Tutorial 06: A fast, clear loop

You will build: a drive program that shows its loop speed, with buttons to turn bulk reads and debug telemetry on and off. The main track does bulk reads for you, so this lesson is only about how it works inside.

You will learn: how to measure your loop speed, how bulk reads make it faster, and how to lay out telemetry so drivers find what they need.

You need: a mecanum drivetrain (change to TankDrive for a standard one). Tutorials 01-04.

Full program: Tut06FastLoop.java Reference: hardware.md: BulkReads, util.md: LoopTimer, telemetry.md

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1. Why loop speed matters

Everything your robot does happens once per loop: read the sticks, read the sensors, decide, set the powers. At 25 loops per second, the robot reacts 40 ms (milliseconds, thousandths of a second) late, PID control (the lift holding its height, Tutorial 07) gets jumpy, and driving feels mushy. At 100+ it feels instant.

2. Measure it

LoopTimer loopTimer = new LoopTimer();
...
while (opModeIsActive()) {
    loopTimer.update();      // first thing in the loop
    ...
    TelemetryHelper.value(telemetry, "Loop", loopTimer.getHz(), "Hz");
}

Always measure before and after a change. Guessing is usually wrong.

3. Bulk reads

A hub is the Control Hub or Expansion Hub the motors and sensors plug into. Every time your code reads an encoder or a sensor on a hub, the Control Hub sends a message and waits for the answer: about 2 ms each. Four drive encoders plus a lift encoder is about 10 ms per loop, just waiting.

A bulk read asks the hub for ALL its readings in one message. Two ways:

AUTO (easy, start here):

BulkReads.auto(hardwareMap);   // one line in INIT

MANUAL (fastest): you clear the saved readings yourself, once, at the top of every loop:

List<LynxModule> hubs = BulkReads.manual(hardwareMap);
...
while (opModeIsActive()) {
    BulkReads.clear(hubs);     // FIRST line of the loop
    ...
}

If you forget clear in MANUAL mode, the readings never change. The robot will act very strangely (a PID that never sees the lift move). That is why AUTO is the safe default.

The program lets you switch bulk reads on and off with A while it runs, so you can see the difference in Hz. (It sets the hub mode directly for this demo; normal programs just call BulkReads.auto or manual once.)

4. Telemetry the driver can use

During a match, the driver glances at the screen for half a second. Put what they need at the top, and hide the rest:

// What the driver needs: at the top.
TelemetryHelper.section(telemetry, "Driver");
TelemetryHelper.flag(telemetry, "Bulk reads (A)", bulk);
TelemetryHelper.value(telemetry, "Loop", loopTimer.getHz(), "Hz");

// Debug numbers: at the bottom, and only when asked for.
if (showDebug) {
    TelemetryHelper.section(telemetry, "Debug (B)");
    for (int i = 0; i < wheels.length; i++) TelemetryHelper.motor(telemetry, names[i], wheels[i]);
}
telemetry.update();

• section puts a --- Driver --- heading line, so groups are easy to find.
• motor puts power, position and speed on ONE line.
• Telemetry also costs loop time. Many lines = slower loop. Show debug only when needed (B).
• Call telemetry.update() once per loop.

Run it

1. START. Note the Hz with bulk reads ON.
2. Press A (bulk reads OFF). The Hz drops, because each wheel read is now a separate message.
3. Press B to show the debug section: the Hz drops a little more. Telemetry is not free either.

Write down your numbers. A typical result: 60 Hz without bulk reads, 150+ Hz with.

If something goes wrong

Problem	Fix
Readings frozen	MANUAL mode without BulkReads.clear(hubs) at the top of the loop.
Hz is very low (< 30) even with bulk reads	Look for sleep() in the loop, or a camera/vision process running. Turn off debug telemetry.

Try this

1. Change the program to BulkReads.auto(hardwareMap) and remove the clear line. Compare Hz with MANUAL.
2. Add 20 telemetry lines in a for loop. How much does the Hz drop?
3. Show the loop time in ms (getAverageMs()) instead of Hz. Which is easier to understand?

Next

Tutorial 07: PID: hold a lift at a height