IMU, Encoders, and Bulk Caching

Reliable motion feedback without slow loops.

Team Workflow and Competition ReadinessCore

In this lesson, you will:

Initialize the IMU with correct orientation.
Read encoder values with units.
Use manual bulk cache intentionally.

Concept narrative

Encoders and the IMU are how the robot remembers movement. Bulk caching is how the code reads many hub values without making every loop pay for each read separately.

Robot mental model

A fast loop should have a rhythm: clear cache, read sensors, compute decisions, write hardware, update telemetry. Breaking that rhythm creates stale data or inconsistent timing.

Implementation walkthrough

Set hub caching to manual, clear it once near the start of each loop, then read heading and encoder values. Validate by pushing the robot and rotating it by hand before powered tests.

BulkCacheLoop.javaJava

for (LynxModule hub : hubs) hub.clearBulkCache();
double heading = imu.getRobotYawPitchRollAngles().getYaw(AngleUnit.RADIANS);
int ticks = frontLeft.getCurrentPosition();
telemetry.addData("heading rad", heading);
telemetry.addData("front left ticks", ticks);

Common mistakes and debugging

Wrong heading units, reversed encoder signs, and stale cached values all produce confident-looking but wrong data. Print raw values and move the robot slowly to verify signs.

Practice

Build a feedback dashboard that shows heading, drive encoder ticks, loop rate, and whether cache was cleared this loop.

Checkpoint

Heading changes in the expected direction.
Encoder ticks increase as expected.
Cache clear happens once per loop.
The test record includes the setup, prediction, and observed result.
A teammate can repeat the check from the saved evidence without guessing.

Reflection check

Check your understanding before moving on.

With manual REV Hub bulk caching enabled, when should each hub cache be cleared?

Once per control-loop iteration before reads.

Once per match after STOP.

Only when an encoder reaches its target.

A robot turns clockwise but yaw decreases when the lesson expects positive clockwise. What should be checked first?

The Road Runner trajectory builder.

The chosen coordinate convention and IMU orientation parameters.

Whether telemetry strings are too long.

0 of 2 answered

References

FIRST FTC DocsOfficial SDK, Robot Controller, and programming reference.Learn Java for FTCFTC-focused Java book and exercises by Alan G. Smith.Game Manual 0FTC community reference for programming, controls, and robot design.