm: fan line (° L/R)
3. 10° right, speed 20: fan line
3. 10° left, speed 20: fan line
3. 10° right, speed 50: fan line
4. 4 quarter turns (gyro): fan line ÷ 4
4. 2 half turns (gyro): fan line ÷ 2
5. 4 × N = ____ rotations: fan line ÷ 4