Intakes and claws
How robots pick game elements up — rollers, compliant wheels and claws — and the design rules that make an intake grab every time.
By the end you can
- Compare active intakes and claws and choose one for a given game element
- Size an intake roller's surface speed against the robot's drive speed
- Apply the reliability, consistency and controllability rules to an intake design
Almost every point in FTC starts with picking something up. The intake is the mechanism that turns "the robot is near a game element" into "the robot has the game element" — and the faster and more reliably it does that, the more cycles you get per match.
A phrase you will hear around FIRST is "touch it, own it": the moment any part of the intake touches a game element, the element should end up inside the robot. Every design decision in this lesson is in service of that.
Two families: active intakes and claws
- Active intake
- A powered mechanism — spinning rollers, wheels or tubing — that pulls game elements in continuously while it runs. The driver gets close and the intake does the rest.
- Claw (passive intake)
- A gripper that closes on one game element, usually driven by a servo. The driver must line up, close, and lift.
| Active intake | Claw | |
|---|---|---|
| Speed of collection | Fast — drive over and it is in | Slower — line up, then grip |
| Driver precision needed | Low | High |
| Small or many pieces | Excellent | Poor |
| Large, odd-shaped pieces | Can struggle | Excellent |
| Uses a motor port | Usually | Usually not — servos only |
| Moving parts | More | Fewer |
Game Manual 0 puts it bluntly: for small game pieces, active intakes beat claws in nearly every game. Claws win for large, awkward elements that rollers cannot control, and when you are short of motor ports.
Active intakes
Compliant wheels and rollers
- Compliant wheel
- A soft, flexible rubber wheel made for intakes. It squashes against a game element to grip it, which makes it forgiving of pieces arriving slightly off-centre or at an angle.
- Durometer
- How hard a rubber is. Softer (lower durometer) grips better but wears faster; harder lasts longer but grips less. Intakes usually want the softer end.
The key idea is compression. Set the wheels so the gap between them (or between the wheels and a wall) is a little smaller than the game element. The wheels then squash onto it and grip. Too little compression and the wheels spin against the piece without moving it; too much and the piece jams or the motor stalls.
You will not get the compression right on paper. Build the first prototype with adjustable spacing — slots instead of holes, or extrusion you can slide — and tune it with real game elements.
Tubing intakes
Some teams use loops of surgical tubing spun on a roller. Game Manual 0 notes these either need high speed (around 800–1000+ RPM) because the tubing is floppy, or stiffer tubing inside the surgical tubing at a lower speed. They are excellent at sweeping up small pieces, but they can grab more pieces than you wanted.
Worked example: roller surface speed
What matters for an intake roller is not its RPM but how fast its surface moves:
surface speed = RPM × π × diameterSay your drivetrain is a goBILDA Strafer, which goBILDA rates at about 5.6 ft/s, and your intake uses 2-inch compliant wheels.
Driven straight off a 312 RPM motor:
surface speed = 312 × π × 2 in ≈ 1,960 in/min ≈ 2.7 ft/sThe robot can drive into a game element twice as fast as the roller surface can pull it in. Drive in at full speed and the intake pushes the piece along the floor instead of swallowing it.
Driven off a 1150 RPM motor instead:
surface speed = 1150 × π × 2 in ≈ 7,230 in/min ≈ 10.0 ft/sNow the roller surface is moving well over the drive speed, so the piece gets pulled in even when the driver arrives fast.
Faster is not automatically better
A roller that is too fast can fling pieces back out or past where they are meant to stop. Match the speed to the piece, and expect to tune it. The gear ratio tool is handy for working out the reduction between a fast motor and the roller.
Claws
A claw is often the first mechanism a team thinks of. It can be the right answer, especially for large pieces. A few things make the difference between a claw that grabs reliably and one that drops things:
- A wide mouth. Make the open claw much wider than the game element, so the driver does not have to be precise.
- Funnelling. Angled guides that centre the element as the claw closes reduce how accurate the driver has to be.
- Grippy, slightly soft contact faces. Hard plastic on hard plastic slips. A layer of rubber or foam increases friction and conforms to the shape.
- Protect the servo. The claw is on the end of the robot and gets hit. Support the servo properly and do not make its output shaft carry the impact.
Rules that apply to every intake
Game Manual 0 groups intake design around a few principles. They make a good review checklist for any design:
- Reliable. Intakes have lots of moving parts and often stick outside the robot, where they get hit. Either build them strong, or make them flexible enough to bend and spring back — polycarbonate and spring-loaded mounts are common.
- Consistent. Pick up elements the same way every time, from every angle they can be lying at — and pick up the right number.
- Controllable. Once the element is in, it stays where you want it. The driver should be able to clear a jam without help, and ideally see the element (clear polycarbonate helps).
- Efficient. Get the element from the floor to where it scores by the shortest path. Every extra handoff is another place for it to get stuck.
Picking up too many is a real mistake
Most FTC games limit how many game elements a robot may control at once, and the penalty for going over can cost more than the extra piece is worth. Design the intake to stop at the limit. The exact number changes every season, so check the current Competition Manual.
Check yourself
Your robot drives at about 5 ft/s. Its intake roller surface moves at about 3 ft/s. What happens when the driver drives into a game element at full speed?
Check yourself
This season's game element is a large, irregular object, robots may only control one at a time, and every motor port is already used. What is the best starting point?
Next
Picking a piece up is half the job. Next: lifting it to where it scores, with linear slides.
Sources and further reading
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