Mechanical Engineering Hack Chat

Join us on Wednesday, September 30 at noon Pacific for the Mechanical Engineering Hack Chat with Adam Zeloof!

Almost every non-trivial project involves some level of cross-discipline work. If you build a robot, for instance, you need to worry not just about the electronics but also the mechanical design. You need to make sure that the parts you use will be strong enough to deal with the forces that it’ll face, you have to know how much power it’ll take to move your bot, and you have to deal with a thousand details, from heat flow to frictional losses to keeping things moving with bearing and seals.

Unfortunately for many of us, the mechanical engineering aspects of a project are foreign territory. We lack the skills to properly design mechanical systems, and so resort to seat-of-the-pants decisions on materials and fasteners, or over-engineering in the extreme — the bigger the bolt, the better. Right?

Some of us, though, like Adam Zeloof, actually know a thing or two about proper mechanical engineering. Strength of materials, finite element analysis, thermodynamics — all that stuff that most of us just wing are Adam’s stock in trade. Adam brings a trained mechanical engineer’s skillset to his multi-discipline projects, like the Rotomill or his reverse-engineered ride-share scooter. And many of you will have been lucky enough to see Adam’s excellent 2019 Superconference talk on thermal design for PCBs.

Adam joins us on the Hack Chat to talk about anything and everything to do with mechanical engineering. Join us with your burning — sometimes literally — questions on how to make your designs survive the real world, where things break and air resistance can’t be ignored.

join-hack-chatOur Hack Chats are live community events in the Hackaday.io Hack Chat group messaging. This week we’ll be sitting down on Wednesday, September 30 at 12:00 PM Pacific time. If time zones baffle you as much as us, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.

Continue reading “Mechanical Engineering Hack Chat”

A Crash Course In Thermodynamics For Electrical Engineers

It’s a simple fact that, in this universe at least, energy is always conserved. For the typical electronic system, this means that the energy put into the system must eventually leave the system. Typically, much of this energy will leave a system as heat, and managing this properly is key to building devices that don’t melt under load. It can be a daunting subject for the uninitiated, but never fear — Adam Zeloof delivered a talk at Supercon 2019 that’s a perfect crash course for beginners in thermodynamics.

Adam’s talk begins by driving home that central rule, that energy in equals energy out. It’s good to keep in the back of one’s mind at all times when designing circuits to avoid nasty, burning surprises. But it’s only the first lesson in a series of many, which serve to give the budding engineer an intuitive understanding of the principles of heat transfer. The aim of the talk is to avoid getting deep into the heavy underlying math, and instead provide simple tools for doing quick, useful approximations.

Continue reading “A Crash Course In Thermodynamics For Electrical Engineers”

DIY Ram Pump Obeys The Laws Of Physics

Despite the claims of “free energy” on the title of the video below, this is not yet another wacky perpetual motion story. We here at Hackaday fully support the laws of thermodynamics, and we think you should too. But you have to admit that a pump that works without any apparent energy inputs looks kind of shady at first glance.

The apparatus in question is a ram pump, a technology dating back all the way to the 18th century. The version that [Junkyard – Origin of Creativity] built uses commonly available materials like PVC pipes and fittings. About the only things on the BOM that might be hard to scratch up are the brass check valves, which should probably be flap valves rather than the easier to find spring valves. And the only custom part is an adapter to thread the plastic soda bottle that’s used as an air chamber to the PVC, which a 3D printer could take care of if you choose not to hack a bottle cap like [Junkyard] did. The video below shows the impressive lift achieved just by tapping the kinetic energy of the incoming flow.

There, the Second Law of Thermodynamics remains inviolate. But if you still think you can get something for nothing, check out our roundup of perpetual motion and Overunity quackery.

Continue reading “DIY Ram Pump Obeys The Laws Of Physics”

A Refrigerator Cooled By Rubber Bands

Ever noticed that a rubber band gets warmer when it’s stretched? The bands also get cooler when allowed to snap back to relaxed length? [Ben Krasnow] noticed, and he built a rubber band cooled refrigerator to demonstrate the concept. The idea of stretching a rubber band to make it hotter, then releasing it to make it cooler seems a bit counter intuitive. Normally when things get smaller (like a gas being compressed) they get hotter. When pressure is released the gas gets cooler. Rubber bands do the exact opposite. Stretching a rubber band makes it hot. Releasing the stretched band causes it to get cooler.

No, the second law of thermodynamics isn’t in jeopardy. The secret is in the molecular structure of rubber bands. The bands are made of long polymer chains. A relaxed rubber band’s chains are a tangled mess. Stretching the band causes the chains to untangle and line up in an orderly fashion. By stretching the band you are decreasing its entropy. The energy of the molecules in the band don’t change, but entropy does. All the work one does to stheatwheelretch the band has to go somewhere, and that somewhere is heat. This is all an example of entropic force. For a physics model of what’s going on, check out ideal chains. If you’re confused, watch the video. [Ben] does a better job of explaining entropic force visually than we can with text.

To test this phenomenon out, [Ben] first built a wheel with rubber bands as spokes. Placing the wheel in front of a heater caused it to slowly rotate. [Ben] then reversed the process by building a refrigerator. He modeled his parts in solidworks, then cut parts with his Shaper handheld CNC. The fridge itself consists of an offset wheel of rubber bands. The bands are stretched outside the fridge, and released inside. Two fans help transfer the thermal energy from the bands to the air. The whole thing is hand cranked, so this would make a perfect museum or educational demonstration. Cranking the fridge for 5 minutes did get the air inside a couple of degrees cooler. Rubber is never going to displace standard refrigerants, but this is a great demo of the principles of entropic force.

For more thermodynamic fun, check out [Al Williams] recent article about building a DIY heat pipe.

Continue reading “A Refrigerator Cooled By Rubber Bands”

DIY Vacuum Chamber Proves Thermodynamics Professor Isn’t Making It All Up

[Mr_GreenCoat] is studying engineering. His thermodynamics teacher agreed with the stance that engineering is best learned through experimentation, and tasked [Mr_GreenCoat]’s group with the construction of a vacuum chamber to prove that the boiling point of a liquid goes down with the pressure it is exposed to.

His group used black PVC pipe to construct their chamber. They used an air compressor to generate the vacuum. The lid is a sheet of lexan with a silicone disk. We’ve covered these sorts of designs before. Since a vacuum chamber is at max going to suffer 14.9 ish psi distributed load on the outside there’s no real worry of their design going too horribly wrong.

The interesting part of the build is the hardware and software built to boil the water and log the temperatures and pressures. Science isn’t done until something is written down after all. They have a power resistor and a temperature probe inside of the chamber. The temperature over time is logged using an Arduino and a bit of processing code.

In the end their experiment matched what they had been learning in class. The current laws of thermodynamics are still in effect — all is right in the universe — and these poor students can probably save some money and get along with an old edition of the textbook. Video after the break.

Continue reading “DIY Vacuum Chamber Proves Thermodynamics Professor Isn’t Making It All Up”