RimstarOrg

3 Articles

Hand-Cranked Cyclotron

October 14, 2015 by 10 Comments

Okay, not actually a cyclotron… but this ball cyclotron is a good model for what a cyclotron does and the concepts behind it feel kooky and magical. A pair of Ping Pong balls scream around a glass bowl thanks the repulsive forces of static electricity.

It’s no surprise that this comes from Rimstar, a source we’ve grown to equate with enthralling home lab experiments like the Ion Wind powered Star Trek Enterprise. Those following closely will know that most of [Steven Dufresne’s] experiments involve high voltage and this one is no different. The same Wimshurst Machine he used in the Tea Laser demo is brought in again for this one.

A glass bowl is used for its shape and properties as an insulator. A set of electrodes are added in the form of aluminum strips. These are given opposite charges using the Wimshurst machine. Ping Pong balls coated in conductive paint are light enough to be moved by the static fields, and a good crank gets them travelling in a very fast circuit around the bowl.

When you move a crank the thought of being connected to something with a chain pops into your mind. This feels very much the same, but there is no intuitive connection between the movement of the balls and your hand on the crank. Anyone need a prop for their Halloween party?

If you don’t want to buy or build a Wimshurst machine you can use a Van De Graaff generator. Can anyone suggest other HV sources that would work well here?

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sunflower engine

A Sunflower Heat Engine

August 28, 2015 by 11 Comments

Looking for a cool science experiment to do with the kids? Why not build a type of heat engine that resembles a sunflower? [Steve] from Rimstar.org shows us how!

It’s actually a pretty ingenious little project. Using metal foil scraps from a coffee bag, [Steve] created a perfectly balanced wheel that looks kind of like a sunflower. When the foil petals come close to heat they try to expand, but much like a bimetal strip, the materials making up the packaging expand at different rates to straighten the heated petal. This moves the center of gravity of the wheel off-axis, causing a rotation. As the wheel spins, the foil petal cools off, and another one is heated, creating continual movement — at least until the heat supply is taken away!

It’s a lot of work to get the balance just right, but thanks to an ingenious axle design it’s pretty easy to make adjustments. The wheel actually floats on a nail with its point stuck to a magnet, and the other end is suspended by a series of magnets. It’s pretty much as close to a friction free axle as you can get!

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Ball Bearing Motor Rolls For Reasons Unknown

January 29, 2014 by 97 Comments

[RimstarOrg] has brought us an oldie but goodie this week. He’s built a ball bearing motor, a design which has been causing engineers and scientists to squabble for decades. [RimstarOrg] used a microwave oven transformer with a 70 turn primary coil and a single turn secondary coil to create a low voltage, high current AC power supply. Needless to say, there’s a real risk of fire or electrocution with a setup like this, so be careful if you try this one at home. [RimstarOrg] then built the motor itself. He de-greased two ball bearings then installed them on a metal shaft along with a wooden flywheel. The entire assembly was then mounted on a board so the wheel could spin freely. Two copper straps hold the bearings to the board. Finally, the transformer is wired into the copper straps. In this configuration, the current will flow through the outer race of one bearing, through the balls, and into the inner race. The current then passes down the axle and passes through the other bearing. There is very little resistance in this circuit, so it can only be powered on for a few seconds at a time before things start to melt down.

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