One Robot's Story: How to Build Own Robot: 3. Chassis Selection

The Plan

Preparation steps may take a lot of time. I and my son spent more than two months learning the basics and running small experiments with Arduino. We used a custom-built starting kit, passed a couple of beginners ramp-up courses, played with Arduino board, sensors, LED and electric motors driven by transistors. Ultimately, we figured out what can we expect from the Arduino-based robot, and what kind of the tasks it can perform.

We decided to build a rather big robot which should be able to wander around the rooms. It needs to be capable going over 5 cm (2 inches) doorsteps (because that is the height of the doorsteps in our house. Also, the robot must be stable and capable of wearing lots of sensors, a video camera or a cell phone, and/or some small TFT screen. Imagination instantly paints some caterpillar-chassis robot 10 cm high and 20x20 cm long and wide (~4x8x8 inches).

It took some time before we found a good chassis for our needs. Lots of vendors provide many models of the wheel and caterpillar truck robot chassis. However, most of them look much like a cheap plastic toy, not a serious purpose equipment.

We made our choice once accidentally discovered this video on YouTube:

All out doubts disappeared - we want this one!

At a first glance - the platform is well made, fits our requirements and has a serious and mature design. The manufacturer produces a wide range of flavors which differ in size and color.

Our choice is gold-colored mid-size double-decker DT300 with the Espduino kit.

DIY DT300 WIFI Double Layer Decker Tracked Model Tank Compatible With Arduino UNO R3

At the bottom of this post, we list some other chassis flavors. The selection is very impressive!

We selected double decker to have spare space for all possible future expansions. The plan is to place the electronics on the lower deck, and an LCD screen or a video camera on the upper deck.

Another particularly interesting part of this set is Espduino kit. Actually - this kit includes two boards.

The first board - ESPduino. This is a mix of the standard Arduino UNO form-factor and an ESP8266 microcontroller. It is a much more powerful platform. Besides the Arduino-like functionality, it provides access to WiFi connectivity. The board comes with the firmware which allows out of the box user-friendly WiFi configuration. Special mobile applications are available on Google Play for the tank remote control.

The second board is a very cool control shield for motors and servos. It can be installed right on top of Arduino UNO-like boards. It can drive 2 DC motors and 16 servo machines. Looks like it is intended for the robots with an automated arm. We did not plan to use that many servos but anyway - it is always a good idea to have a couple of extra PWM connectors.

As a summary - buying this kit we expected to receive a complete platform to build a ready to go robot. It will connect to WiFi and accept commands from the remote control mobile application. Sounds like an epic win, isn't it?

The Reality

In couple weeks the long-awaited package finally arrived. It was a nice box with lots of painted metal pieces, nuts, bolts, wheels, motors and wires.

To be honest, we were a bit nervous about this purchase. What is the quality of this rather expensive kit from the unknown to us Chinese company, which we saw only on couple pictures and a YouTube video?

But when we opened a box and started assembling our chassis - all our concerns vanished instantly. All metal parts are made very precisely and carefully. No sharp edges, all holes, and cuts are nicely polished. The coating is accurate, nice and resistant to scratching and wearing. All wheels are mounted on bearings so the friction resistance is negligible. All parts fit each other perfectly well.

Assembly instructions downloaded from the manufacturer's website were quite clear and straightforward. Overall the assembly process was as exciting as playing with Lego or assembling some table from IKEA😌

Two DC motors included in the kit are paired with the speed reducers and are really a perfect match for the tank of this size and weight. Motors also have built-in Hall-sensors, so you can track from your firmware the actual wheels rotation speed.

Motor's working voltage is 9V, with the max. current 1200 mA. This means, if connected directly to Arduino, these motors will instantly burn its power circuits. We need an external power source as well as a special motor driver schema.

A partially assembled chassis (without an upper deck) looked pretty nice!

We placed some wirings, Arduino UNO, and power bank here so you can feel the real scale.

Speaking about electronics part of our package - we were a bit surprised. Instead of expected Espduino kit, we've got some strange board in shield-like form-factor (so it can be placed on top of Arduino UNO, connecting right to the standard extension slots).

It appeared to be ESP13 - a shield which opens easy access for Arduino projects to the WiFi. It is based on the same ESP8266, but can't work easily as a stand-alone module. We'll play with this module later.

Of course, Banggood's Support apologized for the mistake and refunded the corresponding amount right after my inquiry. Without hesitation, we ordered a replacement in the same online shop. Ultimately we arrived at the following combination:

Arduino MEGA 2560 - as the main microcontroller board (in the next post we'll discuss a bit why we use this board instead of the simple UNO)
The simplest ever Motor Drive Shield. At that time - we were thinking it is the best possible choice. It took us couple more months to realize - there are much better options. We'll come back to this in the next posts.