penguin

Perception-Enabled Navigation and General-Utility INtelligence

Hybrid differential legged-wheeled biped rover for embodied AI, computer vision, and autonomous navigation.

Status

• Controller manufactured and partially assembled.
• Soldering and hardware validation in progress.
• Mechanical components currently being printed.

Table of Contents

• penguin
  • Status
  • Overview
  • Features
    • Controller
    • Mechanical
  • Architecture
    • Systems
  • Electrical
    • Power System
    • Microcontroller
    • Motor Drivers
    • Vision Interface
    • Sensor and I2C Interface
  • Mechanical
    • Chassis
    • Leg Assembly
  • Firmware
  • Repository Structure
  • Gallery

I built penguin cause I wanted to create an intelligent robot from the ground up.

Overview

Put simply, Penguin is a platform for experimentation with intelligent robotics.

The project began as a simpler, maze-solving rover for a course project (MREN 178 - DSA). My team couldn't deliver the rover in time so we scaled down. I had already started with hardware, which pushed me to adopt the project into my own, with the intent to expand it past maze-solving.

After that term (Winter '26), I designed a controller PCB and the necessary compoments for the chassis.

Now its June, and I'm documenting everything and writing firmware.

Features

Controller

The controller is powered by a 7.4V LiPo Battery and driven by an ESP32-S3 (N16 1U).

Below is a list of features from power circuits to various peripherals.

• Power-entry circuitry with OC/OV protetction, RPP, PI-filter, and dual-mosfet BMS.
• Regulation circuit featuring buck converter, 5V ORing, and LDO for logic power (3V3)
• ESP32-S3 breakout circuitry with USB differential routing, S3 boot mode selection and reset toggle.
• Controlled power delivery via CMOS circuits for main motor power.
• N20 motors with encoders for wheels driven by a DRV8833 chip.
• DS3218 20kg Servo motors for hip joints, driven by PWM signals from S3.
• OV2640 camera with FPC connector and three-level voltage regulation.
• I2C bus with three ToF sensors, OLED screen, and GPIO expander.
• Audible and visual indicators.
• cool silkscreen penguin.

Mechanical

• Three-layer internal stackup for housing motors, controller board, and routing cables.
• Integrated vents and ports for sensors and devices, air flow, and weight reduction.
• Hybrid locomotion system with wheels and legs.
• Multi-bar leg assembly - pivot arm, mounting arm (hip), leg.

Architecture

Systems

Electrical

This section provides low-level explanations of the significant circuits of each "module" of the controller.

I encourage you to clone the repo or you use KiCanvas to look at the schematic and board files.

All electronics were designed with KiCad.

Power System

Power Entry

The 7.4V battery power enters through a Molex Micro-Fit (3mm Pitch) header, where it is then met with a 12V 7A fuse for over-current protection. A PTC resettable fuse was selected for durability.

The positive battery line is then protected from voltage spikes with a Transient Voltage Supression (TVS) diode placed in paralell for clamping.

• The diode's standoff @ 9V
• Breakdown @ 10V
• Clamps @ 15.4V

The positive line then goes through a Reverse Polarity Protection (RPP) circuit, using a P-Channel MOSFET for lossless efficiency (lower V drop than standard diodes).

A Zener diode and resistor is placed between the MOSFET's gate and source for gate over-voltage protection.

A bulk electrolytic (100μF) capacitor, ferrite bead, and high-frequency (0.1μF) capacitor are then placed to create a third-order low pass filter (π-filter).

• This is used to smooth voltage spikes and reduce EMI.

The ferrite bead was primariy selected for its saturation current and DCR.

The approximate current draw with safety margin $I_{net}$ is 5A.

$I_{\mathrm{sat}} = 1.5 \times I_{\mathrm{net}} \approx 10 A$

Minimize heat dissipation.

$DCR$ is 10Ω

$P_{heat} = DCR \times I_{\mathrm{sat}} \approx 0.25 W$

Battery-Management-System (BMS)

The BMS system uses the negative terminal of the battery and features a HY2120 protection IC with a dual-mosfet to form the system's GND.

The IC uses the balance tap of the battery (VC ~ 3.7V nominal) to monitor the level of Cell 1, while using the main positive terminal (VDD ~ 7.4V nominal) to monitor Cell 2.

This allows the IC to indepdently track each cell's voltage and trigger the dual-MOSFET to cut off power if either cell suffers from overcharge or overdischarge.

Voltage Regulation (I)

The controller uses a cascade regulation system, starting with the TPS5405DR buck converter.

The input voltage is VBATT (7.4V), after the protection and filtering circuitry, and the output is 5V.

The $R_{osc}$ value will determine the switching frequency of the converter.

Switching frequency is governed by the relationship. $$R_{\text{OSC}} (\text{k}\Omega) = 21.82 \cdot f_{\text{SW}}^{-1.167}$$

I chose a value of 100kΩ for a $f_{SW}$ of approximately 271 kHz

For the soft-start capacitor $C_{ss}$ , I chose a value of 10nF for a soft-start time of 5ms

The values below were taken from the TPS5405DR Datasheet

$$ C_{SS} = \frac{t_{SS} \cdot I_{SS}}{V_{REF}} $$

$$ C_{SS} = \frac{(5,\mathrm{ms})(2,\mathrm{\mu A})}{0.8,\mathrm{V}} = 12.5,\mathrm{nF} \approx 10,\mathrm{nF} $$

The inductor values were chosen using the equation below.

$$ L=\frac{V_{out}\left(V_{in}-V_{out}\right)} {V_{in}f_{sw}\Delta I_L} $$

Using our calculated $f_{sw}$ from above and our voltage requirements (8.4V in, 5V out): $$ L= \frac{(5,\mathrm{V})(8.4,\mathrm{V}-5,\mathrm{V})} {(8.4,\mathrm{V})(525,\mathrm{kHz})(0.3,\mathrm{A})}

\approx 10,\mathrm{\mu H} $$

The Schottky diode is rated for the 2A output current and 8.4V

5V ORing

The 5V rails from both USB and the buck converter are combined using an OR-ing circuit (Dual Ideal Diodes) to prevent backfeeding before feeding the second stage of regulation.

In this configuration, the outputs of both LM66100 ideal diode controllers are tied together to form the shared 5V rail. The CE pins of each device are also tied to the output rail, ensuring both controllers are only enabled once the rail is present

Voltage Regulation (II)

The second stage of voltage regulation involes a Low-Dropout Regulator (LDO), the AMS1117

It is fed the combined 5V rail from the OR-ing circuit to produce the controller's logic-level voltage: 3V3

Controlled Motor Power Delivery

The power for the N20 and Servo motors is controlled using a complementary-MOSFET (CMOS) setup, driven by a digital HIGH from the S3.

• When the control signal is low or floating, the N-channel MOSFET remains off and a pull-up resistor holds the gate of the P-channel MOSFET at the supply voltage, keeping it disabled and disconnecting the load rail.

• When the control signal is driven high, the N-channel MOSFET turns on and pulls the P-channel gate low, creating sufficient gate-source voltage to enable conduction and connect the supply to the load.

This controlled power line, VMOT = 7.4V powers the supply voltage of the DRV8833 chip, and is converted via local buck converter to produce VSERVO = 5V

Voltage Sensing

A resistor divider circuit is used to produce a signal to be read by the S3's internal ADC.

• $R_1 = 100,\mathrm{k\Omega}$
• $V_{batt} = 7.4,\mathrm{V}$
• $V_{out} = 2.8,\mathrm{V}$

$$ R_2 = \frac{R_1 \cdot V_{out}}{V_{batt} - V_{out}} $$

$$ R_2 = \frac{100,000 \cdot 2.8}{7.4 - 2.8} = 50,\mathrm{k\Omega} \approx 47,\mathrm{k\Omega} $$

Microcontroller

The controller is driven by an ESP32-S3-WROOM-1U-N16 microcontroller.

The U and N16 model was selected for layout flexibility and memory capacity (16MB).

A MCP23017 GPIO expander was used to accomodate space for all digital inputs/outputs (via I2C)

Digital IO

Mode Select and Reset Toggle

The S3 can be put into BOOT mode and RESET with onboard buttons.

BOOT mode determines whether the chip runs existing code from flash memory or waits to download new firmware.

• The ESP32 samples the BOOT pin (GPIO0) during reset to determine the boot mode.
• It is active-low: when pulled to GND during reset, the chip enters UART bootloader mode for flashing firmware.
• The circuit uses a momentary push-button to GND and a 10kΩ pull-up resistor to ensure a defined high state during normal operation.

BOOT0 Level	Boot Mode
HIGH	Programming Mode
LOW	Memory Mode

RESET controls the Enable (EN) pin which is the ON/OFF (reset) switch for the ESP32.

• It is active-low: when pulled to GND it turns off the chip, and when released, it restarts.
• The circuit consists of a momentary push-button, a pull-up resistor to ensure the chip is enabled by default, and a 1µF capacitor to filter out button noise.

Motor Drivers

The N20 wheel hub motors are driven by a DRV8833 chip, and their encoder signals are routed to digital pins on the S3.

They are connected via 6-Pin Molex Nano-Fit (2.50mm Pitch) headers, and feature decoupling across the motor terminals and on the encoder power supply.

The Servo hip motors are driven by PWM signals from the S3, and are connected by a single 4-Pin Molex Nano-Fit header.

The connector has decoupling on the power supply, and series resistors on the signal lines to improve signal integrity and reduce noise.

Vision Interface

The controller interfaces with an OV2640 camera via FPC-connector.

The camera is configured in 8-bit mode using adjacent digital pins for frames.

Power supply is divided into three levels:

• DVDD: 1.2V
• AVDD: 2.8V
• DOVDD: 3.3V

These conversions are acheived through the use of fixed-output-voltage LDOs (LP5907MFX) with local decoupling.

Series low-resistance resistors were added on the camera's clock signals (PCLK, XCLK) in series for signal integrity and EMI reduction.

• I used only S3 pins, not expander pins, for the data pins D2-D9 and HREF, VSYNC pins.

Sensor and I2C Interface

The controller interfaces with three VL53L0X Time-of-Flight (ToF) sensors for ranging (obstacle detection, SLAM - potentially).

This interface is achieved through I2C.

The sensors are connected through a single 7-Pin Molex Nano-Fit header, connecting the sensor power, I2C clock and data signals, and the shutdown XSHUT pins of each sensor.

Decoupling capacitors and shutdown pull-ups are placed locally.

Additional I2C Devices

• IMU (LSM6DSL)
• Mini OLED Screen
• OV2640 Cam

Indicator Components

• RGB LED
• Passive LEDs for simple indication
• Buzzer for audible indication

Mechanical

This section provides insight on the mechanical components of Penguin: the chassis and leg assembly.

In no way am I a CAD-expert, so this was definitely a learning experience with lots of iteration.

Projected geomtery was clutch.

I used Fusion360 to design everything.

Chassis

The chassis consists of several components attatched with pegs and magnets.

Base Plate

The base plate forms the start of the internal stack-up.

It contains Servo pads for the hip motors to rest on, a port for an ON/OFF switch, and a battery slot with vents.

It acts as the "floor" of the Servo bay and the bottom of the chassis.

It connects to the rest of the chassis through pegs to insert into the inside face of each wall.

Mid Plate

The mid-plate is the rough center of the internal stack-up.

It is the mounting point for the controller board and connects to internal shelves on each side wall.

This inner section above the mid-plate and under the lid forms the controller bay.

Side Walls

The side-walls enclose the internal stack-up, and provide mounting points for several chassis components.

They have cutouts for the Servo shafts, arm joints, and house components like the external antenna and RGB indicators.

The top face has short holes for magnets that align with holes on the lid.

Nose

The nose contains ports for the ToF sensors, OLED screen, and an RGB indicator.

There is also a cable port connecting to the controller bay for routing.

It mounts to each walls with pegs, and has short holes for magnets that align with holes on the lid.

Stern

The stern features a USB-port and fits inside the walls.

It uses M3 screws to secure it in place.

Lid

The lid contains a porthole for the camera, and is magnetically mounted on the top surface of the walls and nose.

Leg Assembly

The leg assembly consists of the Servo mounting arm, pivot arm, and the wheel hub assembly.

Mounting Arm

This is the contact point between the leg assembly and the hip motor, it's responsible for driving the assembly.

The Servo uses the disc-horn, and fits into a cutout on the mounting arm, and is secured in with the stock machine screw into the shaft.

The end of the arm mounts onto the wheel hub assembly using bearings on each hole, an M3 shoulder bolt, and a nut.

Pivot Arm

The pivot arm maintains proper orientation for the assembly as the suspension moves up and down.

It uses the same mounting as the mounting arm (bearing, shoulder bolt, nut), and is mounted slightly higher at a 40° angle on the wheel hub assembly.

Wheel Hub Assembly

This component houses the N20 motors through a cutout and U-Channel cover to secure them.

The top of the assembly contains the two mounting points for the pivot and mounting arms.

Cables are routed up the back side of it.

Firmware

Repository Structure

Gallery

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Jeevan Sanchez, 2026