Team 2822 Concept

Falcon

Articulating Reach Arm · 4-DOF arm + 55W speed drivetrain

🧪 Concept · Documented Override 2026–27

Falcon retro poster — vintage halftone illustration of a falcon

// LINEAGE FROM V.1

From V.1

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

Changed

Lift → 4-DOF articulating arm (formerly “Mantis”); wrist-motor allocation study.

Because

V2.0 exploration — any-angle scoring for variable cup orientations.

Evidence

Wrist-motor allocation study; arm-vs-lift tradeoff analysis (pending bench tests).

[ NOT BEING BUILT — Team 2822A pivoted to Skimmer. This page preserved as engineering notebook reference for the 4-DOF arm architecture analysis. ]

📛 Why "Falcon"

The 4-DOF arm folds back over the chassis center at rest, then strikes forward to grab a cup-on-pin combo from the back-loader — the same dive-and-strike motion a falcon uses on prey. The shoulder, elbow, wrist, and claw mirror the falcon's articulated wing-and-talon action: fold, deploy, grip, retract. The fastest bird in the fleet, matching the 5-motor 55W speed-focused drivetrain. Bird family with Heron, Crane, Stork, and Osprey; the raptor of the articulated-arm family.

Architecture Reach geometry Motor budget Torque analysis Manipulator analysis Decision matrix CAD starting point Port map Build log

Architecture at a glance

Drivetrain5 × 11W Blue (600 RPM) · 55W · 5:3 reduction · 4″ omni
Top speed6.28 ft/s
Shoulder11W Red 100 RPM (rubber band assist)
Elbow11W Red 100 RPM
Wrist5.5W half-motor (200 RPM fixed)
Claw5.5W half-motor (200 RPM fixed)
Total motors9 motors · 88W exactly (R10a cap)
Arm reach17″ (9″ upper + 8″ forearm)
Shoulder pivotY=6″, H=4″
ChassisAluminum (~2.5 kg lighter than steel)

Reach geometry — 4-DOF arm at three positions

The 4-DOF arm (shoulder, elbow, wrist, claw) is most easily understood as a planar 2-link manipulator with the wrist and claw acting as orientation/grip. The shoulder and elbow together place the end-effector anywhere in a semicircular workspace within their combined reach.

Side view — 4-DOF arm at three positions

Three positions: rest folded back over chassis (gray dashed), reaching short goal at ~25″ forward (orange), reaching tall goal at full vertical extension (green). Yellow arc is the 17″ reach envelope from the shoulder pivot — the boundary the end-effector cannot exceed.

Reach math — can it actually hit each goal?

Forward kinematics check: Shoulder pivot at (X=0, Y=4" above chassis top, 6" back from front edge) Upper arm L1 = 9", Forearm L2 = 8", Total reach = 17" Goal heights (from field tile): Alliance .... 3.25" \to end-effector height needed ~7" (above goal rim) Short ....... 5.77" \to end-effector height needed ~10" Tall ........ 8.77" \to end-effector height needed ~13" Geometric check (worst case = tall goal): Shoulder height above floor = 5.5" (1.5" chassis + 4" tower) End-effector vertical reach above shoulder = 13 - 5.5 = 7.5" Pythagorean: needs L1 + L2 \geq \sqrt(forward² + 7.5²) At 25" forward: \sqrt(25² + 7.5²) = 26.1" \to 17" arm cannot reach (tall goal too far) Solution: drive closer. At 15" forward: \sqrt(15² + 7.5²) = 16.8" \to reachable. Falcon must drive within 15" of the tall goal to score on it.

⚠

The 17″ reach is sufficient only with disciplined positioning. Drivers cannot hover at random distances and expect the arm to extend — they need to approach within ~15″ of the goal for tall scoring. Build muscle memory for the approach distance during driver practice. The chain bar in Osprey doesn't have this constraint (the lift moves vertically rather than reaching), but its peak height is lower.

Motor budget — the 88 W is exact

Falcon is at the cap with no slack. Every motor is allocated; there's no spare port for a sensor that needs PWM, no headroom to swap a Blue for a Red on the drivetrain. The manipulator analysis later in this page leans on this: if the manipulator change frees a port, that's a real strategic option.

🔧

Toggle mech — consideration with implementation paths. Falcon as currently spec'd has no powered toggle interaction mechanism: the 88 W is fully consumed by drive (5 × 11 W) + arm (4 motors). Closing this gap requires reallocating motors, swapping the manipulator, or going passive. Four paths under consideration — the team picks one before Phase A scrimmage based on which trade-off fits Falcon's role on the alliance.

Toggle mech — four implementation paths

Path 1 — Manipulator swap + single 5.5 W toggle. Replace V5 claw (5.5 W electric) with pneumatic pincers (0 W electric, 1 cylinder + 1 solenoid per R25). Frees 5.5 W for one toggle motor. Mount: 1×2×9 aluminum C-channel on chassis right (or left) flank, vertical, wheel center at 12.5″ off tile (matches toggle on top of perimeter wall). 5.5 W half-motor with 12T → 24T = 2:1 chain reduction to 4″ flex wheel. Same single-side bracket geometry as Pelican’s current toggle. Cost: commits Falcon’s manipulator to pincers (loses claw flexibility); single-side coverage requires chassis pivot for opposite-side toggles.

Path 2 — Drop drive motor + dual-side mirrored 2 × 5.5 W toggle. Reduce drivetrain from 5 × 11 W → 4 × 11 W (frees 11 W). Allocate 11 W as 2 × 5.5 W mirrored toggle motors, one on each chassis flank — same dual-side geometry as Osprey. Mounts: 1×2×9 C-channel each side, mirrored, 4″ flex wheels at 12.5″ off tile. Independent driver button bindings (L-trigger + R-trigger). Cost: ~10% drive top-speed reduction (Falcon was speced as a 5-motor speed drive); ~3 build hours for the mirrored brackets. Benefit: any toggle reachable without chassis reorientation; the V5 claw is preserved.

Path 3 — Drop drive motor + single 11 W toggle. Reduce drivetrain 5 → 4 motors (frees 11 W); allocate the full 11 W to one toggle wheel. Mount: 1×2×9 C-channel on one flank, 11 W full motor with 18T → 24T = 1.33:1 reduction to 4″ flex wheel (more torque than 5.5 W variant). Cost: same 10% drive speed reduction as Path 2; only single-side coverage. Pays the drive-speed cost without the dual-side benefit. Use case: if bench-testing shows 5.5 W is marginal against actual toggle resistance and the team wants the headroom.

Path 4 — Passive mechanical plow (no motor). Fixed bumper or wedge at chassis front, ~3″×6″×0.090″ aluminum or polycarb (custom plastic per R24; counts against the 12-piece custom-plastic budget). No motor cost — 88 W stays drive + arm. Toggle engagement is “drive-by”: the plow contacts the toggle face as the robot drives past the wall. Cost: can’t deliberately toggle without driving past the wall; coverage is opportunistic, not strategic. Benefit: zero-W and zero-port cost; preserves all motor allocations; works as a backup if motor pressure increases mid-Phase A.

Decision pending Phase A bench-test data on toggle resistance and the team’s manipulator-swap timing. The pincer-swap (Path 1) and dual-side mirrored (Path 2) are the architecturally clean options — pick one of those. Path 3 is a fallback. Path 4 is an emergency option.

Motor budget allocation — 88 W cap

Bar widths proportional to wattage. 88W cap line is at the right edge of the claw segment — zero spare. Manipulator swaps that free a motor port (pneumatic pincers) open up real options for additional motors elsewhere.

Manipulator swap impact on motor budget

Manipulator	Current claw replaced by	Wattage change	What you can do with the freed budget
V5 claw (baseline)	—	±0 W	No change. Status quo.
Pneumatic pincers	0 motor cost (cylinder + solenoid only)	−5.5 W	Free 5.5 W → add a 5.5 W motor anywhere (e.g., 6th drive motor for back center, or roller intake at the loader, or kept as spare port for sensor)
Polycarb tube	1 × 5.5 W rotation motor	±0 W	Net same. Optional advanced: drop the wrist motor (the tube's rotation provides a similar but different orientation DOF), freeing 5.5 W for elsewhere.

Torque analysis — can the shoulder lift the load?

The shoulder motor must hold the entire arm + payload at every reachable position. The hardest case is full horizontal extension at the tall-goal pickup angle, where the moment arm to the cup is at its maximum.

Shoulder torque at full extension — with rubber band assist

Free-body diagram at full horizontal extension. Cup gravity load (0.4 lb at 17″) creates the worst-case moment around the shoulder. Rubber band assist (8 × #64 bands stretched between chassis-fixed anchor and arm at 6″ out) provides counter-torque, drastically reducing the motor's required output.

The math — shoulder torque without and with rubber band assist

Torque demanded by the load: τ_load = F \times L = 0.4 lb \times 17" = 6.8 lb-in Add the arm's own weight (~0.6 lb at center of mass, ~9" from shoulder): τ_arm = 0.6 \times 9 = 5.4 lb-in Total τ_demand = 6.8 + 5.4 = 12.2 lb-in 11W Red 100 RPM motor (V5 motor): Stall torque \approx 14 lb-in nominal τ_demand / τ_stall = 12.2 / 14 = 87% \to motor at near-stall, will overheat ───────────────────────────────────── With rubber band assist (8 \times #64 bands @ ~10 lbf at full stretch): Perpendicular moment arm to attachment point: ~6" (varies with angle) τ_assist = 10 lb \times 6" = 60 lb-in counter-torque But assist is highest when arm is up, and decreases at horizontal where load is worst. Effective assist at horizontal (geometry-derived): ~50% of peak = 30 lb-in Net motor torque required: τ_net = max(0, τ_demand - τ_assist) = max(0, 12.2 - 30) = 0 lb-in (Assist exceeds demand at horizontal — motor only needs to control position, not lift weight.) Motor utilization with assist: ~30% peak \to no overheating, smooth control

🎯

The rubber-band assist is non-negotiable. Without it, the shoulder motor runs near stall during every cup-grab cycle, will trip its internal thermal protection within 2–3 minutes of match play, and will fail under repeated cycles. The 8 × #64 band sizing comes from working backward from "I want τ_net ≈ 0 at horizontal." Document the band count in the engineering notebook with this math — it's a strong R&D narrative.

Manipulator analysis — three choices

Falcon is currently spec'd with the V5 claw as the end-effector. This analysis revisits that choice in light of the two alternatives that the team is also exploring (pneumatic pincers and the polycarb tube). The scoring differs from the equivalent analysis on the Heron page because Falcon's existing wrist motor already provides one DOF of orientation control — this changes the value proposition of each manipulator.

Option A — V5 Claw (current baseline)

What it is: the standard VEX 276-2270 claw, driven by the existing 5.5 W half-motor at the wrist. Open/close via motor; hold via PID or stall current.

Build interface: mounts to the wrist's 1×1×3 C-channel via two #6-32 bolts. Already designed and partially built — this is the path of zero additional construction work.

Element handling: grips pin (1.6″) cleanly. Cup waist (2.32″) requires the claw to open ~3″, which is at the upper end of its range. Combo (pin-in-cup) is unreliable — the claw must span the full cup OD (3.16″) and the gripping force is concentrated at two points, allowing the cup to slip off the pin during transport. Cycle time: ~600 ms motor-limited.

Option B — Pneumatic Pincers

What it is: two pivoting jaws actuated by a single short-stroke pneumatic cylinder mounted to the wrist face plate. Replaces both the claw motor and the claw assembly with a cylinder + solenoid + jaw plates.

Build interface: 3″ × 4″ aluminum base bolted to the wrist plate. Cylinder mounts vertically; jaw pivots at 1.5″ either side of cylinder centerline. Air line routes from chassis tank (R25 max 2 tanks) up the upper arm, across the elbow, along the forearm, to the cylinder. Ferrule strain reliefs at every joint.

Element handling: jaw spread of 1.5″–4″ (shaped jaws can span the full range). With curved pin-conforming jaws, the pin-in-cup combo is grippable at the cup's waist with the pin retained inside — better than the claw. Cycle time: ~150 ms (essentially instant).

Option C — Polycarbonate Tube

What it is: heat-bent polycarbonate tube with pneumatic string cinch and 5.5 W axial-rotation motor. Replaces the claw entirely. The tube's rotation motor sits where the existing claw motor is — same port, same wattage, different mechanism. See design study + CAD guide.

Build interface: tube end caps mount to the wrist plate via 4 × #4-40. Rotation drive sits behind the tube (5.5 W motor + 1:5 sprocket reduction). Air line for cinch routes up the arm same as for pincers.

Element handling: all three element types reliably (tube ID 2.55″ accepts cup waist 2.32″ with margin; pin sits inside until cinched; combo handled at cup waist with pin retained). Cycle time: ~300 ms (cinch fast; rotation adds slight setup).

Falcon-specific note: the tube's rotation feature is partially redundant with the existing wrist motor — the wrist tilts the end-effector relative to the forearm; the tube rotates around its own axial axis. Different DOFs, but combined gives 5-DOF orientation, which is more than Override scoring requires. Consider dropping the wrist motor if going with the tube, freeing 5.5 W.

Decision matrix — manipulator choice for Falcon

Score 1–5 (5 = best). Same six dimensions used on Heron, but scored for Falcon's specific architecture (wrist motor present, 88 W cap with no slack, build already in progress).

Dimension	V5 Claw (baseline)	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 of work from current state	5 already built; 0 hours	4 remove claw, add pneumatics; ~6 hrs	1 R24 fab + plumbing + drive; ~12 hrs
Programming difficulty PID loops + state machine	4 claw PID + 4 arm PIDs (5 axes total)	5 digital out + 4 arm PIDs (4 axes)	2 cinch + tube rotation + 4 arm PIDs (6 axes)
Driving ease cognitive load on driver	4 5 controls (sh, el, wr, claw, drive)	5 5 controls but pincers binary; less holding	2 6 controls (sh, el, wr, cinch, rotate, drive)
Element flexibility cup / pin / combo	3 pin OK, cup OK, combo unreliable	4 all three with shaped jaws	5 all three reliably; combo grip is best-in-class
Motor budget impact opens spare for 6th drive or sensor	3 88 W exact, no spare	5 −5.5 W → free port for 6th drive or sensor	4 ±0 baseline; if wrist dropped, +5.5 W spare
Total (out of 30)	22	28	18

🎯

Recommendation for Falcon: pneumatic pincers (28/30). The combination of (1) fastest cycle time, (2) lowest programming load (binary digital output), (3) freed 5.5 W motor budget that could become a 6th drive motor or a sensor port, and (4) better element flexibility than the claw is decisive. The build cost (~6 hrs to swap claw for pincers assembly) is the only meaningful penalty, and it's modest given the in-match payoff. The polycarb tube scores low here precisely because Falcon already has a wrist motor — the tube's rotation DOF is mostly redundant, and the build/programming/driving costs are not offset by a unique capability gain.

📊

Falcon vs. Heron: same manipulator, different score. Pneumatic pincers wins on both architectures, but the polycarb tube ranks higher on Heron (17/30) than Falcon (18/30 — sorry, actually similar, but the tube wins on Osprey where it was originally specified because Osprey has no other orientation DOF). The lesson: the right manipulator is architecture-dependent. Don't carry a manipulator decision from one robot to another without re-running the matrix.

Decision matrix — Falcon vs. Heron vs. Osprey

With each robot's recommended manipulator (pincers for Falcon if swap is approved, pincers for Heron, pincer/tube for Osprey), where does Falcon sit in the fleet?

Dimension	Osprey (chain bar + pincer/tube)	Falcon (4-DOF + pincers)	Heron (stacked + pincers)	Spoonbill (4-bar + rot claw)
Goal coverage	3 alliance + short, tall is tight	5 all three goals + load + endgame	5 all three + reach over partner	5 all 3 + orientation control
Cycle time (avg)	4 committed loader-arc-goal ~8 s/cycle	5 ~2.0 s/cycle (4-DOF + instant grip)	3 ~3.5 s/cycle (sequencing 2 lifts)	3 ~7-10s/cycle; toggle 2-3s extra
Build complexity	4 familiar parts	3 articulating arm; in-progress	2 two stacked mechanisms + pneumatics	2 rot claw + dual toggle = highest
Driving cognitive load	4 2 controls	2 5 controls (4 arm DOFs + drive)	3 4 controls	3 rotation presets + back-into gesture
Notebook story	4 tower-height + dive-strike metaphor	4 articulating arm + torque math + manipulator swap	5 stacked architecture rare; many decision matrices	5 rotating-bill + DOF + 2-point grip
Risk of failure (higher = lower risk)	4 single lift motor; chain skip is main risk	4 arm tunable; assist sized correctly	2 2 mechanisms = 2× tuning, 2× failure modes	3 88W cap; 10 motors; worm gear
Total (out of 30)	23	23	20	21

🎯

Falcon with pincers leads the fleet at 23 points (Osprey: 23, Heron: 20). The pincers-swap recommendation isn't a luxury — it's what moves Falcon from a comparable-to-Osprey architecture into a clearly-best one. The articulating arm's flexibility advantage gets unlocked only when the manipulator is also fast and binary. Stick with the V5 claw and you keep the 22-point baseline; commit to the pincers swap and Falcon pulls ahead.

CAD starting point — numbers for OnShape

Most of the chassis and arm CAD is already done by team 2822A. This section documents the universal manipulator interface at the wrist face plate — the standardized bolt pattern that lets any of the three manipulators bolt onto the same wrist subassembly.

Wrist face plate — universal manipulator mount (exploded)

The 2.0″ × 3.0″ × 0.090″ aluminum face plate is bolted to the wrist via four hidden #6-32 bolts on the back side (not shown). The four #4-40 holes on the front face accept any of three manipulator adapters. The 0.50″ center hole passes pneumatic line and electrical for whichever manipulator is in use.

Wrist face plate dimensions (CAD-ready)

Feature	Spec	Purpose
Plate dimensions	2.0″ × 3.0″ × 0.090″ 6061-T6 aluminum	Stiff enough for cantilever load; light (~0.05 lb)
Front-face bolt pattern	4 holes ⌀0.116″ at corners of a 1.5″ × 2.5″ rectangle, centered on plate	#4-40 clearance; matches the bolt pattern on each manipulator adapter
Center pass-through	1 hole ⌀0.50″ at plate center	Pneumatic line (1/8″ OD) + 2-conductor motor lead pass through to manipulator
Back-face mounting	4 holes ⌀0.140″ for #6-32 to wrist bracket	Hidden behind plate; attaches to wrist's 1×1×3 C-channel
Edge clearance	≥ 0.20″ between any hole edge and plate edge	Avoids cracking when torquing bolts

Manipulator adapter dimensions

Manipulator	Adapter spec	Adds weight	Hours to swap
V5 claw	1×1×3 C-channel bracket bolted to plate; claw 276-2270 + 5.5 W motor	0.45 lb	0 (already built)
Pneumatic pincers	3″ × 4″ × 0.090″ Al base + cylinder mount block + 2 jaw plates + 2 pivot pins; cylinder VEX 276-2470 single-acting	0.55 lb	~6 hrs from claw
Polycarb tube	End caps from VEX 1×1×3 + tube body + rotation sprockets + 5.5 W motor	0.40 lb	~12 hrs from claw (includes R24 fab)

💡

Designing the face plate first means the manipulator decision is reversible. If pincers turn out to underperform during driver practice, swapping back to the claw is a 30-minute job (4 bolts + a motor connector). The plate is the team's "options preserver" — build it before committing to any specific manipulator.

Port map (template — fill in as built)

The port assignments below are the planned layout. Update as the actual build is wired. Mirror these in robot-config.cpp so software and hardware match.

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	5th drive motor; chassis center rear
6	Shoulder	11W Red 100 RPM	rubber band assist (8 × #64)
7	Elbow	11W Red 100 RPM	—
8	Wrist	5.5W half-motor	200 RPM fixed
9	Claw / pincers / tube	5.5W half-motor or pneumatic out	Depends on manipulator selected
10–21	Spare	—	Reserved for sensors and post-swap expansion

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: ___

Engineering notebook references

Coming soon. Cross-references to the EN4 notebook entries that document each design decision. Examples once filled: "Decision to add 5th drive motor: see EN4 p. 14." "Rubber band sizing: see EN4 p. 22." "Manipulator decision matrix: see EN4 p. 28."