Team 2822 Concept

Stork

Compact Vertical Lift · DR4B (double-reverse four-bar) + level manipulator

🧪 Concept · Exploring Override 2026–27

Stork retro poster — vintage halftone illustration of a stork

// LINEAGE FROM V.1

From V.1

Spartan Hero Bot V1.0 chassis-class drivetrain and toggle architecture.

Changed

Lift → DR4B exploratory build; manipulator un-scored in the fleet matrix.

Because

V2.0 exploration — DR4B variants for compact endgame applications.

Evidence

DR4B timing comparisons (pending build).

📛 Why "Stork"

The DR4B's compact folding action mirrors a stork at rest — one leg folded flat against its body while the other supports its weight. As the bird sets the folded leg down, it unfolds straight to the ground; the DR4B's carriage descends along the same near-vertical path. The stork's reputation for careful, precise delivery (the cultural trope and the bird's actual feeding behavior — slow, deliberate strikes at fish) matches the mechanism's role in the fleet: not the highest-reaching architecture, but the most precise placer of payloads at compact endgame positions. Bird family with Heron, Crane, and Osprey; raptor counterpart Falcon.

What it is Architecture Reach envelope Motor budget Torque Manipulator analysis Decision matrix CAD starting point Build sequence Open questions Port map Build log

What this is

A double-reverse four-bar (DR4B) lift architecture: two four-bar stages stacked, with the upper stage pivoting at the lower stage's end-platform. The two stages are coupled by chain-and-sprocket so they move in synchronized opposition — the upper stage rises as the lower stage rises, doubling the vertical travel. The carriage stays level throughout via the parallelogram constraint at each stage. Significantly more vertical reach than a single four-bar, but folds flat in a much smaller deployed footprint than Crane's six-bar.

Why it earns a fleet slot

Override's SG12 rule limits endgame vertical expansion to 18″. A Crane (six-bar) at full extension is well past 18″ and would need to retract before the buzzer. A DR4B's folding nature means the entire mechanism can collapse to under 6″ tall — below the endgame limit even with the carriage at the bottom of its travel. The architecture's compactness is what earns it the fleet slot, not raw reach.

Architecture geometry

The DR4B is two four-bar stages stacked. Stage 1 pivots at a tower fixed to the chassis. Stage 2 pivots at Stage 1's end platform. The two stages are coupled by a chain that runs from the tower-fixed sprocket up to a sprocket at Stage 2's pivot — this chain forces Stage 2 to rotate in the opposite direction to Stage 1, which causes the two motions to add at the carriage. The result is roughly 2× the vertical travel of a single four-bar at the same arm length.

Side view — DR4B at three positions

Three positions overlaid: stowed (gray dashed, both stages folded flat — under 6″ tall), mid-lift (orange, both stages at 45° — reaches short goal), full extension (green, both stages vertical — reaches tall goal). The coupling chain forces Stage 2 to rotate in opposition to Stage 1, doubling the vertical travel.

Approximate dimensions for prototyping

Subsystem	Dimension	Value	Notes
Chassis	Width × depth × height	18″ × 18″ × 4″	Per R3
Tower	Height (chassis top → Stage 1 pivot)	3–4″	Lower the better
Stage 1 arm	Length (lower-arm pivot to upper-arm pivot)	12″	Each four-bar arm
Stage 1 parallelogram	Vertical separation (upper to lower)	2.5–3″	Smaller = stiffer
Stage 2 arm	Length	12″ (matched to Stage 1)	Stages must be the same length for chain coupling to work
Coupling chain	Pitch and run length	#25 chain, ~24″ run	Routes from tower-fixed sprocket up to Stage 2 pivot's coupling sprocket
Carriage	Mounting plate dim	2″ × 3″ × 0.090″ Al	Universal manipulator mount (same spec as Heron and Crane)
Total vertical reach (carriage)	Floor to manipulator center, max	24–28″	Sum of both stage sweeps + tower
Stowed height (carriage at bottom)	Floor to top of folded mechanism	~5–6″	Below SG12 18″ endgame limit with margin

🎯

The compact stowed height is the architecture's whole point. A six-bar (Crane) at carriage-bottom is still 8–10″ tall because the bars are stacked. A DR4B at carriage-bottom folds the bars on top of each other — final height is roughly tower height + bar thickness, often 5–6″. This means the robot can clear the SG12 endgame limit with the carriage in resting position; the team doesn't need a separate "fold for endgame" sequence at the buzzer.

Reach envelope vs. fleet

Stork sits in the middle of the fleet's vertical-reach lineup. Less than Heron's stacked architecture, comparable to Crane's six-bar, more than Osprey's chain bar. Its differentiator is the stowed-vs-extended profile — the gap between collapsed and full-reach is the largest in the fleet.

Stowed-vs-extended profile comparison — Stork in fleet context

Each column shows two stacked bars: faint dashed = stowed height (carriage at rest), solid = extended height (full reach). Stork is the only architecture where the stowed bar sits well below the SG12 endgame limit (red dashed line at 18″) and the extended bar reaches near the top of the fleet. The combination is unique.

Robot	Max vertical reach	Stowed height	Best at
Osprey (chain bar)	~22″	~6″	Alliance + short goals; simplest
Skimmer (swing arm)	~22″	~10″	Fast scoring; pin-on-floor pickup; 355Z-inspired
Crane (six-bar)	~28″	~9″	Highest single-mechanism reach
Stork (DR4B)	~26″	~5–6″	Endgame-compact + tall-goal reach
Falcon (4-DOF arm)	~25″	~4″ (folded back)	Angle flexibility; reach at any height
Heron (stacked 4-bar+chain)	~28″	~7″	Tall + horizontal reach over partners

📊

Stork's distinguishing trait isn't peak reach, it's the combination of "high reach" + "lowest stowed height." Crane reaches slightly higher (28″ vs 26″) but at the cost of a 9″ stowed footprint. If endgame compactness is part of your strategy — for example, parking under a low feature or transitioning quickly between tall-goal scoring and ground-level pickup — Stork is the only architecture in the fleet that combines both.

Motor budget — with toggle allocated

DR4B's coupling chain means a single motor drives both stages in sync. That's efficient: one motor for the entire lift. The freed motor budget allows for a real toggle mech, and still leaves headroom.

Motor budget arithmetic (Stork baseline): Drive : 5 \times 11 W Blue (600 RPM) ........ 55.0 W DR4B : 1 \times 11 W Red (100 RPM) ......... 11.0 W (single motor drives both stages) Toggle : 1 \times 5.5 W half-motor ............ 5.5 W Manip : 1 \times 5.5 W half-motor ............ 5.5 W (claw or polycarb tube rotation) Subtotal ............................... 77.0 W Headroom ............................... 11.0 W Cap (R10a) ............................... 88.0 W

11 W headroom means a sixth drive motor (Blue 11 W → 66 W drive total, +20% top speed) is available without breaking the cap, OR the headroom can stay as a reserve for a sensor port, a roller, or anything else that comes up during the build.

Manipulator-specific motor budget impact

Manipulator	Motor cost	Total power (with toggle)	Headroom
V5 claw	1 × 5.5 W	77.0 W	11 W (6th drive motor possible)
Pneumatic pincers	0 motors (cylinder + solenoid)	71.5 W	16.5 W (6th drive + small spare, OR 7th drive if Blue's swapped to Red 200 RPM)
Polycarb tube	1 × 5.5 W (rotation)	77.0 W	11 W (6th drive motor possible)

Torque analysis — DR4B coupling load

Stork's DR4B couples two stages with a chain so a single motor drives both. The motor sees the combined torque demand of both stages through its 1:7 reduction. The worst case is both stages at horizontal (mid-extension) where both segments contribute their full moment arm.

Worst-case load — both stages horizontal at mid-extension

DR4B at horizontal mid-extension is worst-case for the drive motor. The chain coupling means a single motor at the bottom pivot drives both stages — so the motor sees the cumulative torque from both segments plus the carriage mass at the 24″ tip.

The math

DR4B torque demand at horizontal mid-extension: Cup payload .................. 0.5 lb at 24" ........ 12.0 lb-in Carriage + manipulator ....... 0.6 lb at 23" ........ 13.8 lb-in Stage 2 self-weight .......... 0.5 lb at 18" (CG) ... 9.0 lb-in Mid-platform ................. 0.3 lb at 12" ......... 3.6 lb-in Stage 1 self-weight .......... 0.5 lb at 6" (CG) .... 3.0 lb-in Total τ_demand ............................................. 41.4 lb-in 11W Red 100 RPM with 1:7 sprocket reduction: Stall torque (output-side) .............................. 98 lb-in τ_demand / τ_stall = 41.4 / 98 = 42% \to near thermal limit, will overheat in match ───────────────────────────────────── With rubber band assist (12 \times #64 distributed across both stages): Stage 1 assist (8 bands @ ~10 lbf, 6" perpendicular) ..... 60 lb-in peak Stage 2 assist (4 bands @ ~5 lbf, 6" perpendicular) ...... 30 lb-in peak Effective at horizontal (geometry-derived) ..... ~32 lb-in net Net motor torque required: τ_net = 41.4 - 32 = ~9 lb-in (9% utilization, well under thermal limit)

⚠

DR4B's 12-band distribution is non-trivial. Stage 1 carries Stage 2's weight as well as the carriage, so it needs more assist (8 bands). Stage 2 only carries the carriage, so 4 bands suffice. The distribution must be tuned: too many bands on Stage 2 and the carriage launches upward at zero load; too few on Stage 1 and the lift sags under payload. Build Phase 5 stop-point check: with no payload, the lift should hold any position without motor power; with cup + pin payload, the motor should need some torque to hold position but not be at thermal limit.

Manipulator analysis — tube wins for Stork

Stork's DR4B preserves manipulator orientation (level throughout the lift via the parallelogram constraint at each stage). That makes the polycarb tube's axial-rotation feature uniquely valuable here — same logic that applies to Crane and Skimmer, opposite to the Falcon situation where the wrist motor already provides orientation control.

Decision matrix — manipulator choice for Stork

Dimension	V5 Claw	Pneumatic Pincers	Polycarb Tube
Cycle time grip → release per element	3 ~600 ms motor-limited	5 ~150 ms instant pneumatic	4 ~300 ms cinch + orient
Build difficulty hours, parts count, R-rule risk	5 stock VEX, ~2 hrs	3 custom jaws + plumbing, ~6 hrs	1 R24 fab + plumbing + drive, ~12 hrs
Programming difficulty PID + state machine	3 claw PID + DR4B PID + toggle	4 digital out + DR4B PID + toggle	3 cinch + tube rotate + DR4B + toggle
Driving ease cognitive load on driver	3 3 controls (lift, claw, toggle)	4 3 controls; pincers binary	3 4 controls (lift, cinch, rotate, toggle)
Element flexibility cup / pin / combo	3 pin OK, cup OK, combo iffy	4 all three with shaped jaws	5 all three; cinch holds combo at cup waist; tube rotation orients
Architecture fit DR4B preserves orientation — no other rotation source	3 manipulator is fixed-orientation	3 manipulator is fixed-orientation	5 tube rotation adds the only orientation DOF Stork has
Total (out of 30)	20	23	21

🎯

Recommendation for Stork: pneumatic pincers (23/30), with polycarb tube (21/30) as a near-tie. Pincers wins on cycle time and build cost; tube wins on element flexibility and architecture fit. The decision becomes: "do you value the tube's rotation enough to absorb 6 extra build hours and an extra driver control?" If the team has already built a tube for a different architecture (Skimmer, say), reusing that work shifts the answer toward the tube. If starting fresh, pincers is faster to victory.

Decision matrix — Stork vs. fleet

With each robot's recommended manipulator, where does Stork sit overall?

Dimension	Osprey chain bar + claw	Stork DR4B + pincers	Crane six-bar + tube	Heron stacked + pincers
Goal coverage	3	4	5	5
Endgame compactness	4	5	2	3
Build complexity	4	2	3	2
Driving cognitive load	4	3	3	3
Notebook story	3	5 DR4B + chain coupling = rich	4	5
Risk of failure (higher = lower risk)	5	2 chain alignment is fiddly	3	2
Total (out of 30)	23	21	20	20

⚠

Stork ties with Crane and Heron at the concept-architecture mid-pack (20–21). Osprey's simplicity still leads the matrix. The fleet's pattern is now visible: each "advanced" architecture trades complexity for one specific advantage — Crane for raw reach, Heron for horizontal extension, Stork for endgame compactness, Falcon for angle flexibility. None individually beats Osprey-with-claw on overall score; they earn their fleet slots through the specific scenarios where their unique trait matters most.

CAD starting point

Subassembly dimensions

CHASSIS18″ × 18″ × 4″ aluminum 1×2 box rail
DRIVE5 × 11W Blue 600 RPM, 5:3 reduction, 4″ omni
TOWER (STAGE 1 PIVOT)3.5″ tall, centered laterally and longitudinally
STAGE 1 ARMS12″ pivot-to-pivot, 2.5″ parallelogram height
STAGE 1 MID-PLATFORM2″ × 3″ × 0.090″ Al; carries Stage 2 pivots and chain coupling sprocket
STAGE 2 ARMS12″ pivot-to-pivot (matched to Stage 1), 2.5″ parallelogram height
CARRIAGE2″ × 3″ × 0.090″ Al with universal #4-40 hole pattern (same as Heron / Crane)
DR4B DRIVE11W Red 100 RPM, mounted at chassis tower-side, 1:7 sprocket reduction (12T → 84T) on Stage 1 lower-arm shaft
COUPLING CHAIN#25 chain, 12T sprocket on tower-fixed shaft, 12T sprocket on Stage 2 mid-platform pivot — routed up through tower interior
RUBBER BAND ASSIST12 × #64 bands distributed across both stages (sized for cup + pin combo at full extension)
TOGGLE MECHFlex-wheel toggle on side of chassis, 5.5W half-motor, 200 RPM fixed; wheels positioned to engage toggle elements at floor level during normal drive

OnShape document structure

Part Studio 1 — Chassis & Tower: chassis frame, drive motor mounts, tower, battery and brain mounts.
Part Studio 2 — DR4B Stage 1: Stage 1 lower arm + upper arm, mid-platform, sprockets, rubber band anchor points.
Part Studio 3 — DR4B Stage 2: Stage 2 lower arm + upper arm, carriage plate, manipulator mount.
Part Studio 4 — Coupling system: chain routing, tensioner, idlers if needed.
Part Studio 5 — Toggle mech: flex wheel mount, motor, support arms.
Assembly — Stork: mate all part studios + selected manipulator.

Build sequence — if you commit to Stork

Phase 1 — Chassis + drivetrain (week 1). Standard rolling chassis. Drive practice can begin.
Phase 2 — Tower + Stage 1 only (week 2). Build the tower and Stage 1 four-bar with rubber band assist. Tune Stage 1 PID at three setpoints. Stop point check: Stage 1 mid-platform rises smoothly to its full 12″ sweep with no sag.
Phase 3 — Stage 2 on test stand (week 2, parallel). Build Stage 2 four-bar on a separate test stand. Verify the parallelogram geometry holds the carriage level through its sweep. Stop point check: Stage 2's carriage tracks level without coupling chain.
Phase 4 — Couple Stage 2 onto Stage 1 (week 3). Mount Stage 2 to Stage 1's mid-platform. Install the coupling chain. This is the make-or-break phase: chain alignment must be precise or one stage will lag the other, breaking the parallelogram constraint and tilting the carriage. Stop point check: when Stage 1 rotates, Stage 2 rotates the same amount in opposite direction, and the carriage stays perfectly level throughout the combined motion.
Phase 5 — Manipulator + toggle integration (week 4). Mount the chosen manipulator on the carriage. Mount the flex-wheel toggle on the chassis side. Test full pickup-place cycles and toggle operations. Stop point check: 100 cycles loader → goal → loader without dropping a payload, plus 20 toggle activations without interference.
Phase 6 — Driver practice + iteration (weeks 5–7).

⚠

Phase 4 chain coupling is where DR4B builds typically fail. If chain is loose or misaligned, the two stages drift out of sync and the carriage tilts — defeating the architecture's whole point. Budget 6–8 hours for Phase 4 and don't move on until the carriage tracks level through the full sweep. If Phase 4 takes more than 12 hours of fiddling, the chain routing may be flawed; consult Crane or Heron as alternates with simpler kinematics.

Open questions for the team

Coupling method. Chain (documented) is most common, but belts and gear trains are alternatives. Chain has the most slack tolerance but the most maintenance; belt is cleaner but harder to retension; gear is precise but heavy.
Stage length matching. Both stages must be exactly the same length for the chain coupling to work cleanly. If you want unequal stage lengths (more reach in one direction), the coupling sprocket ratio has to compensate — significantly more complex.
Rubber band distribution. 12 × #64 across both stages is a starting estimate. The actual distribution depends on each stage's geometry; Stage 1 carries Stage 2's weight as well as the carriage, so it needs more assist than Stage 2.
Manipulator selection. Pincers wins the matrix on speed. If the team is also building Skimmer (which uses the polycarb tube), reusing that tube design on Stork is a strong notebook story even if it scores slightly lower per the matrix.
Endgame strategy. Stork's compactness advantage assumes the team uses it — what's the strategic plan for the last 10 seconds of the match?

Concept sketches

To be added during prototyping. iPad sketches showing the coupling chain routing, rubber band placement, and stowed-vs-extended profile.

CAD exploration

To be added once CAD prototyping begins. OnShape document link with all 5 part studios.

Decision log

To be filled in. Each significant design decision and the reasoning — especially the chain-routing geometry, since that's the failure-prone subsystem.

Port map (template)

Pre-allocated port assignments for Stork's planned motor layout. If the team commits to building Stork, copy this table into robot-config.cpp and update as wired.

Port	Subsystem	Motor / sensor	Notes
1	Drive front-left	11W Blue 600 RPM	5:3 reduction · 4″ omni
2	Drive front-right	11W Blue 600 RPM	reversed
3	Drive mid-left	11W Blue 600 RPM	—
4	Drive mid-right	11W Blue 600 RPM	reversed
5	Drive back-center	11W Blue 600 RPM	OR 6th drive if pneumatic pincers manipulator (Stork has 11–16 W spare)
6	DR4B drive (both stages)	11W Red 100 RPM	1:7 sprocket reduction at Stage 1 lower-arm shaft · single motor drives both stages via chain coupling · rubber band assist (12 × #64 distributed)
7	Manipulator	5.5W half-motor (claw or tube rotation) OR pneumatic out (pincers)	Pincers frees this port
8	Toggle	5.5W half-motor	Flex-wheel toggle on side of chassis
9–21	Spare	—	Reserved for sensors and post-swap expansion
ADI A	Limit switch	—	Stage 1 zero-position reference
ADI B	Pot V2	—	Stage 1 position feedback (chain coupling makes Stage 2 redundant to track)

Build log (template)

Each build session adds an entry: date, team members, what was attempted, what worked, what didn't, decisions made.

Template entry:
2026-MM-DD · Team members: ___ · Phase: ___
What we attempted: ___
What worked: ___
What didn't: ___
Decision made: ___
Next session focus: ___