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Design and Preliminary Testing of a Three-Degree-of-Freedom Motion Table
Section 0: System Overview
An aircraft in three-dimensional space exhibits six degrees of freedom—three translational (surge, sway, heave) and three rotational (roll, pitch, yaw). In training, research, and industrial testing, motion simulators are built with varying degrees of freedom. A 6-DoF simulator reproduces all six axes of motion, while a 3-DoF simulator captures only the rotational movements of roll, pitch, and yaw. This document presents both the mechanical design and preliminary testing of our custom 3-DoF motion table.
Section I: Mechanical Design & Hardware Specifications
1.1 Frame & Materials
The table’s structural frame is constructed from aluminum extrusion profiles, selected for their light weight, high strength, and excellent thermal conductivity.
- Manufacturing:
High-pressure extrusion of heated aluminum billets through custom dies yields precise, uniform cross-sections. - Key Properties:
- Strength-to-Weight Ratio: Ideal for dynamic, load-bearing applications.
- Corrosion Resistance & Aesthetics: Durable silvery finish conveys a modern appearance.
- Thermal Conductivity: Enhances energy efficiency compared to steel.
Figure 1. Cross-section and extruded view of aluminum profile.
1.2 Inertial Measurement Unit (IMU)
A MEMS-based MPU-6050 module integrates a 3-axis accelerometer and 3-axis gyroscope with an onboard Digital Motion Processor (DMP), enabling advanced 9-axis sensor-fusion and overcoming alignment challenges of discrete sensors.
| Sensor | Range Options | Resolution | Current Draw | Key Features |
|---|---|---|---|---|
| Accelerometer | ±2g, ±4g, ±8g, ±16g | 16-bit | 500 µA (active) | Shock detection, programmable interrupt, 10 000 g shock tolerance |
| Gyroscope | ±250, ±500, ±1 000, ±2 000 °/s | 16-bit | 3.6 mA (active), 5 µA (standby) | Programmable digital low-pass filter |
Figure 2. MPU-6050 internal block diagram showing accelerometer and gyroscope axes.
1.3 Ferrite Bead EMI Filter
A passive ferrite bead choke acts as a low-pass filter to attenuate high-frequency EMI on power and data cables:
- EMI Suppression: Reduces switching-noise emissions on USB or power leads.
- Interference Immunity: Blocks external RF noise (e.g., cell-phone interference).
- Operation Principle: Forms series inductance with the cable; impedance rises with frequency.
Ferrite bead: passive EMI-suppression component
1.4 Wiring Diagram
| Component | Wire Count | Signal Names |
|---|---|---|
| Gyroscope | 4 | GND, 5 V, SCL, SDA |
| Motor | 3 | Power & control lines |
| Encoder | 4 | GND, 5 V, SCL, SDA |
| Slip Ring | 12 | Various signal lines |
Figure 3. Simplified wiring schematic for sensors, motors, and slip ring.
Section II: ANSYS Simulation
In the first phase, static and dynamic analyses were performed in ANSYS on the 3-DoF table model.
- Structural Stability: Verified that the frame endures expected loading without yielding or excessive deformation.
- Dynamic Behavior: Identified natural frequencies and mode shapes to ensure operation avoids resonant excitation.
Control-System Implications:
Results dictated the use of a high-performance microcontroller featuring:
- High Processing Frequency for real-time kinematics and control.
- Low-Latency I/O to manage concurrent stepper- and DC-motor feedback loops with minimal jitter.
Section III: Torque & Speed Performance Testing
Bench tests on the selected stepper and DC motors yielded the following:
- Static Torque–Speed Curve: Stall torque vs. rotational speed across the operating range.
- Load-Dependent Speed Test: RPM variation under incremental torque loads.
From these data we determined:
- Maximum Continuous Torque without thermal overload.
- Speed Regulation under variable mechanical loads, ensuring precise angular control.
Section IV: Modal Analysis & Resonance Mitigation
4.1 Structural Modal Analysis
Modal testing revealed several natural frequencies within the controller’s operational bandwidth—posing potential resonance risks.
Mitigation: Tune control-loop gain profiles and command-slew rates to avoid exciting these modes.
4.2 Stepper Motor Resonance
Stepper motors exhibit intrinsic resonance peaks that can cause missed steps or oscillations.
Strategy:
- Map critical resonance frequencies in the torque–frequency spectrum.
- Configure microstepping rates and acceleration ramps to bypass these resonant regions.
Together, these measures ensure vibration-free operation and high-precision positioning throughout the workspace.
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