// Section 01

Lift Mechanisms 🏆

The history of lifts in VRC, how each mechanism works, and the three questions every team must answer before choosing one.

Three Questions Before You Build

How high does the piece need to go?

Low goal (under 24") → Four-bar or direct arm. Mid height (24"–36") → Six-bar or chain bar. Maximum height (36"+, vertical stacking) → DR4B. Choosing too complex a lift for the scoring height wastes motors and build time.

Does the end effector need to stay level?

If stacking objects or placing them precisely → yes, you need a parallel linkage (four-bar, six-bar, DR4B, or chain bar). If just lifting to dump or hang → a direct arm may suffice and saves significant build complexity.

How many motors can you afford?

V5 robots have 8 motors. A typical drive uses 4–6. Remaining: 2–4 for mechanisms. A four-bar can run on 1–2 motors. A DR4B typically needs 2–3. More complex lift = fewer motors for intake and endgame.

Historical Context — Which Lift Won Each Lifting Game

Skyrise 2014-15 — DR4B Dominated

Teams had to build a 7-section Skyrise tower as high as possible — requiring maximum vertical reach while keeping the piece level. The DR4B's near-vertical rise and centered weight made it the dominant design. Team 118 was among the first to pioneer a truly stable DR4B. AURA (VEXU) and 2587Z also ran landmark versions. The lesson: when vertical height is the primary scoring mechanic, DR4B is the answer.

In The Zone 2017-18 — DR4B + Chain Bar

Scoring cones on mobile goals required both high reach (for tall cone stacks) and precise placement. DR4B remained dominant for maximum stack height. Chain bars (pioneered by AURA in Sack Attack, popularized by 929U) emerged as a strong alternative — simpler to build, adequate reach, excellent for mobile goal manipulation. Team 8059 adapted the chain bar concept into an early DR4B, creating history.

Tower Takeover 2019-20 — Four-Bar / Tray Bots

Stacking cubes in goal zones changed the meta entirely. The most successful robots used a tilting tray + four-bar for intake deployment rather than a traditional vertical lift. Maximum height was not the priority — stable stacking and cycle speed were. This season showed that game object type and scoring mechanic always overrides lift tradition.

Tipping Point 2021-22 — Four-Bar + Chain Bar

Mobile goal manipulation required lifting goals into home zones and elevating at match end. Four-bar lifts for mogo pickup dominated, with chain bars offering an alternative for goal post latching. DR4B was largely overkill — scoring height did not justify the complexity. This reinforced the rule: match lift complexity to scoring height requirement.

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// Section 03

Four-Bar Linkage

A four-bar keeps the end effector at a fixed orientation throughout the lift motion. This is the most common lift in competitive VRC because it solves the “keep the piece level” problem without stacking complexity.

    
  Four-bar linkage diagram
  
  Ground link (chassis)
  
  Input
  
  Coupler (arm)
  
  Output
  
  output stays
  level (parallel)
  input and output links rotate in parallel — the coupler always stays horizontal

How It Works

A four-bar has exactly four rigid links connected at four pivot points: the robot chassis (ground link), the driven arm, the output link (carries the end effector), and a coupler connecting them. When the driven arm rotates, the output link maintains its angle relative to ground — meaning whatever is attached to it stays level. This is called a parallel four-bar when the two side links are equal length and parallel.

Key Design Rules

Equal-length parallel links. For a true fixed-orientation output, the two side bars must be the same length and the pivot points must form a parallelogram. Measure in CAD, not by eye.
No slop in pivot joints. Each of the four pivots adds angular error. With 0.5° of slop at each pivot, the output can drift 2° — which is visible at full extension. Use proper shoulder screws or bearing flats at every pivot.
Counterweight or rubber band assist. Four-bars have a heavy moment arm at full extension. Adding elastic to assist the upward motion reduces motor load and allows a smaller motor reduction while still holding position.
CAD the full range of motion. Before cutting metal, animate the four-bar in Onshape through its full travel. Check for interference with the robot body, wheels, or electronics at every position.

Six-Bar Preview

A six-bar adds a second linkage stage on top of a four-bar, increasing reach and height without losing the parallel motion property.

The output link of the first four-bar becomes the ground link of the second stage
Result: more height and reach than a single four-bar, still maintains parallel end effector
Cost: more complexity, more flexure points, harder to tune PID accurately
Use when: a four-bar doesn't reach high enough and a DR4B is overengineered for the task

How It Works — Motion Path

Best for

✓ Low-to-mid scoring height (under 30")
✓ Mobile goal pickup and carry
✓ Tray deployment for stacking
✓ First lift for new builders
✓ Motor-limited robots (can run 1–2 motors)

Limitations

✗ Cannot reach maximum scoring heights
✗ Swings forward — eats into robot footprint
✗ Weight forward — tip risk under heavy load

💡

Historical note: The four-bar dominated Tipping Point (2021-22) for mobile goal pickup. The key insight was that scoring height did not justify DR4B complexity — a well-built four-bar is significantly faster to iterate and more reliable under match conditions.

Motor Budgeting

Typical four-bar: 1–2 V5 motors. Gear ratio recommendation: 100 RPM motor with 5:1 torque ratio for moderate loads. For heavy game objects (mobile goals), compound ratio of 15:1 or higher. Rubber band assist significantly reduces motor load — always add rubber bands opposing gravity.

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// Section 03

Six-Bar Lift 📈

More reach than a four-bar with manageable complexity. The six-bar was pioneered in VRC by AURA from New Zealand and adds one more link to extend both height and horizontal reach.

★ Intermediate 🧰 Engineer focus

A six-bar lift adds one extra link compared to a four-bar, extending the reach farther out and higher. The end effector still stays parallel throughout the motion. AURA (the New Zealand VRC/VEX U team) is widely credited with first applying the six-bar to VRC competition. It was later popularized by New Zealand teams and integrated into DR4B designs as the upper stage for extra height.

Six-bar advantages

✓ More reach than four-bar from same base
✓ Still manageable build complexity
✓ Commonly used as the top stage of a DR4B
✓ Good intermediate choice (2–3 motors)
✓ AURA-pioneered — well documented

Limitations

✗ More slop potential than four-bar
✗ Heavier than four-bar
✗ Still limited vs DR4B for maximum height
✗ Wider swing arc — more field footprint

💡

VRC history note: AURA was the first to apply the six-bar in VRC competition. The six-bar became especially important as the top stage of a DR4B (called a DR4B-6 or DR6B), giving extra height without the full complexity of adding a second four-bar.

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// Section 04

DR4B — Double Reverse Four-Bar 📈

The most powerful lift in VRC history. Two stacked four-bars rise nearly vertically, keeping weight centered. Dominated Skyrise and In The Zone. Screw joints are the secret.

⚡ Advanced 🧰 Engineer — 2+ weeks to build well

The DR4B (Double Reverse Four-Bar) stacks two four-bar stages — the second one faces the opposite direction as the first. This allows the lift to rise almost completely vertically rather than swinging forward, keeping the robot balanced and reaching significantly greater heights than a single four-bar or six-bar.

Screw Joints — The Secret to DR4B Stability

333A Tutorial — VEX Forum Community Standard

It is a well-known insight among veteran VRC teams: use screw joints whenever possible on bar lifts. A screw joint uses a partially-threaded screw as the pivot axle rather than a standard axle. This virtually eliminates slop, which translates into a more stable lift that rises with more precision and less wobble.

Using 2" screws as axles for the DR4B mid-section rigidly connects both sides of the lift while also serving as the pivot. This single change has the greatest impact on DR4B stability of anything you can do. The 333A tutorial on VEX Forum is the definitive reference — link below.

DR4B Weight Classes

SigBots Wiki defines four weight classes for DR4B design. Choose based on your game's height requirement and motor budget.

Heavyweight

Long arms, maximum bracing, very tall. Found in VEXU. Not practical for VRC motor limits. Study for design principles.

All-Round

2 V5 motors, mid-section power, decent bracing. Fits most VRC applications. Start here. 491A In The Zone is the reference.

Lightweight

Possibly 1 V5 motor, standoff bracing, half-cut channels. Good for lighter game objects (cones, caps). 5225A ITZ was a reference.

Featherweight

Bare minimum. Single centerline. Very space-efficient. Usually has a separate actuator on the end. 8000A ITZ was the example.

Key Build Rules

■ Build it twice. After your first DR4B, examine every mistake, document them, and rebuild. The second build will be dramatically better.

■ Minimize slop at every joint. Slop multiplies through the two stages. A 1mm slop at the base becomes 3–4mm at the top arm.

■ Do not use turntable bearings. They are too heavy and create excessive friction at the pivot points. Use standard bearings.

■ Cross-brace the mid-section. The middle connection between stages determines stability more than anything else. Box it.

■ Rubber bands are not optional. Always add bands to counteract gravity. Size the motor ratio assuming bands are installed.

🔗 DR4B Tutorial by 333A — VEX Forum →

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// Section 05

Chain Bar — Virtual Four-Bar 🔗

A chain and sprocket replace two of the four-bar links, keeping the end effector level with one arm instead of four. Pioneered by AURA (New Zealand) in Sack Attack. Simpler than a true four-bar. Popular in In The Zone and Tipping Point.

★ Intermediate 🧰 Engineer focus

A chain bar uses a single swinging arm and a chain-sprocket system to keep the end effector level — simulating the parallelism of a four-bar with one fewer physical bar. The key is a static (non-rotating) sprocket mounted at the lift tower. As the arm rises, the chain drives the end effector at the same rate, keeping it level without requiring a full four-bar linkage structure.

How to Build It

1

Static sprocket at the tower pivot. This is the most important step. The sprocket must be locked to the tower (does not rotate with the arm). Use a gear insert drilled out or a free-spinning sleeve — the arm's main gear rotates around it, the sprocket stays fixed.

2

Chain connects static sprocket to end effector sprocket. As the arm swings up, the chain rotates the end effector at exactly the rate needed to maintain level. Both sprockets must be the same size.

3

Remove excess chain links — replace with zip ties. Since the chain never travels fully over the sprocket (most of it just hangs), you can remove several links and replace them with a high-strength zip tie as the "chain link." This reduces weight and simplifies tensioning.

Chain bar advantages

✓ Simpler than true four-bar linkage
✓ Good reach with single arm
✓ Excellent for goal latching / claw mounts
✓ Compact when folded
✓ 1–2 motors sufficient

Limitations

✗ Chain can skip under load if tension wrong
✗ Less height than DR4B
✗ Static sprocket setup tricky for beginners
✗ More slop than rigid four-bar linkage

🏭

AURA origin: The chain bar (also called "chain lift" or "virtual four-bar") was pioneered by AURA, the New Zealand VEX team, in the Sack Attack season. Team 8059 adapted from the concept and the mechanism became a staple of VRC. The AURA archive at aura.org.nz has the original tutorials.

🔗 Chain Lift Tutorial — VEX Forum →

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// Section 02

Direct Arm / Pivot Arm

The simplest lift. One pivot point, one or two motors, an arm that swings. If the game lets you get away with it, this is the right choice.

How It Works

A direct arm rotates around a single fixed pivot — the simplest lift geometry.

Pros: minimal parts, easy to build, easy to code with motor presets
Cons: the end effector follows an arc, not a straight vertical path — height and horizontal reach both change as the arm rotates
Best for: claw mechanisms, dumpers, or any game requiring scoring at one consistent height
Motor requirement: increases with arm length — longer arms need higher gear reduction

When to Use It

Scoring height requires less than a 90–120° swing from floor to target
The end effector does not need to remain level (dumper, catapult, claw that releases)
You have limited motor budget and need the simplest possible mechanism
Speed matters more than precision — direct arms move fast because they are light

Gear Ratio for Arm Motors

Torque increases with arm length and load.

A long arm with a heavy game piece at the end requires significantly more torque than a short arm with no load
Calculate your gear ratio early: torque × gear ratio = output torque available
If the arm stalls under load, increase gear reduction or shorten the arm — don't just add motors

Arm Presets in Code

Use position presets driven by encoder counts rather than timing. Timing-based arm moves drift as batteries discharge. Encoder-based presets are repeatable across a match. Set presets for: floor pickup, carry position, scoring height, and safe travel height. See the Full Competition Code guide for implementation.

⚠️ Stop Building If…

Arm flex under load
Arm bends when carrying a piece. Add a brace or use a stiffer beam cross-section.

Motor overheating on hold
Arm is too heavy or ratio too low. Add a counterweight or increase reduction.

Pivot shaft walking
Shaft moves axially under load. Add a collar on each side of the pivot bearing.

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// Section 07

Lift Decision Guide ⚒

If the new game is a lifting game, which lift do you prototype first? Use this guide to decide based on game object characteristics before kickoff day research is complete.

Decision Framework

If the game requires...	First prototype	Historical precedent
Vertical stacking as high as possible	DR4B	Skyrise (2014-15), In The Zone (2017-18)
Picking up and moving goals / large objects	Four-Bar	Tipping Point (2021-22), Tower Takeover (2019-20)
Latching onto game elements + placing on posts	Chain Bar	In The Zone (2017-18), Sack Attack (2012-13)
Mid-height goal scoring (24"–36")	Six-Bar	In The Zone variants, various games
Endgame hang / climbing	Direct Arm or PTO	High Stakes (2024-25), Over Under (2023-24)

Motor Budget by Lift Type

Four-Bar / Chain Bar

1–2 V5 motors. Gear ratio 1:5 to 1:7 with rubber band assist. Can share a motor with intake using a PTO. Lowest motor cost.

Six-Bar

1–2 V5 motors. Slightly more torque needed than four-bar. Gear ratio 1:5 to 1:9. Rubber bands important — heavier arm.

DR4B

2 V5 motors recommended minimum. All-round class: motors at mid-section. Heavyweight: bottom + middle. 1:7 to 1:15. Rubber bands essential.

Direct Arm

1 V5 motor for light loads. 2 motors for heavier objects or endgame use. Simplest and fastest to prototype.

Preseason 4-Week Lift Build Plan

Week 1 — Analyze the game

Watch the reveal video 5+ times. Identify: max scoring height, required reach, whether end effector must stay level, expected cycle rate. Map these to the decision table above. Identify your first prototype lift before touching metal.

Week 2 — Prototype first lift

Build a rough prototype of your chosen lift type. Do not worry about aesthetics — test the motion path, check if scoring height is achievable, and identify any geometry problems. Iterate arm length and gear ratio.

Week 3 — Competition-quality build

Rebuild the lift with screw joints, proper bracing, and consistent geometry on both sides. Add rubber bands. Run 20+ consecutive cycle tests. Measure actual cycle time and compare to game analysis.

Week 4 — Integration and driver practice

Integrate the lift with intake and drivetrain. Add limit switches or position control. Begin timed driver practice runs. Document every design decision, test result, and change for the notebook.

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// Section 05

Reliability & Maintenance

A lift that works at 8:00 AM must also work at 3:00 PM. These are the failure modes that only appear after repeated cycles — which is when they matter most.

High-Cycle Failure Points

Pivot bearings wear loose. After hundreds of cycles, bearing flats can spin in their holes. Check by hand — any play in a pivot bearing means it needs to be tightened or replaced. Check pivots after every competition day.
Elastic stretches and loses assist force. Rubber bands fatigue. Mark your rubber band configuration and check tension before each match. Carry spares in the pit box with the same known count and stretch.
Shaft collars migrate inward. Collars on pivot shafts can walk under load. Loctite your shaft collar set screws and check at each pit stop.
Motor overtemperature on long cycles. A lift that is up for long periods with the motor holding position generates heat. Add a hold current limit in code — switch to a lower holding power once the target position is reached.

Pre-Match Lift Check

Manually move the lift through its full range — no binding, no grinding, smooth through the whole travel
Check all pivot screws — none backing out, all seated
Test elastic tension — same tension as after last successful match
Run 3 full cycles and verify position preset accuracy

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// Section 06

Testing Checklist & Notebook Evidence

Lifts fail under match conditions that never appear during casual testing. Run these tests before calling the lift competition-ready.

🔬 Lift Testing Checklist

20 consecutive full cycles (floor to max height and back)

Record: cycle time, any binding, any missed presets

Hold test: hold max height for 30 seconds under load

Check motor temperature afterward. Should be warm but not hot.

Preset accuracy: 10 repeats at each target height

All presets must land within 1° of target angle consistently

All pivot joints checked for play

Zero perceptible slop in any of the four (or eight) pivots

Elastic assist force verified and documented

Count rubber bands, note attachment points — reproducible after replacement

Robot size check with lift in starting position

Lift folded must fit within legal size limit

Notebook Evidence

CAD screenshot of lift at full extension with height dimension labeled
Comparison table: Direct arm vs four-bar vs six-bar vs DR4B with pros/cons for your specific game application — this is your decision matrix
Gear ratio calculation showing torque at pivot vs motor output — shows you verified the system will not stall
Cycle time data table from 20 repeat cycles — average and variance
Preset accuracy data — measured position vs. target at each preset height

🎰

Intake Design

Picking up what the lift scores

🔁

PTOs & Motor Sharing

Share drive motors with your lift

🤖

Full Competition Code

Arm presets, hold current, macros

⚙️

Mechanism Concept Sprint

CAD your lift before building

🔬 Check for Understanding

Your four-bar lift reaches its target height reliably in practice but fails to complete the movement 30% of the time in matches. What is the most likely cause?

The PID constants need re-tuning for the heavier load

Motor stall under real game-element load — practice testing doesn't apply the same resistance the mechanism encounters during scoring

The gear ratio is too high, reducing speed

A wiring fault that only shows up under high current draw

Correct. Practice testing rarely applies the same load as actual match use. A lift that works freely will stall when compressing against a goal structure or element. Test with realistic load and log stall current. This is also what judges want to see in your testing data.

📝

Notebook color guide for this mechanism:
■ Purple — Decision matrix comparing this mechanism against alternatives. Include weighted criteria and selection conclusion.
■ Orange — CAD screenshot, build notes, and any design changes made during assembly.
■ Cyan — Test protocol with hypothesis, data table (n≥5), and conclusions. Include the failure mode you found and how you addressed it.

⚙ STEM Highlight

Physics: Torque, Mechanical Advantage & Four-Bar Kinematics

A four-bar lift maintains a constant angle of the output link regardless of arm position — this is the key geometric property that keeps game elements from tipping during the lift. The geometry follows from the constraint that all four links form a parallelogram: as the driving link rotates, the output link translates without rotating. Torque requirements change throughout the range of motion as the effective moment arm changes, which is why lifts that hold comfortably at mid-height can stall at full extension.

Motor selection for lifts is a torque problem, not a speed problem. Calculate peak torque at the worst-case arm angle and select motors and gearing to provide at least 1.5× that value with a full game element load.

🎤 Interview line: "We selected our lift geometry using torque analysis — we calculated the worst-case load at maximum extension and chose our gear ratio to give us 1.5× safety margin. The test data in our notebook confirms we hit that target under match conditions."

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Related Guides

🎯 Flywheel Shooters → 🎰 Intake Design → 🚫 Stall Detection →

▶ Next Step

Lift selected. If your game requires a dedicated shooting mechanism, learn flywheel design next.

🎯 Flywheel Shooter Guide →

📝

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