Hopper and Bulk Storage
Some FRC games reward holding and scoring many game pieces per trip rather than cycling one at a time. When the robot needs to store 5, 10, or 50 game pieces internally before scoring them, you need a hopper. The hopper's job is to hold game pieces in bulk, keep them from jamming, and feed them reliably toward the scoring mechanism when it's time to score.
Hopper design looks simple (it's just a box, right?) but the details of funneling, agitation, and feeding are what separate a robot that dumps 30 balls into a goal from one that gets 15 balls stuck in a corner.
When you need a hopper
Not every game needs one. A hopper is relevant when:
The game piece is small enough that the robot can hold many at once (balls, small foam objects)
The scoring strategy benefits from high-volume dumps or rapid-fire sequences rather than one-at-a-time cycles
The field layout rewards collecting many pieces at once and scoring them all in one trip
If the game uses one large game piece at a time (like 2023 cones/cubes or 2024 notes), you don't need a hopper. You need a single-piece conveyor path (see the Conveyor Types page).
Hopper types
A large open volume inside the robot where game pieces sit on the bellypan or on a false floor. Pieces enter from the intake and pile up inside. Gravity and the robot's shape contain them.
How it works: The intake pushes pieces over the bumper and they fall into the open volume. The hopper walls (polycarb panels, aluminum sheet, or the frame itself) contain them. To feed the scorer, the robot drives to the scoring location and either dumps the pieces out or runs a floor conveyor to push them toward the scorer.
Key details:
The floor should be sloped toward the scoring outlet so pieces naturally roll or slide toward the exit
Use polycarbonate for the walls so you can see inside (helps with debugging and lets the driver see how full it is)
Round game pieces will roll around during driving. Add features to keep them from piling up in one corner (angled walls, powered agitators, sloped floor)
The intake opening needs to be large enough that pieces don't bounce off the bumper and back onto the field
Best for: Games with many small spherical pieces where volume matters more than precise piece positioning (2017, 2026).
FRC examples: 254's 2017 hopper (150+ fuel capacity), many 2026 fuel cell hoppers
Same as an open floor hopper but the floor itself is a conveyor (polycord, flat belt, or a series of rollers) that actively moves pieces toward the scoring outlet.
How it works: Pieces enter from the intake and land on the powered floor. When the conveyor runs, all pieces in the hopper move toward the outlet. The outlet feeds into the scoring mechanism (usually a vertical feeder leading to a shooter).
Key details:
The conveyor moves pieces in one direction only (toward the outlet)
A polycord conveyor floor is the most common implementation. Strands of polycord running the length of the hopper push pieces along.
The conveyor speed doesn't need to be fast. It just needs to keep pieces moving toward the outlet without stalling.
Angled funnel walls at the outlet narrow the stream from the full hopper width down to the width the scorer needs (usually one game piece wide for a shooter feed)
Advantages over passive floor: Pieces don't get stuck in corners. The conveyor actively clears the hopper. Feeding is more consistent because you're not relying on gravity and robot driving to shake pieces loose.
Disadvantages: More motors, more weight, more complexity.
FRC examples: 254's 2017 polycord floor hopper, many 2022 and 2026 powered hopper floors
A narrow channel that holds pieces in a single-file line. Pieces enter at one end and exit at the other. This is an indexer more than a hopper, holding 2 to 5 pieces in a controlled sequence.
How it works: The channel is sized so pieces can only pass through one at a time. Rollers or belts along the channel walls push pieces forward. The pieces stack up in order: first in, first out.
Key details:
The channel width and height must be carefully sized to the game piece. Too tight and pieces jam. Too loose and pieces rotate or stack on top of each other.
Powered walls (rollers, polycord, or belts) keep pieces moving through the channel
This approach gives you control over piece order and spacing, unlike a bulk hopper where pieces are jumbled
Best for: Games where you hold a small number of pieces (2 to 5) and need to feed them one at a time in a controlled manner (2022 with 1 to 2 cargo, 2024 with 1 to 2 notes). Also useful as the feed stage between a bulk hopper and a shooter.
FRC examples: Many 2022 cargo indexers holding 1 to 2 balls in a channel
Funneling
The hardest part of hopper design is getting pieces from a wide storage area into a narrow scoring outlet without jamming.
The jam problem: If 10 balls are all trying to reach a 1-ball-wide outlet at the same time, they wedge against each other at the funnel and nothing moves. This is the number one failure mode of hopper-based robots.
How to prevent jams:
Gradual funnel angle
Don't narrow from full hopper width to outlet width in a short distance. A long, gradual funnel gives pieces room to rearrange as they converge. Steep funnel walls cause bridging.
Powered funnel walls
Polycord or rollers on the funnel walls actively push pieces inward and break up bridges. Much more effective than passive walls.
Agitator
A roller, paddle, or set of spinning fingers near the outlet that breaks up jams by physically disrupting piece-to-piece contact. Even a simple hex shaft with zip ties sticking out can work as an agitator.
Sloped floor
Gravity assists the conveyor in moving pieces toward the outlet. Even a 5 to 10 degree slope helps.
Oversized outlet
If the scorer can accept pieces two or three wide and then single them out internally, the funnel doesn't need to narrow as aggressively.
Prototype the funnel with actual game pieces at actual capacity. A hopper that works with 5 balls will jam with 30 because the weight of the pile pushes pieces into each other at the funnel. Always test at maximum capacity.
Capacity planning
Bigger isn't always better. The hopper needs to hold enough pieces to justify the trip (more pieces per cycle = more points per cycle), but every cubic inch of hopper volume is space that could be used for other mechanisms.
How to size the hopper:
Estimate how many pieces you can realistically score per trip based on your shooter fire rate and match time
Add a buffer (if you can score 20 per trip, build the hopper to hold 25 so you're not intake-limited)
Model the hopper volume in CAD and verify the game pieces actually fit at the capacity you're targeting (game pieces don't pack perfectly, especially spheres)
Packing efficiency: Spheres only fill about 64% of a rectangular volume (random packing). If your hopper volume is 5000 cubic inches and the game piece is 100 cubic inches, you don't get 50 pieces. You get roughly 32. Account for this in your capacity calculations.
Materials and construction
Walls
Polycarbonate
Transparent (driver and pit crew can see inside), lightweight, impact resistant. 1/16" or 1/8" polycarb sheet.
Floor
Polycord on 3D printed hubs (powered) or polycarbonate sheet (passive)
Powered floor is better for feeding. Passive floor works if the hopper is sloped and the game piece rolls easily.
Funnel walls
Polycarbonate with optional polycord or rollers
Same transparency advantage. Add powered surfaces if jamming is an issue.
Frame
Aluminum tube or standoffs
The hopper attaches to the main robot frame. Use standoffs to create the hopper volume above the bellypan.
The hopper-to-scorer feed
The transition from the hopper outlet to the scoring mechanism is the most jam-prone part of the entire game piece path. This is where you need the most attention during prototyping.
Vertical feeder: For shooter-based robots, pieces typically need to go from a horizontal hopper up to a shooter mounted higher on the robot. This vertical path is usually a channel with powered rollers or belts on both sides that squeeze the piece and carry it upward. The compression between the two sides needs to be enough to lift the piece against gravity but not so much that the piece deforms or the motor stalls.
Direct feed: For robots that score by dumping (driving up to a goal and releasing pieces), the hopper outlet can just open. A trap door, hinged panel, or reversed conveyor floor pushes pieces out.
Single-file feed: For shooters that fire one piece at a time, the hopper needs to deliver pieces in single file. This means the funnel narrows to one-piece width, and the feed path between the funnel outlet and the shooter entrance is a constrained channel (see the Queue / Channel tab above).
Common issues
Pieces jam at the funnel
Funnel too steep, no agitation, or pieces bridging
Widen the funnel angle. Add powered walls or an agitator. Test at full capacity.
Pieces get stuck in corners
No slope on the floor, corners not rounded, or dead spots with no powered surface
Slope the floor toward the outlet. Round the corners with polycarb bends. Add polycord to the floor.
Pieces bounce out of the hopper
Intake velocity too high, or hopper walls too low
Add a polycarb lid or lip on the hopper walls. Reduce intake roller speed once the piece is past the bumper.
Feed to scorer is inconsistent
Speed mismatch between hopper conveyor and feeder, or compression wrong in vertical feed
Match conveyor speeds at the transition. Adjust compression in the feeder channel. Prototype this transition specifically.
Capacity lower than expected
Didn't account for packing efficiency of spheres
Recalculate with 60 to 65% packing efficiency for spheres. Increase hopper volume or accept lower capacity.
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