Programs / Auto-Learn-AprilTagApproach

Autonomous // Student lesson

Auto-Learn-AprilTagApproach

AprilTag Approach

Follow Auto-Learn-AprilTagApproach through acquisition, centering, and a camera-range approach to 24 inches. Learn identifies an educational example, not permission to run it. This sample sends real motor commands but has no wall guard or validated camera freshness gate; study its branches and limitations before any separately authorized hardware review.

The comments call five centered observations frames, but the source counts loop checks without deduplicating images and retains the count across missing-target checks. Its endpoint projection uses yaw in X/Y, and its autonomous back-right direction differs from the TeleOp. None of these source details should be silently rewritten into a safer imaginary program.

Start with a question

What evidence would distinguish a robot that reached its target from one that merely stopped because time ran out?

By the end, you can…

Trace the 3-second acquisition, 6-second centering, and 8-second approach limits.
Explain complete-half target selection and the retained red/blue choice after acquisition.
Calculate reconstructed center range and signed steering from the source equations.
Distinguish zero on vision loss, loop-count centering, range completion, and timeout.

Start learning Jump to Code Quiz Download Blocks (.blk)

Before running: Ask your supervisor first. Keep Driver Station STOP ready.

Read · predict · explain

Build the idea, one block at a time

Read these steps before exploring the full program. The numbered blue comments in the diagram link back to the matching step.

01Prepare the autonomous direction profile

Actual Blocks for this section

Blocks to notice

set Direction
BRAKE
RUN_USING_ENCODER
set four powers 0
MsTransmissionInterval 50

The autonomous source reverses FL and BL but sets both FR and BR FORWARD. All four use BRAKE and RUN_USING_ENCODER and begin at zero. This differs from Start and AprilTagTeleOp, where BR is REVERSE. Encoder mode here is not a RUN_TO_POSITION destination, and the approach stop is chosen from camera range rather than an encoder distance.

For example: A uniform +0.25 request is intended as forward only with this autonomous mounting profile; copying the TeleOp BR setting changes the convention.

Think first

Does RUN_USING_ENCODER mean the program sets a 24-inch encoder target?

Show Answer

No. No encoder-position target controls this approach; 24 is a camera-center range in inches.

02Start the reviewed AprilTag pipeline

Blocks for Start the reviewed AprilTag pipeline — Actual Blocks for this section

Blocks to notice

setPollRateHz 100
pipelineSwitch 0
Limelight start
telemetry READY

Setup requests 100 Hz polling and pipeline 0, then this section starts the camera and reports the intended 24-inch behavior. Verify that slot 0 detects the correct AprilTags. A fast poll request provides opportunities to read results, not proof of a new processed frame, a correct pipeline, or a current pose.

For example: Repeatedly polling one result at 100 Hz can still provide only one image's geometry.

Think first

Can a requested 100 Hz poll rate certify five independent frames for centering?

Show Answer

No. Independent frames require frame identity or timing evidence, which this source does not check.

03Preview geometry with zero drive requests

Blocks for Preview geometry with zero drive requests — Actual Blocks for this section

Blocks to notice

while opModeInInit
call scanTags
red tag telemetry
telemetry update
idle

INIT scans continuously and displays the red tag distances and red-center estimate while the setup's motor requests remain zero. Red display can be unavailable even if the camera sees blue; display emphasis is not target-selection policy. The later acquisition can select either complete alliance center.

For example: Only blue groups 2 and 3 can form a usable blue center while the red-center row still says not available.

Think first

Does a missing red-center INIT row force the autonomous to reject a complete blue center?

Show Answer

No. Acquisition compares complete red and blue centers, not just the displayed red row.

04Open acquisition only after START

Blocks for Open acquisition only after START — Actual Blocks for this section

Blocks to notice

waitForStart
selecting true
selectedId -1
selectedRange 9999
resetRuntime

waitForStart prevents the autonomous motion phases from starting early. The source then enters selecting mode with no selected alliance (-1), a 9999-inch comparison sentinel, and a fresh acquisition timer. Those are target-state variables, not physical tag IDs or sensor measurements.

For example: selectedId -1 means nothing has been acquired. IDs 30 or 38 in the image are mapped to halves before a center can be chosen.

Think first

Does pressing START automatically mean selectedId becomes 0?

Show Answer

No. A complete matching pair still has to be observed during acquisition.

05Choose the first scan with a usable nearer center

Blocks for Choose the first scan with a usable nearer center — Actual Blocks for this section

Blocks to notice

active AND selectedId < 0 AND runtime < 3
call scanTags
nearest range comparison

Acquisition scans for up to 3 seconds while selectedId stays negative. In the first usable scan it compares complete red and blue centers and picks the nearer, with red winning a tie. It does not search all three seconds for a globally best target: a selection ends the acquisition loop. Motors retain zero during this phase; no acquired center leads to the stopped result.

For example: At 0.2 seconds red is complete at 50 inches and blue is absent: red is acquired then, even if blue might appear nearer at 1 second.

Think first

If only IDs 30 and 31 appear for the whole 3 seconds, is red acquired?

Show Answer

No. Both belong to the first red half, so no red center can be built.

06Count centered checks and inspect the loss branch

Blocks for Count centered checks and inspect the loss branch — Actual Blocks for this section

Blocks to notice

selecting false
centered 0
runtime < 6
ABS currentTx <= 2
centered + 1
set fixed turn powers

After acquisition, selection is locked and centering runs for at most 6 seconds. found with |tx| <= 2 degrees increments centered and requests zero; five checks permit approach. Off-center found observations reset centered and turn: positive error gives FL/BL +0.18, FR -0.24, BR -0.18; negative error reverses signs. Missing target requests zero but does NOT reset centered. No frame timestamp is deduplicated, so these are not guaranteed five consecutive distinct camera frames.

For example: Centered counts 1,2; a missing result leaves 2; three more centered checks can reach 5. Re-reading one old centered image can also increment the counter.

Math breakoutClosed-loop camera centeringmeasure → turn → measure again → stop inside ±2°

The robot repeatedly corrects fresh angle error instead of guessing one perfect turn.

Think first

Does an off-center found result at +3 degrees preserve centered = 2?

Show Answer

No. The turn branch resets it to 0; a missing-target branch, unlike this off-center branch, leaves the count unchanged.

07Approach a center range, not a bumper gap

Blocks for Approach a center range, not a bumper gap — Actual Blocks for this section

Blocks to notice

targetRange 24
runtime < 8
if found
currentRange <= targetRange
currentTx > 2 / < -2
set approach powers

After centered >= 5, the program stores startRange and targetRange = 24 inches. While active, not done, and under 8 seconds, found range <= 24 requests zero and sets done. Above 24, FL/FR/BL/BR are 0.30/0.26/0.30/0.20 for tx > 2; 0.20/0.36/0.20/0.30 for tx < -2; otherwise 0.25/0.31/0.25/0.25. Missing target requests zero but permits reacquisition of the same alliance within the timer. There is no approach angle-edge or obstacle gate. The targetRange >= 10 check always passes for the assigned 24; it is not a measured already-close check.

For example: At range 30 and tx +3 degrees, use 0.30/0.26/0.30/0.20. At range exactly 24, all powers become zero and done true. startRange minus currentRange is only a change in camera range, not verified chassis travel.

Math breakoutClosed-loop camera centeringmeasure → turn → measure again → stop inside ±2°

The robot repeatedly corrects fresh angle error instead of guessing one perfect turn.

Think first

Does a target loss at 2 seconds make done true or allow blind forward travel?

Show Answer

Neither. It commands zero without setting done; the same selected target can resume guidance before the 8-second timeout.

08Label the outcome before ending vision

Blocks for Label the outcome before ending vision — Actual Blocks for this section

Blocks to notice

done result COMPLETE / STOPPED
set four powers 0
Limelight stop

Range completion, acquisition failure, centering timeout, approach timeout, and Driver Station STOP are different outcomes. Cleanup requests zero from all four motors and stops the camera. COMPLETE describes reaching the source's camera-center threshold; it is not proof of a 24-inch bumper clearance, exact travel, validated fresh imagery, or competition readiness.

For example: An 8-second timeout with range still 30 inches produces a stopped outcome, not successful arrival merely because the wheels stopped.

Think first

Can Driver Station STOP during approach be counted as reaching the range goal?

Show Answer

No. Only the found-and-range <= 24 branch sets done for completion.

09Erase visibility before each scan

Blocks for Erase visibility before each scan — Actual Blocks for this section

Blocks to notice

set found false
set r4Seen / r5Seen / b4Seen / b5Seen false
set tag distances to not visible

scanTags clears found, the four endpoint flags, and the displayed tag distances before inspecting a result. Red-center display becomes not available. TeleOp also clears the four sticker-distance displays. Old coordinates can remain in variables, but cleared flags prevent a missing half from completing a center. Resetting state is not the same as proving the camera returned a new frame.

For example: A scan with R4 and R5 can set found true. A later scan containing only R4 leaves r5Seen false and cannot rebuild the red center.

Think first

May yesterday's r5 coordinates complete today's red center when r5Seen is false?

Show Answer

No. Both endpoint flags must be true in this scan; stored numbers alone are insufficient.

10Read a result, then its fiducial list

Blocks for Read a result, then its fiducial list — Actual Blocks for this section

Blocks to notice

getLatestResult
is not null
FiducialResults
set list

The non-null branch reads the result's list of fiducials, meaning recognized markers. A non-null result can still contain an empty list. These AprilTag sources do not check IsValid, Staleness, pipeline index, or a distinct frame timestamp here. Calling getLatestResult does not itself guarantee a fresh image, so this sample is not a validated freshness guard.

For example: An empty current list builds no center. Repeated retrieval of an old nonempty result could repeat the same geometry even though all flags were reset.

Think first

Does the non-null test prove that the image is less than 250 ms old?

Show Answer

No. There is no age comparison in this scan; null handling and freshness are separate checks.

11Repeat camera-space geometry for each tag

Blocks for Repeat camera-space geometry for each tag — Actual Blocks for this section

Blocks to notice

for each tag in list
TargetPoseCameraSpace
set pose

For each fiducial, the source retrieves its TargetPoseCameraSpace: position plus orientation relative to the camera, not a robot field pose. The instructional convention calls x left/right, y up/down, and z forward/back; yaw and pitch describe rotation, not wireless transmit/receive. Later projection formulas must be read literally and checked against the SDK pose convention before any physical use.

For example: Two tags in the list produce two passes through the position, angle, ID, and offset calculations; they are not two distinct camera frames.

Think first

Is a camera-space tag pose automatically a field location of the robot?

Show Answer

No. It is a relative camera-to-tag observation; field localization would need additional transforms and references.

12Keep signs until distance is calculated

Blocks for Keep signs until distance is calculated — Actual Blocks for this section

Blocks to notice

position.x
position.y
position.z
set x / y / z

The pose getters copy all three signed coordinates in meters. Signs matter when adding an offset and when computing steering. Squaring for range removes signs only at that later calculation; taking absolute values first would lose which side the reconstructed center lies on.

For example: A practice pose (-0.30, 0.40, 0.00) m has a 0.50 m range, but its negative x is still important to direction.

Think first

Do x = -0.30 m and x = +0.30 m contribute different amounts to x*x?

Show Answer

No. Both contribute 0.09 square meters, although their signed positions differ.

13Use degree-based yaw and pitch

Blocks for Use degree-based yaw and pitch — Actual Blocks for this section

Blocks to notice

orientation.yaw
orientation.pitch
SIN
COS

The source copies yaw and pitch from the pose and passes them to Blocks trig operations, which use degrees. Yaw is taught as a left/right rotation and pitch as a tilt. Do not insert a student radians conversion into this chain: it would change the inputs the Blocks operations expect. Review the exact axis mapping as well as the angle units.

For example: At yaw = 0 and pitch = 0, cosines are 1 and sines are 0, so an offset changes only the source's endpoint X.

Think first

Should a 90-degree pose angle be manually replaced with about 1.57 before the COS block?

Show Answer

No. This Blocks operation expects degrees; cos(90 degrees) is 0.

14Measure the line to a tag center

Blocks for Measure the line to a tag center — Actual Blocks for this section

Blocks to notice

multiply x*x / y*y / z*z
add
square root
multiply 39.3701
FiducialId
TargetXDegrees

Square each camera-space coordinate, add all three, take the square root, then multiply by 39.3701 inches per meter. This range is to the individual visible tag center, not yet a sticker or alliance center. The source also reads the physical tag ID and its raw TargetXDegrees; later center steering replaces that raw angle with a reconstructed-center angle.

For example: For (0.30, 0.40, 0) m: sqrt(0.09 + 0.16) = 0.50 m, or about 19.685 inches.

Math breakout3D Pythagorean distancerange = √(X² + Y² + Z²)

Three perpendicular camera measurements combine into one straight-line range.

Think first

What goes wrong if you omit y when it is 0.40 m in this example?

Show Answer

You get 0.30 m instead of 0.50 m and understate the full camera-to-tag distance.

15Require a pair of matching half-groups

Blocks for Require a pair of matching half-groups — Actual Blocks for this section

Blocks to notice

set group -1
set offset 0
group 0 / 1 / 2 / 3
endpoint seen flags

Each tag begins unassigned at group -1 and offset 0. IDs 30-33 form group 0 and reconstruct R4; 34-37 form group 1 and reconstruct R5. Groups 2 and 3 similarly reconstruct B4 and B5 from IDs 38-41 and 42-45. One visible tag from each matching pair of groups is sufficient; two tags from only one group are not.

For example: IDs 30 and 37 can supply both red endpoints. IDs 30 and 31 supply only the R4 half, however many times they are read.

Think first

Can group 0 plus group 3 form a complete red or blue center?

Show Answer

No. The required pairs are 0 with 1, or 2 with 3.

16Convert tag identity into a signed known offset

Blocks for Convert tag identity into a signed known offset — Actual Blocks for this section

Blocks to notice

compare FiducialId
set group
set offset
set R1Distance through B8Distance

IDs 30-37 are R1-R8; 38-45 are B1-B8. Within each four-tag sticker the centers sit at -6.5, -2.75, +2.75, +6.5 inches. To reconstruct endpoint 4, the first half uses offsets +13, +9.25, +3.75, 0; to reconstruct endpoint 5, the second half uses 0, -3.75, -9.25, -13. These are signed tag-to-endpoint corrections, not the tag's measured range. TeleOp additionally uses tag-to-sticker offsets +6.5, +2.75, -2.75, -6.5.

For example: R1 at ID 30 is 13 inches left of R4, so its endpoint correction is +13. R8 at ID 37 gets -13 to reconstruct R5.

Think first

For R6, ID 35, is the endpoint offset +3.75 or -3.75 inches?

Show Answer

It is -3.75 inches: move back along the strip from R6 to R5.

17Project the strip offset exactly as written

Blocks for Project the strip offset exactly as written — Actual Blocks for this section

Blocks to notice

divide offset by 39.3701
COS yaw
SIN yaw
COS pitch
SIN pitch
set endpoint X / Y / Z

Let d be the signed inch offset divided by 39.3701. The source reconstructs X = x + d*cos(yaw)*cos(pitch), Y = y + d*sin(yaw)*cos(pitch), Z = z - d*sin(pitch). Notice that yaw contributes to X and Y in these actual Blocks, while pitch changes Z. That is not the usual simplified claim that yaw rotates an offset between X and Z. Treat pose-axis interpretation as a supervised verification task, not an already proven physical model.

For example: For d = 0.10 m, yaw = 90 degrees and pitch = 0, the written equations add about 0 to X, +0.10 to Y, and 0 to Z.

Math breakoutRotate a known AprilTag offsetΔX = d·cos(yaw)·cos(pitch) ΔY = d·sin(yaw)·cos(pitch)

Sine and cosine split one known strip distance into camera-axis pieces.

Think first

At yaw = 0 and pitch = 90 degrees, what is the signed Z correction for positive d?

Show Answer

Z decreases by d, because the source subtracts d*sin(pitch); X and Y corrections are zero.

18Average coordinates, then find range and bearing

Blocks for Average coordinates, then find range and bearing — Actual Blocks for this section

Blocks to notice

r4Seen AND r5Seen
add endpoints / 2
square root
atan2
redCenterDistance

A complete red pair averages R4 and R5 coordinates; a complete blue pair averages B4 and B5. Each midpoint's 3D magnitude becomes its inch range. atan2 uses center X as the numerator-like Y socket and center Z as the X socket, giving atan2(center X, center Z) in degrees. This reconstructed bearing, not the raw visible tag's tx, guides centering. It is a geometric midpoint estimate, not full field GPS or multi-camera triangulation.

For example: Endpoints (-0.20, 0, 1.00) and (+0.40, 0, 1.00) m yield center (0.10, 0, 1.00), range about 39.57 inches, and tx about +5.71 degrees.

Math breakoutMidpoint and center bearingcenter = (A + B) ÷ 2 angle = atan2(X, Z)

Average two reconstructed endpoints, then calculate the signed turn toward their center.

Think first

Can you obtain the same midpoint by averaging the two endpoint ranges?

Show Answer

Not in general. Average the signed coordinates first, then compute the center's magnitude.

19Choose once, then retain the alliance

Blocks for Choose once, then retain the alliance — Actual Blocks for this section

Blocks to notice

if selecting
compare range < selectedRange
set selectedId 0 / 1
set currentRange / currentTx
set found true

Acquisition starts with selecting true, selectedId -1, and selectedRange 9999. Red is tested first; blue replaces it only when strictly nearer in the same scan, so a tie retains red. Once acquired, selecting becomes false: later scans update only the selected alliance's complete pair. Another nearer alliance cannot take over. currentRange is inches, currentTx is degrees, and found gates use of those values.

For example: Acquire red at 40 inches. A later scan with only a blue center at 20 inches leaves found false instead of switching targets.

Think first

With red and blue both at 40 inches in a selecting scan, which wins?

Show Answer

Red, selectedId 0. Blue's strict less-than test cannot replace an equal range.

Try it without a robot

Make the math make sense

tag range (in) = sqrt(x*x + y*y + z*z) * 39.3701: Camera-space position is in meters. Include height y, and convert the 3D straight-line distance to inches.
d = offset (in) / 39.3701: Put a known strip offset in meters before adding it to the pose.
endpoint X = x + d*cos(yaw)*cos(pitch); Y = y + d*sin(yaw)*cos(pitch); Z = z - d*sin(pitch): These are the actual source projections, using degree-based Blocks trig. Do not replace them with an assumed X/Z yaw formula. The physical pose-axis interpretation needs supervised verification.
center = (endpoint 4 + endpoint 5) / 2 on each axis: Average reconstructed endpoint coordinates, not tag ranges. One observation from each matching half is required.
center range = sqrt(X*X + Y*Y + Z*Z)*39.3701; center tx = atan2(X,Z): Range includes all three axes. The Blocks atan2 sockets hold X-socket = center Z and Y-socket = center X, giving the signed horizontal angle in degrees.
centered check: found AND |currentTx| <= 2; continue while centered < 5 AND time < 6 s: The source counts loop checks, not verified distinct frames, and does not reset centered on a missing target.
range goal: found AND currentRange <= 24 in: This is camera-to-reconstructed-center straight-line range, not a wheel travel or bumper-clearance target.
displayed distance traveled = startRange - currentRange: The source subtracts ranges. Rotation, camera offset, target motion, and 3D geometry can make this different from actual chassis displacement.

Use a notebook or talk through your answer with a partner. You do not need a robot to predict what these blocks will do.

1. Trace the timers and retained target

Write phase and power decisions for: no complete pair for 3 seconds; red acquired at 0.2 seconds; blue later becomes nearer; centered counts 1,2, missing, centered, centered, centered. Compare that sequence with a found +3-degree observation after count 2. Identify why the counter is not a proof of five fresh consecutive frames.

2. Choose exact approach outputs

On paper list FL/FR/BL/BR at range 30 inches with tx +3, +2, -2, and -3 degrees. Then trace a missing target, reacquisition at range 26, arrival at exactly 24, and an independent 8-second timeout case. Which cases set done?

3. Measure the right thing

Calculate a 3D tag range for x 0.30, y 0.40, z 0 m. For endpoints (-0.20,0,1) and (+0.40,0,1), find midpoint range and angle. Explain why startRange 40 minus currentRange 24 does not by itself prove 16 inches of robot travel or 24 inches of bumper clearance.

Full commented Blocks program

One source program, in one column. Calls connect any named helper routines; they are not separate programs. Click a numbered blue comment to return to its explanation.

Back to explanations Download Blocks (.blk)

Ask your supervisor before importing or running these Blocks. Viewing the program does not control the robot.

Section in context

Full Blocks program

FTC Blocks-to-Java for this segment. Generated from the selected source Blocks using FTC SDK generators, with an atan2 adapter matching the SDK's degree conversion where needed. This excerpt uses the original program's variables, devices, and methods; it is not standalone. Review the lesson's setup notes for required helpers.

For supervisors: 90-minute teaching plan & robot setup

Before the robot is used

Safety: Treat this as source analysis, not a deployment request. Learn and enabled metadata are not competition or physical-run approval. Autonomous sends real powers, has no wall guard, no age/pipeline validity checks in scanTags, and no approach edge-angle limit. Its centered counter is not five verified consecutive fresh frames. Any independently authorized bench demonstration needs wheels clear, exclusion space, an operator, and a supervisor at STOP. Do not use a camera-range endpoint as a bumper-clearance guarantee.

Required hardware & dependencies

Four mecanum drive motors named front_left_drive, front_right_drive, back_left_drive, and back_right_drive; verify each configured name against its physical cable and wheel.
FTC Robot Controller, Driver Station, secure battery, and a notebook. Motor direction settings are specific to the source and mounting, not universal wiring instructions.
Limelight 3A named limelight with calibrated AprilTag pipeline 0; correct tag sizes, camera mounting, and expected ID 30-45 geometry.
Accurate target-layout reference and tape measure for a separate stationary range audit; encoder-capable drive motors for the source's RUN_USING_ENCODER configuration.

Source remains AprilTagAuto.blk. Required native Blocks/devices are Limelight 3A named limelight, four drive motors, and an AprilTag pipeline 0 with the expected ID 30-45 layout. No helper ZIP is supplied. An educational name and enabled flag are not authorization; independently review axes, frame age, centering logic, calibrated range, and wheel directions before physical use. This page does not deploy anything.

Robot setup checklist

Inspect AprilTagAuto.blk and resolve native motor and Limelight Blocks without deploying. No helper installation or ZIP is claimed.
Verify autonomous FL/BL REVERSE, FR/BR FORWARD, BRAKE, RUN_USING_ENCODER, zero INIT powers, 100 Hz poll request, and 50 ms telemetry transmission request.
Review the literal endpoint equations against the real camera pose convention. Check the half-group target layout before accepting a reconstructed center.
Document absent age/distinct-frame checks and the centered counter's loss behavior. Source timeouts limit duration but do not certify a safe route or stopping distance.

90-minute teaching sequence

0-15 min
Compare direction profiles and identify each timer's phase.
Look for: BR FORWARD in Auto; 3/6/8 seconds belong to different phases.
15-35 min
Reconstruct endpoints, midpoint range, and bearing.
Look for: Signed offsets in meters and literal X/Y yaw projection.
35-60 min
Trace first usable selection and centered-counter branches, including loss.
Look for: Locked alliance, zero on loss, retained counter, no frame deduplication.
60-90 min
Calculate exact approach powers and classify outcomes; quiz and exit ticket.
Look for: Strict +/-2 comparisons, actual FR bias, and completion distinct from timeout.

Observation notebook

Notebook: autonomous evidence, counters, commands, and stop reason
Phase / elapsed time	Selected alliance / found	Range / tx	centered or done	Decision
Acquire / 0.2 s	Red / true	50 in / +3 degrees	selectedId 0	End acquisition; retain red
Center / within 6 s	Red / false	Old values not usable	centered remains 2	Four zero requests
Approach / within 8 s	Red / true	24 in / any reported tx	done true	Four zero requests; range threshold reached
Approach / 8 s	Red / true	30 in / 0 degrees	done false	Timeout, not arrival

Mark freshness as unverified. Record range change separately from tape-measured chassis travel; a timeout or STOP is never relabeled successful completion.

Troubleshooting · stop before investigating

Acquisition stops without choosing a target.: Check for a matching pair of halves, pipeline contents, device mapping, and the 3-second maximum. Seeing many same-half tags is insufficient.
A nearer blue target does not replace acquired red.: That is the selecting=false policy. Only the chosen alliance can restore found during centering and approach.
Five centered checks arrive implausibly fast or survive a dropout.: The source counts loops without frame deduplication and omits loss reset. Record the limitation rather than claiming five fresh consecutive frames.
A robot direction would disagree with TeleOp.: Keep physical outputs disabled; compare BR FORWARD versus REVERSE and inspect mounting and encoder mode. Do not assume a shared hardware profile.
Display says distance traveled but independent tape disagrees.: The display is startRange-currentRange, not direct odometry. Check camera offset, target motion, height, and pose projection before interpreting it.

Exit ticket & assessment

Name the three phase time limits.
Explain the counter behavior on missing versus off-center targets.
State what <= 24 measures and why an educational label is not approval to run.

Assessment: Require a correct phase trace, matching-half selection, counter-loss explanation, exact powers at +/-2 boundaries, and outcome classification. Students must recognize absent freshness/wall guards and the autonomous-specific direction profile.

Extension challenge: On paper design a comparison of camera range change, independent tape displacement, and verified fresh-frame counts. Describe improvements as proposals without editing the supplied Blocks or deploying.

Teacher key · discuss after students predict

Timer and counter trace

Acquisition exits on first selected center or at 3 seconds; center has 6 seconds; approach has 8. Counts 1,2,missing,3,4,5 can reach the gate because missing does not reset. A found +3 result resets to 0.

Approach outputs

At range 30: tx +3 gives 0.30/0.26/0.30/0.20; +2 and -2 give 0.25/0.31/0.25/0.25; -3 gives 0.20/0.36/0.20/0.30. Loss is zero; exactly 24 with found sets done.

Range interpretation

The 0.30/0.40/0 pose gives 0.50 m, about 19.685 inches. The midpoint practice gives about 39.57 inches and +5.71 degrees. A 16-inch range reduction is not independently verified robot travel.

Threshold guard

targetRange is assigned 24, so targetRange >= 10 always passes. Its else label about already being within 24 is not a measured current-range branch; the actual <=24 check is inside approach.

Auto-Learn-AprilTagApproach

By the end, you can…

Build the idea, one block at a time

01Prepare the autonomous direction profile

02Start the reviewed AprilTag pipeline

03Preview geometry with zero drive requests

04Open acquisition only after START

05Choose the first scan with a usable nearer center

06Count centered checks and inspect the loss branch

07Approach a center range, not a bumper gap

08Label the outcome before ending vision

09Erase visibility before each scan

10Read a result, then its fiducial list

11Repeat camera-space geometry for each tag

12Keep signs until distance is calculated

13Use degree-based yaw and pitch

14Measure the line to a tag center

15Require a pair of matching half-groups

16Convert tag identity into a signed known offset

17Project the strip offset exactly as written

18Average coordinates, then find range and bearing

19Choose once, then retain the alliance

Make the math make sense

1. Trace the timers and retained target

2. Choose exact approach outputs

3. Measure the right thing

Your turn

Before the robot is used

Required hardware & dependencies

Robot setup checklist

90-minute teaching sequence

Observation notebook

Troubleshooting · stop before investigating

Exit ticket & assessment

Teacher key · discuss after students predict

Timer and counter trace

Approach outputs

Range interpretation

Threshold guard