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R21 from cardboard - Construction

The video about R21

About R21

Robot R21, mail2code, based on Raspberry Pi and ATmega328
Figure 1:
In the previous chapter I presented you a first rover for my mail2code system, which came out of the 3D printer, I would now like to show you that such a vehicle can also be produced with much simpler tools.
The mechanic of Rover R21 is mostly made of cardboard. Even if R20's tracks may look "cooler", it doesn't offer any added value in terms of learning effect compared to the R21's cardboard discs. The dimensions are similar and both robot platforms offer a variety of options for attaching extensions to the chassis.

If you want to learn programming or are just curious how mail2code works, here is the mail2code project page.


Robot R21, Parts
Figure 2:
Basic material of R21 is 2mm cardboard, which can be cut very easily with a sharp knife or scissors and all parts can afterwards be assembled with glue. Up to 3mm plywood or 2mm plastic could also be used - both materials can also be cut with a knife, although not quite as easily.
The construction drawings can either be transferred to the cardboard using a ruler and a pen, or simply glued on.
Hot glue or superglue are suitable adhesives if you need something quick, wood glue is for people with a little more time.mehr Zeit.

Robot R21, Chassis
Figure 3:
For the chassis, the cut out parts form a box after gluing.

Robot R21, Wheels
Figure 4:
The two servos for continuous rotation, which serve as drive motors, are screwed to this. The screw holes must be pre-drilled with a 1.5mm drill or, as shown here, with a very small screwdriver. Each wheel is composed of two cardboard discs with a diameter of 45mm, which are glued to the servo horns. For better traction, I glued two more discs on each wheel after the first tests and fitted tires made of rubber rings.

Robot R21, Skid plate
Figure 5:
A skid plate is glued to the bottom rear of the chassis.

Robot R21, Boards
Figure 6:
Attachment points for the Raspberry Pi and the microcontroller are made of a stack of cardboard pieces into which holes are drilled. The Raspberry Pi is attached to the front of the chassis, the microcontroller at the back - here I installed a cheaper nano board with an ATmega328 microcontroller.

Parts list:

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Part Online shop Remarks
Raspberry Pi Raspberry Pi on

Raspberry Pi on eBay UK

Raspberry Pi 4 on Amazon
Central brain. Model 4 has sufficient computing power for desktop applications, but in principle the robot also works with the less powerful predecessor models.
Raspberry camera module Raspberry camera on

Raspberry camera on eBay UK

Raspberry camera module on Amazon
USB cameras work, too, but the Raspberry camera offers a lot more software features.
Powerbank Powerbanks on

Powerbanks on eBay UK

Powerbank on Amazon
Two outputs needed, one for the Raspberry Pi and the second for the servos.
Standard Servo Standard servo on

Standard servo on eBay UK

RC servo on Amazon
Camera servo
Servos for continuous rotation 360 degree Servos on eBay UK

360 degree Servos on eBay UK

360 degree servo on Amazon
2 pieces needed as drive motors. Note that standard size servos are required!
3mm nuts and bolts 30mm screws M3 on

Nuts M3 on

30mm screws M3 on eBay UK

Nuts M3 on eBay UK

M3 screws on Amazon

M3 nuts on Amazon
30mm thread length, cut the screws where they are too long.
Micro USB cable USB cables on

USB cables on eBay UK

USB cables on Amazon
Power supply of Raspberry Pi and servos.
Shorter is better.
If a Raspberry 4 is used, you'll need a USB cable type C!
Resistors 1kΩ Resistors on

Resistors on

Resistors on Amazon com

Resistors on Amazon uk
LEDs LED assortments on

LED assortments on

LEDs on Amazon com

LEDs on Amazon uk
5mm diameter, white
Prototyping board Prototype boards on

Prototype boards on

Prototype boards on Amazon com

Prototype boards on Amazon uk


Robot R21, Elektronic Components
Figure 7:
The essential electronic components are the same for both vehicles and consist of a Raspberry Pi, two RC hobby servos for continuous rotation, a power bank and a microcontroller.
An ATmega2560 board like with R20 can of course also be used, however to my mind, the smaller and cheaper board is the better option for a cardboard robot. For the electronics, which in the simplest version consists of pin headers for the servos and a few resistors, I used a prototyping board that still has room for extensions.

Robot R21, Energy supply
Figure 8:
The power bank for the energy supply is inserted into the chassis from the rear.
From the power bank, one output leads to the Raspberry Pi and the second to the servos. Raspberry Pi and microcontroller board are also connected via an USB cable.

Robot R21, bumper
Figure 9:
As a first upgrade, I give the robot bumpers with switches that can be used to detect whether the rover has hit an obstacle. On the back side of the cardboard bumpers is a wire connected to ground.

Robot R21, bumper switch
Figure 10:
At the corners of the chassis are the wire counterparts that lead to GPIO pins of the microcontroller. These simple switches are closed as soon as the rover hits an obstacle.

Software / Download

The circuit layout and the drawings for the cardboard parts are available as Download
The software isn't really finished yet. How it works in principle can be found on the mail2code website.

Test drives

Have a look at my RoboSpatium to see what robots are currently available for a test drive. Have fun!

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