Element Capture — Pin Tube + Cup Grabber Prototypes

SECTION 0 / 5

Three Paths to Capture — Tube A, Tube B, or Grabber

R24 caps any single polycarb piece at 4″ × 8″, which caps a one-piece bent tube at ID 2.42″. That's enough for the Pin but blocks the Cup. The audit's clamshell pattern — two polycarb halves bolted together with no chemical bond — clears the developed-length limit and opens the door to a wider Tube B. This section walks the geometry, sizes the three options, and lines them up against the existing fleet.

The R24 Wall

R24a caps each plastic piece at 4″ × 8″ × 0.070″. A tube heat-bent from one sheet has a developed length equal to its outer circumference. The 8″ sheet width is the binding constraint:

Max legal tube OD: 8.00″ / π = 2.5465″ Round DOWN to 2.54″ for a 0.02″ safety margin. At wall 0.060″: Max legal ID = 2.42″. Source: /polycarb-tube-r24-audit/ Sheet 1.

Element diameters from the 2026-27 Override manual (Appendix A, ⌀ = across-corners on the hex cross-sections):

Element section	⌀ across-corners	Fits 2.42″ ID tube?	Radial slack
Pin neck	1.40″	YES	0.510″
Pin mid section	2.35″	YES — tight	0.035″
Pin base flare	3.16″	NO	—
Cup waist	2.32″	YES	0.050″
Cup rim	3.16″	NO	—

⚠

Why a single-piece tube fits the Pin but not the Cup. The Pin enters the tube neck-first (1.40″), slides up until the mid section (2.35″) is captured by the cinch, and the base flare (3.16″) hangs out the bottom of the 4″ tube. The Cup has no narrow end — both rim (top) and base (bottom) are at 3.16″ flare width, so it can't enter a 2.42″ tube in any orientation. Tube B's two-piece clamshell sidesteps this by going wider than any single sheet could form, at the cost of one extra polycarb piece against the 12-piece R24 budget.

Element Cross-Sections vs Max-Legal Tube ID

Both elements have a 3.16″ flare section. The Pin's flare is at one end (the base) and can hang outside the tube while the mid grips. The Cup has flare width at both ends, so longitudinal insertion is geometrically blocked.

The Three-Option Plan

▸ Tube A — R24-Legal Pin Pickup (single-piece)

POLYCARBID 2.42″PIN ONLYCINCH GRIP1 PIECE

Heat-bent 4×8×0.060 polycarbonate. Pin enters neck-first, cinch pulls 1mm Spectra cord through two opposed holes at the tube midpoint, gripping the 2.35″ pin mid section. Used on Skimmer (2822A). Optionally paired with the two-piece clamshell funnel cap for improved Path B (loader) catch.

▸ Tube B — R24-Legal Cup Tube (two-piece clamshell)

POLYCARB ×2ID 3.50″CUP + COMBORIM-GRIP CINCH2 PIECES

Two heat-bent clamshell halves bolted together at the seam (no bond — same R24-legal pattern as the audit's funnel cap). The 3.50″ ID admits the 3.16″ cup rim with 0.17″ radial slack — well within the 1″ pneumatic cylinder's stroke budget. Cinch grips the cup at the rim; the body hangs below the tube. Pin-in-cup combos transit naturally: the pin nests in the cup, the cup is held by Tube B. Candidate hosts: a configurable-end-effector bot like Heron or Falcon, or a future cup-specialist build.

▸ Cup Grabbers — Non-Tube Mechanisms (established alternative)

V5 CLAWPNEU. PINCER2-FINGER GRIPEXTERNALCUP ± COMBO

The Cup gets gripped externally at its waist (2.32″) or rim (3.16″) by a 2-finger end-effector. Already deployed: Pelican (2822C) uses a V5 claw on a four-bar lift; Osprey (2822E) uses a pneumatic pincer on a chain bar. Both Heron and Falcon list claw/pincer as one of their swappable end-effector options. Kept on this page as the established alternative against Tube B.

💡

Notebook framing. "Override has two scoring elements with non-overlapping diameter envelopes. We sized an R24-legal single-piece tube (ID 2.42″) for the Pin; the same approach can't admit the Cup's 3.16″ rim, so we either go to a two-piece clamshell tube (Tube B, ID 3.50″) or to a fundamentally different mechanism family (external grabber). We are prototyping both Tube B and the grabber so the alliance can pick the right mechanism per bot, with the comparison documented in the decision matrix." A rule-driven, geometry-anchored decision — the kind of reasoning judges score well.

SECTION 1 / 5

Tube A — R24-Legal Pin Pickup

The polycarb tube prototype, sized to R24's maximum legal ID. Pin enters neck-first; cinch gripping pulls a Spectra cord through two opposed holes at the tube midpoint to clamp the 2.35″ mid section against the tube wall. This section breaks down the geometry, cinch math, fabrication, and two pickup paths.

Dimensional Spec

Inner Diameter

2.42″

Outer Diameter

2.54″

Wall

0.060″

Length

4.00″

Outer Dev Length

7.98″ / 8.00″

Pin Mid Clearance

0.035″ radial

Both developed-length conventions (outer surface and neutral axis) are under R24's 8.00″ limit. Mandrel target is 2.40″ OD — polycarb has 1–2% spring-back after heat-forming, so finished ID typically lands between 2.41″ and 2.45″. If post-fabrication measurement shows ID < 2.39″, the pin mid won't fit; use a slightly larger mandrel on the next attempt.

Pin Entry Geometry

Side View — Pin in Tube, Cinch Engaged

The pin's neck (1.40″) clears the tube freely; the mid (2.35″) sits in the cinch zone with 0.035″ radial slack on each side; the base flare (3.16″) is too wide for the tube and hangs below the bottom edge. Total pin length is 6.5″ vs tube length 4.0″ — the pin is always longer than the tube.

Cinch Force Math

The cinch's job is to take up the 0.035″ radial slack and apply enough normal force to prevent pin slip under transit accelerations. With the corrected (tighter) tube ID, the cinch travel budget shrinks dramatically vs the older 2.55″ spec.

Cinch travel: Slack to take up = 0.035″ radial = 0.07″ diametral Plus preload for grip = ~0.05″ Total cinch stroke needed: ~0.12″ VEX 1″ pneumatic cylinder stroke = 1.00″ Margin: 8\times (very comfortable) Cinch force: Cylinder @ 100 psi = 78 lbf push Routing losses (axle bend, hole edges) = ~30% Net cinch force on pin = ~50 lbf Pin mass = 0.16 lb Peak transit accel (chain bar tip) = ~30 ft/s² (~1g) Required hold force = 0.16 lbf Safety factor = 50 / 0.16 = 300:1

✅

Why the tighter tube is actually better for the cinch. At the old 2.55″ ID the cinch had to traverse 0.20″ radial slack before contacting the pin mid — that ate cylinder stroke and made the grip geometry less efficient (string chord at a shallow angle). At 2.42″ the cinch engages almost immediately and the string wraps the pin at a steeper, more efficient angle. The R24 correction is also a grip-quality upgrade.

Two Pickup Paths

Skimmer's architecture supports two distinct ways the pin enters the tube. The geometry analysis above applies equally to both; what differs is the catch reliability and where the pin starts.

Path	How	Catch reliability	Funnel needed?
Path A roller-transfer	Front roller (see /skimmer-roller-cad/) catches the pin against the chassis and rolls it up into the tube top.	High — the roller's compliance and width swallow alignment error.	No.
Path B loader direct catch	Pin drops from the loader into the tube top during teleop. No roller staging.	Medium at bare tube; the 2.42″ mouth is narrower than the 3.16″ pin flare, so catch tolerance is the difference (~0.4″ radial).	Yes — clamshell funnel widens the effective catch mouth to 4.5″ (see audit Sheets 4–5).

Fabrication Summary

Full bench-side procedure lives in the mentor handout (21 pages). The headline numbers:

Sheet: 4″ × 8″ × 0.060″ polycarbonate, clear. Buy 4 sheets minimum for first-time fabrication.
Mandrel: 2.40″ OD aluminum (McMaster 8975K237 is 2.4″). Wipe clean of oils before forming.
Heat: 280–310°F (verified with IR thermometer). Above ~370°F the polycarb yellows and is permanently compromised.
Cinch holes: two 1/16″ holes, drilled flat-pattern before forming, positioned so they land 180° apart at the tube's axial midpoint after wrap.
Seam: open ~10° gap (NO bonding). End brackets mechanically clamp the tube to maintain circular cross-section.
R24 piece count: tube = 1 piece. Optional clamshell funnel adds 2 more pieces (3 total against the 12-piece limit).

⚠

R24 trip wire. The line that gets teams DQ'd is melting vs heating. The forming temperature is above polycarb's ~295°F glass transition but below ~370°F where it melts and degrades. Use a non-contact IR thermometer at the sheet surface. Document the temperature range in the build log. A clear, undistorted bend won't be questioned; a yellowed or flow-lined bend will be.

SECTION 2 / 5

Tube B — R24-Legal Cup Tube (Two-Piece Clamshell)

A wider polycarb tube, made R24-legal by splitting the cylinder into two clamshell halves bolted together at the seams. The same multi-piece pattern the audit established for the funnel cap, applied here to a full-length tube sized for the Cup's 3.16″ rim.

Why a Clamshell, Not a Single Piece

R24's plastic-piece limit applies per piece, not per assembly. R24d forbids chemical bonding but explicitly permits mechanical fastening. A two-piece tube assembled with bolts is fully compliant. The audit already uses this pattern for the Tube A funnel cap (two half-cone pieces, mouth 4.5″); Tube B applies the same trick to a cylinder.

Max cup-tube OD on a 2-piece clamshell: Each half flat pattern = half-arc \times tube-length Half-arc \leq 8.00″ (the 8″ sheet dimension) Full circumference \leq 16.00″ Max OD = 16.00 / π = 5.09″ We don’t need anywhere near the max — cup rim is 3.16″, so OD ~3.6″ gives clean grip without wasted air budget. Sized for the cup: ID 3.50″ / OD 3.62″ / wall 0.060″ Half-arc = π \times 3.62 / 2 = 5.69″ (well under 8″)

Dimensional Spec

Inner Diameter

3.50″

Outer Diameter

3.62″

Wall

0.060″

Length (axial)

3.50″

Each Half Flat Pattern

5.69″ × 3.50″

R24 Piece Count

2 of 12

Cup Rim Clearance

0.17″ radial

Seam Bolts

4 × #4-40

Both flat-pattern dimensions (5.69″ arc, 3.50″ axial) fit inside R24's 4″ × 8″ envelope with ~0.50″ safety margin on the axial dimension. Mandrel target: 3.50″ OD — a length of 3.5″ PVC pipe at 3-1/2″ nominal works for the first prototype; aluminum mandrel for the production part.

Cup Grip Geometry — Rim, Not Waist

Tube B can only grip the cup at one place: the rim (3.16″). The waist (2.32″) is too narrow — the cinch would need 1.23″ of stroke to close that much diametral gap, which exceeds the 1″ VEX cylinder's travel. This forces a specific axial layout: the cinch holes are positioned so they land at the rim's axial location when the cup is fully inserted.

Grip target	Cup ø	Diametral slack	Cinch stroke (+0.05 preload)	1″ cyl budget
Cup rim (top edge)	3.16″	0.34″	0.39″	2.6× margin
Cup waist (middle)	2.32″	1.18″	1.23″	EXCEEDS — no grip

Side View — Cup in Tube B, Cinch at Rim

The cup enters mouth-up from the loader. Rim lands at the tube's axial midpoint where the cinch closes against the 3.16″ rim with 0.39″ stroke. Cup waist hangs lower in the tube with too much slack to grip; cup base hangs below the tube entirely. With a pin nested in the cup at intake, the pin rides inside the cup throughout transit — the cinch holds the cup, the cup holds the pin.

Cinch Force Math

Cinch travel (cup rim grip): Diametral slack to close = 0.34″ Plus preload for firm grip = ~0.05″ Total cinch stroke needed: 0.39″ VEX 1″ pneumatic cylinder stroke = 1.00″ Margin: 2.6\times (comfortable, less than Tube A) Cinch force: Cylinder @ 100 psi = 78 lbf push Routing losses (axle bend, hole edges) = ~30% Net cinch force on cup rim = ~50 lbf Cup mass = 0.31 lb (heavier than the pin) Peak transit accel = ~30 ft/s² (~1g) Required hold force = 0.31 lbf Safety factor = 50 / 0.31 = 160:1

✅

Pin-in-cup combo is native to Tube B. The cinch closes on the cup rim from outside; the cup's interior is untouched. A pin nested inside the cup at intake stays nested through transit — the cup serves as a carrier. No combo-specific logic, no extra mechanism. As long as the lift preserves cup-mouth-up orientation, the pin doesn't fall out.

Fabrication — Where It's Harder Than Tube A

Tube A is one piece, one heat-form session, two cinch holes. Tube B is two pieces, two heat-form sessions, plus seam alignment. The work doubles before you reach the cinch.

Step	Tube A (single-piece)	Tube B (clamshell)
Stock cut	1 piece, 4×8 rect	2 pieces, 5.69″ × 3.50″ each (cut from one 4×8 sheet with care, or from two)
Drill (pre-form)	2 cinch holes, mid-axial	2 cinch holes + 4 seam bolt holes per piece (8 seam holes total)
Heat-form sessions	1 session on 2.40″ mandrel	2 sessions on 3.50″ mandrel (one per piece)
Seam assembly	None (open seam)	Align halves, insert 4 × #4-40 + nylock nuts, snug-tighten without cracking polycarb
Inspection complexity	1 piece traced flat against R24 template	2 pieces traced + photo of mechanical assembly proving no bond
R24 piece count	1 piece	2 pieces (3 with funnel)

⚠

Seam alignment is the new failure mode. If the two halves form at slightly different curvatures, the seams won't line up flush at the bolt holes and the assembled tube will be ovalized rather than circular. Mitigation: use the same mandrel for both halves (don't reuse a tool-marked one), clamp each half to the mandrel during cooling at the same orientation, and pre-drill the seam holes through both halves stacked together so the patterns match by construction.

What Tube B Cannot Do

Tube B is purpose-built for the Cup. It does NOT replace Tube A. Two failure modes worth documenting explicitly:

Tube B cannot grip a Pin. The pin's largest section (mid, 2.35″) leaves 1.15″ diametral slack in a 3.50″ ID tube. Closing that gap requires 1.20″ cinch stroke — more than the 1″ cylinder provides. Pin would rattle inside Tube B with no effective grip.
Tube B cannot grip a Cup at the waist. The waist (2.32″) leaves 1.18″ diametral slack — same problem. Cinch position has to be set for the rim and only the rim. If a cup enters base-first instead of rim-first, the cinch lands in the wrong spot and the cup is held by friction alone (poor reliability).

🎯

Why this matters for autonomous. The bot has to KNOW which orientation the cup is in when caught. Sensor candidates: a limit switch at the tube top that fires when the rim enters; an optical sensor reading the cup's transparent half (the dark/transparent transition marks rim location); or a fixed mechanical guide that funnels the cup rim-first regardless of loader orientation. Pick one and document it in the build log — without orientation certainty, the cinch can engage on the wrong section.

Path B (Loader Catch) on Tube B

Tube B's 3.50″ ID is significantly wider than Tube A's 2.42″, which buys back some of the catch tolerance. The catch story is different from Tube A's:

Path	Tube A (pin)	Tube B (cup)
Effective catch mouth	2.42″	3.50″
Target diameter	1.40″ pin neck	3.16″ cup rim
Radial tolerance	0.51″	0.17″
Funnel needed?	Yes for Path B — clamshell funnel widens mouth to 4.5″.	Possibly — raw tube tolerance is tight. A 4.5″ clamshell funnel on top of Tube B would buy 0.67″ radial — same pattern as Tube A's funnel.

Conclusion: Tube B may still want the clamshell funnel cap for Path B reliability. Total piece count would then be 4 (2 tube halves + 2 funnel halves), still well under the 12-piece R24 budget.

SECTION 3 / 5

Cup Grabbers — Non-Tube Alternative

Tube B is the polycarb route to cup capture; this section covers the established non-tube alternative. The 2-finger external grabber (V5 claw or pneumatic pincer) is already deployed on Pelican and Osprey and is the right answer for some bots even with Tube B available. Read this section as the comparison case against Tube B, not as a duplicate path.

Where the Cup Gets Gripped

An external grabber has two natural grip points on the Cup: at the waist (2.32″ diameter, narrowest section) or at the rim (3.16″ diameter, top edge). The grip point determines the grabber's required opening and force budget.

Grip point	Diameter	Required grabber opening	Grip nature
Waist (mid)	2.32″	~2.4″ open → ~2.2″ closed	Form-fit — waist is the narrow region between rim and base; gripper seats naturally and won't slide off vertically.
Rim (top)	3.16″	~3.3″ open → ~3.0″ closed	Friction — rim is the widest part; the grabber relies on inward force, not geometry, to hold. Easier to grab from above (loader drop).

💡

Recommendation. Grip the waist when the lift carries the Cup horizontally or with the Cup mouth up. Grip the rim when the Cup is being picked up off the loader floor and the grabber descends onto it from above. Pelican's V5 claw on a four-bar lift naturally drops onto the rim from above; a chain-bar-mounted pincer is better suited to waist grip during the swing.

Fleet Cup-Grabber Options

▸ Option 1 — V5 Claw

MOTORIZED5.5W or 11WRIM OR WAIST2-FINGERPELICAN 2822C

Two-finger motorized claw, standard VEX part. Continuously variable grip force via motor current. Already deployed on Pelican (2822C) as the V1.5 Hero Bot end-effector on a four-bar lift. Falcon and Heron list the claw as one of their swappable manipulator options.

Pros: proven part, simple wiring, continuously adjustable grip strength. Works for both rim and waist grip with no hardware change — just tune the close angle.
Cons: consumes a motor port (V5 claw is its own port, not shared with the lift). Grip force depends on motor stall; sustained grip can heat the motor on long matches.

▸ Option 2 — Pneumatic Pincer

PNEUMATICBINARY OPEN/CLOSEDWAIST PREFERREDOSPREY 2822E

Two-finger pincer driven by a single-acting pneumatic cylinder (typically 1.0″ bore VEX cylinder with return spring). Already deployed on Osprey (2822E)'s chain bar end. Heron and Falcon list pneumatic pincer as an alternative end-effector.

Pros: zero motor cost (uses a solenoid, no motor port). Instant full-force close (no ramp-up like a motor). Grip force is set by air pressure, not by sustained current — no heat issue.
Cons: binary (open / closed, no in-between). Consumes a solenoid port and air budget. Pneumatic plumbing adds build complexity. Air tank capacity limits per-match cycle count (~30–60 cinch cycles depending on tank size and cylinder volume).

▸ Option 3 — Tube B (clamshell polycarb)

SEE SECTION 2ID 3.50″RIM-GRIP CINCH

The two-piece clamshell tube documented in Section 2. Listed here so this section's option list stays exhaustive. Tube B sits between the two grabber options in the build-complexity dimension (harder than a V5 claw, comparable to a pneumatic pincer) and wins on grip-by-geometry rather than grip-by-friction. See the Decision Matrix in Section 4 for the side-by-side score.

Pin-in-Cup Combo Transport

Override scoring rewards Pins nested inside Cups (SC3). Any cup-grabber needs to transport the combo without dropping the Pin. The key constraint is cup orientation through the lift arc — if the Cup rim ever points below horizontal during transit, the Pin can fall out.

Lift architecture	Combo orientation behavior	Combo transport
Four-bar lift (Pelican 2822C)	Preserved. Parallel-motion arms keep the claw orientation level through the entire lift cycle. Cup mouth stays up.	Native — no extra hardware needed
Chain bar (Osprey 2822E)	Preserved. 1:1 chain ratio keeps the manipulator level through the 180° sweep, like the four-bar.	Native — no extra hardware needed
Swing bar (legacy V1)	Flipped at 180° unless a 5.5W wrist counter-rotates the grabber.	Requires wrist motor + coordinated control
Stacked reach (Heron)	Preserved when the chain-bar end-effector is used (Heron's published config).	Native — no extra hardware needed

✅

Combo handling beats single-element handling. A bot that can score a pin-in-cup combo in one cycle scores both points without two trips to the loader. Pelican (four-bar + V5 claw) and Osprey (chain bar + pincer) are the fleet's best-positioned designs for combo work. Skimmer (tube) cannot do combos — it picks the Pin only.

SECTION 4 / 5

Decision Matrix — Per Element & Per Bot

Side-by-side scoring of Tube A, Tube B, and the two viable cup grabbers across the criteria that matter for Override. Scores are 1 (worst) to 5 (best), with one-line reasoning. Per-bot mechanism assignments follow.

Mechanism Matrix

Criterion	Tube A (pin)	Tube B (cup)	V5 Claw (cup)	Pneu. Pincer (cup)
R24 legality	5 ID 2.42″ legal w/ margin	4 legal as 2-piece; seam scrutiny	5 commercial part, no polycarb	5 commercial parts, no polycarb
Grip reliability	5 300:1 cinch safety factor	5 160:1 cinch SF; geometric grip	4 motor torque, tunable	5 full-bore air = high force
Pin-in-cup combo	1 cup can’t enter Tube A	5 grip cup rim, pin nests inside	5 grip cup, pin nested	5 grip cup, pin nested
Motor port cost	4 5.5W for tube rotation	4 5.5W for tube rotation	3 5.5W or 11W for claw	5 0 motors, solenoid only
Air budget cost	3 1 cylinder per cycle	3 1 cylinder per cycle	5 0 air	3 1 cylinder per cycle
Build complexity (higher = simpler)	2 heat-form polycarb + cinch	1 2 heat-form + seam alignment	5 drop-in commercial	3 pneumatic plumbing
Per-match cycle count	3 air-limited ~30–60	3 air-limited ~30–60	5 unlimited (motor)	3 air-limited ~30–60
Element specificity	2 PIN ONLY	2 CUP ONLY (+ combo)	4 cup ± combo	4 cup ± combo
Notebook story	5 R24 audit + heat-form custom	5 clamshell innovation + symmetric arch	3 commercial = less custom	4 pneumatic integration
Totals	30	32	39	37

💡

How to read the totals. Tube A and Tube B are element specialists — each handles one element well and the other not at all. The grabbers are cup generalists with higher totals because they win on build complexity and motor/air efficiency. The polycarb tubes win on notebook story and cinch-grip reliability. Pick the path that matches your bot's strategic role: a Pin specialist gets Tube A; a Cup specialist with strong polycarb fabrication chops gets Tube B; a Cup-focused bot with motor budget to spare gets V5 claw; a Cup-focused bot prioritizing motor-port economy gets the pincer.

Per-Bot Mechanism Assignments

Bot	Lift	Primary mech	Element focus	Combo capable?
Skimmer 2822A	2-bar swing arm	Tube A (polycarb pin pickup)	PIN	No
Pelican 2822C	Four-bar lift	V5 claw (deployed)	CUP + combo	Yes (orientation preserved by four-bar)
Spoonbill 2822D	Four-bar lift + 5.5W claw rotation	V5 claw with active wrist (deployed)	CUP + combo + orientation flips	Yes — plus active reorientation of pin or cup during transit
Osprey 2822E	Chain bar	Pneumatic pincer (primary) / Tube A (secondary)	CUP + combo (pincer) or PIN (tube)	Yes (chain bar preserves orientation)
Heron	Four-bar + chain bar end-effector	Swappable: claw / pincer / Tube A / Tube B	Configurable — strong Tube B candidate (orientation preserved end-to-end)	Depends on end-effector
Falcon	4-DOF arm	Swappable: claw / pincer / Tube A / Tube B	Configurable — arm DOF lets Falcon orient any end-effector arbitrarily	Depends on end-effector
Future "cup specialist" bot (TBD)	Four-bar or chain bar (orientation-preserving)	Tube B (or pincer)	CUP + combo	Yes

Fleet-Level Analysis — Per-Bot Matrix & Meta Read

The per-mechanism scoring above asks "which manipulator is best." The per-bot question — "which manipulator fits each bot, and what's the fleet meta" — gets its own page so it can be referenced independently of the mechanism-level prototyping detail. The standalone page covers:

The 6×4 compatibility matrix — every bot scored against every manipulator with status tag and one-line reason
Per-bot recommendation — primary + fallback for each bot
Commitment status — what's locked vs. still open across the fleet
Fleet meta read — tiered bot ranking, alliance pairing analysis, tier-shifting sensitivity

📊

See /fleet-manipulator-matrix for the full per-bot matrix and meta read. That page is the strategic counterpart to this one — this page (element-capture-prototypes) is the mechanism-level engineering source; the fleet matrix page is the alliance-level synthesis.

Sensitivity — What Would Shift the Choice?

If air budget is tight (small tank, long matches): V5 claw jumps for cup work because it doesn't draw on the air budget at all. Tube B and pneumatic pincer both drop — they share the air cost.
If the team has zero pneumatic experience: V5 claw wins for cup work on simplicity. Tube B and pincer both require pneumatic plumbing.
If polycarb fabrication is the team's strength (Skimmer-style culture): Tube B's score climbs — team takes the build-complexity hit comfortably and gets the notebook story of two custom polycarb mechanisms covering both elements.
If the strategy is pin-only (skip cups entirely): Tube A is the right answer for every bot. Tube B and cup grabbers become moot. (This is Skimmer's case.)
If the strategy is cup-only (skip pins): Tube A doesn't get built. Cup mechanism is Tube B vs claw vs pincer per bot.
If a bot needs to do both Pin and Cup on the same robot: not possible with a single end-effector. Either build two manipulators on different arms (Heron-style stacked reach) or specialize per-bot in the alliance.
If R24 inspection becomes a recurring pain point: Tube B's clamshell seam draws more scrutiny than a single-piece tube. Both are legal, but inspector friction is higher on two-piece. Cup grabbers (commercial parts) avoid this entirely.

SECTION 5 / 5

Prototype Roadmap

Order of operations to get all three prototypes from CAD to a tested bench mock-up. Tube A and Tube B both go through the 3D-print-first sequence already documented in the R24 audit. The cup grabber leverages existing fleet builds — the prototyping work there is on integration, not on the grabber itself.

Tube A — Build Sequence

3D print prototype. Print the corrected-dimension tube (ID 2.42″ / OD 2.54″ / L 4.00″) on the Bambu P2S in PLA, walls = 5 loops. Vertical orientation. Reference: audit Sheet 0, "Bambu P2S 3D print prototype" section. Estimated 2–3 hours.
Bench-test fit. Verify pin enters neck-first, mid section seats with 0.035″ radial slack, base flare hangs out the bottom. Verify pin cannot enter base-first (flare blocks). Verify cup cannot enter (rim and base both block).
Bench-test cinch. Drill the two 1/16″ opposed holes at the tube midpoint. Thread 1mm Spectra cord. Pull manually with a fish scale — verify the cord seats the pin against the opposite wall with < 10 lbf pull. (Real cylinder will provide ~50 lbf.)
If prints check out: fabricate the real polycarb tube per the mentor handout on a 2.40″ OD mandrel. Measure finished ID; if it lands in 2.41–2.45″ range, proceed. If outside, adjust mandrel and re-form.
Install on Skimmer: per /spartan-hero-polycarb-tube-intake. Hex shaft through end caps, 5.5W rotation via 1:5 sprocket reduction, pneumatic cylinder for cinch.
50-cycle bench test (target: 0 drops): pin in, cinch, lift to deposit height, cinch release, pin out. Repeat 50 times. Document drops and failure modes.
Anneal the production tube per the handout's Step 9 (250°F for 7 min, oven-cool). This is the difference between 50 cinch cycles and 500.

Tube B — Build Sequence

Order of operations parallels Tube A's, with two extra steps for clamshell assembly. Total time: roughly 1.8× Tube A's investment per prototype, plus the seam-bolt alignment.

3D print both halves. Model the clamshell pair in OnShape (see audit's OnShape Method B for sheet-metal flat-pattern workflow; apply to the half-cylinder geometry rather than the half-cone). Export each half as STL. Print on the Bambu P2S in PLA, walls = 4 loops. Lay-flat orientation with tree supports under the curved edges. Estimated 2 hours per half, 4 hours total.
Bench-test assembly. Drill matching 1/8″ seam bolt holes through both halves stacked together (this guarantees the patterns match). Insert 4 × #4-40 socket cap screws + nylock nuts. Snug-tighten until the seams meet without crushing the plastic. Verify the assembled tube is circular (caliper across diameter at multiple axial positions; deviation < 0.040″).
Bench-test cup fit. Drop the cup into the assembled tube mouth-up. Verify rim seats at the cinch zone (axial midpoint). Verify body hangs below the tube. Verify a pin nested in the cup stays nested.
Bench-test cinch. Drill the two 1/16″ cinch holes at the tube midpoint, 180° apart, positioned so neither hole lands within 0.25″ of the seam (seam stress + cinch stress = crack risk). Thread Spectra cord. Verify manual pull seats the cup rim with < 10 lbf.
If prints check out: fabricate the real polycarb halves. Heat each on a 3.50″ OD mandrel (3-1/2″ PVC pipe works for prototype; aluminum for production). Use the same mandrel for both halves to guarantee matching curvature. Cool each half clamped to the mandrel.
Assemble production halves: drill seam holes through both stacked (per step 2). Mechanical assembly only — no adhesive, no solvent. Verify assembled ID at multiple axial positions.
Install on chosen host bot (Heron, Falcon, or future cup specialist). End caps and rotation drive parallel Tube A's design but sized for the larger diameter; 5.5W motor + sprocket reduction sized for the larger rotating mass.
50-cycle cup bench test (target: 0 drops): cup in mouth-up, cinch, lift, release, cup out. Then 50-cycle pin-in-cup combo test: cup with pin nested, cinch on cup rim, lift through full arc, release. Document drops and orientation-failure cases.
Anneal both halves together at 250°F for 7 min, oven-cool. Same stress-relief value as Tube A.
(Optional) Build the Path B funnel cap (4.5″ mouth clamshell) on top of Tube B if loader-catch bench tests show poor reliability without it.

Cup Grabber — Integration Sequence

Less hardware prototyping needed — both V5 claw and pneumatic pincer are commercial / already-built parts. The work is in matching the grabber to each bot's lift and tuning for cup grip.

V5 claw on Pelican: already in progress per Pelican page. Bench-test required: cup grip force at the rim (top-down approach), grip force at the waist (side approach), grip-and-hold during a complete four-bar lift cycle.
Pneumatic pincer on Osprey: already in progress per Osprey page. Bench-test required: cup grip at waist during chain bar sweep, air consumption per cycle (size air tank accordingly).
Pin-in-cup combo test (both bots): load a pin into a cup. Grip the cup with claw or pincer. Run the full lift cycle. Verify the pin does not fall out at any point (rim never below horizontal).
Heron / Falcon: end-effector decision pending. Use the decision matrix in Section 3 to commit to claw vs pincer based on the team's pneumatic experience and motor budget. Document the choice in the engineering notebook with explicit reference to this matrix.

Combined Bench Tests

Test	Pass criteria	Bot(s)
Tube A pin grip solo pin, 50 cycles	0 drops, no string fatigue, finished ID drift < 0.005″	Skimmer
Tube A Path A catch roller-transfer	20 / 20 catches with pin alignment offset ± 0.5″	Skimmer
Tube A Path B catch direct from loader	Bare tube: 14 / 20 catches. With clamshell funnel: 19 / 20 catches.	Skimmer
Tube B cup grip solo cup mouth-up, 50 cycles	0 drops, cinch lands consistently on rim (not waist), seam bolts stay snug	Heron / Falcon / future cup bot
Tube B pin-in-cup combo cup loaded with pin nested, 50 cycles	0 pin drops AND 0 cup drops during full lift cycle	Heron / Falcon / future cup bot
Tube B Path B catch cup direct from loader	Bare tube: target ≥ 15 / 20 (tight ~0.17″ radial). With 4.5″ funnel: ≥ 19 / 20.	Heron / Falcon / future cup bot
Tube B seam integrity post 200-cycle	No crack propagation from seam bolt holes; bolt torque drop < 30%	Heron / Falcon / future cup bot
Claw cup grip (rim) top-down approach	0 / 20 drops during full lift cycle	Pelican
Pincer cup grip (waist) side approach	0 / 20 drops during full chain bar sweep	Osprey
Pin-in-cup combo (claw)	0 / 20 pin drops during cup transit	Pelican
Pin-in-cup combo (pincer)	0 / 20 pin drops during cup transit	Osprey

Notebook Documentation

For each prototype, the engineering notebook entry should cover:

Decision rationale with explicit reference to the R24 audit and this page's decision matrix.
Bench-test data (cycle count, drop count, failure modes).
R24 compliance evidence: photo log per the mentor handout's Engineering Notebook Documentation section, 1:1 PDF tracing of the tube flat pattern, piece count against the 12-piece limit.
Cross-team coordination: which bot got which mechanism and why (alliance strategy view).

Cross-References

R24 audit (canonical dimensions): /polycarb-tube-r24-audit/
Earlier hero intake page (review — some numbers superseded by audit): /spartan-hero-polycarb-tube-intake
OnShape CAD guide: /polycarb-tube-onshape-guide
Mentor fabrication handout: /polycarb-tube-fabrication-guide
Skimmer (Tube A host bot): /skimmer.html
Skimmer front roller (Path A): /skimmer-roller-cad/
Pelican (V5 claw host bot): /pelican.html
Osprey (pneumatic pincer host bot): /osprey.html
Heron (swappable end-effector concept): /heron.html
Falcon (4-DOF arm concept): /falcon.html

🎯

Open follow-ups. (1) The hero intake page's decision matrix still scores "Pin-in-cup combo: 5" for the (single-piece) tube path — that row is stale; the right value is 1 for Tube A and 5 for Tube B; update with the two-tube context. (2) Confirm Cup base diameter from Override manual Appendix A — this page approximates it equal to the rim (3.16″); base diameter doesn't affect Tube B's rim-grip strategy but does affect cup-orientation sensors. (3) Add a 1:1 PDF tracing of the Tube B clamshell halves to the team's R24 compliance binder before any inspection event. (4) Decide which bot is the first Tube B host (Heron is the leading candidate per the per-bot table); coordinate end-cap design with the chosen bot's lift geometry.