Deceleration

Deceleration is controlled by three main parameters that work together to ensure the robot can slow down and stop accurately. Understanding these important for tuning your robot's path following behavior.

Natural Deceleration

The natural deceleration is the maximum braking power your robot can apply in any direction, based on its motor and wheel setup.

Natural Forward Deceleration

Measured in units per second² (units/sec²), this represents the maximum deceleration the robot can achieve when moving forward or backward.

• Configuration: naturalForwardDeceleration
• Type: ConfigVar<Double> (required)
• Units: units/sec²
• Purpose: Used to calculate how far the robot will coast when no power is applied, and to estimate excess velocity after coasting through remaining path distance

Natural Strafe Deceleration

Measured in units per second² (units/sec²), this represents the maximum deceleration the robot can achieve when strafing.

• Configuration: naturalStrafeDeceleration
• Type: ConfigVar<Double> (required)
• Units: units/sec²
• Purpose: Similar to forward deceleration, but applied to sideways movement

Maximum Deceleration Constraint

The maximum deceleration constraint is an optional limit on how much deceleration the robot can apply during path following. This is useful when you want to limit the robot's deceleration rate, such as to avoid aggressive stops that might cause the robot to tip.

• Configuration: maxDecelerationConstraint
• Type: ConfigVar<Double>
• Default: Constraint.NONE (unconstrained/infinity)
• Units: units/sec²
• Purpose: Limits maximum deceleration, this is used to ensure the robot can still reach its target within the remaining path distance

How It Works

When the constraint is active (not set to Constraint.NONE), the algorithm:

1. Checks if the robot can stop within the remaining path distance using this deceleration limit
2. Calculates the velocity needed to coast down to the target velocity
3. Reduces the target velocity if necessary to ensure the robot can stop in time

If the deceleration constraint is too restrictive, the robot may not be able to stop at the exact target position.

How Deceleration Parameters Work Together

The Foresight algorithm uses these three parameters in four steps:

1. Coasting: The robot coasts (applies no power) to naturally decelerate based on naturalForwardDeceleration and naturalStrafeDeceleration
2. Distance Calculation: It measures the remaining distance to the target to find the speed needed to stop on time.
3. Constraint Application: If maxDecelerationConstraint is set, it checks if the robot can slow down accurately within that limit.
4. Velocity Adjustment: If necessary, it lowers the target speed so the robot stops accurately within the remaining distance.