Omni Wheels Move This CNC Plotter

We’ve always had a soft spot for omni wheels and the bots that move around somewhat bumpily on them. Likewise, CNC pen plotters are always a welcome sight in our tip line. But a CNC plotter using omni wheels is new, and the results are surprisingly good.

Built from the bottom of a spring-form baking pan, [lingib]’s plotter is simplicity itself. Four steppers turn the omni wheels while a hobby servo raises and lowers the pen. The controller is an Uno with a Bluetooth module for smartphone control. Translating wheel rotations into X- and Y-axis motions was not exactly trivial, and the video below shows the results. Lines are a bit wobbly, and it’s clear that the plotter isn’t hitting the coordinates very precisely. But given the somewhat compliant nature of the omni wheels, we’re surprised [lingib] got results as good as these, and we applaud the effort.

[lingib] reports the most expensive part of this $100 build was the omni wheels themselves. We suppose laser-cut MDF omni wheels could reduce the price, or even Mecanum wheels from bent metal and wood. We’re not sure either will help with the precision, though.

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Relive The Dot Matrix Glory Days With Your 3D Printer

With the cost of 3D printers dropping rapidly, we’ve started to see a trend of hackers re-purposing them for various tasks. It makes perfect sense; with the hotend and extruder turned off (or removed entirely), you’ve got a machine that can move a tool around in two or three dimensions with exceptional accuracy. Printers modified to carry lasers, markers, and even the occasional rotary tool, are becoming a common sight in our tip line.

Last year [Matthew Rayfield] attached a marker to his 3D printer and had it sketch out some pictures, but recently he decided to revisit the idea and try to put a unique spin on it. The end result is a throwback to the classic dot matrix printers of yore utilizing decidedly modern hardware and software. There’s something undeniably appealing about the low-fi nature of dot matrix printing, and when fed the appropriate images this setup is capable of producing something which we’ve got to admit is dangerously close to being art.

To create these images, [Matthew] has created “Pixels-to-Gcode”, an online service that anyone can use to turn an arbitrary image into GCode they can feed their 3D printer. There’s a number of options available for you to play with so you can dial in the specific effect you’re looking for. Pointillist images can be created using a tight spacing of dots, but widen them up, and your final image becomes increasingly abstract.

The hardware side of this project is left largely as an exercise for the reader. [Matthew] has attached a fine-point pen to his printer’s head using a rubber band, but admits that it’s far from ideal. A more robust approach would be some kind of 3D printed device that allows you to quickly attach your pen or marker so the printer can be easily switched between 2D and 3D modes. We’d also be interested in seeing what this would look like if you used a laser mounted on the printer to burn the dots.

Back in the ancient days of 2012, we saw somebody put together a very similar project using parts from floppy and optical drives. The differences between these two projects, not only in relative difficulty level but end result, is an excellent example of how the hacker community is benefiting from the widespread availability of cheap 3D motion platforms.

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Pen Plotter From Salvaged Printer Parts

Like many of us, [Benjamin Poilve] was fascinated when he took apart a broken printer. He kept the parts, but unlike most of us, he did something with them, building a neat little plotter called the Liplo. Most pen plotters work by moving the pen on two axes, but [Benjamin] took a different approach, using the friction drive bars from the printer to move the paper on one axis, and a servo to move the pen on the other. He’s refined the design from its initial rough state to create a very refined final product that uses a combination of salvaged, 3D-printed, and CNC-milled parts.

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Make an Impression at the Bar with a CNC Coaster Plotter

If you’re anything like us, your success with the opposite sex at the bar wasn’t much to brag about. But imagine if you had only had this compact CNC polar plotter and could have whipped up a few custom coasters for your intended’s drink. Yeah, that definitely would have helped.

Or not, but at least it would have been fun to play with. This is actually an improved version of [bdring]’s original “Polar Coaster”. Version 2 is really just a more compact and robust version of the original. The new one has a custom controller for the steppers and pen-lift servo, and everything is mounted neatly to the main PCB. Where the original used a timing belt to drive the platter, the new one uses 3D-printed helical gears, and the steppers have been replaced by slimmer motors. It even has an SD card and smartphone UI, and the coasters look pretty good.

There’s no video of the new one, but you can see its predecessor in action below and imagine the possibilities. Snap a picture and have a line art rendition of someone plotted while you’re waiting for drinks? Just remember not to take any laser engraved wooden nickels.

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Maze Generator Keeps Plotter (and Kids) Busy

We can tell that [Jon Howell] is our kind of guy. After updating his vintage 1985 Hewlett-Packard plotter with WiFi and the ability to load SVG files, he obviously needed to find a bunch of stuff to run off with it. Gotta justify those hacks somehow. So he doubled down and decided support a hack with another hack by writing a maze generator to keep his plotter well fed. He was kind enough to unleash his creation on an unsuspecting Internet as an open source project, and now we all can benefit from a couple of reams worth of mazes.

The generator itself is written in Java, and should work on whatever operating system your box happens to be running thanks to the *nix and Windows wrapper scripts [Jon] provides. To create a basic maze, one simply needs to provide the script with the desired dimensions and the paper size. You can define the type of paper with either standard sizes (such as --paper a4) or in the case of a plotter with explicit dimensions (--paper 36x48in).

If you aren’t a big fan of right angles, there’s support for changing the internal geometry of the maze to use a hexagonal or triangle grid. You can even pass the program a black and white PNG “mask” which it will use as the boundaries for the maze itself, allowing for personalized puzzles of whatever shape catches your fancy. [Jon] even ran the Wrencher though his software, leading to the creation of a maze which we can neither confirm nor deny will be making an appearance on our Christmas cards this year.

Whether you need to prove to your significant other that the hours you spent fiddling with your plotter are well spent, or an easy way to entertain the junior humans in your life, you can thank [Jon] for your solution.

Vintage Plotter Turned Fruit Spectrometer

Fruit can be a tricky thing: if you buy it ripe you’ll be racing against time to eat the pieces before they turn into a mushy mess, but if you buy the ones which are a bit before their prime it’s not always easy to tell when they’re ready to eat. Do you smell it? Squeeze it? Toss it on the counter to see if it bounces? In the end you forget about them and they go bad anyway. That’s why here at Hackaday we sustain ourselves with only collected rainwater and thermo-stabilized military rations.

But thankfully Cornell students [Christina Chang], [Michelle Feng], and [Russell Silva] have come up with a delightfully high-tech solution to this decidedly low-tech problem. Rather than rely on human senses to determine when a counter full of fruit has ripened, they propose an automated system which uses a motorized spectrometer to scan an arrangement of fruit. The device measures the fruit’s reflectance at 678 nm, which can be used to determine the surface concentration of chlorophyll-a; a prime indicator of ripeness.

If that sounds a bit above your pay grade, don’t worry. The students were able to build a functional prototype using a 1980’s era plotter, a Raspberry Pi, and a low-cost AS7263 NIR spectral sensor from SparkFun which just so happens to have a peak responsivity of 680 nm. The scanning is performed by a PIC32MX250F128B development board with an attached TFT LCD display so the results can be easily viewed. The Raspberry Pi is used in conjunction with a Adafruit PCA9685 I2C PWM driver to control the plotter’s stepper motors. The scanning and motor control could be done with the PIC32 alone, but to save time the students decided to use the Raspberry Pi to command the PCA9685 as that was what the documentation and software was readily available for.

To perform a scan, the stepper motors home the AS7263 sensor module, and then passes it under the fruit which is laying on a clear acrylic sheet. Moving the length of the acrylic sheet, the sensor is able to scan not only multiple pieces of fruit but the entirety of each piece; allowing it to determine for example if a section of a banana has already turned. The relative ripeness of the fruit is displayed to the user on the LCD display as a heatmap: the brighter the color the more ripe it is.

At the end of their paper, [Christina], [Michelle], and [Russell] note that while the scanner worked well there’s still room for improvement. A more scientific approach to calculating how ripe each fruit is would make the device more accurate and take out the guess work on the part of the end user, and issues with darker colored fruit could potentially be resolved with additional calibration.

While a spectrometer might sound like the kind of equipment that only exists in multi-million dollar research laboratories, we occasionally see projects like this which make the technology much more accessible. This year we saw a compact spectrometer in the Hackaday Prize, and going a bit farther back in time we even featured a roundup of some of the most impressive spectrometer builds on Hackaday.io.

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Mug-O-Matic Plots On Coffee Mugs

There is something fascinating about watching an autonomous machine. An automatic car wash, a soda vending machine that picks up the product behind a window, a plotter, or a robot like a CNC or 3D printer are all interesting to watch. Although [EngineerDog] bills Mug-O-Matic as a tiny CNC, we think it is more of a plotter for coffee mugs. It’s still fun to watch though, as you can see in the video below.

The design has about 60 printed parts and uses a Sharpie at the business end. It accepts gcode and can even emblazon your favorite mug with our own Jolly Wrencher, so you know we like it.

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