If you're here to fill in EDP Step 2 brainstorm slides in your engineering notebook (slides 19–27, gold section), use this guide as a prompt to think with — not as a source to copy from.
The right workflow:
Judges look at the brainstorm section specifically to see real divergent thinking. Notebooks that mirror the structure of a single source page lose rubric credit. Original sketches and team-specific reasoning earn it.
Compliance wheels (also called “flex wheels”) are V5RC's rubber-style wheels that deform under pressure. The deformation is the point: it lets one wheel grip many shapes without precise alignment. They're the foundation of nearly every successful intake design in V5RC.
This guide pairs with engineering notebook template slide 20 (Concept Brainstorm — Intake). For the full intake design framework, see /mechanism-intakes. For Override-specific intake geometry, see /override-intake-geometry.
A traditional wheel is rigid — it preserves its shape against load. A compliance wheel is designed to deform predictably when pressed against an object. This deformation has two important effects:
The deformation depends on two variables: how soft the wheel is (durometer) and how much you compress it (the gap). Get these two right and the wheel does its job; get them wrong and the wheel either slips, tears the cup, or wears out in a single tournament.
Durometer is measured on the Shore A scale — a number from about 30 (very soft) to 90 (very hard). VEX flex wheels come in three main durometers, each color-coded:
Highest grip on smooth plastics. Friction coefficient μ ≈ 0.8 on cup plastic. Deforms generously, wraps around irregular shapes.
Trade-off: wears fastest. Soft compounds shed material against repeated cup contact. May grab too aggressively on first contact — can briefly trap an element before fully seating it. Vulnerable to defensive contact (gets pushed out of position more easily).
Pick this when: the season's elements are smooth-surfaced, lightweight, and you need maximum grip on a single-cycle pickup. Plan to bring spares.
Goldilocks zone. Friction coefficient μ ≈ 0.5 on cup plastic. Predictable deformation (~2.5 lbf per 1/4″ compression at 3″ diameter). Durable enough for full season.
Trade-off: not the highest grip. If your application needs maximum friction, soft 35A wins. But for most V5RC intakes, 45A's grip is enough.
Pick this when: you need a wheel that lasts the season and has enough grip for typical V5RC element handling. Most successful Override intakes will use 45A.
Most durable, lowest deformation. Friction coefficient μ ≈ 0.3 on cup plastic. Useful when you need a wheel that resists wear over a long season of practice + competition.
Trade-off: grip is significantly lower. Compensating with extra compression risks slipping under dynamic load (when the robot accelerates with element gripped) and damaging the element from over-squeeze.
Pick this when: grip is less important than durability — e.g., a transport roller in the middle of an intake chain where the element is already secured, or a contact wheel that just needs to roll without precise grip control.
Once you've picked a durometer, the second variable is gap — how much smaller is the wheel-to-wheel (or wheel-to-surface) clearance than the element itself. The difference is the compression.
For a 3″ dark gray (45A) flex wheel gripping a 1.5″-waist cup:
| Wheel-to-wheel gap | Compression per side | Grip force per side | Behavior |
|---|---|---|---|
| 1.50″ | 0″ (just touching) | ~0 N | Cup falls out |
| 1.375″ | 0.0625″ (1.6 mm) | ~5 N | Light grip, may slip on contact |
| 1.25″ ← recommended | 0.125″ (3.2 mm) | ~10 N | Secure grip, no damage |
| 1.125″ | 0.1875″ (4.8 mm) | ~15 N | Aggressive grip, may damage cup over time |
| 1.00″ | 0.25″ (6.4 mm) | ~20 N | Too much — cup deformation risk |
The pattern: 0.125″ compression per side is the sweet spot for cups. Less and you slip; more and you damage. This generalizes — for any element, target compression of about 1/12 of the element's diameter.
VEX flex wheels come in 2″, 3″, and 4″. The choice is about contact patch size vs packaging:
| Diameter | Contact patch (at 0.125″ compression) | Best for |
|---|---|---|
| 2″ | ~0.5″ long | Small elements (under 1″ diameter); tight packaging on a Clawbot |
| 3″ ← recommended for cups/pins | ~0.75″ long (40% more area than 2″) | V5RC game elements (1-2″ diameter); standard intake size |
| 4″ | ~1.0″ long | Large elements (3″+); but heavy and creates packaging problems |
For Override pins (1.40-3.16″ tapered) and cups (1.5″ waist), 3″ is the sweet spot. 2″ gives too little contact patch on cups; 4″ is overkill and packages awkwardly on a V1 Hero Bot chassis.
Compliance wheels are versatile but they're not always the right tool. Don't use them when:
For an Override cup-handling intake using flex wheels (Architecture D or E from /mechanism-claw):
Soft compound wears fast. A 35A flex wheel on a busy intake will visibly degrade in 2-3 tournaments. If your team commits to 35A for grip, commit to keeping spares in the toolbox.
Compression isn't free. Every 0.125″ you compress, the wheel pushes back with force. This force is real load on the motor driving the wheel. If your intake motor is undersized, more compression means more current, more heat, more thermal throttling risk during a long match.
Flex wheels don't handle long-axis grip. A flex wheel pinching a cup at its waist holds well laterally (around the perimeter). But pulling the cup straight out of the grip (along the wheel rotation axis) is much weaker — one good push from a defensive robot can extract the cup. Side-grab geometries (like Architecture E) are inherently more defense-resistant than top-pinch geometries.
Star-cut flex wheels exist. Some teams modify flex wheels by cutting them into a star pattern — this increases compliance dramatically (the wheel deforms more for a given gap). It's a season-tradition modification, but it also reduces wheel life and changes the math above. See /override-intake-geometry for the star-cut geometry trade-offs before doing this.
For slide 20 (Concept Brainstorm — Intake), document: