Pneumatic Pincer Manipulator — Override Design Guide

For: Team 2822 Spartan Design (Phase A fleet) Use cases: Osprey chain bar tip; Falcon-class arm tip; any V1.5 manipulator alternative to the V5 claw Rule compliance: R25 pneumatics, R28 modifications, SG6 possession, R24 polycarb Source authority: Override v0.1 manual + Appendix A drawings

When Pincers Win (and When They Don't)

Choose pincers when: - The cycle is committed and repetitive (one motion per cycle, like Osprey's chain bar sweep) — pneumatic speed compounds over 20+ cycles per match - The lift architecture has no wrist DOF (pincer adds binary grip without needing another motor) - The team wants pneumatic experience on their fleet for engineering-notebook coverage

Don't choose pincers when: - The team has zero pneumatic experience and a deadline. Plumbing failures are common on first builds. Add a build week. - The bot is at the 88W cap with a V5 claw already working. Don't trade something working for something theoretical. - Cycle complexity is unpredictable (pincer is binary; if you need partial-grip or proportional control, a motor-driven claw is better).

The Override-Specific Design Constraints

These are the numbers the pincer geometry has to satisfy. Pulled from Appendix A drawings; pin is hex-profile and tapered, cup is hourglass-shaped.

Pincer open span (jaws apart): must clear the largest combined element to enter from above or the side. A cup-on-pin combo at the loader is the worst case. Set open span to 3.6″ to accept a cup (3.16″) with 0.2″ margin per side.

Pincer closed span (jaws together): must grip the smallest working element securely. Cup waist (2.32″) and pin neck (1.40″) are the two targets. Set closed span to 1.3″ so the pincer can grip a pin neck. The cup waist (2.32″) will be gripped before full closure — that's expected and correct.

Effective travel per jaw: (3.6 − 1.3) / 2 = 1.15″ if symmetric, or 2.3″ total stroke if one jaw moves and the other is fixed.

Loader compatibility: Pincer open span (3.6″) must fit inside the loader chute ID (3.39″–3.74″ per Figure A9). 3.6″ is at the limit. Reduce open span to 3.4″ if your robot lifts up into the loader chute to receive (some chain bar geometries do this). Verify before fabrication.

Mechanical Design — The Jaws

Jaw geometry

Two opposing jaws, each shaped to nest around the cup waist (curved inner profile) or pin neck (V-notch or flat hex contact). The dual-shape comes from the element geometry: cup waist is convex (round), pin neck is hexagonal.

Recommended jaw profile (inner surface):

   ─── jaw inner surface ───
   ┌────────────────────────┐
   │ ╱╲                  ╱╲ │   ← V-notch at the tips
   │╱  ╲      ◯         ╱  ╲│   ← curved center for cup waist
   ╲   ╱   (cup        ╲   ╱
    ╲ ╱     waist)      ╲ ╱
     V        ◯           V    ← V-notches grip pin neck

The V-notches at the two extremes grip a pin (1.40″ neck) by its hex flats; the curved center grips a cup (2.32″ waist) by its circumference. One jaw shape serves both elements.

Jaw material

Anti-slip drawer liner (legal per R20 with size limits — max 12″ × 15″, no piece) bonded to the inner jaw surface dramatically improves grip on the smooth cup and pin surfaces. Cut to fit the contact zone only; don't cover the V-notches.

Mounting

Pincer mounts to whatever the arm tip presents. For Osprey: a 2″ × 3″ × 0.090″ aluminum plate at the chain bar tip is the universal manipulator mount (same pattern as the V5 claw's mount). The pincer baseplate bolts to this plate via four M3 fasteners.

Center of grip should align with the manipulator's expected element position. If the lift drops the pincer 4″ above the goal at deposit, the cup waist (when held) should be ~3″ above the goal — the pincer opens, cup falls 3″ onto the goal. Don't position the grip center such that the cup falls through the goal post.

Pneumatic System

Cylinder selection

Standard VEX pneumatic cylinders come in single-acting (return spring) or double-acting (two air ports) configurations. For pincers:

Recommendation: single double-acting cylinder, 2″ stroke, mounted parallel to the jaw axis, with a center-pivoting linkage that translates linear cylinder motion to opposing jaw rotation.

Force calculation: at 60 psi (typical working pressure below the 100 psi R25 max), a 0.75″-bore cylinder delivers ~26 lbf of linear force. After a 2:1 linkage (jaw amplification trades force for distance), each jaw closes with ~13 lbf at the contact surface. More than enough for cup/pin grip — over-grip is more common than under-grip and crushes elements.

To reduce grip force: lower the regulator to 40 psi. Cup deformation under over-grip is a real failure mode at 80+ psi.

Solenoid

One single double-acting solenoid valve (4-port, 2-position) controls the cylinder. Connect: - Port 1 (input): to the pressure tank - Port 2 (return): vented to atmosphere - Ports 3 & 4 (cylinder): one to each end of the cylinder

When the V5 brain energizes the solenoid, air flows to one cylinder port (jaws close); when de-energized, air flows to the other (jaws open via spring return or the second port).

Wiring: VEX 12V solenoids connect via the Pneumatic Control Module (NOT legal under ; replace) — actually use a 3-wire digital out port on the V5 brain through a relay or via additional 12V power per if running VEX U, or simply use a standard single-solenoid V5-compatible valve for V5RC. The team's existing pages document this.

Tubing

1/8″ ID polyurethane tubing, routed from the tank → regulator → solenoid → cylinder. Standard VEX pneumatic kit components are all R25-compliant. Keep tube runs short to minimize actuation delay.

Tank sizing

R25 allows max 2 VEX air tanks charged to 100 psi max. Each tank holds ~0.5 cubic inches of free air at 100 psi. A 2″ stroke × 0.44 in² piston area = ~0.88 in³ of air consumed per actuation cycle (both directions = ~1.76 in³ total).

At 100 psi, 1 tank ≈ 50 cylinder actuations before drop to ~30 psi (insufficient). Two tanks = ~100 actuations per match. Override matches are 2:00 long; at a 5-second cycle, that's 24 cycles per match. Two tanks gives 4× margin — comfortable.

If running 60 psi instead of 100: lower stored energy, but jaw force at 60 psi is still ~13 lbf — sufficient. You get ~30 actuations per tank, 60 per match with two tanks. Still comfortable.

Build Sequence

Estimated time: 8–12 hours spread across 2–3 sessions. Plumbing failures consume more time than mechanism failures; budget for leaks.

1. CAD the jaw profile (1 hr) — sketch in Onshape, dimension the V-notches and curve, export as DXF for cutting. Confirm 3.6″ open span fits the loader chute and 1.3″ closed span grips the pin neck.
2. Cut and bend the jaws (2 hr) — laser-cut or hand-cut polycarb to the DXF, heat-bend the curve. Drill jaw pivot holes.
3. Build the baseplate + linkage (2 hr) — 2″×3″ aluminum baseplate with jaw pivot bosses; cylinder mounting bracket; linkage arms connecting cylinder rod to both jaws via a 2:1 mechanical advantage. Use VEX hex shafts and bearing flats.
4. Plumb the pneumatic system (2 hr) — tank → regulator → solenoid → cylinder. Use thread sealant (PTFE tape is R21-legal only for pneumatic fittings). Test for leaks by pressurizing and listening / soap-water testing each joint.
5. Test actuation off-robot (1 hr) — bench-test the pincer with the cylinder energized/de-energized. Confirm open span (3.6″ ± 0.1″), closed span (1.3″ ± 0.1″), and actuation time (target < 200 ms).
6. Mount to lift (1 hr) — bolt baseplate to chain bar or arm tip. Verify clearance throughout the arm's range of motion. Re-test actuation under arm motion.
7. Element grip test (1 hr) — pick up and release each element type 10 times: pin (hex flat down), pin (hex corner down), cup (right side up), cup (upside down), pin-on-cup combo. Document any orientation that fails ≥2/10; iterate the jaw profile.

Programming Pattern

Single solenoid on a 3-wire port (treat as digital out):

// VEXcode V5 Pro example
digital_out pincer_solenoid = digital_out(PORT_A);  // pin A on the brain's 3-wire ports

// Close the pincer
pincer_solenoid.set(true);
wait(0.15, sec);  // wait for jaws to close (actuation time)

// Open the pincer
pincer_solenoid.set(false);
wait(0.15, sec);  // wait for jaws to open

Pattern for the match cycle:

// In driver-control loop
if (controller.ButtonR1.pressing()) {
    pincer_solenoid.set(true);   // close
} else if (controller.ButtonR2.pressing()) {
    pincer_solenoid.set(false);  // open
}
// Press R1 to close-and-hold; press R2 to release

Auton routine:

// Pick up element at loader
move_to_loader();
pincer_solenoid.set(true);   // close on element
wait(0.2, sec);              // confirm grip

// Travel to goal
lift_to_height(13.0);        // inches above tile
move_to_goal();

// Deposit
pincer_solenoid.set(false);  // open
wait(0.2, sec);              // element falls onto goal
lift_to_height(0);           // arm back to rest

Sensor feedback (optional, V2 polish): a V5 Optical Sensor pointed at the grip zone can confirm "element present" before commanding close, preventing wasted air on empty closes. Worth adding if your team has spare sensor ports.

Inspection & Rule Compliance

R25 (pneumatics): - Max 2 VEX air tanks (276-8749) ✓ - Max 100 psi ✓ - Compressed air only used to actuate legal pneumatic devices ✓ - No on-robot recharging ✓ - All commercial pneumatic components rated for 100+ psi (verify with documentation if challenged) ✓

R28 (no modifications to electronic/pneumatic components): - Cylinders, solenoids, tubing must be unmodified except for cutting tubing to length and assembling using existing threads ✓ - No drilling cylinder bodies, no custom valves ✓

R24 (polycarb): - Jaws cut/bent legally from polycarb sheet ✓ - Not chemically treated, melted, or cast ✓ - Total polycarb on robot (across all subsystems) within team's tracked count ✓

R21 (tape): - PTFE tape OK on pneumatic fittings only ✓ - No tape used elsewhere on the pincer beyond labels/cable management ✓

SG6 (possession): - Pincer can only hold 1 pin OR 1 cup OR 1 nested pin-cup combo at once ✓ - The pincer's binary grip enforces this naturally — it can't grab a second element while closed on one

Failure Modes & Tuning

Decision Reference — Pincer vs V5 Claw vs Polycarb Tube

Quick reference if the team is choosing between manipulators mid-build:

Notebook Entry Template

When the team installs the pincer on Osprey (or another bot), the engineering notebook should document:

1. Problem statement — why the team chose pincers over the V5 claw (cycle time, build experience, etc.)
2. Design iteration — first jaw profile sketch, what failed in bench testing, what was changed
3. Constraint check — R25 compliance, SG6 possession compliance, loader chute fit (3.6″ open span vs 3.39″ chute ID)
4. Bench-test data — 10-trial element-grip table for each orientation (hex flat, hex corner, cup upright, cup upside-down, pin-on-cup combo). Pass rate per orientation.
5. Field-test data — first scrimmage cycle time vs goal; comparison to V5-claw cycle time on a sister-bot if available.
6. Rejected alternatives — V5 claw rejected because (...). Polycarb tube rejected because (...). With rationale.

Judges score the iteration narrative more than the final result. Document the rejected jaw profile attempts as carefully as the working one.

Drafted for Spartan 2822 fleet (Osprey 2822E primary, Falcon-class secondary). Cross-references: /osprey, /falcon, /spartan-hero-bot, override-intake-geometry, R25 inspection checklist.

Rule citations verified against Override v0.1 manual (April 27, 2026). Figure references: A5 (pin), A6 (cup), A9 (loader). If rules update in a manual revision, re-verify before fabrication.