[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.
[Brad] just acquired a 32×32 RGB LED matrix and he jumped right into the deep end with his first project. To try out his skills on the device he used an Arduino to drive a slew of pixels with bouncing-ball physics.
The demo starts off with a hail storm of multi-colored falling pixels. In the center of the storm is the cursor, which he controls with a PS2 mouse. That happens to be a ball mouse which makes sense as we don’t remember having seen any optical mice as of late that weren’t USB. The PS2 protocol is easy to read using a microcontroller; more about that in [Brad’s] project write up.
By holding down the left mouse button he can draw persistent pixels on the screen. The falling balls then interact by bouncing off of the obstacles. The image above shows a frame on three sides of the screen which has trapped the pixels near the bottom. He can also erase pixels, which has the effect of draining the trapped balls like a hole in a bucket of water. Neat!
Bouncing ball physics are fun to experiment with. Here’s one being driven by an analog computer.
Lasers normally emit only one color, or frequency of light. This is true for laser pointers or the laser diodes in a DVD player. [Kevin] caught wind of state-of-the-art research into making variable wavelength lasers using shaken grains of metal and decided to build his own.
When [Kevin] read a NewScientist blog post on building variable frequency lasers built with shaken metallic grains, he knew he had to build on. He dug up the arxiv article and realized the experimental setup was fairly simple and easily achievable with a bit of home engineering.
[Kevin]’s device works by taking thousands of small ball bearings and putting them in a small vial with Rodamine B laser dye. To vibrate the particles in the dye, [Kevin] mounted his container of dye and bearings on an audio speaker and used a frequency generator to shake the ball bearings.
When a small 30mW green laser shines through the vial of ball bearings and dye, the laser changes color to a very bright yellow. By vibrating the vial at 35 to 45 Hz, [Kevin] can change the frequency, or color of the laser.
[Kevin] can only alter the frequency of the laser by about 30 nm, or about the same color change as a reddish-orange and an orangish-yellow. Still, it’s pretty amazing that [Kevin] was able to do state-of-the-art physics research at home.
Sadly, we couldn’t find any videos of [Kevin]’s variable frequency laser. If you can find one send it in to the tip line and we’ll update this post.
Batman’s ability to fly is a falsehood. Or at least so says science. We didn’t know science was into disproving super-hero movies (that’s a deep well to drink from) but to each his own. But back in December the Journal of Physics Special Topics took on the subject with their scholarly paper entitled Trajectory of a Falling Batman. The equations presented in the two-page white paper may be above your head, but the concepts are not.
It’s not that Batman can’t fly in the way explained in the film. It’s that he can’t land without great bodily harm. By analyzing the cape in this frame of the film, researchers used Batman’s body height to establish wing span and area. The numbers aren’t good. Top speed will reach about 110 km/h with a sustained velocity of 80 km/h. That’s 80 mph at top speed and just under 50 mph when he comes in for a landing.
The Ranque-Hilsch vortex tube is an interesting piece of equipment. It can, without any moving parts or chemicals, separate hot and cold compressed gasses that are passed through it. Interestingly enough, you can cobble one together with very few parts for fairly cheap. [Otto Belden] tossed one together in a weekend back in 2009 just to see if he could do it. His results were fairly good and he shared some video tutorials on its construction.
His latest version, which you can see in the video below, takes compressed air at about 78degrees and spits out about 112degrees on the hot side and 8degrees on the cold side. Not too bad!
Cool picture, huh? Wait until you see the video footage of this LED-adorned RC helicopter flying on a dark night. But this isn’t an art project. Analyzing the long-exposure photography turns out to be a great way of clearing up some of the physics of flight which otherwise are not at all intuitive. The helicopter used here has different colored lights on the nose and tail, as well as lights on the rotors.
Depending on how the aircraft is moving, different 3D spirography is captured by the camera. When you zoom in on part of the flight path it becomes clear that there are wider arcs on one side of the fuselage than there are on the other. This has to do with the forward progress of the aircraft and the rotation of the blades. The phenomenon is well known by helicopter enthusiasts, and accounted for in the design. But what we didn’t realize is that it actually translates to a theoretical speed limit for the aircraft. Our childhood love of Airwolf — the TV helicopter that could outrun jets — has been deflated.
You should remember the helicopter physics videos featured here last month. This is the latest offering and we’re still wanting more!
If you’ve ever wondered how a helicopter is able to fly, or would just like to see some awesome RC piloting, the four videos after the break should be just the thing! Although the basic physics of how one works is explained in the last three, one would still be hard pressed to explain how [Carl] is able to fly his RC helo the way he does. The video has to be seen to be believed or even explained, but one of the simpler tricks involved taking off a few feet, doing a forward flip, and flying off backwards and upside-down!
As explained in detail in the other videos, a helicopter is controlled by something called a swash plate on the main rotor, which in short translates a linear action into a rotational one. The same thing is done with the tail rotor, but you’ll have to check out the videos after the break for a full explanation! Really ingenious that someone could come up with this analog control system to use before computers were available.
Of particular interest to physics geeks, an explanation of gyroscopic precession is given in the fourth video. Controlling a helicopter may not work exactly the way you thought!