Fluid Simulations in the Kitchen Sink

In an age of ultra-powerful GPUs and cheap processors, computational techniques which were once only available to those with a government-sized R&D budgets are now available to the everyday hacker. An example of industry buzzword turned desktop software is the field of “computational fluid dynamics”, which put simply allow modeling how gasses or liquids will behave when moving through a cavity under specific conditions. Extensive utilization of these fluid simulations are often cited as one of breakthrough techniques which allowed SpaceX to develop their engine technology so rapidly when compared to Apollo and Shuttle era methods.

But just because anyone with a decent computer has access to the technology used for developing rocket engines doesn’t mean they have to use it. What if you prefer to do things the old-fashioned way? Or what if, let’s me honest, you just can’t figure out how to use software like Autodesk CFD and OpenFOAM? That’s exactly where [Desi Quintans] found himself when developing GUST, his cooling duct for i3-type 3D printers.

[Desi] tried to get the big name fluid simulation projects working with his prototype designs for an improved cooling duct, but had no end of trouble. Either the learning curve was too steep, or the simulation wasn’t accurate enough to give him any useful data. But remembering that air is itself a fluid, [Desi] took his simulation from the computer to the sink in order to better visualize what his cooling duct was doing to the airflow.

[Desi] printed up a box with a hole in the bottom that would connect up to his nozzles under test. As the volume of water in the box would be a constant between tests, he reasoned that this would allow him to evaluate the different nozzles at the same pressure. Sure enough, he found that the original nozzle design he was using caused chaotic water flow, which backed up what he was seeing in his experiments when mounted onto the printer.

After several iterations he was able to tame the flow of water by using internal baffles and fins, which when tested in water created something of a laminar flow effect. When he tried this version on the printer, he saw a clear improvement in part cooling, verifying that the behavior of the air and water was close enough for his purposes.

We’ve seen other projects that successfully used fluid simulations in their design before, but the quick and dirty test procedure [Desi] came up with certainly has its charms.

Filed under: 3d Printer hacks, hardware

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Bolt Together 2 X 72 Belt Grinder

Below I have included some drawings and models that should hopefully help you with the dimensions and hole layouts. I included the drawings as pdf’s and the .step file for the entire assembly so you can see how it all fits together. If you do not have a 3D modeling software I have also included a 3D pdf that will anyone with adobe acrobat (its free) to be able to view the assembly as well.

Note: While making this I made some changes and these drawings and models are not 100% the same as what I show being made. I will address the changes in each step as they differ from the drawings.

Material List:

2in x 2in square tubing in the following lengths:

One 5in long tube

Two 10in long tubes

One 11in long tube

1.5in x 1.5in square tubing in the following lengths:

One 7in long tube

One 17in long tube

One 12in long tube

Two pieces 2in x 6.5in x .25in (this can be thinner but it is nice if it is thicker because it will be threaded)

Two pieces 4in x 4in x .125 (this can be thicker if you want but not any thinner)

Four 2in long pieces of 2in angle iron

One piece at least 2.5in x 8in x .25in for the tool rest

One piece 2in x 2in x .25in (I made mine more around 2in x 4in x .25in which you will see later)

One piece 1.5in x 1.1in x .375in for one half of the hinge

One piece 2in x 2in x .375in for the other half of the hinge

Parts list:

Lots of bolts (each step will show the bolts you need, most are 3/8in bolts but they don’t have to be)

Lots of lock nuts (these are important as this vibrates a lot and you don’t want it coming apart)

Two adjustable position handles (I used these 3/8 x 1 1/4 ones)

Flat platen tool (I bought this one but the second link I provided has the plans for one if you can make it)

Guide, tracking, and drive wheels (I bought mine form here but the third link shows how you can make your own)

A gas spring (I used a 7in 100N/22lb spring from amazon but it is no longer available)

A handle (I turned a 2 x 2 piece of wood into a handle but you could buy whatever you want)

A motor (This completely depends on what you have or the power you want, I have a 1hp motor with a vfd to provide variable speed control)

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Someone Finally Did It With A 555

Someone Finally Did It With A 555

[Jarunzel] needed a device that would automatically click the left button on a mouse at a pre-set interval. For regular Hackaday readers, this is an easy challenge. You could do it with an ATtiny85 using the VUSB library, a few resistors and diodes, and a bit of code that emulates a USB device that constantly sends mouse clicks over USB every few seconds. You could also do it with a Raspberry Pi Zero, using the USB gadget protocol. Now, this mouse-clicking gadget would be connected to the Internet (!), programmable with Node or whatever the kids are using these days, and would have some major blog cred. If you’re feeling adventurous, this mouse clicker gadget could be built with an STM32, Cypress PSoC, or whatever microcontroller you have in your magical bag of hacker tricks.

Then again, you could also do it with a 555 timer.

The reason [Jarunzel] couldn’t use any of the fancy hackertools for this build is because the system wouldn’t accept two mouse devices. No matter, because Maplin has a neat kit with a 555 timer and a relay. The relay is wired up across the microswitch in the mouse, and setting the values correctly makes the mouse click about once per second, with a click duration of about 100ms. Good enough.

With the kit built, wired into the mouse, a small app built to test the device, and a nice project box constructed, [Jarunzel] had exactly what he needed. There’s even a video of this mouse clicker in action. You can check out that riveting footage below.


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Alexa – NodeMCU: WeMo Emulation Made Simple

Let’s connect a 4 Channel relay module to control 2 lamps and 2 outlets as shown in above diagram.

We will create 4 “single smart devices”:

  • Light1 ==> Relay 1 ==> NodeMCU D5
  • Light2 ==> Relay 3 ==> NodeMCU D7
  • Outlet1 ==> Relay 2 ==> NodeMCU D6
  • Outlet2 ==> Relay 4 ==> NodeMCU D8

and 3 groups of combined devices:

  • All Devices (Light1, Light2, Outlet1 and Outlet2)
  • Living Room (Light1 and Outlet1)
  • Bed Room (Light2 and Outlet2)

Download and open the file NODEMCU_ALEXA_WeMos_4X_Fauxmo_EXT.ino from my GitHub and change the dummy wifi credentials, with your own:

/* Network credentials */

Confirm that you have properly defined the pins where the relays are connect:

/* Set Relay Pins */
#define RELAY_1 D5 #define RELAY_2 D6 #define RELAY_3 D7 #define RELAY_4 D8

Now, we must define the “name” as our devices will be understood by Alexa:

// Device Names for Simulated Wemo switches
fauxmo.addDevice("Light One"); fauxmo.addDevice("Light Two"); fauxmo.addDevice("Outlet One"); fauxmo.addDevice("Outlet Two"); fauxmo.addDevice("Bed Room"); fauxmo.addDevice("Living Room"); fauxmo.addDevice("All Devices");

And, we must at setup(), define the “callback” function:


The loop() should be:

void loop()
{ fauxmo.handle(); }

The callback function should be developed as below (this is only for Light1):

/* ---------------------------------------------------------------------------
Device Callback ----------------------------------------------------------------------------*/ void callback(uint8_t device_id, const char * device_name, bool state) { Serial.print("Device "); Serial.print(device_name); Serial.print(" state: "); if (state) { Serial.println("ON"); } else { Serial.println("OFF"); } //Switching action on detection of device name if ( (strcmp(device_name, "Light One") == 0) ) { if (!state) { digitalWrite(RELAY_1, HIGH); } else { digitalWrite(RELAY_1, LOW); } }

Note that I used “!state” inside the “if statement”, because the 4 channel relays use reversed logic for activation.

On the Serial monitor you can see the messages exchanged:

[WIFI] Connecting to ROVAI TIMECAP
............................. ==> CONNECTED! [WIFI] STATION Mode, SSID: ROVAI TIMECAP, IP address:

Now, let’s ask to Alexa to find your device. There are 2 methods to do it:

  1. Using the Alexa App in your Smartphone
  2. Asking Alexa to do it directly using voice command, like: “Alexa (in our case “Computer”), Find connected devices” as shown in the video below:


Once Alexa has discovery your device, you can give her voice commands as shown below:


The above screenshot shows the Serial monitor response.

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Catalog of visualization types to find the one that fits your dataset

Catalog of visualization types to find the one that fits your dataset

There are a lot of visualization methods to choose from, and it can be daunting finding the right visual for your data, especially for those just starting out. The Data Viz Project by ferdio is a work-in-progress catalog that aims to make the picking process a bit easier. Start with a bunch of chart types and filter by things like shape, purpose, and data format. If you’re stuck, this should help get the juices going.

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DIY ant killer

Homebrew ant killer made from sugar, borax, and water is very effective in keeping ants out of the house. Dissolve a half cup of sugar with 1.5 tablespoons of borax into 1.5 cups of warm water. Then dip a cotton ball into the solution and set it on a countertop (where kids and pets won’t eat it). The ants will flock to it and 12 hour later, you won’t see any more ants for a long time. Get a one-pound bag of borax on Amazon for $8.50 (which you can also use to make slime).

Image: Balaram Mahalder/Wikipedia

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Multiple Monitors With Multiple Pis

One of the most popular uses for the Raspberry Pi in a commercial setting is video walls, digital signage, and media players. Chances are, you’ve probably seen a display or other glowing rectangle displaying an advertisement or tweets, powered by a Raspberry Pi. [Florian] has been working on a project called info-beamer for just this use case, and now he has something spectacular. He can display a video on multiple monitors using multiple Pis, and the configuration is as simple as taking a picture with your phone.

[Florian] created the info-beamer package for the Pi for video playback (including multiple videos at the same time), displaying public transit information, a twitter wall, or a conference information system. A while back, [Florian] was showing off his work on reddit when he got a suggestion for auto-configuration of multiple screens. A few days later, everything worked.

Right now, the process of configuring screens involves displaying fiducials on each display, taking a picture from with your phone and the web interface, and letting the server do a little number crunching. Less than a minute after [Florian] took a picture of all the screens, a movie was playing across three weirdly oriented displays.

Below, you can check out the video of [Florian] configuring three Pis and displays to show a single video, followed by a German language presentation going over the highlights of info-beamer.

Filed under: Raspberry Pi

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