Go From Resin Caster to Resin Master

When it comes to resin casting, time is of the essence. It helps to gather everything you’ll need and have it within reach before starting. But if you don’t know what you don’t know, it can be difficult to anticipate needs. Luckily, [Botzen Design] has a few tricks up his sleeve that will save time, materials, and sanity for novices and old hands alike.

It may seem somewhat obvious to mix up resin in a disposable or reusable plastic cup. But not all cups are created equal. Polypropylene cups won’t outgas into your resin, but polystyrene will. If you use a silicone cup or any polypropylene food container marked #5/PP, cured resin will peel cleanly off of the cup walls.

For some reason, the giant jugs of resin [Botzen Design] uses don’t come with pumps. How do they expect someone to meter out exact amounts of resin and hardener while pouring them out of gallon jugs? Stadium-style condiment pumps at a restaurant supply store make things much simpler while avoiding costly spillage.

Our favorite tip (and seemingly [Botzen Design]’s as well) is the drip hammer. When air bubbles mature into craters, they can be filled easily and precisely with a drop or two of wet resin. A pipette would probably just get clogged, but an icicle of cured resin hanging from a stick makes the perfect drip applicator.

Want to get into resin casting but don’t know where to start? Hackaday’s own [Gerrit] has you more than covered.

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Mendocino Motor Drives Cubicle Conversations

Mendocino motors are solar-powered electric motors that rely on pseudo-levitation.  The levitation comes from magnets mounted on either end of the shaft, which repel same-field magnets fixed below them into the base.  When light shines on the solar panels, current flows through connected magnet wire windings, creating an electromagnetic field that interacts with a large stationary magnet mounted underneath. These constantly repelling forces spin the shaft, and the gaps between the solar panels provide the on-off cycle needed to make it spin 360°.

As [Konstantin] discovered, building this simple motor and getting it to spin depends on a lot of factors. The number of windings, the weight of each solar panel, and the magnet sizes all figure in. [Konstantin]’s struggles are your gain, however. His Instructable takes the guesswork out of the tolerances and he designed a nice, open-source 3D-printed structure to boot.

You’re right, these motors can’t do much work. But it would definitely look cool on your desk and might even start a conversation or two. If not, whip up this little electromagnetic train.

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SimpleSumo Bots Teach More than Fighting

[MechEngineerMike] wrote in to share the enthusiasm over SimpleSumo, a series of open source, customizable robots he designed for mini-sumo battling and much more. For the unfamiliar, mini-sumo is a sport where two robots try to push each other out of a ring. [Mike]’s bots are simplified versions designed for education.

[Mike] was inspired by a video of some kids building mini-sumo bots who were doing anything and everything to personalize them. He vowed to make his own affordable, easy-to-build bots with education firmly in mind. His other major requirement? They had to be as easily customizable as that one potato-based toy that eventually came with a bucket of parts. As of this writing, there are 34 interchangeable accessories.

[Mike]’s first idea was to build the bots out of custom 3D-printed building blocks. He soon found it was too much work to print consistent blocks and switched to a modular cube-like design instead. SimpleSumo bots can do much more than just fight each other. [Mike] has written programs to make them flee from objects, follow lines, find objects and push them out of the ring, and beep with increasing frequency when an object is detected.

The bots are completely open source, but [Mike] sells kits for people who can’t print the parts themselves. He’s made a wealth of information available on his website including links to outside resources about mini-sumo, Arduino, programming, and 3D design. How about a complete series of assembly videos? First one is after the break.  Don’t know how to build a battle ring? He’s got that covered, too.

For a sumo bot that’s more brains than brawn, check out Zumo Red, the smart sumo.

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Solving Mazes with Graphics Cards

What if we told you that you are likely to have more computers than you think? And we are not talking about things that are computers while not looking like one, like most modern cars or certain lightbulbs. We are talking about the powerful machines hiding in your desktop computer called ‘graphics card’. In the ordinary gaming rig graphics cards that are much more powerful than the machine they’re built into are a common occurrence. In his tutorial [Viktor Chlumský] demonstrates how to harness your GPU’s power to solve a maze.

Software that runs on a GPU is called a shader. In this example a shader is shown that finds the way through a maze. We also get to catch a glimpse at the limitations that make this field of software special: [Viktor]’s solution has to work with only four variables, because all information is stored in the red, green, blue and alpha channels of an image. The alpha channel represents the boundaries of the maze. Red and green channels are used to broadcast waves from the beginning and end points of the maze. Where these two waves meet is the shortest solution, a value which is captured through the blue channel.

Despite having tons of cores and large memory, programming shaders feels a lot like working on microcontrollers. See for yourself in the maze solving walk through below.

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Control System Fundamentals by Video

If you’ve had the classic engineering education, you probably have a hazy recollection of someone talking about control theory. If you haven’t, you’ve probably at least heard of PID controllers and open loop vs closed loop control. If you don’t know about control theory or even if you just want a refresher, [Brian Douglas] has an excellent set of nearly 50 video lectures that will give you a great introduction to the topic. You can watch the first lecture, below.

You might think that control systems are only useful in electronics when you are trying to control a process like a chemical plant or a temperature. However, control theory shows up in a surprising number of places from filters to oscillators, to the automatic gain control in a receiver. You’ll find the background behind many familiar results inside control theory. Sort of like when you take calculus and you discover how they came up with all the formulas you memorized in geometry.

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Lock In Amplifiers

If you have about an hour to kill, you might want to check out [Shahriar’s] video about the Stanford Research SR530 lock in amplifier (see below). If you know what a lock in amplifier is, it is still a pretty interesting video and if you don’t know, then it really is a must see.

Most of the time, you think of an amplifier as just a circuit that makes a small signal bigger in some way — that is, increase the voltage or increase the current. But there are whole classes of amplifiers designed to reject noise and the lock in amplifier is one of them. [Shahriar’s] video discusses the math theory behind the amplifier, shows the guts, and demonstrates a few experiments (including measuring the speed of sound), as well.

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Scooter Wheels Keep DIY Barn Doors on Track

[MotoGeeking] built a giant spray booth and is in the process of making customized, air-filtering barn doors for it. When it came to buy hardware to move the doors, though, he found all the ready-made options to be prohibitively expensive. You know what comes next: he designed barn door hardware from the ground up, and did it as cheaply as possible.

After intensely studying many images of barn doors and hardware, [MotoGeeking] decided on the right wheels and went from there. Kick scooter wheels fit the bill nicely, since they are designed to support a lot of weight and come with their own bearings and spacers. And they’re cheap, too — just $9 for a pair.

[MotoGeeking] found some C channel extruded aluminium that seemed to be a perfect match for the wheels, but the wheel was quick to bind whenever it touched the sides. He solved that one by epoxying a length of round bar into the bottom corners. This allows the wheel to move freely while forcing it to stay centered in the track.

In designing the 1/4″ aluminium brackets, [MotoGeeking] took a measure thrice, order once approach to selecting the fasteners. You probably know by now that McMaster-Carr has free CAD drawings for every little thing. [MotoGeeking] imported the ones he liked into Illustrator and built around them. This helped him get it right the first time and kept the headaches and hair-tearing away. Watch the giant door skeleton glide effortlessly on its track after the break.

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