Almost everyone who is involved with 3D printing thinks to themselves at some point, “this could all be done using a closed-loop system and DC motors”. Or at least everyone we know. There’s even one commercial printer out there that uses servo control, but because of this it’s not compatible with the rest of the (stepper-motor driven) DIY ecosystem.
[LoboCNC] wanted to change this, and he’s in a unique position to do so, having previously built up a business selling PIC-based servo controllers. His “servololu” is essentially a microcontroller and DC motor driver, with an input for a quadrature encoder for feedback. The micro takes standard step/direction input like you would use to drive a stepper motor, and then servos the attached DC motor to the right position. It even signals when it has an error.
Continue reading “Is It A Stepper? Or Is It A Servo?”
Give some mundane, old gear to an artist with a liking for technology, and he can turn it into a mesmerizing piece of art. [dmitry] created “red, an optic-sound electronic object” which uses simple light sources and optical elements to create an audio-visual performance installation. The project was the result of his collaboration with the Prometheus Special Design Bureau in Kazan, Russia. The inspiration for this project was Crystall, a reconstruction of an earlier project dating back to 1966. The idea behind “red” was to recreate the ideas and concepts from the 60’s ~ 80’s using modern solutions and materials.
The main part of the art installation consists of a ruby red crystal glass and a large piece of flexible Fresnel lens, positioned in front of a bright LED light source. The light source, the crystal and the Fresnel lens all move linearly, constantly changing the optical properties of the system. A pair of servos flexes and distorts the Fresnel lens while another one flips the crystal glass. A lot of recycled materials were used for the actuators – CD-ROM drive, an old scanner mechanism and old electric motors. Its got a Raspberry-Pi running Pure Data and Python scripts, with an Arduino connected to the sensors and actuators. The sensors define the position of various mechanical elements in relation to the range of their movement. There’s a couple of big speakers, which means there’s a beefy amplifier thrown in too. The sounds are correlated to the movement of the various elements, the intensity of the light and probably the color. There’s two mechanical paddle levers hanging in there, if you folks want to hazard some guesses on what they do.
Check out some of [dmitry]’s earlier works which we featured. Here’s him Spinning a Pyrite Record for Art, and making Art from Brainwaves, Antifreeze, and Ferrofluid.
Continue reading “Circuit Bender Artist bends Fresnel Lens for Art”
In the open hardware world, we like to share 3D design files so that our friends and (global) neighbors can use and improve them. But we’ve all printed things from time to time that we’d like to keep secret. At least this is the premise behind this article in Science which proposes a novel method of 3D-printer-based industrial espionage: by recording the sound of the stepper motors and re-creating the toolpath.
Unfortunately, the article is behind a paywall so we’re short on the details, but everyone who’s played the Imperial March on their steppers has probably got the basic outline in their mind. Detecting the audio peak corresponding to a step pulse should be fairly easy. Disentangling the motions of two axes would be a bit harder, but presumably can be done based on different room-acoustic filtering of the two motors. Direction is the biggest question mark for us, but a stepper probably has a slightly audible glitch when reversing. Keeping track of these reversals could do the trick.
What do you think? Anyone know how they did it? Does someone with access to the full article want to write us up a summary in the comments?
[Thanks LVfire via Ars Technica]
[Edit: We were sent a copy of the full article (thanks [PersonUnknown]!) and it doesn’t explain any technical details at all. Save yourself the effort, and have fun speculating, because reading the article won’t help.]
Brushless DC motors, and their associated drive electronics, tend to be expensive and complicated. [Ottoragam] was looking for a cheaper alternative and built this Brushed DC motor servo controller and the results look pretty promising. Check out the video after the break.
He needed a low cost, closed loop drive for his home-brew CNC. The servo drive is able to supply a brushed DC motor with up to 7 A continuous current at up to 36 V which works out to about 250 W or 1/3 HP. It does closed loop control with feedback from a quadrature encoder. The drive accepts simple STEP and DIRECTION signals making it easy to interface with micro controllers and use it as a replacement for stepper motors in positioning applications. All of the control is handled by an ATmega328P. It takes the input signals and encoder data, does PID control, and drives the motor via the DRV8701 full bridge MOSFET driver. There’s also some error detection for motor over-current and driver under-voltage. Four IRFH7545 MOSFETs in H-bridge configuration form the output power stage.
This is still work in progress, and [Ottoragam] has a few features pending in his wish list. The important ones include adding a serial interface to make it easy to adjust the PID parameters and creating a GUI to make the adjustment easier. The project is Open Source and all source files available at his Github repository. The board is mostly surface mount, but the passives are all 0805, so it ought to be easy to assemble. The QFN footprint for the micro controller could be the only tricky one. [Ottoragam] would love to have some beta testers for his boards, and maybe some helpful comments to improve his design.
Continue reading “Brushed DC Servo Drive”
This one is a bit dated, but the lessons are still relevant. [Zach Hoeken] posted about the challenges he faced building a CNC stepper driver. He was experimenting with Toshiba motor drivers back in 2012.
The modular motor driver boards he built were based on the THB6064AH – capable of 1/64th step, and 4.5 Amps at up to 50V. [Zach] built a test jig to run the boards through their paces. A couple of messed tracks was the least of his problems – easily fixed by cutting traces and using jumper wires to correct the errors. But the header footprints for the motor drive boards got reversed. The only way out was to solder the headers on the back side.
LESSON : Always check footprint orientation and pin numbering before sending boards to fab.
The surprising part was when someone as experienced as [Zach] messed up on Ohms Law. Based on the current he wanted the motors to run at, his sense resistors needed to be 3.2W, but he’d used SMD footprints (0805 likely) instead. Those tiny resistors couldn’t be used at all, and the 5W resistors plonked on looked like an ugly hack.
Continue reading “Fail of the week : Watt a loss”
Turning the classic toy Etch-A-Sketch into a CNC drawing tablet intrigues a large number of hackers. This version by [GeekMom] certainly takes the award for precision and utility. Once you build something like this, you can hardly stop writing firmware for it; [GeekMom] produced an entire Arduino library of code to allow joystick doodling, drawing web images, and a self-erasing spirograph mode. The topper is the version that runs as a clock!
The major hassle with making a CNC version of this toy is the slop in the drawing mechanism. There is a large amount of backlash when you reverse the drawing direction. If that isn’t bad enough, the backlash is different in the vertical or horizontal directions. Part of [GeekMom’s] presentation is on how to measure and correct for this backlash.
The EtchABot uses three small stepper motors. Two drive the drawing controls and the third flips the device forward to erase the previous drawing. The motors are each controlled by a ULN2003 stepper motor drivers. An Arduino Uno provides the intelligence. Optional components are a DS3231 Real Time Clock and a dual axis X-Y joystick for the clock and doodling capability. Laser cut wood creates a base for holding the Etch-A-Sketch and the electronics.
The write up and details for this project are impressive. Be sure to check out the other entries in [GeekMom’s] blog. Watch the complete spirograph video after the break.
Continue reading “Precision CNC Drawing with EtchABot”
Camera slides can make for interesting dolly shots in your videos, or can spice up an otherwise drab time-lapse sequence. When it came time for one of his own, [Bob] did what any hacker would do and rolled his own motorized camera slide in the wood shop.
We always like to see work based on a hacker’s own prior art, and [Bob] managed to leverage parts and techniques from his impromptu claw machine build for this slider. The rollers in this project use the same 3/4″ angle aluminum and skateboard bearings as the previous build. The bearings roll on a plywood strip capped with the same angle stock for durability and low friction. The stepper motor bracket and pillow blocks are 3D printed, as are the timing pulleys. [Bob] admits that the whole rig is a little noisy and blames it on the rough quality of the pulley prints. He has plans to replace them with commercially available pulleys, which should help; one further suggestion we have is to code a soft-start algorithm into the ATtiny85 to eliminate that jerkiness you see when he demos the slider in the video below.
There are plenty of ways to move a camera along a single axis, and a surprising number of them use parts from the roller sports. We’ve covered quite a few of them before, like this slide that uses skateboard trucks, or this non-motorized rig built from fence posts and inline skate wheels.
Continue reading “Mostly Wood Motorized Camera Slider”