What is a Spherical Robot and How to Build One? | 5+ Important Applications

Spherical Robot

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The subject of discussion: Spherical Robot and its features

Spherical Robot | Spherical Rolling Robot

Spherical Robot Definition

A Spherical Robot or Spherical Rolling Robot, otherwise called a spherical mobile robot, is a ball-shaped robot that is mobile with a spherical exterior shape. A spherical robot includes a spherical-shaped shell that serves as the robot’s body and an internal driving unit generally known as Robot’s IDU that allows it to drive. Rolling over surfaces is how most spherical mobile robots fly.

spherical robot
Image Credits: Hossein Vahid Alizadeh, Spherical RobotCC BY-SA 4.0

The rolling motion is usually achieved by moving the robot’s centre of mass (i.e., a pendulum-driven system), but other driving mechanisms are also possible. Though, in a broader context, a spherical co-ordinate system in a stationary-robot, contains 2-rotary type and 1-prismatic type joints (example: Stanford Arm ).

The spherical shell is generally constructed of solid translucent plastic, opaque or flexible material for unique drive mechanisms and other special applications, this spherical shell will seal the robot from the external environment. There are re-configurable spherical robots that can turn the spherical surface into various configurations and perform tasks other than rolling.

Spherical robots can be self-contained or controlled remotely (teleoperated), because of the spherical body’s mobility and closed structure, nearly all spherical robots utilized wireless telecommunication between the internal drive unit and the external control unit (navigation system). The bulk of these robots’ power comes from a battery inside the robot, but several spherical robots use solar cells. Spherical mobile robots are classified according to their application or drive mechanism.

Spherical Robot Design

Ball-shaped objects have incredible maneuverability, making it worthwhile to explore the advancement of spherical robot designs. Another significant benefit of such robotics is their ability to withstand harsh environmental environments.

The basic idea of the robot drive system and architecture principle is seen below. A dome houses the robot’s interior components inside it(1). The base (2) serves as the foundation for all mechanical building components. Two DC motors provide a drive mechanism with wheels (6) mounted on the platform’s sides and in contact with the sphere.

Image Source: AUTOMATICS

The roller (3) has two degrees of freedom and can freely move around the sphere’s inner surface and the roller and base are connected by a shaft (4), which keeps all components in place. The spring (5) in the shaft’s middle ensures that the roller and the robot’s wheels never break in touch with the sphere’s inner surface.

The operating centre, control mechanisms, engines, and batteries are all housed on the chassis. This focusses on mass of robot, together with the construction’s centre of mass. The interior elements’ orientation relative to the sphere can be changed using the current configuration. Around the same time, the direction of the centre of mass shifts, causing the spheroid to shift.

The interaction between the individual modules is depicted in the diagram below:

Image Source: AUTOMATICS

Spherical Robot Configurations

Internal Cart Configuration

A four-wheel or three-wheel cart is mounted inside a sphere in a hamster ball configuration. Changes in velocity of wheel orientation may also be used to steer. This solution is comparatively easy though comprises a uniform shaped sphere; additionally, the wheels may miss contact with the sphere’s inner surface because of movement’s disruption.

Configuration with Internal Cart, Shaft and Roller

The cart’s wheels stay in contact with the sphere’s inner surface thanks to a shaft, spring, and roller combination and for the post-balanceing the structure, allowing the number of cartwheels to be limited to two. Omnibola, a well-known robot, has an inverted configuration with the drives on the spheroid’s top.

Pendulum Configuration with an Axle

A pendulum arrangement necessitates an axle to link the sphere to the internal structure. The axle provides a solid foundation for the pendulum, which can shift the centre of mass and produce both rotation and the sphere’s tilt. This approach constrains the robot’s stability, and the internal axle restricts the sphere’s rotating capacities.

Flywheel-based Design Configuration

For a limited period, a momentum or reaction wheel is used to tilt the internal pendulum or increase the sphere’s torque. Control Momentum Gyroscope (CMG) systems are used to rotate large satellites or space stations in more complex designs.

Multiple Mass-shifting Design Configuration

A series of actuators is used to propel multiple mass-shifting designs. The configuration shown here utilized for accurate position of the centre of mass within the sphere, but movement generation is complex and inefficient because of several actuators are operating continuously.

Wind-powered Robot Configuration

Environmentally friendly constructions are limited explicitly to particular uses only. This machinery that can redirect external force and utilize for robotic controlling application. The wind will maintain the Mars exploration robot research concept seen below, but travel direction cannot oppose wind movement.

Underwater Robot Configuration

Another example of a construction that needs a unique environment to function is an underwater robot. A spherical robot that navigates inside the piping of nuclear reactor cooling systems using internal valves and pumps was created to detect toxic material leakage and corrosion.

Deformable Body Design Configuration

Form-memory alloy (SMA) wire is a light material that, when heated, returns to its original shape. A spherical robot made of this material has a lot of stability, but its orientation is unpredictably erratic and difficult to manage.

MorpHex – a combination of spherical robot and hexapod

MorpHex is a ball-shaped robot with several legs across its body that can be assembled into a ball. The robot’s legs can also drive and rotate despite its circular form. Motion is restricted in the ball-shaped mode due to the complex structure of the solution and the unusual position of the robot’s legs. Furthermore, such a structure is vulnerable to adverse weather conditions.

Compared to all of the alternatives mentioned earlier, the architecture built on an internal cart with a shaft and roller has the most stability in terms of movement generation sophistication.

Control of Spherical Rolling Robot

Consider a three-dimensional pendulum suspended at the middle of a sphere for a spherical handheld robot. There are three standard control methods for such a device:

  1. Control by supply voltage to the motor.
  2. Control by the rotation speed of the motor.
  3. Control by the torque of the motor.

No supporting device is required for supply voltage control. Without any processing, the motor’s voltage is the lowest level supply. On the other hand, the other two methods necessitate the use of specific supportive structures. Even if the rotation parameters are not measured, the sphere rotation may be constant. As a result, concentrating on regulating the pendulum or motor concerning the sphere is sufficient.

Spherical Robot Work Envelope

Polar robots have a combined linear joint and two rotary joints and a twisting joint, and an arm attached to a robotic base. The axes construct a spherical work envelope and a polar coordinate system and are also known as spherical robots. This configuration’s working envelope sweeps out a volume between two incomplete spheres. The architecture physically limits the vertical and horizontal planes’ angular rotation. These constraints create the conical dead areas above and below the Robot structure.

Spherical Robot Example | Mobile Spherical Robot

They hope to integrate into it a GPS to follow specified routes to patrol and incorporate radar sensors to help move about obstacles and required to use GPS in it, so that it can patrol around pre-determined paths, as well as radar sensors to help it avoid obstacles.

Image Credit: Rotundus

What is a Spherical Robot used for? | Spherical Robot Applications

This type of robots are used for observation purpose, control application, aquatic and planetary exploration, re-habilitation, child education, and entertaining  purpose etc. The applications of spherical robots can be seen in amphibious robots to operate on both ground and water.

The general public will purchase commercial spherical robots. GroundBot, Roball, and QueBall are some of the latest commercial toys and Sphero’s BB-8, which is based on the robot character of the same name featured in the 2015 film Star Wars: The Force Awakens and Samsung Ballie is a personal robot that looks like a spherical rolling tennis ball and is unveiled at Samsung CES2020.

According to Sajid Sadi, vice president of Samsung’s research team, Ballie’s mobility allows it to react to an individual no matter where they are. Parents might ask Ballie to check up with their children to see if they’ve finished their homework or to keep track of what TV shows and movies they’re watching.

Some other basic applications of spherical robots are also listed below:

  1. Machine tool handling
  2. Spot welding
  3. Assembly operations
  4. Fettling machines
  5. Diecasting
  6. Gas welding
  7. Painting
  8. Arc welding

Spherical Robot Advantages and Disadvantages

Advantages

Spherical Robots are thought to have several advantages, including low-friction locomotion, constrained spaces, Omni-directional flight without ever overturning, and so on. Because of these benefits, spherical robots are more viable than conventional mobile robots. The benefits of a spherical robot are many, and its architecture is straightforward.

The sensors and instruments enclosed within the sphere are well protected. Rotundus is very light, weighing just around 25 kilogrammes, but the weight advantage is compounded when the rotundus is covered. As a result, it has a low density and can float. As a result, it can be used on-road, off-road, and even in water.

Sealing the bot has additional benefits beyond just allowing it to have a low density so that it can float; it also means that no sand gets inside to cause problems with the motors and other components. Electrical sparks (if any) on the interior are often sealed off, making the valuable robot in gas leak situations. The robot’s nature also makes it a very quiet operator.

Disadvantages

The Spherical Robot has a lower profile than other commercial robots, one of the main drawbacks. The robot’s work envelope is also limited due to the Z-axis’s lack of a linear actuator.

How to build a Spherical Robot?

The process of building a typical spherical robot configuration is listed below.

  1. Put together the drive system.
  2. Prepare the motors and connections, paying close attention to the sound and negative aspects. While you might weld wires directly to the motor and ESC, connectors make it a lot simpler in the long run.
  3. Install the gear by screwing the drive wheel adaptor into the gear and hub with the bore set screw hub (gear flange side down).
  4. Check the Orientation of the Wheels. Since the wheels are not symmetrical, they can be positioned in two different ways. On one foot, there are ridges and a shallower taper. The ridges on the spokes may be turned outwards.
  5. Place the fixed gear in the wheel, then the other half of the wheel adapter, and then securely screw it together.
  6. Mount the planetary engine to the motor. Make sure the mount is angled so that as the screws are twisted, they fall into the mount.
  7. Drive Shaft is attached. Ensure that the coupling is forced in as far as possible into the motor and that the shaft is pushed in as far as possible (this will result in the correct length later). Make sure the couplings are tightened so that the hex screws are seated on the shaft’s smooth side.
  8. Install the motor.
  9. With the flange on the outside of the channel, position the bearing in the motor assembly’s upper hole and this bearing has been sandwiched in-between the medium and the joint that holds it in place. The screws consistently secure each components ’til the joint is flush with the channel.
  10. Install the bearings in the joints. To each shaft, add a spacer. Install the pinion gear. Ensure that everything is pressed together closely on the shaft but not so tightly that friction is created.
  11. Assemble the wheel assembly and place it on the top shaft. Make sure the fixed screws are screwed onto the shafts’ smooth sides.
  12. Connect to the main body. Connect the ESCs and set up the power distribution. The receiver, Mixer, Capacitor, and Ballast should all be mounted.
  13. Cut a circle for the top of the sphere and glue the tabs on it.
Image Source: DIY Sphere Robot

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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