Quick Builds

Quick Builds, created by calling .quickBuild() in a movement builder, skip the full motion profiling process. This makes them extremely fast to generate and allows the follower to decide how fast to move while the robot is already following the path.

For a holonomic drivetrain, a quick build stores only the path geometry and heading interpolation. During every follower update, Apex finds the closest point on the path and calculates the corrections needed to stay on it. It then uses a waterfall power priority to decide which commands receive the available motor power.

Tank drives are handled a little differently because their Ramsete controller requires velocity targets. A tank quick build generates a basic acceleration-and-deceleration profile, but it does not solve the complete coupled power model used by a profiled build. The waterfall described below applies to holonomic drivetrains.

When Should I use a Quick Build?

Quick builds are good for most paths, but they work best when:

A slip-proof localization method is being used (i.e. two-wheel odometry)
The path is generated during the runOpMode phase because computation is minimal
The path is simple with no sharp curves (i.e. lines)
Translational speed is prioritized over accuracy and repeatability

Quick builds should almost never be used when:

Complex path constraints need to be added
Drive encoders are being used for localization
High accuracy/consistency is the priority

Waterfall Power Priority

Imagine starting with a bucket containing 1.0, or 100%, of the robot’s available power. Each control stage takes what it needs from the bucket, then passes whatever remains to the next stage.

Heading receives power first. If the robot is facing the wrong direction, Apex applies the required turning correction and reserves that power before doing anything else:

\(P_{remaining} = 1 - |P_{turn}|\)

Path correction receives power next. This includes feedback that pushes the robot toward the path and centripetal feedforward that pushes it inward around a curve. Apex limits this correction to the power remaining after the turn.

Forward motion receives power last. It can only use what remains after the robot has been given enough power to face the correct direction and stay on the path.

This ordering is what makes the system behave well without a complete motion profile. If the robot drifts away from the path, the correction grows and automatically leaves less power for moving forward. The robot slows down, returns to the path, and then speeds back up as the correction shrinks. Continuing forward is never treated as more important than being under control.

The Limitation

The waterfall can react to a difficult curve, but it cannot fully prepare for one. A quick build may enter a sharp turn too fast and only reduce forward power once turning and path correction begin consuming the power budget. A Profiled Build examines the curve ahead of time and plans the slowdown before the robot reaches it.

Quick builds still regulate forward velocity and slow down near the end of the path. On holonomic paths, translational velocity constraints can also change the maximum target speed at chosen points. However, acceleration and angular constraints require a profiled build.

Using Quick Builds

Call .quickBuild() at the end of a movement builder:


Path path = Builder.holonomicPath(startPose)
        // Add path segments and heading interpolation.
        .quickBuild();

Quick builds are useful for simple paths, testing, and movements where fast generation matters more than maximum speed through complex geometry. They are also generally recommended for point turns. For the difference between the two profiling styles, see Motion Profiling.