Week 10. Mechanical Design & Machine Design
Image Courtesy: Photo by Pavel Neznanov on Unsplash
This week comes with 2 parts. First part is Mechanical Design, which involves the process of transforming ideas and concepts into practical and functional designs for mechanical devices and systems. It encompasses the creation of 2D and 3D models, drafting and documentation, selection of appropriate materials, consideration of structural integrity and performance, and adherence to relevant standards and regulations.
Second part is the Machine design, which specifically deals with the design of machines that serve a particular purpose or perform specific functions. This could include anything from simple mechanisms and tools to complex industrial machinery and equipment. Machine design takes into account factors such as load requirements, kinematics, power transmission, safety considerations, and ergonomics.
Assignment Tasks:
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Group Assignment: Design a machine that includes a mechanism with actuation, automation and application. Build the mechanical parts and operate it manually.
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Individual Assignment: Document the group project and individual contribution.
Machine week was the most talked-about week since the beginning of this course, and everyone was excited. The first day was spent brainstorming, but after a few hours we realised that this may get out of hand because everyone has so many great ideas, most of which are quite exciting, and we need to build all those machines. But time is the enemy in this situation. So we decided to trim the ideas short, and by the end of the day, we had decided on this Scara Robot idea, which we got from How to Mechatronics..
Individual Assignment
Learning Process
What is Scara Robot?
The SCARA acronym stands for Selective Compliance Assembly Robot Arm or Selective Compliance Articulated Robot Arm. Scara is a type of Industrial robot. The SCARA robot is most commonly used for pick-and-place or assembly operations where high speed and high accuracy is required. Generally a SCARA robot can operate at higher speed and with optional cleanroom specification.
Our robot has 4 degrees of freedom and it’s driven by 4 NEMA 17 stepper motors. Additionally, it has a small servo motor for controlling the end effector. The brain of this SCARA robot is an Arduino Mega board which is paired with a CNC shield and DRV four A8825 stepper drivers for controlling the stepper motors.
Stepper Motor
A stepper motor is a type of electric motor that converts electrical pulses into precise mechanical motion. Unlike traditional electric motors that spin continuously, stepper motors move in small, precise steps or increments. A stepper motor consists of a rotor and a stator. The rotor is the rotating part of the motor, while the stator is the stationary part. The stator contains multiple coils of wire that are energized in a specific sequence to cause the rotor to move in small steps. Stepper motors can be classified into two main types: unipolar and bipolar. Unipolar stepper motors have two sets of coils that can be energized independently, while bipolar stepper motors have only one set of coils that must be energized in a specific sequence to achieve the desired motion. Stepper motors are often controlled by a specialized driver circuit that provides the necessary electrical signals to the motor. These signals control the timing and sequence of the electrical pulses that drive the motor, allowing precise control over its motion.
Servo Motor
A servo motor is a type of motor that is designed to provide precise control over the rotation of its output shaft. Unlike typical motors that rotate continuously, servo motors can rotate to a specific angle and hold that position until commanded to move again. This is achieved through the use of a feedback mechanism, such as a potentiometer or encoder, that provides information about the current position of the motor. The controller then uses this information to adjust the motor’s output and direct it to the desired position.
Servo motors come in various sizes and with different specifications, such as torque, speed, and voltage. They can be controlled using a variety of methods, including analog signals, pulse-width modulation (PWM), or digital communication protocols such as I2C or UART.
Gears
Gears are mechanical components that transmit power and motion between two rotating shafts. A gear consists of a wheel with teeth around its circumference, which meshes with another gear with teeth of the same size or different sizes. When one gear rotates, the teeth on the gear meshing with it cause the other gear to rotate as well. The size and shape of the teeth on the gears determine the speed, torque, and direction of the rotation.
The most common types of gears include spur gears, bevel gears, worm gears, and helical gears. Spur gears are the simplest and most common type, with teeth that are straight and parallel to the axis of rotation. Bevel gears are used to transmit power between shafts that are at an angle to each other. Worm gears are used to transmit power between perpendicular shafts, and they have a higher gear ratio than other types of gears. Helical gears have teeth that are angled along the gear’s axis, which reduces noise and vibration compared to spur gears.
Here in our project, we used a 4 nos Nema 17 stepper motor, one Servo motor, and a set of spur gears for the mechanism. So the first objective was to split the work among the team members. Everyone initially worked on everything due to the excitement. We suddenly understand that Time is our greatest enemy. Thus, we divided our entire project. I was initially tasked with designing the base, 3D printing it, and assembling it alongside Mr. Sreyas. I was collaborating with others while Sreyas created the design in Fusion so that it would also work with other parts.
The initial sketch was roughly made like this for our Scara Robot.
Even if we followed the How to Mechatronics approach exactly, we wouldn’t use every single component in the same way. We only use the items in our inventory to create our Scara. As a result, we chose to modify some design components, notably the bearing. Unfortunately, none of the thrust bearings included in the reference design are present in our inventory. As a result, Mr. Jojin, our instructor, proposed a design that may convert a linear bearing to a thrust bearing.
The design for the base was made by Sreyas and sent for 3D printing. Meanwhile, I was gathering all the other required parts from our inventory and sorting them out for easy installation.
3D printing of gears is done using Sindoh machine.
Sorting and organising each component makes it easier for us to quickly put everything together. After printing the Base portion and all the gears, we put everything in place. Beginning with belts and gears.
Part details of the base.
Connection details for the assembly to the base part.
Assembly of base part is shown in the video.
The base assembly is connecting with gears and belt. After that the whole assembly is connecting towards the top part.
While we were busy assembling the base part, Sibin began working on programming. So as soon as our assembly completed, we moved the item to Sibin and tested it there. It worked perfectly, and we were all thrilled.
In between me & Sibin went to help Praveen for assembling the Hand of Scara. He was designing and making the hand part in coordination with Mufeed.
At this point, everyone is aware of what we are doing and what the outcome will be. Following this, each of us was given certain tasks to complete, and I started designing the End effector. In Fusion 360, where Sreyas shared a group for the project, I began designing the end effector.
Initially, I designed the end effector in the same manner as our reference design. However, after printing the servo-connected section and assembling it, I discovered that the servo’s flange is not suitable for our design. I went back and created a new flange for the servo as a result, which required me to redesign some of the components that connect to the flange. A brief video shows a glimpse of the design of the end effector. Actual file is attached below.
Finally, after a number of revisions and a few failed 3D prints, I had a working model. which led to another amazing moment for all of us.
After this trial, I returned right away to finish the remaining half and create the pre-final, which was once more tested and approved.
After that, the task at hand was to cut the rod to the necessary length and join it to the Hand of the Scara. Following multiple tests, we made the decision to include a bush in the catching position as well, providing us with greater grip when picking an object. And that choice turned out to be the right one. We finally put everything together and successfully finished our group project.
And the completed Scara Robot.
Downloads
Download End Effector File here
Help Taken & Other References
Chat GPT used for doubt clearing and content helps.