How do compliant wheels work in an intake?

Compliant wheels are flexible rubber wheels primarily used in intakes, not drivetrains . They work by rotating along an axis to propel game elements into a collection bin . Compliant wheel intakes are particularly effective for controlling large game elements with flat surfaces, such as cubes or rectangular prisms . They offer adjustability and forgiveness for different game element orientations and intake angles .

The durometer, or hardness, of the rubber affects traction and longevity; a lower durometer is recommended for maximum grip when intaking game elements . Compliant wheel intakes can be designed as spring-loaded, allowing them to pivot to accommodate a game element and then snap back, or as locked intakes where the wheels are fixed in place . These intakes operate at slower RPMs than surgical tubing intakes and generally require more torque, as they are designed to pick up one element at a time . While very controllable and good at propelling elements to a desired location, they are not generally used for picking up small elements and can only pick up one specific element shape .

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Types of Intake > Roller and Wheeled Intakes > Solid Wheel Intake

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Solid wheel intakes use wheels such as grip and traction wheels to pick up game elements. They can be effective in picking up large game elements which do not have much tolerance difference.

However, compliant wheel intakes generally will be more effective because compliant wheels offer more adjustability and forgiveness for the game elements. Compliant wheels also accounting for different game element orientations (the game pieces can get rotated when being controlled) and intake angles (the orientation of the game piece before it reaches the intake).

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Types of Intake > Roller and Wheeled Intakes

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Roller and wheeled intakes refer to types of intakes which work by having some sort of hard or pliable object rotate along an axis. Wheeled intakes use different kinds of wheels (solid traction, compliant, or foam wheels) that propel the game element to the collection bin. Roller intakes are wider, and can sometimes intake more than one game element.

Term: Compliant Wheel — A compliant wheel is a flexible rubber wheel that is primarily used for intakes. These are NOT designed for use in drivetrains.

The available bore options vary depending on the vendor. As with the compliant wheels, durometer (hardness of rubber) affects both traction and longevity, sacrificing one for the other. However, in the case of intakes, a lower durometer is recommended to have maximum grippiness for intaking game elements.

Durometer refers to the hardness of rubber. Having a high durometer translates to a harder rubber surface, more durability, but less traction. A low durometer means a softer rubber, worse durability, but improved traction.

Examples of compliant wheel are Andymark's Compliant Wheels, and goBILDA's Gecko Wheels.

(Figure: A 2" compliant wheel)

(Figure: A 4" compliant wheel)

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Types of Intake > Roller and Wheeled Intakes > Compliant Wheel Intake

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Spring-Loaded Intakes: A spring-loaded intake is able to pivot in order to accommodate a game element when it is passing through the intake, but will snap back when the element has gone through. A spring-loaded intake requires more thought, but guarantees that the intake wheel will always be in contact with the desired element.

A locked intake simply means that the wheels are locked into place and cannot pivot.

The compliant wheel intake is most commonly used with large game elements such as the glyphs in the 2017-2018 season, Relic Recovery. Compliant wheel intakes excel at controlling elements with flat surfaces such as cubes or rectangular prisms. They suffer at picking up balls.

In this game, robots had to pick up glyphs, which were 6 inch foam cubes, from the center pit and place them in the cryptobox. This game had many wheeled intakes primarily because the wheels had consistent and controllable contact with the glyphs. Wheeled intakes were able to propel the glyphs in a consistent fashion from the point of contact to the deposit plate, which would flip up to deposit the glyphs.

Wheeled intakes can be spring-loaded or locked into place. Teams could choose one or mix; in Relic Recovery, some teams spring-loaded the set of wheels that made contact first, and then had a fixed set in the back. This is up to the design team's choosing.

Wheeled intakes operate at much slower RPM than surgical tubing intakes, as wheeled intakes are meant to pick up one element at a time. They generally require more torque than a surgical tubing intake, which is geared for speed.

Term: Surgical Tubing — Surgical tubing is generally latex or rubber tubing. Its most common use case is in active intakes, and has been popular among teams for many seasons. Surgical tubing has a hollow center and is sold in different diameters and wall thicknesses. Teams can experiment with different kinds of surgical tubing, as well as adding polyurethane tubing (clear tubing that is stiffer than rubber or latex tubing) in order to make the tubing more stiff.

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Types of Intake > Roller and Wheeled Intakes > Foam Wheel Intake

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A foam wheel intake has the same principles as a compliant wheel intake, except that it uses foam wheels. It is generally recommended that teams stick to compliant wheels as they are grippier and easier to control.

(Figure: 6299 ViperBots QuadX, Res-Q)

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Types of Intake > Roller and Wheeled Intakes > Compliant Wheel Intake > Advantages

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Very controllable
Propels elements to desired location
Great at picking up large elements

Picks up only one element at a time
Elements can get jammed in a bad position
Not generally used for picking up small elements
Can generally only pick up one specific element shape

(Figure: 9971 LanBros, Finalist Alliance First Pick (Detroit), Relic Recovery, springloaded)

(Figure: 8680 Kraken-Pinion, Relic Recovery)

(Figure: 2856 Tesseract, Relic Recovery, 2 & 4 in. compliant wheels, 2 in. omni wheels)

(Figure: 11115 Gluten Free, Finalist Alliance Captain (Detroit), Relic Recovery, springloaded)

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Active Intake

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There's one main rule when it comes to intakes in FTC: you need one. Before diving in, what is an intake in the first place?

Intake A mechanism designed to pick up game elements using some component of rotational motion powered by a motor.

An intake is differentiated from a claw as an intake does not grasp individual game elements using a pinching motion, but rather sucks the element in through a variety of means such as wheels, tubes, etc.

There are multiple parts of an effective intake: intake geometry, intake type and material, and speed. However, a common rule of them is the faster the intake, often the more effective it is. For example, near the end of Rover Ruckus, many of the top performing teams used a 3.7:1 (1600 RPM) motor or a 5.2:1 (1000 RPM) motor on their intake.

Tip: While not a necessity, it is highly recommended that teams dedicate at least one motor to their intake if possible.

Attention: When it comes to intakes: "Touch it, own it" is a really valuable concept.

When your intake comes in contact with game elements, you want it to instantly control them. You should design with a margin for error, both in the orientation of the game piece and in the alignment of the robot. For example, look at FRC® Team 694's ball intake on their 2019 robot:

(Figure: FRC 694 StuyPulse, Deep Space)

When this robot drives up to a ball, it barely has to point itself at the ball before the ball is instantly locked in between the two rows of wheels. What makes it so effective is the immense amount of testing that went into its design. The team tried a number of intake shapes, initially building with wood and rubber bands, and recorded which shapes were most effective. By testing their intake design out before competition, they didn't have to guess whether it would work as intended: they put it on the field with confidence.

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