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This note has been lightly edited with AI assistance for clarity. All technical content and observations are my own.

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Quick Context

Just wrapped up the GT IEEE Robotech Hackathon - 36 hours straight of building a "mother-daughter" rover system.

Our team Tachy-Astroach took first place,

which was unexpected but awesome.

The concept: a quadruped "mother" rover carries a small RC "daughter" rover. Mother launches daughter to scout ahead, both controlled wirelessly.

Huge Shoutout to my awesome teammates who made this possible:

  • Zerun Wang: Quadruped mechanical design, inverse kinematics algorithms.
  • Hongyi Lyu: All other structural CAD design, 3D printing, mechanical assembly.
  • Yuting Zheng: Firmware post, controller UI design, presentation video editing.
  • Peijie Liu (me): All electronics/circuitry design & build, communication protocol.
  • Full project details on our DevPost page.

You all are my goats 🐏 ！

The Discovery / Solutions

Custom Controller Build - Structural Diode Hack

No time for PCBs, so I went full old-school with protoboard and flying wires.

The hack I'm actually proud of: Instead of buying an RC controller enclosure, I used thick leads from salvaged high-power diodes as structural elements to mechanically join multiple protoboards together. Bent them into the rough shape of a handheld controller, soldered them between boards for both structural support AND ground distribution.

Core components:

  • ESP32 as main controller
  • 3 analog joysticks for multi-axis control
  • 2 OLED screens (status display + telemetry)
  • NRF24L01 module for wireless communication

PCA9685 Power Hack for Eight High-Power Servos

Eight servos on a quadruped = serious current demands. Standard PCA9685 servo driver boards aren't designed for this.

Modifications made:

  1. Added bulk capacitors - lots of them - to handle servo current spikes
  2. Tin stacking - literally piled solder onto the back traces to increase current capacity (probably added 3-4x the copper cross-section)
  3. Power rail separation hack - separated servo power rail from chip power, then fed servos directly from 2S LiPo (8.4V) while keeping PCA9685 chip at safe 5V

Daughter Robot - Simplicity Wins

The sub-rover was intentionally minimal:

  • Single H-bridge driving TT motor + PWM servo for steering
  • NRF24L01 receiver
  • MPU6050 gyro for attitude feedback
  • 9V alkaline battery with simple linear regulation

Nothing fancy, but it worked first try.

What Failed - The Wheel-Leg Hybrid

We originally planned wheel-leg hybrid locomotion - mount DC motors with wheels on each leg to drive like a car on flat ground, walk like a quadruped on rough terrain.

What killed it: SLA-printed Tough2000 resin gears were impossibly hard and brittle. We could NOT get them to mesh properly with the competition-provided motor shafts without cracking. After 6 hours of trying, we scrapped it and went pure quadruped.

Key Takeaways

  • Structural diode leads as protoboard joiners actually work great
  • Solder stacking is a valid emergency solution for current capacity boost
  • Keep subsystems simple when racing the clock - simplicity saved us
  • Test material properties BEFORE committing to geared mechanisms
  • Trust my teammates in their domains - let them own their parts completely

Wireless Protocol I Developed

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/*******************************************************
 * radio_protocol.h
 * Shared radio protocol definitions for Controller, Mother, and Kid

/******************** TARGET ENUM ********************/
enum Target : uint8_t { 
  TARGET_MOTHER = 0, 
  TARGET_KID = 1 
};

/******************** PACKET STRUCTS ********************/
// Keep structs fixed-size and identical across nodes.
struct ImuData {
  float ax, ay, az;    // acceleration
  float roll, pitch, yaw; // angles (or attitude)
};

struct CmdPacket {
  uint8_t  seq;        // increments every send
  uint8_t  target;     // TARGET_MOTHER / TARGET_KID
  int16_t  leftPower;  // e.g. -1000..1000 (Mother: left wheel, Kid: 0)
  int16_t  rightPower; // e.g. -1000..1000 (Mother: right wheel, Kid: 0)
  int16_t  kidPower;   // -1000..1000 (Kid: forward/back, Mother: 0)
  int16_t  kidSteer;   // -1000..1000 (Kid: turn left/right, Mother: 0)
  int8_t   winch;      // -1 rev, 0 stop, +1 fwd
  uint8_t  flags;      // spare bits for future
};

struct TelPacket {
  uint8_t seq;
  uint8_t linkFlags;   // bit0=kidOnline, bit1=controllerTimeout, etc.
  ImuData imuM;
  float   distM;
  float   speedM;      // optional, can be 0 if unused
  ImuData imuK;        // optional, can be 0 if unused
  float   distK;       // optional
};

/******************** RADIO ADDRESSES ********************/
// 5-byte addresses for direct star topology (Plan A)
// Controller communicates directly with both Mother and Kid
static const uint8_t ADDR_C2M[6] = "C2M01"; // Controller -> Mother (CMD)
static const uint8_t ADDR_M2C[6] = "M2C01"; // Mother -> Controller (TEL)
static const uint8_t ADDR_C2K[6] = "C2K01"; // Controller -> Kid (CMD)
static const uint8_t ADDR_K2C[6] = "K2C01"; // Kid -> Controller (TEL)

/******************** RADIO CONFIGURATION CONSTANTS ********************/
// Shared radio settings across all nodes
static const uint8_t RADIO_CHANNEL = 90;
static const rf24_datarate_e RADIO_DATA_RATE = RF24_250KBPS;
static const rf24_pa_dbm_e RADIO_PA_LEVEL = RF24_PA_LOW;
static const uint32_t FAILSAFE_MS = 200;  // Failsafe timeout (200ms)

#endif // RADIO_PROTOCOL_H

References

Just a quick note from my engineering journal. More detailed projects in Technical Projects.