💡 Introduction – Turning Vision Into Action
MemoDroid started as a bold idea:
Could I, as a single developer, design and build a fully functional robotic arm – complete with motion recording, Bluetooth control, a mobile interface, and smooth servo handling – in just a few weeks?
As a full-time computer science student balancing a packed academic semester and a demanding job, this wasn’t just a project. It was a test of focus, engineering, and willpower.
I took on this challenge as part of an IoT & Robotics course led by Dr. Yehuda Rosilho not knowing just how deep it would go. What followed was a true end-to-end engineering journey – every circuit, every line of code, every screw placed with intent and urgency.
📜 Goal & Core Idea
MemoDroid was designed to solve a real problem:
“Make it easy for anyone to automate small, repetitive tasks at home or work using a robotic arm.”
Key objectives:
- Remote control via mobile app
- Ability to record and replay movement routines
- Smooth, human-like servo transitions
- Intuitive UI for non-technical users
- Expandability (360° rotation, multiple profiles, scheduling)
But beyond the functionality, I wanted to design something accessible. MemoDroid isn’t just a robotic arm – it’s an approach to democratize robotics.
🧰 Planning & Architecture
🔨 Hardware Stack
| Component | Description |
|---|---|
| Arduino Uno | Main microcontroller for servo control and logic |
| PCA9685 | 16-channel I²C PWM driver for precise motor control |
| 6 Servos Total | 5 standard + 1 continuous rotation |
| HC-05 Bluetooth Module | Wireless communication bridge with the mobile app |
| Breadboard + Jumpers | Prototyping and connection base |
| 6V 2A External Power | Dedicated supply to stabilize servo load |
➕ The Sixth Motor: 360° Servo
Halfway through the project, I added a 6th servo – the Hitec HSR-1425CR, a continuous rotation servo. Unlike the others, it doesn’t rely on angles – it uses PWM signal range to control speed and direction.
📲 Mobile Application
🛠️ Implemented Functionalities in the Arm and App
- 🎮 Manual Control for Each Servo
Real-time control via Bluetooth using commandss1tos6.
Supports both standard 180° servos and a continuous rotation servo (servo6). - 💾 Save & Replay Movement Routines
SAVE: Stores the current position of all servosRUN: Replays the saved sequence to automate tasks
- ⏱️ Custom Speed Control (Built from Scratch)
Speed control is not provided by default in servo movement.
I implemented a manual speed mechanism using delay injection between servo position updates.
The delay can be adjusted dynamically via thess<value>command to simulate different movement speeds. - 📡 Reliable Bluetooth Command Parsing
Developed a robust input buffer and parser to handle fragmented Bluetooth transmissions, ensuring commands are processed correctly even when split across multiple reads.
Supported commands include:RUN– Start executing saved routineSAVE– Save current positionsPAUSE– Temporarily stop executionRESET– Clear saved positions
Communication is done via custom serial protocol:
s1<angle>
s2<angle>
...
s6<mode> (1-5)
Each message is sent to the Arduino and interpreted by the core parser.
⚙️ Firmware & Control Logic
🌟 Command Handling
All servo commands are processed via handleCommand(), which intelligently reads commands like s2130 and moves the relevant motor.
For Servo 6:
s6<1–5> → mapped to:
1 = full reverse (0)
2 = slow reverse (45)
3 = stop (90)
4 = slow forward (135)
5 = full forward (180)
🧐 Buffered Bluetooth Parser
One of the hardest bugs I encountered was due to Bluetooth message fragmentation. Data arrived in pieces, like:
s3
1
80
This caused misfires and corrupted commands. To solve this:
- I built a custom string buffer
- Extracted complete commands using
indexOf('s') - Deferred processing until a full command was available
Now the robot reads fragmented Bluetooth messages perfectly every time.
🧪 Calibration & Testing
I implemented a TestCalibration() routine and spent hours adjusting and observing each servo to get ranges right:
- Servo 1: 0-45°
- Servo 2: 100-130°
- Servo 3: 150-270°
- Servo 4: 0-270°
- Servo 5: 45-180°
- Servo 6: 1-5 (mapped to continuous rotation behavior)
This fine-tuning ensured that MemoDroid behaves like a real robotic system, not a toy.
⚠️ Roadblocks I Overcame
| 🛡️ Obstacle | 🛠️ Solution |
|---|---|
| Motors jittering from insufficient power | Switched to 6V 2A external supply |
| No PCA9685 or HC-05 parts in simulator | Manually designed the full electronic scheme |
| Bluetooth messages broken mid-stream | Built a custom buffered parser |
| Complex calibration ranges | Developed test functions + manual tuning |
| Debugging during silent failures | Added real-time Serial Monitor logs |
✅ Results & Capabilities
- Built a functional robotic arm from scratch
- Added 360° motor support
- Built a mobile controller from scratch
- Implemented data recording and replay
- Created a stable custom communication protocol
- Made everything intuitive and modular
💻 Technical Architecture Snapshot
[Mobile App] → Bluetooth → HC-05 → Arduino Uno
↓
Command Parser & Logic Handler
↓
PWM via PCA9685 → Servo Motors (1–6)
🌐 Open Source
All firmware and design files are available here:
👉 GitHub: BlackD0C/RoboticArm
🌬️ What’s Next?
In future releases, I’d like to expand MemoDroid with:
- ☑️ Cloud scheduling + remote logging
- 🧠 Computer vision for object detection
- 🕹️ Joystick or gesture control
- 🌐 Web interface for control from any device
🧐 Reflections
MemoDroid was a passion project I brought to life from the ground up – writing the code, designing the circuits, building the app, and refining every detail.
This project taught me:
- That debugging hardware is 10x harder than software
- Why protocols and parsing matter
- And most importantly: with enough focus, you can do more than people expect – even alone
🙏 Final Thoughts
MemoDroid isn’t just a robot.
It’s a personal victory. A product of discipline, late nights, self-learning, and never giving up.
“You don’t need a team of engineers or unlimited time. Just a clear goal, smart planning, and the will to execute.”