Weekly Assignments Final Project About me

WEEK 12

Mechanical Design, Machine Design

How the week started

How the week ended

Week 12’s Assignment

Mechanical Design (Part 1 of 2)

Group assignment:

  • Design a machine that includes mechanism + actuation + automation + application.
  • Build the mechanical parts and operate it manually.
  • Document the group project.

Individual assignment:

  • Document your individual contribution.

Machine Design (Part 2 of 2)

Group assignment:

  • Actuate and automate your machine.
  • Document the group project.

Individual assignment:

  • Document your individual contribution.

Link to group assignment

Introduction and Concept

The idea of a Lazy Susan table came up during a brainstorming session, brought forward by Mishael.

What is a Lazy Susan Table?

A Lazy Susan turntable on a dining table

A Lazy Susan is a rotating tray usually placed at the centre of a dining table so that food can be easily shared among everyone seated around it. The traditional version is manually turned by hand someone simply spins it to bring a dish closer to them.

Mechanism + Actuation + Automation + Application

We liked the mechanical working of the Lazy Susan concept and decided to keep that as the foundation. Building on the knowledge from our output week on motors and guided by input from our instructors, we settled on a stepper motor for actuation. Through further discussion, the idea of a voice-controlled turntable came up. At that point my mind was full of questions, how can that even be done? Will it actually work? How exactly would it work? Our instructors walked us through the options and told us we could either integrate Alexa to control the turntable with Xiao esp32 or use a Raspberry Pi to automate it.

I chose to work on the electronics part of the machine. We already had the basic idea that we needed a stepper motor and concluded that the NEMA 17 17HS19-2004S1 would be the right fit.

Working Principle

The rotary table is connected to Alexa. When a command such as "Alexa, ask Lazy Susan to give popcorn to Ardra" is given, where Lazy Susan is the turntable's name, popcorn is the compartment's name, and Ardra is the position's name. Alexa communicates with the Xiao ESP32-S3 via the MQTT protocol. This causes the specified compartment of the table to rotate to the requested position.

Block Diagram

Block diagram of the Lazy Susan electronics system
Created on draw.io

Working through the block diagram gave us a much clearer picture of how the electronics would be executed and how Alexa would integrate into the whole system.

On a personal note, I would love to have a version of this on my desk while doing craft work more like a tower with multiple layers so I can keep many things within reach. In my own design I would have just one home position so the compartments always rotate back to me.

References

Electronics

To design the circuit board I referred to Kalyani RK's Week 9 documentation and the corresponding group assignment page . The key difference was the microcontroller their board used an ATtiny, but for this project we needed Wi-Fi capability to connect with Alexa, so we went with the Xiao ESP32-S3 .

Schematic Drawing

1 / 5 The whole schematic diagram. The green dashed line is just to denote where the capacitor would be connected.
2 / 5 Since we are using a pluggable Xiao, I used a generic Xiao.
3 / 5 The footprint is Pololu breakout DRV8825. I previously used a generic footprint and faced errors. I have listed what went wrong.
4 / 5 I understood from my last board that adding an LED is always good. I added it to know if the PCB is getting power.
5 / 5 A voltage converter is connected to the Xiao, so the 12V from the screw terminal is converted to 5V. Two capacitors of 10µF are used.
The whole schematic diagram. The green dashed line is just to denote where the capacitor would be connected. Since we are using a pluggable Xiao, I used a generic Xiao. The footprint is Pololu breakout DRV8825. I previously used a generic footprint and faced errors. I have listed what went wrong. I understood from my last board that adding an LED is always good. I added it to know if the PCB is getting power. A voltage converter is connected to the Xiao, so the 12V from the screw terminal is converted to 5V. Two capacitors of 10µF are used.

The schematic was designed to ensure stable power delivery and clear module connections. A voltage converter steps down the input voltage, while capacitors help smooth fluctuations. The LED acts as a simple power indicator, making debugging easier.

PCB Layout

The PCB is single sided. Most of the pin connections use through hole components, so the Xiao, JST connectors, screw terminals, and motor driver are all placed on the back of the board. This allows their pins to be soldered directly on the copper side.

While designing the board, the power connections and the physical placement of the PCB within the assembly needed careful consideration. To understand this, I referred to the 3D model of the rotary table, focusing on the wire grooves and the intended mounting position.

Initially, the plan was to place the PCB on top of the 3D printed motor frame. However, this later changed, and the PCB is now mounted along the vertical face of the motor frame.

To ensure accuracy, Abhishek shared the DXF file of the 3D printed motor frame. This allowed me to mill the PCB to match the exact size and shape, including the 3 mm mounting holes.

1 / 4 The connector pins are kept along the edge of the PCB. This was done after referring to the design of the table. The power and ground wires have thicker mil traces than the rest.
2 / 4 The through hole components are flipped when tracing the path. The capacitor is placed such that it is close to the power and ground in the motor driver. The capacitor is bent and soldered to the backside of the PCB.
3 / 4 JST pins are used so the connection remains the same when plugging, but when tracing the path the component is flipped.
4 / 4 A closer look at the connections given.
The connector pins are kept along the edge of the PCB. This was done after referring to the design of the table. The power and ground wires have thicker mil traces than the rest. The through hole components are flipped when tracing the path. The capacitor is placed such that it is close to the power and ground in the motor driver. The capacitor is bent and soldered to the backside of the PCB. JST pins are used so the connection remains the same when plugging, but when tracing the path the component is flipped. A closer look at the connections given.

PCB 3D Model

The 3D model of the PCB done in KiCAD is shared to Abhishek, who was handling the design part of the machine.

1 / 1 3D model helps to understand the space taken by the PCB and where the outlets are.
3D model helps to understand the space taken by the PCB and where the outlets are.

Breakout Board — Hall Effect Sensor

The AH49E Linear Hall Effect Sensor breakout board was designed based on a reference, but with one important difference. The original reference board used a hall effect sensor that required two capacitors — 100 nF and 10 nF — along with a resistor. The AH49E that we actually used only needs a single 100 nF capacitor, so the design was simplified accordingly.

Hall Effect Breakout Board Reference: Muhammad Chettiyam — Week 11 Input Devices | Fab Academy Kochi 2024

Hall Effect Breakout Board

1 / 4 Hall effect sensor breakout board schematic
2 / 4 Hall effect sensor breakout board PCB layout
3 / 4 Hall effect sensor breakout board 3D view front
4 / 4 Hall effect sensor breakout board 3D view back
Hall effect sensor breakout board schematic Hall effect sensor breakout board PCB layout Hall effect sensor breakout board 3D view front Hall effect sensor breakout board 3D view back

The connection pins use through-hole mounting and are placed on the back of the PCB. The placement slot was designed with enough space for a JST connector and a groove for the wires to pass through cleanly. The hall effect sensor itself sits beneath the ring gear, while the magnet is mounted on the ring gear so the sensor can detect it as it rotates.

Components Used

Xiao ESP32-S3

Xiao ESP32-S3 pinout diagram
Xiao ESP32-S3 pinout diagram. Image source: Seeed Studio — Xiao ESP32-S3 Getting Started

Stepper Motor — NEMA 17 17HS19-2004S1

The NEMA 17 is a bipolar stepper motor with a high torque of 59 Ncm, which makes it well suited for driving a rotating table under load.

Buy: OMC StepperOnline — NEMA 17 17HS19-2004S1

NEMA 17 stepper motor
Image source: DC3D — NEMA 17 Stepper Motor

NEMA 17 17HS19-2004S1 Datasheet: omc-stepperonline.com — 17HS19-2004S1.pdf

Driver Module — DRV8825

Motors are power-hungry devices and can draw more current than is safe without protection. To address this, a motor driver is used to set the current limit and protect the motor. The DRV8825 also offers flexible step resolution — six options in total: full-step, half-step, quarter-step, eighth-step, sixteenth-step, and thirty-second-step modes. Each mode divides the motor's 200 steps per revolution differently, allowing for various levels of movement precision and smoothness.

DRV8825 Driver Module

1 / 2 DRV8825 wiring diagram
2 / 2 DRV8825 driver module pinout
DRV8825 wiring diagram DRV8825 driver module pinout

Image source: MicrocontrollersLab — DRV8825 Pinout
References: DRV8825 with ESP32 Tutorial — MicrocontrollersLab | DRV8825 with Arduino Tutorial — Last Minute Engineers

Electrolytic Capacitor

The capacitor used is a 63 V 100 µF polarised electrolytic capacitor — 8 × 12.5 mm — from Keltron. It is placed between the screw terminal and the motor driver, positioned as close as possible to the driver's power and GND pins to suppress voltage spikes. Since the DRV8825 is pluggable rather than soldered directly, there is enough clearance underneath it to seat the capacitor comfortably.

Electrolytic Capacitor

1 / 2 100µF electrolytic capacitor reference image
2 / 2 Keltron 63V 100µF electrolytic capacitor
100µF electrolytic capacitor reference image Keltron 63V 100µF electrolytic capacitor

Image source: Last Minute Engineers — DRV8825 Tutorial
Source: Ktron — 63 V 100 µF Electrolytic Capacitor Keltron

Hall Effect Sensor — AH49E Linear Hall Effect Sensor

The AH49E is used as a digital switch sensor in this project. Only one pole of the magnet — the south side — triggers the sensor. When the magnet passes over it, the sensor is either activated or deactivated depending on the polarity detected. In the context of this machine, the hall effect sensor is used to home the compartment, meaning it detects when the designated home position has been reached so the table knows exactly where it is in its rotation.

Reference: Understanding the Hall Effect Sensor: A Complete Guide — Evelta
Datasheet: AH49E Datasheet — PDF

learnings : The shape and size of the pcb directly affects the design, one has to aware of the components used and where they are placed on the pcb. a continuous coordination was necessary bwteen the machine designer and the pcb design
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