Builder Dan Bostian explains and demonstrates his 24 pound walking spinner combat bot. He recently won an award for most innovative design at Seattle Bot Battles 2019. Absolutely amazing and a great example of how to use the SPARC weight advantage rules for walkers. (Your bot can be heavier if it uses non-wheel based locomotion.)
A vehicle transfers power from the engine through the transmission and differential. The gears in these components result in a wheel speed expressed in revolutions per minute (rpm). From the wheel speed rpm, the size of the tire determines the final road speed of the vehicle. The calculations can be applied to any vehicle; from a bicycle, to a semi-truck, and even a robot!
Calculate the circumference of the wheel in feet from the diameter. The formula for circumference is the diameter times pi. Pi is a mathematical constant and is 3.1416 to four places. For example, if the wheel is 30 inches in diameter the circumference would be 94.248 inches. Divide by 12 to get 7.854 feet.
Calculate wheel revolutions per mile by dividing 5,280 by the tire circumference in feet. The example tire will make 672.3 revolutions per mile.
Calculate the speed per minute by dividing the wheel speed by the tire revolutions per mile. For example, if the wheel speed is 300 rpm, the example tire is moving at 0.446 miles per minute.
Multiply the miles per minute speed times 60 to convert the speed to miles per hour (mph). Our example tire with a 30 inch diameter turning at 300 rpm will have a road speed of 26.8 mph.
If the calculations need to be made numerous times, a spreadsheet can be set up with the calculations. Then, only the tire diameter and speed in rpm need to be changed to calculate a new road speed.
From my own experience and seeing multiple builds in competition, below is a list of common materials used.
- Aluminum bars or plates
- Lexan sheet (plastic, also used for the arena walls)
- Titanium bars or plates
- Steel bars or plates (less common, as it is heavy)
- UHMW (ultra high molecular weight polyethylene) (tough plastic similar to a kitchen cutting board)
- 3D printed materials (PLA, ABS, PETG, Nylon, Carbon Fiber)
How to choose? Every bot I have seen usually uses a combination of materials for armor, depending on your design and placement. (Protecting the wheels, top/bottom plates for the internal electronics and motors, etc.) As with most materials, each have their own pro’s and con’s. Some are heavier but stronger, some are more flexible but can tear or bend. Choose your materials based on your design, test it, and change as needed.
Note: 3D printing has become extremely popular in recent years. Before you get into 3D printing a bot, make sure understand how it works and the limitations of the materials themselves (filament type). Choosing the wrong filament can mean the difference between a tough bot and one that shatters like glass on impact!
There are a LOT of preferences from builders and, as such, there is no single right/wrong answer to this question. Below is a list of wireless communication methods you could start with, along with a brief description:
Flysky FS-i6X 10CH 2.4GHz AFHDS RC Transmitter w/ FS-iA6B Receiver: ($50 US) This is a good “starter” package which is affordable and relatively simple to use. It was recommended to me by several seasoned competitors at an event in 2019 for Antweight and Beetlweight bots.