Robot Arm Wields Laser, Cares Not For Your Safety

Here at Hackaday we’ve covered a bunch of DIY laser diode projects. And for good reason, they are just cool. We’ve seen people add lasers to their 3D printers, stick one in a milling machine, use a highly modified scanner and even build a simple XY gantry specifically for the task. To say the least there is definitely a wide range of methods for moving around a laser but we’ve never seen anything like what [Sp4rky] sent in to us. He and his friends outfitted an old educational robot arm with a laser.

The robot arm is a 5 axis Armdroid 5100 picked up from eBay for a couple hundred dollars. It didn’t come with a controller but all of the stepper drivers were housed in the base of the arm. After a little tinkering around with the inputs the team was able to get the arm to move by sending serial commands from a PC, through an Arduino Mega which then sends the appropriate signals to the uni-polar stepper drivers. That was the easy part of the build.

The hard part was getting the arm to hold the laser at a consistent angle and height above the table. Inverse Kinematics to the rescue! Since the desired position of the laser, as well as the length of the arm segments is known, mathematical formulas can be derived to determine the necessary arm segment and joint positions while moving the laser around. The process flow starts out with an image in Inkscape, g-code is then generated with this plugin, then sent to the Arduino running a modified version of GRBL that has the inverse kinematic formulas. The Arduino directly controls the stepper drivers and the robotic arm moves. The Arduino also controls 3 constant-current laser drivers made from LM317 regulators. Three laser drivers, why?

Triple Laser Robot[Sp4rky] got his laser diode modules out of surplus medical equipment and, unfortunately, the rated optical wattage was quite low. Since he had 3 diodes, he decided to try to combine the 3 low power beams into one high power beam. This can be done using a prism. A prism splits sunlight into a rainbow of colors because each wavelength(color) of light that passes through the prism is bent a different amount. Since the laser diodes only put out one wavelength of light, the beam bends but does not split or diffuse. A 3D printed bracket points each laser diode at a 3-sided pyramidal prism which sends the combined beam of light straight out the bottom towards the object to be cut or engraved.

This project is cool enough that we would have covered it even if [Sp4rky] wasn’t burning a Hackaday logo. Although it doesn’t hurt for anyone wanting their project to get covered!

Measure Laser Wavelength with a CD and a Tape Measure

Obviously the wavelength of a laser can’t be measured with a scale as large as that of a carpenter’s tape measure. At least not directly and that’s where a Compact Disc comes in. [Styropyro] uses a CD as a diffraction grating which results in an optical pattern large enough to measure.

A diffraction grating splits a beam of light up into multiple beams whose position is determined by both the wavelength of the light and the properties of the grating. Since we don’t know the properties of the grating (the CD) to start, [Styropyro] uses a green laser as reference. This works for a couple of reasons; the green laser’s properties don’t change with heat and it’s wavelength is already known.

It’s all about the triangles. Well, really it’s all about the math and the math is all about the triangles. For those that don’t rock out on special characters [Styropyro] does a great job of not only explaining what each symbol stands for, but applying it (on camera in video below) to the control experiment. Measure the sides of the triangle, then use simple trigonometry to determine the slit distance of the CD. This was the one missing datum that he turns around and uses to measure and determine his unknown laser wavelength.

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DIY Oscilloscope with a Scanning Laser

If you’ve ever used an old-school analog oscilloscope (an experience everyone should have!) you probably noticed that the trace is simply drawn by a beam that scans across the CRT at a constant rate, creating a straight line when there’s no signal. The input signal simply affects the y-component of the beam, deflecting it into the shape of your waveform. [Steve] wrote in to let us know about his home-built “oscilloscope” that works a lot like a simple analog oscilloscope, albeit with a laser instead of  a CRT.

[Steve]’s scope is built out of a hodgepodge of parts including Lego, an Erector set, LittleBits, and a Kano Computer (based on a Raspberry Pi). The Pi generates a PWM signal that controls the speed of a LittleBits motor. The motor is hooked up to a spinning mirror that sweeps the laser across some graph paper, creating a straight laser line.

After he got his sweep working, [Steve] took a small speaker and mounted a mirror to its cone. Next he mounted the speaker so the laser’s beam hits the mirror on the speaker, the spinning sweep mirror, and finally the graph paper display. The scope’s input signal (in this case, audio from a phone) is fed into the speaker which deflects the laser beam up and down as it is swept across the paper, forming a nice oscilloscope-like trace.

While [Steve]’s scope might not be incredibly usable in most cases, it’s still a great proof of concept and a good way to learn how old oscilloscopes work. Check out the video after the break to see the laser scope in action.

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Custom Double-Din Mount for Nexus 7 Carputer

Many new vehicles come with computers built into the dashboard. They can be very handy with features like GPS navigation, Bluetooth connectivity, and more. Installing a computer into an older car can sometimes be an expensive process, but [Florian] found a way to do it somewhat inexpensively using a Nexus 7 tablet.

The size of the Nexus 7 is roughly the same as a standard vehicle double-din stereo slot. It’s not perfect, but pretty close. [Florian] began by building a proof of concept mounting bracket. This model was built from sections of MDF hot glued and taped together. Plastic double-din mounting brackets were attached the sides of this new rig, allowing it to be installed into the dashboard.

Once [Florian] knew that the mounting bracket was feasible, it was time to think about power. Most in-vehicle devices are powered from the cigarette lighter adapter. [Florian] went a different direction with this build. He started with a cigarette lighter to USB power adapter, but he cut off the actual cigarette lighter plug. He ended up wiring this directly into the 12V line from the stereo’s wiring harness. This meant that the power cord could stay neatly tucked away inside of the dashboard and also leave the cigarette lighter unused.

[Florian] then wanted to replace the MDF frame with something stronger and nicer. He modeled up his idea in Solidworks to make sure the measurements would be perfect. Then the pieces were all laser cut at his local Techshop. Once assembled, the plastic mounting brackets were placed on the sides and the whole unit fit perfectly inside of the double-din slot.

When it comes to features, this van now has it all. The USB hub allows for multiple USB devices to be plugged in, meaning that Nexus only has a single wire for both power and all of the peripherals. Among these peripherals are a USB audio interface, an SD card reader, and a backup camera. There is also a Bluetooth enabled OBD2 reader that can monitor and track the car’s vitals. If this project seems familiar to you, it’s probably because we’ve seen a remarkably similar project in the past.

Paper Cutter Becomes A Laser Engraver

Small and powerful laser diodes are getting cheaper and cheaper, and there are a few commercial products that give anyone the ability to cut paper and vinyl with a computer-controlled cutting machine. What happens when you combine the two? The beginnings of a hacked together laser engraver.

For this build, [Peter] is using a Silhouette Portrait, a desktop CNC cutting machine that’s usually used for vinyl decals and intricately cut paper crafts. This machine isn’t limited to mere decorative crafts – it’s been used for cutting PCB stencils and other pseudo-industrial tasks.

Because the Silhouette Portrait has an interface that allows just about any CAM software to control it, the only thing [Peter] needed to make for his experiments in laser engraving was a mount to hold the laser diode. Luckily, the laser had a similar form factor to the cutting blades for the machine, and a bit of tape held everything together.

Focusing the laser was done by unscrewing the lens, and with a bit of trial and error, [Peter] was able to make a few marks in the material of his choice. This isn’t a laser cutter, but with a little more work it will make a fantastic laser engraver.

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DIY Hot Wheels Drag Race Timer

[Apachexmd] wanted to do something fun for his three-year-old son’s birthday party. Knowing how cool race cars are, he opted to build his own Hot Wheels drag race timer. He didn’t take the easy way out either. He put both his electronics and 3D printing skills to the test with this project.

The system has two main components. First, there’s the starting gate. The cars all have to leave the gate at the same time for a fair race, so [Apachexmd] needed a way to make this electronically controlled. His solution was to use a servo connected to a hinge. The hinge has four machine screws, one for each car. When the servo is rotated in one direction, the hinge pushes the screws out through holes in the track. This keeps the cars from moving on the downward slope. When the start button is pressed, the screws are pulled back and the cars are free to let gravity take over.

The second component is the finish line. Underneath the track are four laser diodes. These shine upwards through holes drilled into the track. Four phototransistors are mounted up above. These act as sensors to detect when the laser beam is broken by a car. It works similarly to a laser trip wire alarm system. The sensors are aimed downwards and covered in black tape to block out extra light noise.

Also above the track are eight 7-segment displays; two for each car. The system is able to keep track of the order in which the cars cross the finish line. When the race ends, it displays which place each car came in above the corresponding track. The system also keeps track of the winning car’s time in seconds and displays this on the display as well.

The system runs on an Arduino and is built almost exclusively out of custom designed 3D printed components. Since all of the components are designed to fit perfectly, the end result is a very slick race timer. Maybe next [Apachexmd] can add in a radar gun to clock top speed. Check out the video below to see it in action. Continue reading “DIY Hot Wheels Drag Race Timer”

Laser-Etch Stainless with Only Plaster & Alcohol

Many hobbyists and hackerspaces have the $500 Chinese 40W lasercutters which most of us know are about as successful at etching metals as a featherduster is at drilling. [Frankie] and [Bryan] have figured out a way to use the laser to chemically activate an etching process. See experiment part 2 as well.

First, to be clear, they are using a quality 40W Epilog Zing, not the cheap one, but40W is40W. They mixed the plaster (calcium sulfate) with Isopropyl until it resembled white ketchup. After either thinly painting or airbrushing the material onto the stainless surface (both worked), the mixture is dried with a heatgun then put into the laser. 100% power and 5% speed was what worked for them.

The result was an engrave with a noticeable bite. Something they claim had no effect at all without the mixture.

Stainless steel is an alloy of iron and some chromium – not the same as chrome-plated steel. [Frankie]’s explanation of the chemistry is that the surface layer of the stainless is a transparent chromium oxide. With the heat of the laser, the calcium and chromium swap dance partners. Calcium takes the oxygen and chromium takes the sulfate. The calcium oxide washes off but the chromium sulfate causes the etch.

Next time you’re at your local space, give this a try.