[hw97karbine] has made a pretty cool tennis ball cannon. While making a cannon of this sort is nothing new to us, we were impressed by the effort taken to get a stoichiometrically ideal mixture of 3.2% butane and air in the combustion chamber.
[hw97karbine] filled a syringe with butane and then dosed exact amounts into the chamber using a hole in the back. To control the air mixture he marked lines on the outside of the cylinder with magic marker. Simple but effective.
More rewarding than the methods was the cool slow-mo videography of the explosions in the chamber. You really have to check it out. [hw97karbine] shows clearly the difference between a well-balanced fuel to air mixture and a poorly balanced one. It’s one thing to say that more fuel does not mean better combustion, as we all remember from our personal potato cannon experiences, but it’s another thing entirely to see it.
Odd project materials
[Juliansr] wrote in to tell us about a site that sells bendable, moldable, stretchable, and other ‘able’ materials you might want to use in your next project.
(2 * 9V) = Flashlight
[Lasse] built a flashlight with two 9V batteries. One is a normal battery, the other has been gutted and is used as a connector and enclosure for an LED and resistor.
Ghetto flat screen mount
Don’t despair if you can’t afford a mounting bracket for that new flat screen. All you really need is a few screws and some garbage ties.
Tennis ball stand
This crafty solution to charging a phone makes sure that you’re also able to read the display. Since tennis balls lose their pressurization over time it’s a good use for the flat orbs.
Get your message across while blocking your view of… everything with this message displaying visor. It’s like a Daft Punk helmet without the helmet.
Who needs a robot that can catch a tennis ball? We do. What would we do with it? Probably just throw tennis balls at it, that’s the only use we can think of. The work of University students in Kunzelsau and Vienna, it is actually a prototype for new transport systems for industrial robots. Though they don’t list any specific instances where this is a practical method of transport, we think maybe a tennis ball factory would be a good place to start. We can also envision a robot baseball league between this bot and the extremely dexterous ones we’ve covered before.
Reader [Julian von Mendel] and his team built this tennis ball fetching robot for a competition (translated). The first version used distance sensors to locate the tennis balls for pick-up, but they changed to a camera based approach. The robot has three omniwheels and is designed to calculate the shortest path to the ball despite orientation since it can rotate while traveling. The wheels are monitored using rotation sensors from PS/2 mice. The control is provided by 3 Atmel microcontrollers that communicate via SPI. The multiprocessor design is fairly generic and could be reused for a different style of robot. While their robot performed fairly well, there were some shortcomings. The limited storage space meant frequent trips to drop off balls. The tilting bucket kept them from picking up tennis balls that were against the wall. Also, the bot had to be disassembled for battery swaps. The project is very well documented and they’ve released all of their control code. You can see the robot retrieving a ball after the break. Continue reading “Tennis ball fetcher”