End Effectors & Grippers
The gripper (or end effector) is the part of the robot that directly contacts and controls the game piece during scoring. It sits at the end of whatever positioning mechanism you're using (arm, elevator, wrist) and its job is to grab, hold, and release the game piece reliably. The right gripper type depends entirely on the game piece shape, weight, and how it needs to be placed.
The types
Two sets of powered rollers (or wheels) that spin inward to grab a game piece and outward to release it. The rollers apply continuous compression on the game piece while holding it.
How it works: The game piece enters between two sets of rollers spinning inward. The rollers grip the game piece through friction and compression, pulling it into the claw and holding it. To score, the rollers reverse and eject the game piece.
Key details:
The rollers need enough compression to hold the game piece securely but not so much that it deforms or jams
Roller speed on intake should be fast (grab the piece quickly), roller speed on eject is game-dependent (fast for shooting, slow for placing)
Compliant wheels (flex wheels, 30A to 50A durometer) work well because they conform to the game piece shape
The claw geometry (the spacing and angle of the roller sets) determines what shapes and sizes the gripper can handle
Advantages:
Active grip (rollers hold the piece continuously, not relying on a latch or spring)
Can intake and eject without any separate actuator (just reverse the motor)
Forgiving on alignment because the rollers actively pull the piece in
Works with soft, rigid, round, and irregular game pieces
Disadvantages:
Needs a motor dedicated to the rollers (adds weight at the end of the arm, which is the worst place for weight)
Wiring a motor at the end of a moving arm requires careful strain relief
More complex than passive grippers
Best for: Most game pieces. This is the most versatile gripper type and the default choice for the majority of FRC games.
FRC examples: Most 2023 Charged Up cube/cone grippers, many 2024 and 2025 end effectors, 2026 fuel cell grippers
Two jaws that are held closed by springs, elastic, or rubber bands. The game piece pushes the jaws open on entry, and the jaws snap closed around it. To release, a motor or servo opens the jaws against the spring force.
How it works: The jaws are normally closed (spring-loaded shut). When the robot drives the gripper into a game piece, the piece forces the jaws open against the spring. Once the piece is past the widest point, the jaws snap shut around it. To score, a small motor, servo, or cam opens the jaws and the piece falls out (or is pushed out by a small kicker).
Key details:
The spring force needs to be strong enough to hold the game piece but weak enough that the piece can push the jaws open on entry
The jaw geometry needs a funnel shape that guides the piece in from a range of angles
A sensor (beam break or limit switch) detects when the piece is captured so the driver knows they have it
Adding a small powered kicker or ejector roller inside the claw helps with controlled release
Advantages:
No motor needed to hold the game piece (springs do the work), which saves weight at the end of the arm
Simpler mechanism (fewer moving parts)
Can grab very quickly since the driver just drives into the piece
Disadvantages:
Less forgiving than roller claws because the piece has to physically push the jaws open
Can't actively pull the piece in (the robot has to drive into it)
Release is less controlled than roller ejection
Spring force is a compromise between holding strength and ease of entry
Best for: Rigid game pieces with a consistent shape that the jaws can close around predictably. Works well when weight at the end of the arm is critical.
FRC examples: Some 2023 Charged Up cone grippers, various simple claw designs
Two jaws that open and close under motor or servo power. Unlike a passive claw, the jaw position is actively controlled at all times.
How it works: A motor, servo, or linear actuator opens and closes two jaws. The driver (or software) commands the jaws to open, positions the gripper around the game piece, and commands them to close. The motor holds the jaws closed with active torque.
Key details:
The jaw geometry needs to match the game piece shape for a secure grip
The actuator needs enough force to hold the game piece against gravity and acceleration forces during arm movement
Adding compliant material (rubber, TPU padding) on the jaw surfaces improves grip and conformability
A sensor confirms the piece is captured (current spike on the jaw motor, beam break, or limit switch)
Advantages:
Full control over jaw position and gripping force
Can grip a wider range of game piece sizes by adjusting how far the jaws close
Can grip very tightly for secure transport
Disadvantages:
The motor must actively hold the jaws closed at all times (draws current continuously)
If the motor loses power or code crashes, the jaws may open and drop the game piece
More complex than passive designs
A motor at the end of the arm adds weight in the worst location
Best for: Games where you need precise grip control, variable jaw opening for different game piece sizes, or very secure holding during aggressive robot movement.
FRC examples: Various industrial-style gripper designs, some 2023 cone-specific grippers
A suction cup or vacuum chamber that grips the game piece by creating negative pressure against a flat surface.
How it works: A venturi (powered by compressed air from a pneumatic system) or a small vacuum pump creates suction at a cup or pad. The cup presses against the game piece, and the suction holds it. To release, the vacuum is vented.
Key details:
The game piece needs a relatively smooth, flat, non-porous surface for suction to work
Venturi-based suction requires a pneumatic system (compressor, tank, solenoid)
The suction cup size and shape needs to match the game piece surface
Suction force depends on cup area and vacuum level
Advantages:
Very simple mechanism at the gripper itself (just a cup, no moving parts)
Lightweight at the end of the arm
Can grip flat surfaces that are difficult for jaws or rollers
Disadvantages:
Only works on smooth, non-porous surfaces (won't work on fabric, foam, or perforated game pieces)
Requires a pneumatic system or vacuum pump (significant weight and complexity elsewhere on the robot)
Seal quality degrades with dust, debris, and wear
Slow engagement compared to rollers or passive jaws
Best for: Very specific game pieces with flat, smooth surfaces. Rare in FRC but occasionally the right solution for unusual game piece shapes.
How to choose
Game piece shape
Anything
Rigid, consistent shape
Anything
Flat, smooth surface only
Grip speed
Fast (rollers pull it in)
Fast (drive into it)
Moderate (position then close)
Slow (need seal)
Hold reliability
High (active rollers)
Medium (spring force only)
High (active motor)
Medium (seal dependent)
Weight at end of arm
Heavier (motor + rollers)
Lighter (springs only)
Heavier (motor + jaws)
Lightest (just a cup)
Release control
Excellent (reverse rollers at any speed)
Limited (jaws open, piece falls)
Good (open jaws at any speed)
Good (vent vacuum)
Complexity
Moderate
Low
Moderate
High (pneumatic system)
For most FRC games, roller claw is the default. It handles the widest range of game pieces, actively pulls pieces in (forgiving on alignment), and gives you precise control over both intake and ejection speed. Start with a roller claw unless you have a specific reason to use something else.
Designing for weight at the end of the arm
Whatever gripper you choose, minimizing its weight is critical because it sits at the end of the arm, which is the worst possible location for weight. Every gram at the tip of the arm creates a moment about the pivot that the arm motor and counterbalance have to fight.
Strategies to reduce gripper weight:
Move the motor off the arm. Use a zombie axle (see Arms and Pivots page) to power the gripper rollers from a motor on the frame, transmitting power through the pivot with a belt or chain. This moves the heaviest component (the motor) to the base of the robot.
Use smaller motors. If the gripper doesn't need much torque (light game pieces, low ejection speed), a smaller motor like the Kraken X44 or NEO 550 saves significant weight compared to a full-size Kraken X60.
3D print non-structural components. The gripper housing, roller hubs, and guide plates can be printed to save weight compared to aluminum. Only the structural elements (pivot pins, mounting bolts, shaft) need to be metal.
Use polycarbonate for plates. Polycarb is lighter than aluminum and works well for gripper side plates and guards where the loads are moderate.
Grip surfaces
The material on the jaw or roller surface affects how well the gripper holds the game piece.
Flex wheels (30A to 50A)
High
Roller claws for most game pieces. Conforms to the piece for maximum contact.
Compliant stars
High
Roller claws for rigid or irregular shapes. Star arms wrap around edges.
Grip tape on polycarb
Medium to high
Jaw surfaces or flat contact areas. Cheap, easy to replace.
TPU pads (3D printed)
Medium to high
Jaw surfaces on pinch grippers. Conforms to the piece and absorbs impact.
Bare aluminum or polycarb
Low
Only for guide surfaces where you want the piece to slide, not grip.
Sensor integration
The gripper needs to tell the software whether it has a game piece. Without this feedback, the driver is guessing, and the software can't automate handoffs or scoring sequences.
Recommended sensors:
Beam break across the game piece path inside the gripper. Simple and reliable. Triggers when the piece blocks the beam.
Photoelectric proximity sensor (Banner sensor) aimed at where the game piece sits when captured. One-sided (doesn't need a receiver across from it).
Motor current sensing as a backup. When a game piece loads into the gripper, the roller motor draws a current spike. Software can detect this spike as a "game piece acquired" signal. Not as reliable as a dedicated sensor but works as a secondary confirmation.
Mount the sensor inside the gripper body with a 3D printed housing (see the Sensor Integration page for mounting details). Protect it from game piece impacts and debris.
Ejection and scoring
How you release the game piece matters as much as how you grab it. Different scoring tasks require different ejection strategies:
Place on a shelf or peg
Slow roller reversal or gentle jaw open. The piece should be placed, not thrown. Controlled speed matters.
Drop into a bin or zone
Open jaws or stop rollers. Gravity does the work.
Shoot or launch
Fast roller reversal (the gripper becomes a short-range shooter). Roller surface speed determines ejection velocity.
Hand off to another mechanism
Coordinate roller speed with the receiving mechanism's intake speed so the piece transfers cleanly without jamming or bouncing.
Last updated
Was this helpful?