mecan drive

We recommend building a mecanum drive using 3 to 4-inch diameter wheels with ball bearing supported rollers configured in an "X" shape, where the rollers angle toward the center when viewed from above . Game Manual 0 explains that this "X" configuration allows the force vectors of the offset rollers to combine for movement in any direction, though friction means the robot will drive slightly faster forwards and backwards than it strafes . Game Manual 0 highlights the goBILDA Mecanum Wheels v2 (96mm) and the REV Robotics Mecanum Wheels (75mm) as the gold standard options because their ball bearing rollers minimize friction to provide superior strafing performance compared to wheels with bushings .

While Game Manual 0 notes that mecanum drives offer excellent maneuverability, agility, and acceleration, they suffer from lower traction than standard traction wheels, making the robot susceptible to being pushed around by defenders and unable to traverse rough terrain . Additionally, because each of the four wheels must be powered independently, the system lacks redundancy if a motor or drive connection fails .

To program the drivetrain, developers can use inverse kinematics to calculate individual wheel velocities from the desired robot velocity, or forward kinematics to determine the robot's overall velocity from its wheel speeds . For advanced software implementation, teams can refer to the restricted resources on FTCLib WPILib Kinematics for Mecanum Drive Kinematics (https://docs.ftclib.org/kinematics/wpilib-kinematics/mecanum-drive-kinematics) and Mecanum Drive Odometry (https://docs.ftclib.org/kinematics/wpilib-kinematics/mecanum-drive-odometry), as well as the REV Robotics Docs on Programming Mecanum - Simplified (https://docs.revrobotics.com/duo-control/hello-robot-blocks/part-4-going-beyond/programming-mecanum-simplified) and Programming Mecanum - Refined (https://docs.revrobotics.com/duo-control/hello-robot-blocks/part-4-going-beyond/programming-mecanum-refined) . For physical assembly and setup, teams can consult the restricted REV Robotics Docs on Mecanum Wheel Setup and Behavior (https://docs.revrobotics.com/duo-build/ftc-starter-kit-mecanum-drivetrain/mecanum-wheel-setup-and-behavior) and the Mecanum Drivetrain Kit (https://docs.revrobotics.com/duo-build/mecanum-drivetrain-kit-mecanum-drivetrain) .

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Sources16

Mecanum TeleOp

Game Manual 0·CC BY-NC 4.0

Note: Some common COTS mecanum drivetrain kits are the goBILDA Strafer Chassis Kit (https://www.gobilda.com/strafer-chassis-kit-v5/) and the REV Mecanum Drivetrain Kit (https://www.revrobotics.com/rev-45-2470/).

A standard mecanum drive configuration possesses 4 mecanum wheels oriented in an "X" shape. This means that the rollers are angled towards the center when looking at it from above. This configuration allows one to add up the force vectors generated by the offset rollers and derive movement in any direction. It is important to note that because of friction, perfect movement isn't possible in every direction, so a mecanum drivetrain will be able to drive slightly faster forwards/backwards than any other directions. Combining translation and rotation will also result in slower movement.

In the image above, vectors 1, 2, 3, and 4 are the force vectors created by the mecanum wheels when the chassis is instructed to drive towards the top of the image. All motors are driving forward. The blue and red lines are their X and Y components, respectively. Here are a few examples of how the wheels must be driven to achieve different movements:

Attention: It is strongly advised to not hardcode these movements in; there is a much better way described below that allows for true holonomic movement and is much more elegant.

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WPILib Kinematics > Mecanum Drive Kinematics

This source does not publish a licence, so its text is not reproduced here. Open the source to read it.

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Kinematics > Mecanum Drive > Inverse Kinematics

Game Manual 0·CC BY-NC 4.0

The inverse kinematics of a mecanum drive relate the desired velocity of the robot to the velocity required on the wheels. These are as follows:

vfl = vf - vs - (2r_b · ω)

vbl = vf + vs - (2r_b · ω)

vbr = vf - vs + (2r_b · ω)

vfr = vf + vs + (2r_b · ω)

Open Game Manual 0

Kinematics > Mecanum Drive > Forward Kinematics

Game Manual 0·CC BY-NC 4.0

The forward kinematics of a mecanum drive relate the velocity of the wheels to the forward, strafe, and rotational velocities of the robot, relative to itself. These are as follows:

vf = frac{v_fr + v_fl + v_br + v_bl}{4}

vs = frac{v_bl + v_fr - v_fl - v_br}{4}

ω = frac{v_br + v_fr - v_fl - v_bl}{4*2r_b}

Open Game Manual 0

Holonomic Drivetrains > Mecanum Drive > Mecanum Wheels Miniguide

Game Manual 0·CC BY-NC 4.0

One of the most important features of a mecanum wheel is the mechanism that allows the roller to spin---either bushings or ball bearings. Mecanums which use ball bearings strafe better than those which use bushings, as the rollers can spin with less friction.

Note: In the past, some teams have invested in 6 inch diameter mecanum wheels. These are generally much more expensive and generally do not provide significant performance benefits. We highly recommend sticking with wheels that are between 3 and 4 inches in diameter.

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Holonomic Drivetrains > Mecanum Drive > Advantages

Game Manual 0·CC BY-NC 4.0

Fantastic maneuverability and agility due to strafing, can avoid defense very well
Good acceleration, can have high top speed
Very versatile drivetrain for nearly any game

Suffers in traction, as mecanum rollers have a lower coefficient of friction than traction wheels; cannot traverse terrain
Able to be pushed around on defense
Wheels must be powered independently, so there is no redundancy

CAD Examples of Mecanum Drive (Click to expand) goBILDA COTS Click here to explore this model in OnShape online CAD (https://cad.onshape.com/documents/45549489f570f3694569a2df/w/85ff26b9fca4988ebc4df3b4/e/df9bcea72fcdd7e4aee4134b)

REV COTS Click here to explore this model in OnShape online CAD (https://cad.onshape.com/documents/45549489f570f3694569a2df/w/85ff26b9fca4988ebc4df3b4/e/b8d4a6cfe4f26c5170f40a6c)

goBILDA Custom Click here to explore this model in OnShape online CAD (https://cad.onshape.com/documents/45549489f570f3694569a2df/w/85ff26b9fca4988ebc4df3b4/e/cc2df2fbce0e9ca393696b54)

REV Custom Click here to explore this model in OnShape online CAD (https://cad.onshape.com/documents/45549489f570f3694569a2df/w/85ff26b9fca4988ebc4df3b4/e/40c3266dab2e444011cce79c)

(Figure: Configuration for mecanum wheels, courtesy goBILDA)

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WPILib Kinematics > Mecanum Drive Odometry

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Programming Mecanum - Simplified | REV DUO Control System

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Programming Mecanum - Refined | REV DUO Control System

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Mecanum Wheel Setup and Behaviour | REV DUO Build System

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Mecanum Wheel Setup and Behavior | REV DUO Build System

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Mecanum Wheel Setup and Behavior | REV DUO Build System

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Mecanum Drivetrain Kit | REV DUO Build System

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Channel Drivetrain - Mecanum Upgrade | REV DUO Build System

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Mecanum Drivetrain V2 | REV DUO Build System

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Holonomic Drivetrains > Mecanum Drive > Mecanum Wheels Miniguide > Recommended

Game Manual 0·CC BY-NC 4.0

These wheels are the gold standard of mecanum wheels, if you are buying new mecanum wheels there is very little reason to buy any mecanum wheels not from this section.

goBILDA Mecanum Wheels v2 (https://www.gobilda.com/96mm-mecanum-wheel-set-70a-durometer-bearing-supported-rollers/) ($127.49 with team discount): The goBILDA v2 Mecanum Wheels are the gold standard for teams wanting a quality design in all aspects. They feature a 96mm diameter and a thickness of 38mm, with ball bearing supported, 70A durometer rollers that provide excellent strafing performance. With the use of recessed 16x16mm and 32x32mm holes, these wheels have the largest amount of mounting options and can fit all shaft styles commonly used in FTC®.
REV Robotics Mecanum Wheels (https://www.revrobotics.com/rev-45-1655/) ($127.50 with team discount): The REV Robotics Mecanum Wheels come in at only 75mm in diameter, providing a smaller mecanum wheel option to FTC teams; however, they are not the thinnest option at 40.8mm thick. They feature ball bearing supported rollers that provide exceptional strafing capabilities and traction. The hole pattern featured on these wheels is compatible with Andymark Nubs as well as the REV Robotics Universal Hex Adapter v2 (which is included); however, in order to use other shaft options the use of an adapter or physical modification will likely be required.

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