Robot Moves In Any Direction On Ball Wheels

May 29, 2021 by Danie Conradie 5 Comments

The ability to move in any direction and turn on the spot is a helpful feature on robots that operate indoors around other objects. [James Bruton] demonstrated one possible solution in the form of a robot chassis that can move in any direction with three ball-shaped wheels.

The video after the break is part two of this series. Part one covered the ball wheels themselves, consisting of a pair of half-spheres that can rotate independently with a small roller in the center of each and a driven shaft through the center of the sphere. Three of these are arranged at 120° intervals around the center of the robot, with the main shafts driven by geared DC motors using belts. To move in a straight line some basic trigonometry is used to calculate the required relative speed of each wheel. An Arduino Mega is used to do the necessary calculation when receiving input from the wireless controller.

The motion is remarkably smooth, and we’d be interested to see how it compares with Mecanum and Omniwheels. It seems like the perfect platform for [James]’ Really Useful Robot. He hinted that he might mount a trash bin on it in the future. We would love to see an automatic trash-catching robot, similar to [StuffMadeHere]’s robotic basketball hoop. Continue reading “Robot Moves In Any Direction On Ball Wheels” →

Actively Balancing A Robot With A Gyroscope

May 17, 2021 by Danie Conradie 9 Comments

Self-balancing robots are a common hacker project, but we don’t often see them using spinning gyroscopes to achieve that balance. Robot master [James Bruton] decided to build a robotic platform with active gyroscopic stabilization, starting from a simple proof of concept.

A gyroscope can balance, but cannot actively counteract external forces directly. However, if the gyroscope is tilted around an axis it will exert a force perpendicular to that axis of tilt, known as gyroscopic precession. By tilting the gyroscope with an actuator, and orienting the gyroscope correctly, gyroscopic precession can be used for stabilization. This is known as a control moment gyroscope. [James] demonstrated this with a 3D printed proof of concept, which is used as an IMU to measure the angle of tilt, and use a PID loop to correct the imbalance with a servo actuating the gyroscope.

His second platform used a pair of gyroscopes spinning in opposite directions to compensate for any unintended gyroscopic precession along another axis. A pair of roller skate wheels allow the entire platform to roll along. Due to a slight imbalance in the platform, [James] noticed that the gyroscopes will continue to creep in one direction, until reaching the end-stops and falling over. By adding a second software controller to keep track of how much the gyroscopes have to move to maintain balance, it can continuously calculate and update the balancing point. This prevents the gyroscopes from hitting the end stops.

Control moment gyroscopes are commonly used for attitude control on spacecraft, and to reduce the rolling motion of boats in waves. [James] has plans to combine a control moment gyroscope with the more conventional balancing method, to balance a robot on a single wheel.

We’ve seen a two wheeled RC cars use gyroscopes before, but without the active control part.
Continue reading “Actively Balancing A Robot With A Gyroscope” →

Prioritising Mechanical Multiplexer

May 4, 2021 by Danie Conradie 17 Comments

When automating almost any moderately complex mechanical task, the actuators and drive electronics can get expensive quickly. Rather than using an actuator for every motion, mechanical multiplexing might be an option. [James Bruton] has considered using it in some of his many robotics projects, so he built a prioritizing mechanical multiplexer to demonstrate the concept.

The basic idea is to have a single actuator and dynamically switch between different outputs. For his demonstration, [James] used a motor mounted on a moving platform actuated by a lead screw that can engage a number of different output gears. Each output turns a dial, and the goal is to match the position of the dial to the position of a potentiometer. The “prioritizing” part comes in where a number of outputs need to be adjusted, and the system must choose which to do first. This quickly turns into a task scheduling problem, since there are a number of factors that can be used to determine the priority. See the video after the break to see different algorithms in action.

Instead of moving the actuator, all the outputs can connect to a single main shaft via clutches as required. Possible use cases for mechanical multiplexers include dispensing machines and production line automation. Apparently, the Armatron robotic arm sold by Radioshack in the ’80s used a similar system, controlling all its functions with a single motor.

[James] knows or two about robotics, having built many of them over the last few years. Just take a look at OpenDog and his Start Wars robots. Continue reading “Prioritising Mechanical Multiplexer” →

Robotic Gripper From A Squishy Ball

May 4, 2021 by Danie Conradie 11 Comments

Soft robotic grippers have some interesting use cases, but the industrial options are not cheap. [James Bruton] was fascinated by the $4000 “bean bag” gripper from Empire Robotics, so he decided to build his own.

The gripper is just a flexible rubber membrane filled with small beads. When it is pushed over a object and the air is sucked out, it holds all the beads together, molded to the shape of the object. For his version [James] used a soft rubber ball filled with BBs. To create a vacuum, he connected a large 200cc syringe to the ball via a hose, and actuated it with a high torque servo.

It worked well for small, light objects but failed on heavier, smooth objects with no edges to grip onto. This could possibly be improved if the size and weight of the beads/BBs are reduced.

For some more soft robotics, check out this soft 3D printed hand, and the flexible electrically driven actuators. Continue reading “Robotic Gripper From A Squishy Ball” →

Pool Noodle Robot Shines A Light On The Pros And Cons Of Soft Robots

February 27, 2021 by Danie Conradie 4 Comments

[James Bruton]’s impressive portfolio of robots has always used conventional rigid components, so he decided to take a bit of a detour and try his hand at a soft robot. Using a couple of few inflatable pool noodles for quick prototyping, his experiments quickly showed some of the strengths and weaknesses of soft robots.

Most of the soft robots we see require an external air source to inflate cells in the robot and make the limbs actuate. Taking inspiration from a recent Stanford research project, [James] decided to take an alternative approach, using partially inflated tubes and squeezing them in one section to make the other sections more rigid. He bought a couple of cheap pool noodles and experimented with different methods of turning them into actuators. The approach he settled on was a pair of noodles tied together side by side, and then folded in half by an elastic cord. As one end is squeezed by a servo bellows, the internal pressure overcomes the tension from the elastic cord, and the “elbow” straightens out.

[James] tested various arrangements of these limbs to build a working hexapod robot but to no avail. The simple actuating mechanism was simply too heavy, and could just lift itself slightly. This highlighted a common theme in almost all the soft pneumatic robots we’ve seen: they carry very little weight and are always tethered to an external air supply. The combination of stretchy materials and relatively low pressure compressed air can only handle small loads, at least in Earth gravity and above water. Continue reading “Pool Noodle Robot Shines A Light On The Pros And Cons Of Soft Robots” →

Modular Rover Platform Rolls On 3D Printed Flexible Tank Tracks

October 11, 2020 by Danie Conradie 12 Comments

Master of 3D printed robots, [James Bruton], plans to do some autonomous rover projects in the future, but first, he needed a modular rover platform. Everything is cooler with tank tracks, so he built a rover with flexible interlocking track sections.

The track sections are printed with flexible Ninjaflex filament. Each section has a tab designed to slot through two neighboring pieces. The ends of the tabs stick through on the inside of the track fit into slots on the drive wheel like gear teeth. This prevents the track from slipping under load. The Ninjaflex is almost too flexible, allowing the tracks to stretch and almost climb off the wheels, so [James] plans to experiment with some other materials in the future. The chassis consists of two 2020 T-slot extrusions, which allows convenient mounting of the wheel bogies and other components.

For initial driving tests [James] fitted two completely overpowered 1500 W brushless motors that he had on hand, which he plans to replace with smaller geared DC motors at a later stage.

A standard RC system is used for control, but it does not offer a simple way to control a skid steer vehicle. To solve this, [James] added an Arduino between the RC receiver and the motor ESC. It converts the PWM throttle and turn signal from the transmitter, and combines is into differential PWM outputs for the two ESCs.

Continue reading “Modular Rover Platform Rolls On 3D Printed Flexible Tank Tracks” →

Compliant Quadruped Legs Using Servos

March 22, 2020 by Danie Conradie 4 Comments

Walking robots that move smoothly are tricky to build and usually involve some sort of compliant leg mechanism — a robot limb that can rebound like natural physiology for much better movement than what a stiff machine can accomplish. In his everlasting quest to build a real working robot dog, [James Bruton] is working on an affordable and accessible Mini Robot Dog, starting with the compliant leg mechanism.

The 3D printed leg mechanism has two joints (hip and knee), with an RC servo to drive each. To make the joints compliant, both are spring-loaded to absorb external forces, and the deflection is sensed by a hall effect sensor with moving magnets on each side. Using the inputs from the hall effect sensor, the servo can follow the deflection and return to its original position smoothly after the force dissipates. This is a simple technique but it shows a lot of promise. See the video after the break.

A project can sometimes develop a life of its own, or in the case of [James]’s OpenDog, spawn experimentally evolving offspring. This is number four, and it’s designed to be a platform for learning how to make a quadruped walk properly, and to be simple and cheap enough for others to build. We’re looking forward to seeing how it turns out.

If you missed it, also check out this robot’s weird sibling, self-balancing Sonic.

Continue reading “Compliant Quadruped Legs Using Servos” →