Penny#3

A low-budget three-servo hexapod robot that walks, dances and avoids obstacles using infrared proximity sensors.

3D preview converted from github.com/ssloy/penny at 0526dc4, under WTFPL. View the original files from GitHub (4.5 MB) (opens in a new tab)

What it can do

Written by Robotheca from the project's documents.

Walks as a three-servo hexapod using a repeating four-step gait sequence
Moves forward, backward, and turns left or right depending on obstacle detection
Detects nearby obstacles with two infrared proximity sensors and avoids them
Servo movement planned as constant-speed linear interpolation between keyframes
Low-cost build, roughly ten dollars in parts, intended as a weekend project

This repository has no parts list Robotheca can read yet.

The creator's steps, each with its instructions.

The guide appears here as you scroll.

Guide by @ssloy (README.md), under WTFPL.

Notes written by Robotheca from the project's documents.

ATMega8A-AU microcontroller (QFP-32) as the controller
Three SG90 9g micro servos for leg movement
Two infrared LEDs and two phototransistors as proximity sensors, with 2N3904 transistors
Four AAA battery holder as the power source
Designed by Dennis van Elteren, the motherboard uses the same basic schematic as Penny

Two servos are driven from the 16-bit timer1 PWM outputs (OCR1A and OCR1B)
The center servo is driven from the 8-bit timer2 via a one-shot pulse re-armed at each timer1 capture interrupt
Proximity sensor phototransistor outputs are read through ADC channels 4 and 5
Infrared LEDs are powered through a series resistor R6, which sets their current; the value may need adjusting
Phototransistor collector voltage drops when reflected infrared light is detected, with a closer object giving a stronger signal

Incomplete documentation

How complete the published files are for rebuilding this robot, measured by Robotheca at commit 0526dc4. It isn't a rating of the robot.

3D and CAD files10/20
10 printable parts (STL, 3MF).
Add the CAD source (STEP, or the CAD program's own files) so people can change the design.
Robot description0/15
No URDF.
Add a URDF: the robot can then be seen in 3D and tried in the browser.
Parts list0/20
No parts list in the repository or linked.
Most points to gain: Link to your parts list, or add it to the repository (a CSV or a Markdown table) with quantities, prices and where to buy each part.
Software10/15
Code in this repository, instructions to install or run it.
Say which software framework it uses (ROS 2, LeRobot, Arduino…).
Documentation15/15
README of 14,774 characters with 16 pictures; 5 build steps.
Simulation0/5
No simulation files.
Add a simulation model (MuJoCo, Gazebo, Webots or Isaac).
Licenses10/10
Hardware: WTFPL; software: WTFPL.

Written by Robotheca from the project's documents.

Program the ATMega8 firmware written in C using avr-gcc, or port it to the Arduino environment
Set the 8 MHz clock and configure timer1 and timer2 for fast PWM to drive the three servos at 50 Hz
Set zero and range arrays to calibrate servo neutral positions and movement limits
Start the endless main loop that runs the movement planner, reads the ADC sensors, and updates servo timers

Robotheca doesn't review code. Read it before running it.

Every file of the project: code, CAD, electronics, guides, at commit 0526dc4.

Questions and improvements go to the creator's repository.