Modular Potato Powered Robot

I am currently doing the 3D CAD of the robot body.

For the moment, the robot has no caterpillars. I prefer to stay simple and use wheels for the first prototype.

Here is the right part :

I need to make some adjustments before printing the left part.

I still have to do the central part (on which will come the electronics and the potato).

In the following days, I will try to update my github repository and add details to this project page.

I didn't have potatoes at home, so let's build an Onion Robot for now !

The two supercapacitor are slowly charging (i didn't measure the current/voltage/energy but it's charging) and the undervoltage, overvoltage, good battery indicator work well but the 3V3 regulator can only power very small load when it's connected to the BQ25504.

if i want power bigger load (the i2c motor driver for example), i have to connect the regulator input directly to the supercapacitors

I think the problem of power limitation comes from my layout. I will try to modify the board with tiny wires and fine soldering skill, until i make a version 2 of this board.

The i2c motor driver works perfectly well (μController, H-Bridges, and quad comparator).

I am currently working on the body of the robot (it will be printed in 3D). I hope to post some photos or pictures soon.

I just finished soldering the boards.

I made some mistakes but it was easily repaired.

I have not yet test everything, but the buck boost converter (energy harvesting module) and the quad comparator (motor driver module) is working properly.

Tomorrow, I will try to flash the microcontroller, and test the the H-Bridge ICs...

I wanted to send PCB in production, but i have a problem with the gerber files of the harvesting module : The online gerber viewer (from JLCPCB) does not want it.

There is no problem with the other two modules, and i use the same export parameters.

I tried to export with another computer (and a different OS), but the problem persists.

I also tried to upload the files to another PCB manufacturer (EuroCircuit: we use this manufacturer at my job, but it's a lot more expensive than the Chinese manufacturer), and it works this time...

I don't understand where the problem come from...

I have to look at this more closely (waiting for the results of the robotic contest).

I'm currently building an Arduino Energy logger.

• Arduino Nano

• INA219 Current Sensor (actually with an 0,1 Ohm resistor, i need to change that if i whant mesaure micro or nano ampere)
• RTC module
• SD card breakout (bottom side)
• 128x32 Oled Display
• 18650 Lipo battery + lipo charger module + 5V boost converter

It will be useful for measering power and energy that i can harvest from a potato...

I'm just finished the I2C motor driver board.

There is :

• 2x DRV8839 dual half-bridge driver (it can drive 2 motor in both direction, or 4 in single direction)
• 2x INA180 Current Sensor (1 for each driver)
• 4 sensor input (analog, or digital with a LM339 Quad comparator)
• Atmega168 or 328P (for I2C interface, Speed Control and monitoring)

It's perfboard/breadboard compatible (except for ICSP and UART programming connector).

Here is a 3D model (kicad 3D view) of the Energy harvesting module.

It is based on a BQ25504 Energy Harvester (with MPPT and Battery management), pair with TPS63030 Buck/Boost Converter. It's perfboard/breadboard compatible.

There is also a 1V precision voltage reference.

You can adjust the parameters (Under & Over voltage protection, Output voltage...) by changing the value of some resistors.

I also made a breakout board for BCAP0350 E270 T13 Supercap (350F, 2,7V).
It's also perfboard/breadboard compatible, but you can use M3 Mounting Hole as terminals if you want (for high current).

There will be more details (explanation and schematic) on the main project page.
I still have to do the other modules (I2C motor driver, sensors...) before I can order PCBs and components (and wait for my salary).
I also have to open a GitHub repository to share files and documentation, but I have never used it ...

I juste made some simples calcultation to find out if it's possible to power the robot with potatoes energy.

The energy is harvested from a single potato in two super capacitor (2.7V / 350F).

If i place the two capacitor in series, it gives me a single capacitor of 5.4V / 175F.

The energy inside capacitor is :

I don't want overcharge it, so i will charge at maximum 5V :

To extract maximum energy from capacitor, i need a boost converter. Because of the energy harvesting IC, i can't discharge over 2.2V :

I can store and use 2187.5 - 423.5 = 1764 J (0.49 Wh)

At 3.3V, my two motors use each 25mA (light load). (3.3V * 25mA = 82.5 mW)
The electronics (µC, sensors... ) sould use maximum 50mA. (3.3V * 50mA = 165mW)
In total, i need 0.33W. (2 * 82.5mW + 165mW = 330mW)

With 75% efficency boost converter, i should use 0.44W of power from the capacitor.
With a consumption of 0.44W and a capacity of 0.49 Wh, i can power the robot for 1.11 hours (66 minutes, 49 seconds)


If i want know how long i can charge my capacitor with potatoes, i have to measure how much power i can exctract from it...


Edit after some datasheets reading and power consumption measurement of my new tiny motor...