Giant Robot Bacteria

60000 times bigger than the original

Robot Bacteria - absolutely waterproof with magnetic coupling.

Bacteria come in many shapes and sizes, some with a drive (flagellum), some with hairs on the outer shell, others seemingly smooth. Bacteria vary greatly in size: their diameter ranges from about 0.1 to 700 µm, and in most known species it is about 0.6 to 1.0 µm.

Their size and simple function are fascinating. I cannot work with proteins, carbohydrates and enzymes, but there are technical possibilities for the amateur to build a bacterium.

1 mm = 1 000 μm

Here I am building a waterproof macro-bacterium with a microcontroller, a motor and two stepper motors. The bacterium will move in a liquid medium.

Like its biological model, it is simply built, but does not yet have any sensors.

The basic idea is to make a waterproof drive for water/underwater vehicles whose motor forces are transmitted through the boat hull by magnets.

Microcontroller with BLE or WiFi (ESP32-C3 is best)

Mini Metal Gear Motor DC N20

2 micro stepper motors (4 wires)

LiPo battery 3.7V 250mAh

transistor (BC337)

reed contact (reverse!)

2 rectangular neodymium magnets + additional magnet

3D printed parts can be seen at Tinkercad

• frame
• stepper motor bracket
• gimbal joint
• motor mount
• magnet holder

(Alternatively, you can try to reproduce the plastic parts with glue-reinforced cardboard.)

* big Kinder Surprise Egg or other capsule-like large plastic tin

flat rubber band as propeller

ESP-NOW remote control device. (Instructable)

*The EGG

I read that e.g. in the U.S. surprise eggs are banned to this day, on their import there is a fine of 2500 dollars, because a law of 1938 forbids sweets that contain non-edible objects.

Plastic eggs in the size 7 cm and without content can be ordered from well-stocked online retailers.

According to the manufacturer, the egg is made of PP5 plastic (polypropylene). The PP5 is usually processed at temperatures of 220-270°C. This information is important for the subsequent smoothing of the egg.

The bacterium has no reverse gear. So you can do without an H-bridge and operate the motor via a transistor and the power supply of the microcontroler. To slow down the fast motor I used the PWM method.

If the axis of the motor has a gear wheel, we simply put on the holder for the binding magnet and fix it with super glue.

Later, we only have to attach the magnet with the drive tail to the right place on the outside of the shell.

The ring has a diameter of 6.7 cm and can be easily pushed into the egg later. In it all the parts are fixed. Holes have been made for a lightweight design.

To move the motor and therefore control our bacterium we need a gimbal joint. It consists of two plastic rings that allow us to tilt the motor right/left up/down.

Gimbal Joint and control unit (step 4) are placed in the 3D-printed ring that is simply inserted into the egg body.

With the two stepper motors we control the direction of our drive. The motors are controlled each via 4 pins directly on the microcontroller, we don't need a controller chip!

An ESP32-C3 is just enough for this: 2 x 4 pins for the stepper motors, 1 pin for the transistor of the drive motor. 2 pins would remain for LEDs or sensors.

First, solder four wires to each stepper motor. Use a flux, this makes the difficult soldering easier.

After many experiments with homemade and purchased solenoids (too heavy or too weak) or servos (too big) I returned to stepper motors. The micro version is just suitable for our purposes and quite cheap.

• Insert the motors into the control unit.
• The openings on the brackets still need to be widened with an appropriate drill. Pieces of solid wire or paper clips serve as axes.
• The motors are fixed with super glue.

The mechanism works like an inverted joystick with motors instead of the two potentiometers. The control unit is placed in the ring which is inserted into the egg.

Since our bacterium currently has no sensors, it should be remotely controllable. The best and smallest solution seems to me at the moment an ESP32-C3 with Wifi and BLE on board. The 2.5 GHz radio has a very low range in water, but it will probably be enough for testing purposes.

A brief guide to working with the ESP32-C3 can be found here.

The 4 wires of the motor must be soldered directly to the pins.

Software:

Upload the sketch to your ESP32-C3. You will find help in my instructable here....

and generally for Arduino IDE and microcontrollers here.

I have added the file "MicroStepperWithoutDriver.ino", if you want to make a test with the micro stepper motors.

Remote Control:

As remote control I use an ESP32 with joystick and the protocol ESP-Now. It is simple and effective and has a higher range than normal wifi.

You can find a simple building instruction here.

[Of course you can also use the BLE function or normal WiFi of your ESP32-C3, but I won't go into that here.]

To attach a waterproof switch, I stick to magnets and use a reed contact inside the bacterium. This (reversed!) reed contact is closed until a magnet is attached from outside the shell. 

--> If the bacterium is to be switched off, the magnet is plugged on. To activate the bacterium, the magnet must be removed.

Because the ESP32 supports battery charging, we need to solder two cables to the bottom of the microcontroller. Later we connect the 3.7V battery here with the reed contact in between.

The bacterium has no ballast tanks like a submarine or kind of a fish bladder that allows diving or ascending. We navigate only with the help of the flagellum. The weight must therefore be precisely adjusted for the medium (fresh water) in order to achieve a state of levitation.

For the plastic egg, I calculated a volume of 184 cm³. This means that the whole bacterium should have a weight of exactly 184 grams.

I also filled the egg with water and put it on a digital scale. The result was a weight of x grams of water displacement in the fully submerged state.

As an additional ballast I have distributed a few washers as evenly as possible.

Everything is now stowed away in the plastic egg and the mobility of the parts is checked. The switch is set to off (the magnet is plugged on), then the two plastic halves are put together and the joint is sealed with adhesive tape.

Don't forget to put the tail magnet in the right place.

Outlook for the future I:

if I make it in this smallest space, I would like to add a TDS sensor to control the water quality, indicated by a LED in the bacterium body.

Outlook for the future II:

How about a swarm of bacteria communicating with each other.