Using Photogrammetry To Design 3D Printed Parts

[Stefan] is building a fixed wing drone, and with that comes the need for special mounts and adapters for a GoPro. The usual way of creating an adapter is pulling out a ruler, caliper, measuring everything, making a 3D model, and sending it off to a 3D printer. Instead of doing things the usual way, [Stefan] is using photogrammetric 3D reconstruction to build a camera adapter that fits perfectly in his plane and holds a camera securely.

ScanPhotogrammetry requires taking a few dozen pictures with a camera, using software to turn these 2D images into a 3D model, and building the new part from that model. The software [Stefan] is using is Pix4D, a piece of software that is coincidentally used to create large-scale 3D models from drone footage.

With the 2D images turned into a 3D model, [Stefan] imported the .obj file into MeshLab where the model could be cropped, smoothed, and the file size reduced. From there, creating the adapter was as simple as a little bit of OpenSCAD and sending the adapter model off to a 3D printer.

Just last week we saw photogrammetry used in another 3D object scanner. The results from both of these projects show real promise for modeling, especially with objects that are difficult to measure by hand.

Take Your 3D Printing to the Next Dimension

In what is being hailed as the next great advancement in 3D printing, scientists have been able to get a 3D printed shape to change form when it is exposed to water, bringing 3D printing squarely into the realm of the fourth dimension. Although the only examples we’ve seen so far are with relatively flat prints (which arguably subtracts one “D” from the claim) the new procedure is one which is groundbreaking for the technology.

The process uses cellulose fibers which, when aligned in a particular way and exposed to water, swell in order to change shape. This is similar to how a bimetallic strip in a thermostat works, but they really took their inspiration from biological processes in plants that allow them to change shape according to environmental conditions. It’s hard to tell if this new method of printing will forever alter the landscape of 3D printing but, for now, it’s an interesting endeavor that will be worth watching. The video after the break shows a fast-motion print using the technique, followed by a demo of the print submersed in water.

We often see new technological advancements that use biology as a springboard for new ideas, and this one is no different. There have been building structures inspired by pinecones and this Processing hack inspired by squid. Biology is all around us, and any of it could be used for inspiration for your next project!

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The Triumph of Open Design and the Birth of a FormLabs Aftermarket

Whilst designing hardware, it’s easy to shut the doors, close the blinds, and bury ourselves deeply into an after-hours design session. Although it’s tempting to fly solo, it’s likely that we’ll encounter bugs that others have handled, or perhaps we’ll realize that we forgot to add a handy feature that someone else could’ve noticed before we sent the darned PCB files out for fab. All that said, if we probe the community around us and ask for feedback, we can produce a project that’s far more functional and feature-complete in less time than if we were to design solo. Who knows? With enough eyes giving feedback on your project, maybe others will get excited enough to want one for themselves! [Andrew Werby] and [Zak Timan] on the FormLabs forums did just that: through months of iterative design and discussion on the FormLabs forums, they’ve created the first 3rd party glass resin tank that’s altogether sturdier, longer-lasting, more scratch-resistant, and less distorting than the original resin tank. And guess what? After months of trials through a few brave customers, you too can be the proud owner such a tank as they’re now up for sale on [Zak’s] website.
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Experiments With A Bowden Extruder Filament Force Sensor

We were excited to learn that someone had started working with force sensors on filament extruders, especially after we posted about a recent development in filament thickness sensors.

[airtripper] primarily uses a Bowden extruder, and wanted to be a little more scientific in his 3D printing efforts. So he purchased a force sensor off eBay and modified his extruder design to fit it. Once installed he could see exactly how different temperatures, retraction rates, speed, etc. resulted in different forces on the extruder. He used this information to tune his printer just a bit better.

More interesting, [airtripper] used his new sensor to validate the powers of various extruder gears. These are the gears that actually transfer the driving force of the stepper to the filament itself. He tested some of the common drive gears, and proved that the Mk8 gear slipped the least and provided the most constant force. We love to see this kind of science in the 3D printing community — let’s see if someone can replicate his findings.

 

Solder Stencils with a 3D Printer

If you are soldering with paste, a stencil makes life a lot easier. Sure, you can apply paste by hand with a syringe, but a modern PCB might have hundreds or even thousands of pads. Like a lot of us, [Robert Kirberich] doesn’t like paying to have stencils made and he wondered if he could use his 3D printer to make stencils. He found the answer was yes.

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Thermaltake Gets On The 3D Printing Bandwagon

We’re interested by a move from Thermaltake, a manufacturer of computer cases, fans, and power supplies. Thermaltake has released a computer case designed to be modded by those with a 3D printer. They released a set of models that fits the new case. These are all hosted on a service much like Thingiverse. So if you want a single SSD or a whole rack, print the model. Watercooling? There’s a model for that. In concept, it’s very cool.

We’re not certain how to feel about this. Our initial impression was that if Thermaltake is going to launch a case around 3D printing, they should at lease tune their printer and get some nice prints before they take the press photos. On our second pass we became intrigued. Is this a manufacturer cutting costs, crowd-sourcing design and engineering talent for free, or empowering the user? Arguably, a computer case is a great test bed for this kind of interaction.

Despite out skepticism, we’d like to see more manufacturers take this kind of contributing interest in 3d printing. If only to see where it goes. What other products do you think would benefit from this kind of, print the product you actually want model?

Filament Thickness Sensors, What Are They and What Are They Good For?

I keep up with the trends in 3D printing reasonably well. The other day my friend mentioned that filament thickness sensing had been added to the latest version of the Marlin firmware. I had no idea what it was, but it certainly sounded cool. I had to find out more.

In industrial settings, filament is made by pulling extruding molten plastic at a certain speed into a cooling bath. The nozzle for 2.85mm filament and 1.75 mm filament is actually the same size, but the filament is stretched more or less as it leaves the nozzle. By balancing these three variables the extrusion machine can produce any size filament desired. Like any mechanical system, it needs constant adjustment to maintain that balance. This is usually done by measuring the filament with a laser after it has cooled, and then feeding this information back into the system. The better filament manufacturers have multiple lasers and very fast feedback loops. Some of the best offer +-0.04mm or less variation in thickness between any two points on the filament. Some of the worst have larger errors such as +-.10mm. Because the plastic is fed into the extruder at a fixed linear speed, this makes a variation in the volume of the plastic coming out of the nozzle per second. With the best we see a 4.41% variation in the volume of plastic extruded. With the worst we start to see 10.51% or more.

FIlament variation showing up as a cosmetic defect.
Filament variation showing up as a cosmetic defect.

A printer is dumb. It works under the assumption that it is getting absolutely perfect filament. So when it gets 10.51% more plastic, it simply pushes it out and continues with its life. However, if the filament is off enough, this can actually show up as a visible defect on the print. Or in worse cases, cause the print to fail by over or under extrusion of plastic.

So, what does a filament thickness sensor do to correct this issue? To start to understand, we need to look at how the filament is dealt with by the software. When the slicer is compiling the G-code for a 3D print, it calculates the volume of plastic it needs in order to deposit a bead of plastic of a certain width and of a certain height per mm of movement. That was a mouthful. For example, when a printer printing 0.2mm layers moves 1mm it wants to put down a volume that’s 1.0mm long x 0.4mm wide x 0.2mm high. The filament being pushed into the nozzle has a volume per mm determined by the diameter of the filament.

(\pi (radius_{filament})^{2}*length_{filament extruded})=volume

The volume out per mm of filament in.

(layer_{height}*layer_{width}*length_{move}) = volume

The equation we are trying to balance.

Our goal is to integrate the thickness sensor into these functions to see what the thickness sensor is doing. This is a linear equation, so there’s nothing fancy here. Now, the layer height, layer width, and length of the move are determined by settings and model geometry respectively. These are fixed numbers so we don’t care about them. That leaves us the diameter of the filament and the length of filament extruded. As we mentioned before, typically the filament is assumed to be a fixed diameter. So all the software has to calculate is the length of filament that needs to be extruded per mm of combined movement in the x and y so that our volumes match.

But, we know that one of these variables is actually changing per millimeter as well. The filament diameter! So now we have a problem. If the filament diameter is changing all the time, our equation will never balance! In order to fix this we can add a multiplier to our equation. Since we have no control over the width of the filament we can’t modify that value. However, if we know the width of the filament, and we know the value its supposed to be, we can change the length of the filament extruded. This is because unlike the filament, we have control over the stepper motor that drives the extruder. This value is called the extrusion multiplier, and its determination is what the thickness sensor is all about.

So all the filament sensor does is measure the filament’s current diameter. It takes expected diameter and divides it by the value it just measured to get a simple percentage. It feeds that number back into our system as the extruder multiplier and slows or speeds up the stepper motor as needed. Pretty simple.

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Shadows on the sensor from [inornate]’s variation.
There are a few thickness sensors being toyed with right now. The first, as far as I can tell; let me know if I am wrong in the comments, was by [flipper] on thingiverse. He is in his third version now. The sensor works by casting a shadow of the filament as it passes by onto an optical sensor. The firmware then counts the pixels and works backwards to get the diameter. This value is sent to the Marlin firmware on the printer which does the rest. As is usual and wonderful in the open source community, it wasn’t long before others started working on the problem too. [inoranate] improved on the idea by casting more shadows on the sensor. The technique is still brand new, but it will be interesting to see what benefits it reaps.

Now comes the next question,”Is it worth upgrading my printer with a thickness sensor?” If you typically run poor filament, or if you extrude your own, yes. The current sensors can only measure +- .02mm. So for the best filament, you won’t really see a difference, but for worse stuff, you might. The latest firmware of the Lyman filament extruder, for making your own filament, also supports these sensors, letting you feed back into your production system like the industrial machines. All in all a very interesting development in the world of 3D printers.