Edit: I have posted basic building instructions and a follow up video here: Particle Accelerator Instructions
The idea to build this started out as a joke. I was going to make a gag video where I start describing how I built some completely ridiculous and unbelievable thing (ie, a working particle accelerator) out of LEGO bricks. At some point the video would be interrupted by something completely inane, and hilarity would ensue. Clearly that video hasn’t happened yet, and the more I thought about it the more I figured that, you know what, I’m actually going to build a particle accelerator.
In the end it turned out to be not completely ridiculous or unbelievable. In fact the propulsion system is quite simple. More info and pics after the cheesy video my 10 year old self would be proud of.
I did round the speeds stated in the video up or down to make them more narrative friendly, but they are pretty accurate. By stepping through video frames I was able to determine how long it took the ball to travel around the ring at each power level. The ring has a circumference of around 264 studs and at maximum speed the ball travels around it approximately once every 0.6 seconds. That works out to about 440 studs per second, which is the equivalent of just over 12.5 km/hr.
The particle is a LEGO soccer ball, recently re-introduced in a few of the LEGO Friends sets. To accelerate it I’m just using a pair of LEGO wheels, one of which rotates at high speed, powered by a Power Functions M motor through a simple set of gears (see image below). The other wheel is left to spin freely. As the ball passes between them it is accelerated out into the ring.
I have tried powering both wheels, and it does make the ball go faster, but the additional gearing introduces more vibration into the system. Not to mention the ball is already a bit unpredictable at its current high speed. It will occasionally start bouncing around and come flying out. It only runs completely reliably at about half of the maximum speed.