Reducing Seams In FDM Prints With Scarf Joint Seams

March 11, 2024 by Maya Posch 12 Comments

One unavoidable aspect of FDM 3D printing is that each layer consists out of one or more lines that have a beginning and an end. Where these join up, a seam is formed, which can be very noticeable if the same joint exists on successive layers. Taking a hint from woodworking, a possible solution is now being worked on that involves scarf joints. This research is covered by [Michael Laws] in a recent Teaching Tech video on YouTube, where he also details his own printing attempts with a custom 3D model, and a guide by [psiberfunk/Adam L].

The idea for a scarf joint was pitched practically simultaneously by [vgdh] on the PrusaSlicer GitHub, and [Noisyfox] on the OrcaSlicer GitHub. The basic idea follows the woodworking and metalworking version of a scarf joint, with the overlap between two discrete parts across two heavily tapered ends. As with the woodworking version, the FDM scarf joint is not a silver bullet, and with the under development OrcaSlicer builds a lot of the parameters are still being tweaked to optimize the result.

If it can be made to work, it could mean that scarf joints will soon be coming to an OrcaSlicer and PrusaSlicer release near you. Theoretically it should mean faster prints than with randomized seams as fewer print head adjustments are needed, and it may provide a smoother result. Definitely an interesting development that we hope to see come to fruition.

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μRepRap: Taking RepRap Down To Micrometer-Level Manufacturing

March 10, 2024 by Maya Posch 30 Comments

When the RepRap project was started in 2005 by [Dr Adrian Bowyer], the goal was to develop low-cost 3D printers, capable of printing most of their own components. The project slipped into a bit of a lull by 2016 due to the market being increasingly flooded with affordable FDM printers from a growing assortment of manufacturers. Now it seems that the RepRap project may have found a new impetus, in the form of sub-millimeter level fabrication system called the μRepRap as announced by [Vik Olliver] on the RepRap project blog, with accompanying project page.

The basic technology is based around the OpenFlexure project’s Delta Stage, which allows for very precise positioning of an imaging element, or conceivably a fabrication tool. As a first step, [Vik] upgrade the original delta stage to a much reinforced one that can accept larger NEMA17 stepper motors. This also allows for standard 3D printer electronics to control the system much like an FDM printer, only at much smaller scales and with new types of materials. The current prototype [Vik] made has a claimed step accuracy of 3 µm, with a range of tools and deposition materials being considered, including photosensitive resins.

It should be noted here that although this is a project in its infancy, it has solid foundations due to projects like OpenFlexure. Will μRepRap kickstart micrometer-level manufacturing like FDM 3D printing before? As an R&D project it doesn’t come with guarantees, but color us excited.

Thanks to [Tequin] for the tip.

Fastest FPV drone, pending official confirmation. (Credit: Luke Maximo Bell)

Got To Go Fast: The Rise Of Super-Fast FPV Drones

March 10, 2024 by Maya Posch 28 Comments

Generally when one considers quadcopter drones, the term ‘fast’ doesn’t come to mind, but with the rise of FPV (First Person View) drones, they have increasingly been designed to go as fast as possible. This can be for competitive reasons, to dodge enemy fire on a battlefield, or in the case of [Luke Maximo Bell] to break the world speed record. Over the course of months he set out to design the fastest FPV drone, involving multiple prototypes, many test runs and one failed official speed run.

The components of the third FPV drone attempt, as used with the world record attempt. (Credit: Luke Maximo Bell)

The basic design of these designed-for-speed FPV drones is more reminiscent of a rocket than a quadcopter, with the upside-down propellers requiring the operator first lifting the drone into the air from an elevated position. After this the drone transitions into a level flight profile by rotating with the propellers pointing to the back. This gives the maximum thrust, while the body provides lift.

Although this seems simple, flying this type of drone is very hard, as it’s hard to tell what is happening, even when landing. [Luke] ended up installing a camera in the nose which can rotate to provide him with different angles. Tweaking the flight computer to deal with the control issues that occur at speeds above 300 km/h.

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How Thermal Post-Curing Resin Prints Affects Their Strength

March 10, 2024 by Maya Posch 6 Comments

Tensile strength of resin parts. (Credit: CNC Kitchen) — Credit: CNC Kitchen

Resin 3D prints have a reputation for being brittle, but [Stefan] over at [CNC Kitchen] would like to dispel this myth with the thing which we all love: colorful bar graphs backed up by scientifically appropriate experiments. As he rightfully points out, the average resin printer user will just cure a print by putting it in the sunshine or in a curing station that rotates the part in front of some UV lights. This theoretically should cause these photosensitive resins to fully cure, but as the referenced Formlabs documentation and their Form Cure station indicate, there’s definitely a thermal element to it as well.

To test the impact of temperature during the UV curing process, the test parts were put into an oven along with the UV lamp. Following this uncured, ambient cured and parts cured at 40 to 80 ºC were exposed to both tensile strength tests as well as impact strength. The best results came from the Siraya Tech Blu resin cured at 80 ºC, with it even giving FDM-printed parts a run for their money, as the following graphs make clear. This shows the value of thermal post-curing, as it anneals the resin prints. This reduces their impact strength somewhat, but massively improves their tensile strength.

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Ender 3 Plotter Attachment For Printing Onto Cassettes

March 9, 2024 by Maya Posch 15 Comments

One way to look at FDM 3D printers is as machines that turn filament into three-dimensional objects, but at their core they are much more versatile than that. Since they can move just about any tool around in 3D space, you can also use them for plotter tasks, a fact that [Geoffrey Gao] made use of when he had to write labels for a stack of music tapes. The resulting FS-Plotter project is based around a Creality Ender 3 FDM printer. Standard g-code from PrusaSlicer is used to move a pen around, after the latter has been fitted into a (3D-printed) spring-loaded fixture.

The cassette tape is fitted into its own fixture that is attached to the printer bed to hold it in place, while the writing utensil can move in its spring-loaded fixture to account for some unevenness on the surface it’s writing on. In the linked GitHub project a PrusaSlicer profile is provided that can generate 2D plotter Gcode. Where [Geoffrey] says that this project is very useful to him as a musician is that it enables him to make small runs of tapes with professional printing, without running into extra expenses.

Beyond putting a writing utensil into the holder, it could also be used for light engraving and similar tasks, while still making it possible to switch between the FDM hotend and this plotter attachment as needed. For about $30 in parts, it doesn’t seem like a bad deal to get a small-ish plotter and maybe give that old Ender 3 a second life.

Infotainment system playing back from USB. (Folkert van Heusden)

Create Virtual USB Sticks With A Raspberry Pi Zero

March 9, 2024 by Maya Posch 28 Comments

Playing back music files from USB sticks is a common feature these days, and is built-into the infotainment system in [Folkert van Heusden]’s Opel Astra. Unfortunately such USB playback features often come with a range of limitations on things like audio codecs, and in the case of [Folkert]’s car, a 1000 file limit. This had him looking at an alternative to lugging a lot of USB sticks around to avoid the horror of hearing the same songs within a week while commuting. The solution? Make a Raspberry Pi Zero into a virtual USB mass storage device using the Mass Storage Gadget (MSG) driver in the Linux kernel.

Picking USB storage as the ideal option here comes mostly from the age of the infotainment system, which lacks Bluetooth, and the audio input jack is rather crackly. Of course, having the Raspberry Pi Zero pretend to be a storage device via the MSG driver wouldn’t solve the file limit, but to get around this two Python scripts were written: one which creates images from a folder of music files, and another which randomly picks one of the available images from the Zero’s SD card and configures the MSG driver to use it.

As for the list of future improvements, there is mounting the RPi Zero’s SD card as read-only to deal with the power-off when the car is shut down, and the creating of images requires to be run as root due to the use of loopback devices. As a Proof-of-Concept it does seem to be on the right track.

It’s not just the older infotainment systems that get to have all the fun. If you’re lucky enough to have Linux running in the dashboard, you might be little more than a Bash script away from bending the system to your will.

Extracting SecOC Keys From A 2021 Toyota RAV4 Prime

March 8, 2024 by Maya Posch 7 Comments

With the recently introduced SecOC (Secure Onboard Communication) standard, car manufacturers seek to make the CAN bus networks that form the backbone of modern day cars more secure. This standard adds a MAC (message authentication code) to the CAN messages, which can be used to validate that these messages come from a genuine part of the car, and not from a car thief or some third-party peripheral.

To check that it isn’t possible to circumvent SecOC, [Willem Melching] and [Greg Hogan] got their hands on the power steering (EPS) unit of a Toyota RAV4 Prime, as one of the first cars to implement this new security standard.

As noted by [Willem], the ultimate goal is to be able to run the open source driver assistance system openpilot on these SecOC-enabled cars, which would require either breaking SecOC, or following the official method of ‘rekeying’ the SecOC gateway.

After dumping the firmware of the EPS Renesas RH850/P1M-E MCU via a voltage fault injection, the AES-based encryption routines were identified, but no easy exploits found in the main application. This left the bootloader as the next target.

Ultimately they managed to reverse-engineer the bootloader to determine how the update procedure works, which enabled them to upload shellcode. This script then enabled them to extract the SecOC keys from RAM and send these over the CAN bus. With these keys the path is thus opened to allow any device to generate CAN messages with valid SecOC MACs, effectively breaking encryption. Naturally, there are many caveats with this discovery.

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