264 lines
8.6 KiB
Markdown
264 lines
8.6 KiB
Markdown
# Two-Disc Cycloidal Gearbox Design
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#### 1. Project Description
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The two-disc cycloidal gearbox is designed to convert high-speed, low-torque input from a stepper motor into low-speed, high-torque output. It utilizes two synchronized cycloidal discs that rotate in opposite phases, interacting with drive pins to transmit motion to an output shaft.
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This configuration minimizes backlash and distributes load across multiple contact points, offering smooth and powerful transmission. The system is fully enclosed and features multiple mounting options for external attachments.
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#### 2. Application & Use Cases
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##### Applications
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- Robotics joints and arms
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- CNC rotary tables
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- Precision camera mounts
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- Automated actuators
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- Small-scale industrial machines
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##### How to Use
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- Mount the gearbox base to your motor using the provided holes.
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- Connect the NEMA-17 motor shaft to the input via the motor shaft connector.
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- Attach your load or mechanism to the output shaft area.
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- Power the motor through a driver board and microcontroller (e.g., Arduino).
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- Control the motion using programmed step sequences.
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- Ensure lubrication (grease) between the discs and drive pins for smoother performance and longer lifespan.
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#### 3. Engineering Drawings
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##### Description
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The design is a compact, scalable two-disc cycloidal gearbox intended for high-torque, low-speed applications. Its parametric structure makes it easy to adapt in size and material. The current prototype has a 90 mm diameter and 54 mm height.
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To clearly illustrate the internal mechanics, structural design, and assembly steps, the following visuals are provided:
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- Included Media
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- **Assembly Video** – starts with an exploded view and step-by-step buildup
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<iframe width="560" height="315" src="https://www.youtube.com/embed/ylcnBYmR19A?si=1Pg3t_qRczJDjIow" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
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<iframe src="https://1drv.ms/v/c/62d760a9f409a919/IQSXz1cAg1KlSb5fDzi06m4CAZDB0oQq2RIVgFQe7C54sDk" width="640" height="480" frameborder="0" scrolling="no" allow="autoplay" allowfullscreen></iframe>
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- **Disassembly Video** – shows teardown process in reverse order
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<iframe src="https://1drv.ms/v/c/62d760a9f409a919/IQQ4qZmvm7WjQYJxuO3emguuAbylCQiWgdHhauW3no3YGVE" width="640" height="480" frameborder="0" scrolling="no" allow="autoplay" allowfullscreen></iframe>
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- **Transparent Body Image** – reveals internal components without hiding the casing
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<p align="center">
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<img src="cycloidal-images/Transparent.png" style="border: 2px solid black;" />
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</p>
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- **Visual Assets & Drawings**
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- Engineering Drawing Sheet
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<p align="center">
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<img src="cycloidal-images/2.png" style="border: 2px solid black;" />
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</p>
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- Cross-Sectional Analysis (x2)
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<p align="center">
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<img src="cycloidal-images/SubSectionAnalysis.png" style="border: 2px solid black;" />
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</p>
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<p align="center">
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<img src="cycloidal-images/sectionanalysis2.png" style="border: 2px solid black;" />
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</p>
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- Isometric View
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<p align="center">
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<img src="cycloidal-images/1.png" style="border: 2px solid black;" />
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</p>
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#### 4. List of Materials & Components
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- ##### Standard Components
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| Part | Quantity | Approx. Size |
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| ------------- | -------- | -------------------------------------------------- |
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| Bearing | 2 | Ø65 mm (outer) × Ø50 mm (inner) × 7 mm (thickness) |
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| Bearing | 4 | Ø32 mm (outer) × Ø20 mm (inner) × 7 mm (thickness) |
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| Stepper Motor | 1 | NEMA-17 |
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- ##### Bolts & Nuts (*with available size approximations*)
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Note: If a bolt is slightly longer than needed, it can be trimmed using a saw. Nut sizes should fit snugly but not too tight.
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1. (A) Connecting Base to Base Cover
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- 7 × Flat Head Machine Screws (Type B)
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- Size: M4 × 50 mm
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- Head Diameter: ~7.5 mm
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- 7 × M4 Hex Nuts
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- Edge-to-Edge: ~6.9 mm
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- Thickness: ~3.2 mm
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2. (B) Drive Pins Area (Replaces 5 mm Pins)
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- 4 × M3 × 50 mm Bolts (hex or socket head)
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- Head Diameter: ~5.5 mm
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- 4 × M3 Hex Nuts
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- Edge-to-Edge: ~5.5 mm
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- Thickness: ~2.4 mm
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3. (C) Mounting Points on Top of the Gearbox
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- 7 × M4 Hex Nuts
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- Edge-to-Edge: ~6.9 mm
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- Thickness: ~3.2 mm
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4. (D) Shaft Connector
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- 2 × M3 × 40 mm Bolts
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- Head Diameter: ~5.5 mm
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- 2 × M3 Hex Nuts
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- Edge-to-Edge: ~5.5 mm
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- Thickness: ~2.4 mm
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5. (E) NEMA-17 Shaft Connector
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- 1 × M3 × 6 mm Bolt (may require sanding)
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- Head Diameter: ~5.5 mm
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- 1 × M3 Hex Nut
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- Edge-to-Edge: ~5.5 mm
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- Thickness: ~2.4 mm
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6. (F) NEMA-17 Connector
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- 4 × M3 × 15 mm Bolts
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- Head Diameter: ~5 mm
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- ##### 3D-Printed Components
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- Material: PLA (tested), PETG (recommended for durability)
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- Parts: Housing, base cover, discs, shaft connectors, output caps, circlips
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- Infill: Suggested 40% or more for torque applications
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#### 5. Cycloidal Drive Strength Analysis
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---
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##### **1. Motor Output Torque**
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* **Motor Stall Torque**: 0.45 Nm
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* **Gear Ratio**: 21:1
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* **Estimated Efficiency**: 85%
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$$
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\text{Output Torque} = 0.45 \times 21 \times 0.85 = \boxed{8.03 \, \text{Nm}}
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$$
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---
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##### **2. Load Handling Capability (Based on PLA Disc)**
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###### PLA Parameters:
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* **Yield Strength of PLA**: 50 MPa
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* **Safety Factor**: 3 → Allowable stress = 16.7 MPa
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* **Contact Area (per lobe)**: 5 mm²
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* **Lobes in contact**: 4
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* **Radius from center to lobe force point**: 33.5 mm = 0.0335 m
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* **Infill Density**: 25%
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###### Calculations:
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* **Force per lobe**:
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$$
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F_{\text{lobe}} = 16.7 \times 10^6 \times 5 \times 10^{-6} = 83.5 \, \text{N}
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$$
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* **Total force from 4 lobes**:
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$$
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F_{\text{total}} = 4 \times 83.5 = 334 \, \text{N}
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$$
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* **Torque handling at 33.5 mm radius**:
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$$
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\tau = 334 \times 0.0335 = 11.2 \, \text{Nm}
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$$
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* **Account for 25% infill**:
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$$
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\tau_{\text{safe}} = 11.2 \times 0.25 = \boxed{2.8 \, \text{Nm}}
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$$
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---
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##### **3. Drive Pin Strength (Bolts with PLA Sleeves)**
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###### Assumption:
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* Bolts used instead of precision 5 mm mild steel pins
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* Outer diameter maintained at **5 mm** using **PLA sleeves**
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* Inner bolt shaft assumed 4 mm (typical M4 bolt shank)
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* Steel Yield Strength: 260 MPa
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- **Cross-sectional Area (4 mm bolt)**:
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$$
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A = \frac{\pi D^2}{4} = \frac{\pi \cdot 4^2}{4} = 12.57 \, \text{mm}^2
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$$
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- **Force per bolt**:
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$$
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F_{\text{bolt}} = 260 \times 12.57 = 3,268.2 \, \text{N}
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$$
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- **Total force (4 bolts)**:
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$$
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F_{\text{total}} = 4 \times 3,268.2 = 13,072.8 \, \text{N}
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$$
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- **Torque capacity**:
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$$
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\tau = 13,072.8 \times 0.0335 = \boxed{437.9 \, \text{Nm}} \quad \text{(Safe✅)}
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$$
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> Note: **PLA sleeves** do not contribute significantly to strength — they act as spacers or guides. Only **steel bolts** are load-bearing.
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---
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##### **4. Max Load at 50 mm Arm**
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$$
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F = \frac{\tau_{\text{safe}}}{r} = \frac{2.8}{0.05} = 56 \, \text{N}
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$$
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$$
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\text{Mass} = \frac{56}{9.81} = \boxed{5.7 \, \text{kg}}
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$$
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---
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##### Final Summary Table
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| Category | Value | Safe? |
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| --------------------------- | -------- | ------------------------ |
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| Motor Stall Torque | 0.45 Nm | ✅ |
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| Output Torque | 8.03 Nm | ❌ Exceeds PLA safe limit |
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| PLA Torque Limit | 2.8 Nm | ✅ |
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| Bolt + PLA Pin Torque Limit | 437.9 Nm | ✅ (way overbuilt) |
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| Max Load (at 50 mm arm) | 5.7 kg | ✅ |
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---
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##### Final Conclusion
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The **cycloidal drive system is likely to fail at the PLA disc lobes under full output torque**, especially if printed with only **25% infill**. Although the **bolts (with PLA sleeves)** acting as drive pins are structurally sufficient, the **PLA disc is the mechanical weak point**.
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##### If tested:
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* The drive **will function under light loads (below \~5.7 kg at 50 mm arm)**.
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* Under full load or high-torque demand, **plastic deformation or cracking is expected at the lobes**.
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* The bolts will hold without issue, but **localized PLA wear or failure around the lobes and sleeves is likely.**
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##### Recommendations:
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* Increase **infill to at least 75%** or use a stronger material like **PETG**.
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* Consider **fillet reinforcement** around lobes to distribute stress.
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* Reduce gear ratio or torque output if high load isn't needed. |