Coming June 15th to NYC Resistor, the 2013 Interactive Show. We’re still soliciting for a few more projects, but we’ve already got a great menagerie of really interesting & fun work lined up. This year’s theme is Digital Archeology. Expect to see the old, and the old hacked into new… Our show usually sells out far in advance, so don’t dawdle. Get your tickets here: http://
As a followup to our reverse engineering and configuration of 6DOF PUMA robot arms, we’ve updated our controller source code to have full closed form inverse kinematics support. The math is based on A Geometric Approach in Solving the Inverse Kinematics of PUMA Robots, by Lee and Ziegler (1983). Due to the configuration of prismatic and rotational joints in the PUMA arms, it is possible to derive a two part direct trigonometric solutions to the IK problem for this type of arm.
The IK solution uses the DH Parameters to compute the three joint angles for the major axes (the rotation around the stalk, the upper-arm angle, and the fore-arm angle) such that the center of the spherical joint will be placed at a given XYZ position. There are two binary additional binary parameters for this configuration: RIGHT/LEFT controls the orientation of the arm on the right or left side of the stalk, and OVER/UNDER for the configuration of the elbow pointing up or down. See figure 5 in the paper for a diagram of the four possible combinations of these two parameters.
Once the first three theta angles are known, the second phase of the IK solution computes the last three wrist joint angles given the third binary parameter UP/DOWN, and three vectors: the “approach vector” a that points in the direction of the tool, the “sliding vector” s that points in the direction of the grasping joint, and the “normal vector” n that points towards the top of the tool. Figure 4 from the paper shows the relationship of these three vectors in the hand coordinate system.
This video shows the IK iterating between two points (in RIGHT and OVER mode) and generating a piecewise linear path that holds the tool (a cheap pen) mostly level on a constant heading aligned with the X axis. It is a little jerky since the motor controllers don’t have a way to chain commands between points and my calibration on the joint lengths and angles isn’t perfect. Also note that the wrist joints are cross-coupled and require proportional adjustments based on the other joints positions, so the code has some fudge factors to try to account for this behaviour. There are also some corner cases to be sorted out when the “best” joint angles switch quadrants, which will swing the tool around in a circle.
The code isn’t super clean and can use some refactoring to move the DH parameters into a config file, but hopefully you’ll enjoy the human readable code compared to the machine generated ikfast output.
Rapid prototyping tools are great for quick hacks, but their real power lies in their ability to allow you to quickly iterate and refine a design. Earlier this week I hacked together a primitive nine-channel punched paper tape reader, but it had a number of limitations: the LEDs that I was using to read the bits were noisy and slow, the materials used didn’t mask the light well enough, the tape wasn’t mechanically aligned well, the electronics were a mess and the entire mechanism was difficult to use. This Friday, I decided to do what my third-grade teacher would tell me to do every time I half-assed something: go back and do it right.
This time I used proper phototransistors and IR LEDs I scrounged up around the space (thanks, Miria and Raphael!). Because they’re 5mm in diameter (and the spacing between channels is only 2.54mm), I had to come up with a new sensor packing. This one reads bits from four separate columns over a space of five columns, requiring an internal buffer of five columns to reconstruct a single column of data. Even so, the spacing was tight, and I had to sand down the flanges of the phototransistors and LEDs to make everything fit. I milled simple PCBs for both sides to keep things nice and neat, and used a small surface-mount potentiometer to limit the current to the LEDs in case the paper wasn’t thick enough to block enough light. The light mask is made of black acetal this time, and the spacers include runners to help keep the tape straight. There’s still no automatic feed mechanism, but we now have a reader that’s fast and reliable enough to read tapes in earnest.
The updated code, mechanical drawings, and PCB designs are all up on Github. There are still a few tweaks we’d want if we were going to scan more tapes, but this version works very well. Now we just have to figure out what to do with all these PDP-8 binaries. Any ideas?
(Note to time-travelling computer conservators: in the past/future, please do not store your paper tapes in damp basements. These programs are stinky. The Fortran compiler, in particular, is exceptionally foul. Yours truly, phooky.)
Ever wanted to trick your nails out with a paint-job worthy of notice? This is how… and no need to pay a salon $50 for the glory. We’ll teach you how on Saturday (5:30-8:30pm) after our Laser Class, using templates stamps and other techniques. We’ll have a small selection of polishes, so if you’re after a specific color combo you may want to bring your own. Tickets still available here– be prepared to come with a base-coat or to add one while you’re there. GUYS WELCOME! (Remember you can also paint your toes).
Trammell came across a cache of punched paper tape recently. My immediate impulse was to create the most primitive tape reader possible. Thusly:
The rig is composed of a Teensy++ 2.0, eighteen red LEDs, eighteen resistors, and a few bits of laser-cut plastic. LEDs are used to both illuminate the paper and sense the holes. The sensor design is based on the classic Arduino LED sensing code. It’s not very reliable, but it’s a fun afternoon proof-of-concept.
If you’re interested, the code and design files are up on github.
Some of you may remember the last installment in our on-going series on computational necromancy, where I made a call out to the internet to help revive my bit-rotted copy of the once-lost Cray Operating System. An amazing programmer named Andras has answered that call in a way I would have never thought possible – he not only used his kung-fu to recover an intact copy of COS from my disk image, he wrote a simulator for an entire data center worth of Cray X-MP equipment and got it to boot!
If anyone has been sitting on Cray-1 or Cray X-MP software (or you just have some idea of how to use COS!) for the last 30 or so years, now is the time to come out of the woodwork! Get in touch with me or Andras and we’ll make it happen.
A year ago Super Awesome Sylvia demoed MarioChron for the Adafruit MonoChron dekstop clock kit. It’s really neat — once per minute Mario hits the box and receives a coin, so his score is equal to the time. Now thanks to the GPL license on the code, you can carry it on your wrist with the port of MarioChron to the Pebble Smart Watch:
You can install the prebuilt mario.pbw binary and the source is available for further hacking. Here’s a short video of Mario’s coin collecting action (the jump height has since been fixed in the source code).
The code is a straightforward port that reuses almost all of the original logic. The only change is to rearrange the screen slightly from the MonoChron’s 128×64 LCD to the Pebble’s 168×144. This involved translating the glcdClearDot() and glcdSetDot() calls to 2×2 rectangles using the Pebble’s graphics_fill_rect() functions. Unfortunately the e-paper display on the Pebble is designed for mostly static images, and updating it at 10 Hz for the animation draws far more power than a once-per-minute clock face. This means that this watch face consumes lots of power and the Pebble only lasts part of one day instead of an entire week. Perhaps optimizing the redraws instead of redrawing the entire screen would let it last longer.
Want to learn how to write your own watches for the Pebble? Sign up for the May 18 Pebble programming class at NYCR or come to the hackathon after!
What time is it? It’s time to #MakeAwesomeHappen and learn to program the new Pebble Smart Watch! We’ll be teaching a three hour class on 18 May on how to write custom watch faces that work with the official Pebble SDK. The programming environment is low-level C, with no memory protection, and no emulator nor a debugger, so you’ll need to be fairly comfortable with writing embedded code or at least not afraid to debug with printf()*. If you’ve programmed a device like an Arduino you should be ok with the class. Tickets for the class are on sale for $125. The hackathon afterwards is free!
If you haven’t heard of it, Pebble was the wildly successfull kickstarter project that pre-sold over 80,000 watches. The watch has a 144×168 transreflective e-paper display, an ARM M3, Bluetooth, an accelerometer and lots of potential. MyPebbleFaces has a few hundred ideas for fun projects and many people have already programmed their dream watch faces.
After the class, we’ll be holding an all-night hackathon to write some new watches. Developers from Team Pebble will be here to hack with us and help answer any deep questions about the API. The hackathon is open to everyone with a Pebble and is a great chance to meet other wearable wrist-watch computing enthusiasts in New York. If you don’t have your Pebble yet or don’t want to risk your prized wristwatch, we’ll have a limited quantity of factory seconds that might not be waterproof, might have glue bubbles, or discoloured bezels or other QC issues available for $75. Tickets for the class and hackable watches are available here!
Get that Club Mate cold and those soldering irons hot because it’s time for another Interactive Show! We’re putting out the call to hackers around the globe to come show your stuff at our annual party.
This years theme: Digital Archeology. Think old technology with a new purpose, or new technology retropackaged to look vintage. As always anything interactive applies so use your imagination.
We’re targeting mid-June so there’s plenty of time to get involved. If you’re interested in participating drop us a line.
So, once in a while, I wake up feverish in the middle of the night, screaming “CLAMPS! I NEED MORE CLAMPS!” Oh, you too, huh?
It’s your lucky day! Or rather, this coming Sunday, April 7th is your lucky day, when NYCR and our good friends at the Industry City Distillery will be having our first-ever garage sale. We’ll be selling all kinds of hardware oddities, including:
- Hand tools!
- Power tools!
- Strange, unidentifiable tools meant for neither hand nor eye!
- Microscopes! Boroscopes!
- Audio equipment! Video equipment! Audiovisual equipment!
- Files! Floppy diskettes! Raw steel! Cooked steel!
- A vertical mill! (U-buy, U-move!)
- Electronic bits! Non-electronic bits!
- More VHS recorders than you’re prepared to buy!
- aaannnddd moooooorrrreeee!!!
We’ll be having the sale in beautiful Industry City, Brooklyn, in association with the Industry City Distillery, manufacturers of incredible spirits. Come by to buy! Come by to browse! Come by to meet amazing people!
The sale starts at 11:30 AM, Sunday, April 7th and continues until sunset, at which point we’ll just start calling it a party. The address is 33 35th Street, Brooklyn, NY, just two blocks downhill from the 36th Street Station on the D, N, and R trains. It’s just one stop on the N train from NYCR.
See y’all Sunday!