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Project Overview
Context & Motivation:
Context & Motivation:
This project was not intended to solve a specific real-world problem but to explore my interest in robotics and control systems. My goal was to design and build a platform that would strengthen my programming skills, allow me to experiment with control strategies, and expand my hands-on experience with electromechanical systems. To achieve this, I created a 3D-printed gimbal platform. Since no standard definition exists for this type of system, I have chosen to refer to it as a “turret platform.” Overall, this project gave me a valuable experience in mechanical design, electronic integration, and basic control programming.
System Components:
System Components:
Two 12V DC motors with hall encoders
Provide precise control over the slew and pitch axes.
120V AC to 12V DC converter
Supplies stable power to all electronics.
Two slip rings
Slip Ring 1 transfers power from the stationary base to the rotating components on the turntable.
SlipRing 2 powers electrical components mounted on the turret arm.
ESP32 microcontroller
Selected as the main controller for its versatility.
Features non-volatile SPI flash memory, allowing data retention even after power cycles.
The ESP32 is a 32-bit microcontroller, which enables more efficient handling of complex computations and greater precision in onboard calculations.
Two optical encoders
The optical encoders are used to establish the turret’s origin position and to track its movement relative to the origin in real time.
Hardware Block Diagram
Software:
VS Code (with PlatformIO extension): Programmed the ESP32 microcontroller.
Fusion 360: Designed the CAD model of the system.
Turntable System Design
Design Concept – Planetary Gear Approach
At the beginning of this project, one of my primary design challenges was integrating the electronics into the mechanical system. One option that I considered was to place all electronic components in the stationary base of the turret. However, achieving continuous rotation using this approach would have required slip rings with many electrical connections, which would have significantly increased both the cost and complexity of the turret. To avoid this issue, I decided to house the main electronics inside the rotating turntable.
With this design consideration in mind, my attention then turned to developing a mechanism to drive the turntable’s rotation. To accomplish this, a planetary gear system was selected.
Planetary Gear Motion
Drive System - Initial Design
With the drive system determined, the next step involved developing a test platform to evaluate the mechanical performance of the turntable drive mechanism.
The prototype assembly consists of the following components: base, ball bearing, slip ring, turntable, rotating gear, stationary gear, and motor.
(Figure 1)
The stationary gear and slip ring are rigidly mounted to the fixed base. The slip ring allows electrical power to pass from the stationary base to the rotating turntable. A ball bearing positioned between the base and turntable provides smooth rotational motion and structural alignment. The motor is mounted eccentrically on the turntable and has a smaller drive gear attached to its shaft. This gear engages the stationary gear to transmit torque, enabling controlled rotation of the turntable. (Figure 2)
Figure 1
Figure 2
Prototype Testing and Evaluation
The purpose of testing was to evaluate the system’s speed variation, control responsiveness, and movement stability.
The testing setup consisted of a power supply, motor driver, a 12 V DC motor with an encoder, and a 12 V-to-9 V DC converter to power the ESP32 microcontroller. To assess the system’s performance, I ran multiple programs targeting the key parameters under investigation. Figure 3 depicts one of the tests, in which the turret was controlled using a PS4 controller. This test was to observe its response to speed changes and to evaluate the control range.
Based on testing, several observations were made. One finding was that the bearing between the stationary base and the turntable was functioning as intended; however, loading on the turntable caused rotational (disc) friction. Additionally, the eccentric load from the motor, caused by the motor’s mass being offset from the rotational axis, generated a moment on the turntable, which further contributed to friction and uneven motion during testing.
Based on the test results, it was concluded that the final design required the incorporation of a thrust bearing to compensate for the eccentric load and minimize rotational friction.
Figure 3
Turntable - Final Design
Based on the observations and conclusions from bench testing, I began designing the turntable for the turret. Below, I highlight some of the key features of the final design.
Reinforced Concrete Base Plate
Due to the turret’s rotational inertia from rapid directional changes, I designed the baseplate to increase overall mass for improved stability. I incorporated a reservoir that can be filled with concrete, adding weight to counteract the torque generated during rotation. Since concrete typically requires reinforcement to handle tensile stresses, I embedded bolts with spaced nuts into the baseplate, which are cast into the concrete to provide additional structural support.
Integrated Ball Bearings (Thrust Bearing)
To reduce friction between the turntable and the base, I designed channels for ball bearings to accommodate both the distributed load of the components and the eccentric load from the motor, which generates a moment on the system. Additionally, I incorporated a secondary bearing channel beneath the base-attached plate to counteract off-center loads, minimizing tilting and wobbling during rotation.
Integrated Optical Switch
For positional tracking and homing capabilities, I integrated an optical switch into the turntable. A corresponding tab attached to the stationary base serves as the trigger. As the turntable rotates, the optical switch detects when it passes over the tab and sends a signal to the microcontroller, enabling precise homing.
Pitch Mechanism Design (Belt and Pulley System):
Design Concept – Belt and Pulley System
With the turntable design complete, I shifted my focus to developing the mechanism that would drive the turret's pitch, while maintaining the goal of continuous rotation.
There were several possible approaches to achieve this. The simplest option would have been to attach a motor directly to one of the turret arms to rotate the pitch platform. However, I decided against this for two reasons. First, it would not have been challenging enough for the scope of this project, as my goal was to push my design and problem-solving skills. Second, the approach would have negatively impacted the visual appearance of the final design. I wanted a sleek, enclosed system with minimal visible wiring.
To accomplish this challenge, I began exploring methods to transmit rotational motion through one of the turret arms. There were a few possible approaches:
Design a gear train along the arm to drive the pitch component.
Design a belt and pulley system for power transmission to the pitch component.
I ultimately chose the pulley and belt approach due to the limited precision of 3D-printed gears. A 3D-printed gear train would likely introduce significant backlash, as the backlash from each gear would accumulate, resulting in a larger overall error at the output. This would reduce the accuracy between the motor’s rotation and the resulting pitch movement.
Pulley Calculations
Similar to gears, pulleys operate on ratios that can be used to manipulate the output speed and torque of a system. However, unlike gears, the direction of rotation between two pulleys remains the same.
Before ordering the pulleys, I needed to calculate the appropriate pulley sizes for my application. I wanted to incorporate speed reduction into the system to achieve higher torque output at the pitch component, allowing future modules with greater mass to be supported effectively.
To determine the required pulley sizes, I considered several factors:
Factor 1: Common sizes of continuous-loop GT2 belts.
Factor 2: Common GT2 pulley sizes.
Factor 3: Spatial constraints — all components needed to fit within the turret arm.
Factor 4: Integration of a belt-tensioning mechanism.
I began by creating a preliminary design of the turret arm to establish the boundaries within which all components had to fit. With these parameters defined, I selected the GT2 pulleys for my design and began calculating the required belt lengths.
Equations for Belt Length and Center Distance Calculations
Initial Design and Evaluation
With the belt and pulley calculations complete, I proceeded to create a prototype turret arm to test functionality and verify my calculations. Since the pulleys I had ordered had not yet arrived, I designed the pulleys in CAD and 3D-printed them for testing. (Figure 4)
The test assembly consisted of two face plates representing the inside and outside of the turret arm, a 12 V DC motor with an encoder, three pulleys, and a belt-tensioning mechanism. (Figure 5)
For testing, I programmed a simple code to run the motor at different speeds and in both directions. The purpose of this was to analyze the motor’s performance as well as the overall system performance.
During testing, I made several observations:
The 3D-printed pulleys, although functional, often slipped under high torque. This produced an awful sound, making it easy to detect.
The belt tensioner was not very effective and tended to slip away from the belt over time, causing the belt to become loose.
With the knowledge gained from testing, I began designing the actual pulley system that would be integrated into the turret arm.
Figure 4
Figure 5
Pitch Mechanism - Final Design
This part of the project was the most challenging, as it required multiple prototypes and 3D prints to achieve a final design that met both my functional and aesthetic goals. Outlined below are some key aspects of the design that I would like to highlight.
Belt Tensioners
For tensioning the belts, I designed a screw-based tensioning mechanism. As the screw is tightened, it draws the pulley in, applying tension to the belt. These screws are accessible from the outside of the turret arm, making belt tensioning quick and easy without the need to disassemble the turret.
Arm Assembly
The pulley system consists of a total of eight pulleys, two belts, and two belt-tensioning mechanisms, all housed within a very confined space, making the design highly complex.
Turret Arm Integration on Turntable
With the arm design completed, the motor can now be fully contained within the turntable, achieving my primary goal for the turret arm design.
Second Turret Arm – Slip Ring Integration
Design Concept - Slip Ring Integration
With the turret arm that drives the pitch platform complete, I next focused on designing the opposite turret arm to incorporate a mechanism for transferring electrical signals from the microcontroller to the module on the pitch platform, enabling module control. Similar to the turntable design, I used a slip ring to enable continuous pitch motion. I selected a slip ring with six electrical connections to meet this requirement.
Initial Design and Evaluation
With the slip ring in hand, I needed to design the second turret arm to hold it while connecting its rotating portion to the pitch platform. To do this, I first designed and built a test fixture to evaluate my initial idea for attaching the slip ring to the rotating platform.
The test assembly consisted of a replica of the turret arm upper portion, the slip ring, a slip ring coupler, a coupler plate, a bearing, and the pitch platform connection. The bearing sits in the turret arm replica, while the coupler attaches to the slip ring and features a cross pattern that meshes with the coupler plate. The coupler plate connects to the pitch platform, transferring rotational motion from the pitch platform to the slip ring. (Figure 6)
This design allows the motion of the pitch platform to be effectively transferred to the slip ring.
Figure 6
Second Turret Arm - Final Design
After testing the slip ring integration design, I proceeded to design the second turret arm. Below are key components and features of the final design that I would like to highlight.
Slip Ring/Optical Switch Integration
With the slip ring integrated, I wanted to be able to set a pitch origin. To achieve this, I modified the slip ring coupler plate to include an external tab that crosses the optical switch, indicating the pitch origin.
Arm Assembly
In addition to the slip ring mount, I designed a separate mount for the motor driver, which allows for more space within the turntable to accommodate other electrical components and improve cable management.
Turret Arm Integration
With the second turret arm design complete, the arm fits seamlessly into the turntable, fully housing the electronics and achieving the primary goal of the design.
Turret CAD model Assembly Drawings
Subassembly 1: Base
Subassembly 3: Pitch Arm
Subassembly 2: Turntable
Subassembly 4: Slip Ring Arm
Electronics Integration
With the majority of the mechanical design finalized, the focus shifted to integrating the electronic components and designing a lid to securely enclose and protect them. Figures below illustrate the installation and integration.
Turret Turntable cover
For the turntable electronics cover, I designed a lid that provides access to the microcontroller for program uploads and wire connection checks. The lid includes magnets to prevent accidental opening and ensures it snaps securely back into place.
Conclusion – Final Thoughts
Designing and building the turret was both rewarding and challenging at times. This project pushed me to apply the engineering knowledge I’ve gained from my classes and the skills I've developed through previous projects. With the turret now complete and fully functional, I would like to reflect on the overall process, including improvements I could make and things I might have done differently.
A key lesson I learned is that when designing a system with many complex components, small details can make or break a design. Taking a step back to analyze the entire system often helps identify hidden issues that aren’t immediately apparent. Another key takeaway is to always consider the real-world assembly process; what fits in CAD doesn’t always fit in real life. Finally, keeping detailed documentation proved to be a lifesaver during this project. With so many complex components and design decisions along the way, having clear notes and records made it much easier to troubleshoot issues, track changes, and understand why certain choices were made.
Looking back, there are a few things I would do differently. The first is the turntable mechanism. Although it is functional, I noticed a slight backlash between the Turntable drive gear and the base gear. To address this, I would have designed the gears with a higher pressure angle to reduce backlash. Another change I would have made is my choice of motors and motor drivers. While the motor driver is working, it doesn’t drive the motors until enough voltage is supplied to them, which makes fine-tuning difficult.
Overall, this was a fun and rewarding project, and I am very satisfied with the outcome. I can now apply the lessons and skills I’ve gained from this experience to my future endeavors.
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