Normally when you think of a V8 engine you think of pistons driven by exploding fuel, pushing a crankshaft. [Miller’s Planet’s] version doesn’t use pistons, instead it uses solenoids along with a 3D printed crankshaft. The finished product would make a great science project or classroom demonstration of how a crankshaft converts a reciprocal linear motion into a rotary motion.
There are a lot of 3D printed parts and the links are in the post. A lot of the video (see below) is filmed in the wordless-workshop style with just a few text overlays to explain what is happening. But towards the middle, you’ll hear an explanation of how a solenoid produces force. The real payoff though is at the end, when you get to watch the contraption in motion.
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Building an electric motor from a coil of wire, some magnets, and some paper clips is a rite of passage for many budding science buffs. These motors are simple brushed motors. That is, the electromagnet spins towards a permanent magnet and the spinning breaks the circuit, allowing the electromagnet to continue spinning from inertia. Eventually, the connection completes again and the cycle starts over. Real brushed motors commutate the DC supply current so that the electromagnet changes polarity midway through the turn. Either way, the basic design is permanent magnets on the outside (the stationary part) and electromagnets on the inside (the rotating part).
Brushless motors flip this inside out. The rotating part (the rotor) has a permanent magnet. The stationary part (the stator) has multiple electromagnets. By controlling the electromagnets, the rotor spins. With no brushes, these motors are often more efficient, they don’t generate as much electrical noise, and there is no danger of brushes wearing out. In addition, the electromagnets staying put make the motor easier to wire and, if needed, easier to cool the electromagnets. The principle of operation is similar to a stepper motor. Steppers are usually optimized for small precise steps. Brushless motors are optimized for spinning, not stepping.
[Axbm] built a clever brushless motor out of little more than PVC pipe, some magnets, wire, and iron rods. The plan is simple: construct a PVC frame, build a rotor out of PVC and magnets, and mount electromagnets on the frame. An Arduino and some FETs drive the coils, although you could drive the motors using any number of methods. You can see the whole thing work in the video below.
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Anyone can put out a candle by blowing on it. According to [Physics Girl], that method is old hat. She made an educational video that shows five different ways to put out a candle using–what else–physics.
You might not need alternate ways to put out a candle, but if you are looking to engage students in STEM (Science, Technology, Engineering, and Math), this video along with others from [Physics Girl] might spark interest.
Continue reading “Hacking Candle Extinguishing”
One of my favorite things to do is visit with school kids who are interested in engineering or science. However, realistically, there is a limit to what you can do in a single class that might last 30 to 90 minutes. I recently had the chance to work with a former colleague, a schoolteacher, and The Teaching Channel to create an engineering unit for classroom use that lasts two weeks.
This new unit focuses on an egg drop. That’s not an original idea, but we did add an interesting twist: the project develops a “space capsule” to protect the egg, but also an electromagnetic drop system to test the capsules. The drop system allows for a consistent test with the egg capsule releasing cleanly from a fixed height. So in addition to the classic egg drop capsule, the kids have to build an electromagnet, a safe switching circuit, and a test structure. Better still, teams of kids can do different parts and integrate them into a final product, closely mimicking how real engineering projects work.
There are a few reasons for the complexity. First, given ten class sessions, you can do a lot more than you can in a single day. Second, I always think it is good if you can find exercises that will appeal to lots of different interests. In the past, I’ve used robots and 3D printers for that reason. Some students will be interested in the electronics, others in the mechanics, and still others will be interested in the programming. Some kids will engage in 3D modeling (robot simulation or 3D objects). The point is there is something for everyone.
Continue reading “Kids and Hacking: Electromagnetic Eggs”
In the last Hacking and Kids post, I talked about an activity you can do with kids when you don’t have a lot of time or resources. The key idea was to have fun and learn a little bit about open and closed loop control. One of the things I usually briefly mention when I do that is the idea of a design trade: Why, for example, a robot might use wheels instead of legs, or treads instead of wheels.
Engineers and makers perform trades like this all the time. Suppose you are building a data logging system. You want precise samples, large storage capacity, and many channels. But you also want a low cost and low power drain. You might also want high reliability. All of these requirements will lead to different trades. A hard drive would provide a lot of space, but is more expensive, less reliable, larger, and more power hungry than, say, an SD card. So there isn’t a right choice. It depends on which of the factors are most important for this particular design. A data logger in a well-powered rack might be well served to have a terrabyte hard drive, while a battery powered logger in a matchbox that will be up on the side of a mountain might be better off with an SD card.
We can all relate to that example, but it is pretty boring to a kid. You probably can’t get them to design a data logger, anyway. But if I have about an hour and a little prep time, I have a different way to get the same point across. It is a modified version of the classic “egg drop”, but it is simple enough to do in an hour with very little preparation time.
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[Kerry Wong] took apart a PM2L color analyzer (a piece of photography darkroom gear) and found a photomultiplier tube (PMT) inside. PMTs are excellent at detecting very small amounts of light, but they also have a very fast response time compared to other common detection methods. [Kerry] decided to use the tube to measure the speed of light.
There are several common methods to indirectly measure the speed of light by relating frequency to wavelength (for example, using microwave ovens and marshmallows). However, measuring it directly is difficult because of the scale involved. In only a microsecond, light travels almost 1000 feet (986 feet or 299.8 meters).
Continue reading “Light Speed: It’s not Just a Good Idea”
What hacker doesn’t want a plasma cutter? Even if you aren’t MacGyver, you can probably build this one in a few minutes using things you have on hand. The catch? You probably can’t cut anything more than tin foil with it, and it is probably more a carbon-air arc gouger (which uses plasma) than a true plasma cutter. Still, as [Little Shop of Physics] shows on the video, it does a fine job of slicing right through foil.
If you are like us, you are back now after getting four 9V batteries, some tin foil, a pencil lead, and some clip leads and trying it. If you have more self-restraint than we do, you might want to think about what you are going to put the tin foil over. In the video, they used a laundry basket and a rubber band, but anything that keeps the foil suspended would do the trick.
Although it isn’t really a practical plasma cutter, we were thinking about strapping something like this to a 3D printer and cutting foil stencils. The jagged edges on the video are, hopefully, more from being operated by hand and less from the jagged mini-lightning bolt vaporizing the foil.
Continue reading “Build a Baby Plasma Cutter–Right Now!”