What is Mecanum Wheeled Robot? | 5+ Important Types of Wheeled Robots

Mecanum Wheeled Robot

The Subject of discussion: An Introduction to Wheeled Robot and working of Mecanum Wheeled Robot

Wheeled Robot

What is a Wheeled Robot?

Wheeled robots are robots that use motorized wheels to maneuver across the ground to move. This design is further straightforward than legged robots. In flat terrain, it is easier to design, build, and program for travel using wheel-based design, because of this, they can be better controlled than other .

A wheeled robot- Pioneer 3 AT; Image Source: Jiuguang Wang, CC BY-SA 3.0 , via Wikimedia Commons

The drawbacks of wheeled robots are that obstacles, such as rough ground, steep drops, or low friction areas, can not be well navigated. Wheeled robots are the most common in the consumer market, offering low cost and simplicity with their differential steering.

Robots may have any no of wheels, but minimum 3-wheels are sufficient for equilibrium and additional wheels will add to the balance, but additional mechanisms would be needed to hold all the wheels in the ground if the ground is not level. An interesting type of wheeled robot is the Mecanum wheeled robot, about which we shall learn in the further content.

How does it Navigate?

Many wheeled robots use differential steering, which uses wheels for the movement that are operated separately. By spinning each wheel at a different speed, they can change direction and therefore do not need additional steering movement. These extra wheels may be added wheels not powered by a motor, helping to keep it balanced. This is a concept that we call a differential wheeled robot.

When both the wheel move in the same direction and speed, the robot will travel straight tracks and to rotate the robot about the center of the axis, the wheels should rotate opposite the same speed. For any other combination of rotational speed and direction, the robot’s center of rotation may lie anywhere on the straight line joining the contact points of the wheels with the ground.

Since the robot’s path depends on the two driven wheels’ rotation rate and direction, these quantities should be precisely sensed and regulated.

A differentially steered robot is analogous to the differential gears employed in different automobiles in that both wheels might have variable rotational speed. Still, a differentially steered system would have both wheels driven, unlike the differential gearing system.

In robotics, differential wheeled robots are broadly utilized, as their motion is simple for programming and could be well-controlled. Differential steering is mostly used for its economic price and simple design.

Types of Wheeled Robot

1-wheeled Robot

It isn’t easy to keep a one-wheeled robot upright without external support due to its single point of contact with the ground. There are examples of the one-wheeled robot in experimental robot prototypes. A spherical wheel proves to be advantageous over a traditional disc wheel because it allows the robot to drive on a spherical contour in any direction. Gyroscopes and counter-torque mechanisms are generally used to keep this kind of robot balanced on the ground. Non-holonomic movement is generated through stabilization and tilting using flywheels.

2-wheeled Robot

These types of robots have either a parallel wheel configuration called dicycles or a tandem configuration where one wheel is in front of the other. Each wheel should have a tilt sensor and a wheel encoder to calculate the tilt angle and keep track of the base location, respectively.

Two-wheeled robots are more challenging to balance than other types since to stay upright, they must keep going and center of gravity of the robot’s body is held below the axle.

Due to their efficient nature, two-wheel robots are ubiquitous nowadays. You need to drive about with a few motors & two wheels, but they also have their disadvantages. They utilize 2-wheels and ought to sustain their up-right position. Two-wheeled robots are more difficult to balance than other types and to make it more stable, electrically chargeable battery is placed under It’s bodies.

ROOMBAS are 2-wheeled vacuum cleaner that robotically move around and capable to clean up the roomsurface. They use a front touch sensor and a top-mounted infrared sensor. Segways is an electric vehicles that is capable to self-balance the electric cycle; Ghost Rider is the only 2-wheeled robot contended the Darpa Grand 2005 Challenge.

ROOMBA Robot; Image Source: Larry D. Moore, CC BY-SA 3.0 , via Wikimedia Commons

3-wheeled Robot

There are two types of 3-wheeled robots:

  • Differentially steered. (2-driven wheels with an additional one free rotating wheel that is used to hold the body for balancing.)
  • 2-powered wheels with a single source and the 3rd wheel with power steering purpose.
3- wheeled robot’s arrangement

The robot’s direction might be vary in differentially steered wheels by changing the proportional rotation’s rates of the two wheels that are driven distinctly. The robot will go straight if both the wheels are pushed in the same direction and speed. Otherwise, the center-of-rotation can drop where in the line-joining the two-wheels, depending on the rotation speed and direction.

Within the triangle created by the wheels, the center of gravity in this sort of robot has to lie. The robot can tip over if as well hefty mass is placed on the side of the freely rotating wheel.

4-wheeled Robot

  • 2 powered, 2 free rotating wheels- Same as the differentially steered ones above, but for extra balance with two free rotating wheels. In the meantime gravity center has to stay within the four wheels’ rectangle, it is more stable than the three-wheel version. This leaves a more significant amount of usable space and the center of gravity is advised to keep at the rectangle’s center.
2 powered, 2 free rotating wheels
  • 2-by-2 powered wheels for tank-like movement- this sort of robot employ two pairs of driven wheel. Each pair rotates in the same direction (connected by a line). Having all the wheels spin at the same speed is the tricky part of this propulsion. The slower one will slip if the wheels in a pair don’t run at the same pace (inefficient). The robot won’t drive straight if the couples don’t run at the same pace. Any car-like steering will have to incorporate a good design.
2-by-2 powered wheels
  • Car-like steering- This technique enables the robot to transform in the identical way as of car movement. This is a much more rigid approach to build, making it far harder for dead reckoning. Use of a combustion engine to power a robot is advantageous compared to the previous methods because it utilizes only two output axles with speed and direction of rotation, independent of each other.
Car-like steering

5 or more wheeled vehicles

In the case of more gigantic robots. Though not very much realistic.

The design complications increase with the increase in the number of driven wheels because it is challenging to maintain the same turn speed for the robot to move forward. The robot is likely to deviate from the straight-line path if the left and right wheels’ speed is not the same for a differentially steered robot. The difference in velocity between wheels on the same side causes the slowest wheel to slip.

Often an extra free odometric rotary wheel is attached to the robot. More precisely, this tests how the robot moves. Odometry excludes slip and other motions on the driven wheels and may therefore be incorrect.

The Mars Rovers (Sojourner, Spirit, Opportunity), for instance, is 6-wheeled robot that, after landing, maneuver across Martianterrain and they are used to assess territory, exciting landmarks and to observe the surface of Mars. They have a suspension system that keeps the surface in contact with all six wheels and lets them cross hills and sandy terrain.

Omni-wheeled Robot

One more choice for wheeled robot is that it is easier to have Omni Wheels for robots with all wheels are not mounting on the same axis. Like several smaller wheels that make up a big one, an Omni wheel, the smaller ones have an axis perpendicular to the core wheel’s axis. This enables the wheels to drive in two directions and move holonomically, ensuring that they can move instantaneously in any direction.

Typical Omni wheel Configuration; Image Source: Pacaro at English Wikipedia, Public domain, via Wikimedia Commons

Unlike a vehicle that’s non-holonomically going and needs to be in motion to change its heading, Omni wheeled robots can travel in any direction from any angle without rotating in advance and the triangular platform is utilized for some Omniwheeled robots, with the 3-wheels aligned at 60-degree angles.

The benefits of three wheels in comparison to four wheels are that they are economical and certainity to have 3 points on the equal plane, signifing that each wheel in contact with the ground, and solitary one wheel is in the direction of movement, and can rotate. The disadvantages of Omni wheels utilization is that they have comparatively less efficiency as all wheels are not moving in the direction of motion, that may be reason of friction loss too. For the reason that of the angle measurements of travel, they are more computationally complex in nature.

One such famously utilized Omni-wheeled robot is the Mecanum Wheeled Robot.

Mecanum Wheeled Robot

What is Mecanum Wheel?

The Mecanum wheel is an omnidirectional wheel that allows the robotic vehicle to move on either side and the general forward and backward movement. Bengt Erland Ilon developed the Mecanum wheel idea when he was employed as an Engineer in a company in Sweden. He patented the idea in the United States on November 13, 1972. The other widespread name for it is the Swedish wheel or Ilon wheel, after the founder’s name.

Design of Mecanum Wheeled Robot

The Mecanum wheel is centered on a tireless wheel that is obliquely connected to its rim’s entire circumference with a set of rubberized external rollers. Usually, these set of rubberized external rollers each have an axis of rotation to the wheel plane arround 45° and with the axis line arround 45°.

In Every Mecanum wheel robot it’s wheel has its powertrain and is independently non-steering type. The powertrain is responsible for generating a propelling force that maintains a 90° angle with the roller axle during the spinning motion that can be divided into its longitudinal and transverse vector components.

Design of Mecanum Wheel; Image Source: Mrmw, CC0, via Wikimedia Commons

The typical configuration of a Mecanum Wheeled Robot has a four-wheel arrangement, which is evident in one example of Omni-directional mobile robots called the URANUS. It has alternating left and right side rollers with axes parallel to the vehicle frame’s diagonal at the wheel top. One of the Mecanum Wheeled Robot: URANUS has shown below.

Mecanum Wheeled Robot: URANUS Robot; Image Source: Gwpcmu, CC BY 3.0 , via Wikimedia Commons

The Mecanum Wheeled Robots to move with minimum speed requirements. For example:

  • Driving all 4 wheels at the equal speed in the identical direction can lead to forwarding/backward motion, as the longitudinal force vectors will add together, though the transverse vectors will cancel eachother.
  • Driving (all at the identical speed) both wheels in one direction on one side and other in the opposite direction. This would result in the vehicle’s stationary rotation as the transverse vectors cancel out while the longitudinal vectors pair to produce a torque around the vehicle’s central vertical axis.
  • To move sideways, rotate the diagonal wheels in the same direction at the same speed and the other two diagonal wheels will be  in contrary. Doing so results in the addition of transverse vectors while canceling out the longitudinal vectors.

Combinations of different types of independent wheel motion in the Mecanum Wheeled Robot, aided with a certain amount of rotation facilitate vehicle movement in every possible direction.

Applications of Mecanum Wheeled Robot

The omnidirectional movement and extreme maneuverability in congested environments provided by Mecanum Wheeled Robot have found their applications in the following domain:

  • Mecanum Wheeled Robot is utilized in various Military Activity and Search and Rescue Missions.
  • Mecanum Wheeled Robot is also useful in planetary explorations, for example- MarsCruiserOne, which is a conceptual habitable rover for future space missions.
  • Mecanum Wheeled Robot is also employed in mine operations, which requires good mobility in confined spaces.
  • Mecanum Wheeled Robot Forklifts is utilized for goods transportation for it’s efficient mobility and management of warehouse spaces.
  • Mecanum Wheeled Robot are used in innovative Wheelchair project, for example- OMNI, as Mecanum Wheeled Robot facilitates high mobility in a complex environment and higher degrees of independence.

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About Esha Chakraborty

I have a background in Aerospace Engineering, currently working towards the application of Robotics in the Defense and the Space Science Industry. I am a continuous learner and my passion for creative arts keeps me inclined towards designing novel engineering concepts.
With robots substituting almost all human actions in the future, I like to bring to my readers the foundational aspects of the subject in an easy yet informative manner. I also like to keep updated with the advancements in the aerospace industry simultaneously.

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