January 31, 2007
the mysterious third guy
I'm Sam, the other member of the blimpbots team. I'm a second-year grad student in AI, studying nothing to do with blimps, but I'm working with Jeff on the technical side. I've been out of commission for most of January due to some other commitments, but now I'm full speed ahead on the project.
The completed blimpbot control board 1.0 is up and running, courtesy of Jeff (see the picture here, or Jeff's video below). There are a few details to change in a second revision, but it does what we need. We have arbitrary motor control over bluetooth, which is pretty awesome. The next step is to demonstrate a simple control loop-- we're going to set up one blimp and control it enough to stay at a set altitude. That involves getting a decent start on the control software and camera tracking, at least for the vertical dimension. So there's a bit of software to write, but stay tuned for our first demo.
January 28, 2007
All systems go (?)
Excellent news! The Pulse-Width-Modulated (PWM) signals that control the three independent blimp motors are working just fine under remote control. This means we can control power and direction independently, as hoped. There was a worry that the directional control would not work when all three motors outputs were enabled... but on that front, all systems go.
The Blimpbot also has an onboard 3.3V voltage regulator, to keep the voltage to our future 3-axis accelerometer constant and within acceptable levels. The voltage is then routed to a reference pin on the microcontroller. Since we didn't buy the accelerometers yet, I was trying to use this pin to measure the battery's voltage. (i.e. 3.3V/(Battery Voltage) = Pin value) However, I'm just getting '0' back from the Analog-to-Digital converter. This isn't critical to flight, so I'm going to quit on this for now and hope for a response on the Microchip forums.
In other news, Jason's excited that he might have enough leftover weight to add fun accessories to the Blimpbot. For example, maybe something like electroluminescent wire.
So, how heavy is it?
The Blimpbot circuit board was cut in half today. Don't worry, this is a good thing, as the board came with two identical sets of traces. I had some help making the cut, but broke a table jigsaw in the process. Jason is going to see if we can get access to the high-powered laser cutter for future PCB splits.
So, with a fully-assembled single board, I made some approximate measurements:
- Main board: 15.75g
- BlueSMiRF: 3.25g
- Battery: 18g (from web)
- Total: ~40g
Other news today is that the H-bridges seem to be wired correctly, and they will at least power some blue LEDs that I have with me. Spinning real motors forward and reverse still remains to be tested.
Also, some work on the bluetooth link has Blimpbot 1 talking reliably at 9.6 kbps. We can probably go a lot faster, but it shouldn't be needed.
January 27, 2007
So far, so good
The PCB arrived on schedule yesterday, and after the weekly GROCS meeting, I got started with assembling our actual prototype. Before I touched the PCB, I wanted to get basic serial communication working over Bluetooth. It turns out that our new PIC Microcontroller is so new, the manufacturer didn't finish updating the library that makes serial (USART) easy to implement. So I had to build the library myself, and got a simple test program working shortly thereafter.
And with that, it was time for circuit assembly onto the PCB. The moment of truth for the layout, and my soldering skills. The bluetooth connector was a little too close to the exposed pins on the back, so I angled it out a bit. Everything else kind of dropped into place. And when I powered it up, the example program I had written previously fired up and functioned just as it did in the breadboard. The In-Circuit Serial Programming port worked, too. However, several other parts remain to be tested, so we need to wait a bit before breaking out the champagne (or, alternatley, the sparkling grape juice if on University premises). Check out a time-lapse MPEG video of circuit assembly!
(Video made using our new Axis camera.)
January 25, 2007
Not quite the Graf Zeppelin...
Hi! I'd like to introduce myself, I'm Jason Dietrich, and I'm the Art and Design student who should be taking most of the blame for keeping Jeff and Sam up nights slaving over hot soldering irons. While Jeff's been working on the electronic and camera tracking components of the project, I've been working on coming up with a chassis to secure those components into the blimps themselves.
Most of the preliminary designs were loosely based on the geometry of the Plantraco microblimp. They were modeled in CAD and cut using the U's CNC laser. They fit the miniature motors/gearboxes we've chosen well, but don't have enough clearance for the final PCB or the propellers, so we're back to the drawing board on that. After consulting with design Prof. Jan-Henrik Andersen we may be taking a very different tact on chassis construction. More on that as it evolves.
Wednesday morning we did get to try out the microblimp with a 52" blimp envelope. We had been using oblong party balloons which inflated to aproximately 28". The new envelope killed our mini helium tank, and we didn't even get it all the way full. But even so, it lifted the microblimp chassis, the 18g battery, the microblimp ballast and about $1.65 in loose change (a quarter weighs about 2.5g). These blimp bags are rated to about 106g, which should be more than we need. The microblimp motors were able to muscle the larger bag around at an adequate speed. We also did some rough tests on the strength of the G05 motors and gear box, with their super trick carbon propellers. These motors are about half the size of the micro blimp motors, but due to their gearing and bigger prop, push more air. Nice.
I'm out of town for the next week, but I'm be trying to think blimp.
January 23, 2007
Blimp-tracking cameras selected
It is surprisingly difficult to find wireless cameras which simultaneously support high-resolutions and are open (read: easy to connect with your own arbitrary software). But the Axis-brand cameras shown above appear to be a good fit. They support video capture at 1280x1024 and offer many ways to connect to the feed over a WiFi network. The hardware apparently runs on linux, which is the likely reason for the plethora of supported protocols.
GROCS is helping us order 1-3 of these as part of our our blimp-tracking system.
Sam has also started looking into automatic camera calibration, which should allow us to detect the location and orientation of these cameras -- crucial for setup and quick recovery when cameras get accidentally nudged.
PIC shakeup, PCB sent-to-the-ether
The BlimpBot's schematic has been translated into a PCB layout, and the layout send in for production to expressPCB.com. I sent them the design above, and an actual circuit board will arrive here Friday. There was of course a little money involved too.
Given the short timespan allotted to actually designing the PCB and reworking the schematic (as discussed below), I am crossing my fingers that it does not contain any big mistakes. Time will tell...
UPDATE: The PCB design underwent 2 revisions subsequent to this one. See newer PCB-related-posts for details. Here is the final design.
In other news, we skirted a near-disaster with the original schematic...
On Sunday it was discovered that the microcontroller used in our original design (i.e. all of the schematics below) is a bit insufficient. The short story is that it was only capable of controlling one of the three motors on the blimp. The only alternatives we could find were bigger -- 40 pins versus 18 -- overkill for what we want. Plus, each extra pin means more solder, more square area of PCB, and more weight, all of which are detrimental to miniature helium blimps.
But some more searching revealed the Microchip PIC18F1330, a brand new model with only a slightly incremented part number. This one can do just what we need -- control 3 independent PWM outputs. So the new PIC was added, the schematic revised, and the PCB design laid out, all since Sunday night.
January 20, 2007
Lab work day one
Today I actually put together a small fraction of the blimpbot circuit on a breadboard. Specifically, the parts that have to do with power, ground, power stabilization, the microcontroller, and its status LED.
The good news is that all of this works, and Microchip lets students use their C18 compiler for free! (Works with 18XX series microcontrollers)
The bad news is that one of the 18F1320 PICs we got from SparkFun was defective, so we're left with only one working one at the moment, which makes me slightly nervous.
On another note, the motors arrived, and they are impossibly small. Just compare them to the standard household tack in the photo below.
January 19, 2007
Since we haven't been able to find any help with soldering itsy bitsy components, the design has been revised to use more soldering-iron friendly parts. And a tweak to the serial communications circuit left more pins open, so we can now toggle between two bright LEDs. Other tweaks are contained within the new schematic.
We've also been working through some designs for the assembly which the motors and PCB will attach to. They're looking pretty cool, but Jason would be the appropriate person to discuss that.
January 17, 2007
A revised schematic
After correcting a mistake in the logic for the motor outputs, we have a slightly revised schematic.
One of our current challenges is to find someone who can help us attach very small surface-mount components. The motor drivers and accelerometers are quite small.
January 16, 2007
Team meetings will be held:
- Mondays, starting January 22, at 9:15 AM
- Wednesdays, starting January 17, at 9:15 AM
GROCS-wide meetings will be held:
- Fridays, starting January 19, at 3:30 PM
The usual meeting location is Design Lab 1, in the Duderstadt Center.
Wires floating high
January 13, 2007
We're building some brainy blimps
Welcome to the development blog for the Blimpbots project. The blimpbots team is Jason Dietrich, Jeff Powers, and Sam Wintermute.
The blimps will fly in public spaces, interacting with simple rules, but exhibiting intriguing behavior. Thus they will demonstrate complex systems, and will hopefully pique the interest in this topic, and related topics of computer science, robotics, and control.
But we have a long way to go! We'll keep interested readers abreast of our progress through this blog.