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...