Terraskipper

TerraSkipper V2

A mudskipper-inspired robot I've been building to explore soil monitoring on difficult ground. This version moves the pectoral fins with DC geared motors, uses servos for the tail and sensor placement, and runs on a Raspberry Pi Pico 2 W.

Why a mudskipper?

The project started with soil problems in Egypt's Nile Delta. I wanted to explore a robot that could carry sensors over muddy ground, and the way a mudskipper moves between land and water gave me an idea for the mechanism.

This repo documents the prototype, its design files, and the changes I made while building it. The main things I worked on here were movement, fitting the electronics inside the body, and getting sensor readings from the assembled robot.

What changed in V2

I replaced the front servos with DC geared motors for more torque. I also redesigned the body, added proper PCB mounting, and made the sensor placement mechanism detachable so I could work on it without taking the whole robot apart.

After the first assembly, I reprinted the body at a smaller size. Everything still had to fit inside, so I checked the alignment again and adjusted the parts where needed. The smaller body used less filament and reduced the weight.

Movement and sensors

• Two DC geared motors drive the pectoral fins.
• One servo drives the caudal fin, and two more work the sensor placement mechanism.
• A Pico 2 W runs the uploaded MicroPython firmware.
• The sensor setup includes an MPU-6050, a DS18B20 temperature sensor, capacitive soil moisture sensing, and a TDS input.
• The design has three HC-SR04 ultrasonic sensors. I removed two in the final physical build after running into a sensor fault; the uploaded firmware still includes all three.
• A NEO-7M GPS module is included in the design, but GPS reading isn't implemented in the uploaded firmware.

The motor model changed during the build: my movement notes list JGB37-520 motors, while the original BOM lists JGA25-370 motors. The BOM below records the original estimate.

What the uploaded code does

Firmware/Main.py drives the DC motors forward, sets the servos, reads the ultrasonic sensors and IMU, and prints temperature, moisture, and TDS telemetry. It starts the motors when run.

It's a movement and sensor test program. Autonomous navigation and pH measurement aren't implemented in this file, and the moisture and TDS conversions still depend on calibration for the actual sensors and test conditions.

Mechanical design

I used fillets and chamfers around the body edges, and designed a small vertical slider to lower the sensors toward the soil. The mechanism can be removed separately for repairs.

PCB and wiring

The custom board has two layers, with signals and power routing on top and a ground plane underneath. The design includes two BTS7960 motor drivers and buck converters for the power rails.

I originally considered an ESP32, then switched to the Pico 2 W because I was more comfortable working in MicroPython. The current KiCad schematic and firmware use the Pico 2 W.

Getting it assembled

I rebuilt the circuit one section at a time: power first, then the controller, then the sensors. PCB review also caught missing mounting details, layout changes, and gaps in the CAD and Gerber files.

One of the more frustrating faults was the right motor refusing to move. I swapped the motors to check whether the motor itself was bad, then traced the problem back to the driver's motor B output and fixed it. After assembly I checked the wiring and ran the movement tests again before filming.

Original parts estimate

The recorded estimate is about 5,315 EGP, or $102.50 at the time. It covers the 18 items counted in the original BOM, with the build changes noted above. TDS is present in the schematic and firmware but isn't itemized in this BOM.

Demo and zine

Watch the demo

Open the zine PDF.

Files

• CAD assemblies and STEP model
• Individual SolidWorks parts
• KiCad schematic, PCB, and Gerbers
• MicroPython firmware
• BOM
• Build photos and design screenshots

Earlier stages are in TerraSkipper and Mudskipper.

Build notes by Ziad, as part of the TerraSkipper project.