Zippy Might Be a Small Robot Tank, But That Doesn't Stop It From Moving Fast
This tank affectionately named Zippy is a quick and simple take on a remote-controlled vehicle that can conquer any terrain.
Inspiration for Zippy
After seeing so much news and celebration surrounding the Perseverance Mars rover landing, the maker known as MelloFire wanted to build a much smaller version that could move across several different types of terrain while keeping a low profile. And thus, Zippy was created.
Version 1 of Zippy was constructed from a few simple parts such as a Raspberry Pi Zero W, an L298N 4-channel motor driver, four geared DC motors, and a battery pack/boost converter. As for controlling the robot, the Pi Zero W hosted an internal webserver that served a single webpage with a few buttons corresponding to forward, backward, right, and left, as well as stop. When one got pressed, an asynchronous request would get sent to correct route within the Flask webserver which would change which motors were active and therefore the tank's direction. This model worked well enough to keep MelloFire interested, but there were some things that could be improved, as always.
Improving the base design
The next iteration of the tank came with a large upgrade to the tank chassis itself, which is based off of this design from Thingiverse. The webserver control scheme from before was found to be quite clunky and slow, so MelloFire opted to switch out the phone and webpage solution with a wireless X Box controller instead. This way, signals can quickly be passed from the user to the robot with minimal processing time and lag. A small RGB LED also got added to the top that indicates the current status of the program, with red for a disconnected controller, blue for when the script starts, and green when everything is working correctly.
After some quick experiments in the grass, the batteries that were first used had to be swapped out for some more powerful 16650 cells. By combining these in a three by two configuration, the motors were able to consume all of the current they needed at 7.4V.
Building Zippy 3.0
But even with the new batteries, that still was not enough power for a little tank that was supposed to zip around. Because of this, a single 3000mAh 11.4v LiPo battery pack was connected to the L298N motor driver which provided ample speed to Zippy. Additionally, the battery alarm circuitry was directly integrated into the chassis for quick access and greater convenience when the cells have been depleted.
For the controls, MelloFire kept the X Box remote but also wanted to use the analog triggers for more gradual speed changes. The code was changed to read the trigger values that range from zero to one and map them to PWM duty cycles the motor driver could use.
How well does it work?
This video showcasing Zippy v3.0's capabilities demonstrates just how the robot lives up to its name. The addition of the 11.4v battery pack makes this little tank extremely fast over not just concrete but also gravel, dirt, and even grass. It will be exciting to see what new changes version 4.0 brings, and you can track its progress here in the project write-up.