Sesame, an orange 3D-printed four-legged robot with an OLED face
The open-source robot this kit is based on. Photo: dorianborian (Sesame Robot), Apache-2.0.
First edition

Quadruped Walking Robot (Sesame-based)

An 8-servo walking robot with an OLED face: calibration, walking gaits and IMU balance, explained.

Difficulty
Intermediate to advanced
Build time
3 to 4 evenings
Digital guide €26
Order by email

We reply within a day with the payment details (bank transfer or PayPal) and email you the files right after payment.

You get the PDF, the code and the 3D files by email. Price incl. all taxes.

Kit with parts €93.96

The kit includes the guide. Notify me when the kit is ready.

What you get

  • PDF guide: how legs walk (trot gait), servo calibration, trims, balance with an IMU
  • MicroPython firmware for the Sesame frame with a phone control page and gait code, plus unit tests for the maths that you can run on a computer
  • Links to the Sesame print files (Apache-2.0, credited) and the full parts list

Who it is for

Builders comfortable soldering a small wiring harness. Based on the open-source Sesame robot frame.

Walking is a rhythm: two diagonal legs swing while the other two push. The guide turns that rhythm into a few lines of code you can change, then adds a gyroscope so the robot stays level on a tilted table.

Parts you need

  • 1× LOLIN (WEMOS) ESP32-S2 Mini
  • 8× MG90S metal-gear micro servo, 180°
  • 1× OLED 0.96" 128×64 SSD1306, I2C, 4-pin
  • 1× MPU6500 6-axis IMU module (I2C), MPU6050 compatible registers
  • 1× LM2596 adjustable step-down (buck) module, compact (no display)
  • 1× Electrolytic capacitor 1000 µF (16 V or higher)
  • 1× Mini rocker switch ON/OFF, 2-pin, 15×10 mm (KCD1)
  • 1× Prototype perfboard 5×7 cm
  • 1× Male pin header strip 1×40, 2.54 mm
  • 1× Silicone wire 22 AWG, red + black (per 0.5 m pair)
  • 3× Silicone wire 30 AWG, assorted colours (per 1 m)
  • 1× Heat-shrink tubing assortment (share per kit)
  • 6× Small zip ties 100 mm (pack of 100)
  • 40× M2 × 5 mm self-tapping screw
  • 10× M2.5 × 5 mm machine screw (servo horn)
  • 1× USB-C data cable 1 m (USB-A to C)
  • 1× Sesame print set: internal frame, bottom cover, enclosed top cover, joints R1–R4 and L1–L4 (11 parts) 3D

Not in the kit

  • 7.4 V 2S Li-ion pack (the Sesame author recommends a 14500 800 mAh pack) + matching charger, or a USB-C PD 5 V/3 A supply for tethered use
  • Soldering iron, flux, solder

Full list with shops and cheaper alternatives is in the guide.

Look inside

The first chapter of the guide, free to read.

How a four-legged robot walks

This robot is built on Sesame, a charming open-source quadruped by dorianborian (frame and joints released under the Apache License 2.0). We use its printed frame, joints and wiring layout unchanged, and add our own MicroPython firmware: walking gaits, calibration, a phone page and a balance mode with a tilt sensor.

Two servos per leg

ServoJob
hip (R1, R2, L1, L2)swings the leg forward and back
leg (R4, R3, L3, L4)lifts the foot and puts it down

Eight MG90S servos, a LOLIN S2 Mini board, a small OLED screen as a face, and an IMU (accelerometer + gyroscope) that feels which way the robot is tilted.

A step is a cycle

Watch one leg while a dog walks. It does two things, again and again:

  • Swing (half of the cycle): the foot is up and moves forward.
  • Stance (the other half): the foot is down and moves backward relative to the body, which pushes the body forward.

We describe where a leg is in its cycle with a phase from 0 to 1. In our code:

swing (0≤s<0.5):hip=−Acos⁡(πu),lift=Hsin⁡(πu),u=s/0.5\text{swing } (0 \le s < 0.5):\quad \text{hip} = -A\cos(\pi u),\quad \text{lift} = H\sin(\pi u), \qquad u = s / 0.5 stance (0.5≤s<1):hip=Acos⁡(πu),lift=0,u=(s−0.5)/0.5\text{stance } (0.5 \le s < 1):\quad \text{hip} = A\cos(\pi u),\quad \text{lift} = 0, \qquad u = (s - 0.5)/0.5

AA is the stride (25°), HH the lift (40°). The cosine makes the hip start and stop smoothly instead of jerking; the sine makes the foot rise and land softly.

The trot: diagonal pairs

If all four legs lifted together, the robot would fall. In a trot, the diagonal legs move together: front-right with back-left, front-left with back-right. One pair is at phase 0 while the other is at 0.5. So at every moment two diagonal feet are on the ground, and the body is supported between them.

Turning is the same trot with longer steps on one side. Walking backwards reverses the direction of the hip swing.

Feeling the tilt

The IMU measures two things. The accelerometer feels gravity, so it knows which way is down, but every footstep shakes it. The gyroscope measures how fast the robot rotates, smoothly, but if you add up its readings the angle slowly drifts. A complementary filter mixes both: 96 % “previous angle plus the gyro’s change”, 4 % “what the accelerometer says”. In balance mode, the legs on the low side push down and the legs on the high side pull up, so the body stays level on a tilted board.

What is in this guide

  1. How a four-legged robot walks (this chapter, free)
  2. Parts and printing the Sesame frame
  3. Assembly, wiring and power
  4. The code: gaits, calibration and balance
  5. Troubleshooting and what next

The Sesame project’s own build and wiring guides are linked from this guide; we follow their mechanical build exactly.

Questions

What is Sesame?

An open-source quadruped by dorianborian, licensed Apache-2.0. The frame is theirs; this guide and the MicroPython code are new.

Is the battery included?

No. You can run it from a USB-C power supply, or buy the recommended battery locally.

Digital guide €26
Order by email

We reply within a day with the payment details (bank transfer or PayPal) and email you the files right after payment.

You get the PDF, the code and the 3D files by email. Price incl. all taxes.

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