Basic Electronics 11, Chapter 11: Challenge 1 solution (choose a board for three robots)

Formulas: E = V x C          E(usable) = 0.8 E          P(batt) = P(load) / efficiency          t = E(usable) / P(total)
          linear regulator: battery current = load current, dissipation = (Vin - Vout) x I

(A) Sumo robot: Arduino Uno (or a Nano)
    Reasons: the four IR sensors are 5 V analogue parts, which match the Uno's 5 V logic and 5 V ADC range directly (the Uno has 6 ADC pins, 4 needed);
             no wireless is needed, so there is nothing to pay for; it is forgiving and has the most tutorials, which suits a beginner.
    Logic current at 5 V:   45 mA (board) + 4 x 20 mA (sensors) = 125 mA
    The Uno's regulator is linear, so the battery supplies 125 mA:
        dissipation = (7.4 - 5) x 0.125 = 0.30 W    (a warm regulator, within the board's ability)
    Battery:     E = 7.4 x 1.0 = 7.4 Wh        E(usable) = 7.4 x 0.8 = 5.92 Wh
    Battery power for the logic:  7.4 x 0.125 = 0.925 W
    Runtime of the logic alone:   5.92 / 0.925 = 6.40 h        (check by charge: 1000 mAh x 0.8 / 125 mA = 6.4 h)
    The motors will shorten this a good deal; this is the figure for the logic only.

(B) Phone-driven rover: ESP32
    Reasons: Wi-Fi and Bluetooth are on the chip, so no radio module is needed; two cores (one for the network); plenty of PWM channels for the motors and servo.
             (The Pico W would also do; the ESP32 has more pins and ADC channels.)
    Rail current:   120 + 80 + 30 = 230 mA at 5 V          Load power:  5 x 0.230 = 1.15 W
    Battery power through the 90 % buck converter:   1.15 / 0.9 = 1.278 W
    Battery:     E = 7.4 x 2.2 = 16.28 Wh        E(usable) = 16.28 x 0.8 = 13.02 Wh
    Runtime of the logic:    13.02 / 1.278 = 10.19 h
    GPIO34 is an ADC1 pin (and input-only, which is all a divider needs). ADC2 pins stop working while Wi-Fi runs, so a battery monitor on an ADC2 pin would fail
    exactly when the robot is being driven over Wi-Fi (Basic Electronics 10).

(C) Camera rover: Raspberry Pi 4 for the vision, with a Pico beside it for the motors
    Reasons: image processing needs an operating system and memory (the Pi); the Pi has no ADC and cannot give hard timing, so the Pico drives the motors,
             reads the encoders and the battery divider (Basic Electronics 10).
    Total power:    3.0 + 0.25 + 0.15 = 3.40 W
    Power bank:     E = 3.7 x 10 = 37 Wh        E(usable) = 37 x 0.85 = 31.45 Wh
    Runtime:        31.45 / 3.40 = 9.25 h
    With a Raspberry Pi Zero 2 W (0.8 W under load):   total = 0.8 + 0.25 + 0.15 = 1.20 W      runtime = 31.45 / 1.20 = 26.2 h     (2.8 times longer)
    What you lose: speed and memory (a quad-core 1 GHz chip with 512 MB, against a faster chip with several GB), so the camera frame rate or the image size must be
    smaller, or the vision method simpler; the Pi 4 is the better choice for heavier processing, the Zero 2 W for a light, long-running robot.

Summary table
    Robot   Board                    Logic runtime
    A       Arduino Uno              6.4 h (battery 7.4 V, 1000 mAh, linear regulator)
    B       ESP32                    10.2 h (battery 7.4 V, 2200 mAh, buck 90 %)
    C       Pi 4 plus Pico           9.25 h (power bank 10 000 mAh); Zero 2 W: 26.2 h

Figures for current, power, price and runtime are typical or approximate; real boards differ, so measure the current of your own build with a meter (Basic Electronics 2).