Mark and Lucy build a machine that shoots string, and lets them play with waves.
In "Quad Cargo", we determined that the Alias had 2.5oz – or just under 71 grams* – of cargo capacity. Now it was time to build a frame that we will use to attach what the Alias would need to lift.
Our first attempt was to lay some hollow cardboard tubes across the arms of the copter.
Next, we planned to attached those two tubes together with wooden dowel. I marked the tubes where the dowel would go…
…and then measured out the doweling.
I drilled holes in the tubing for the dowel to pass through.
I glued the pieces together, and and then verified there would be enough clearance for them between the arms and the rotor blades.
There was, but only barely. I was a little concerned about the effect the frame would have on the Alias’ flight characteristics. The frame’s components weighed a little more than 21 grams, but I didn’t know how much the rotor’s thrust would be compromised having the doweling and tubing positioned so close.
So, instead of putting the frame on top of the arms, I moved it to below the arms.
I zip-tied the four corners down…
…and we were ready for our first test flight.
The Alias appeared to respond well. It still felt like we had good control over it.
That is, until I got a little too wild on the stick, and crashed it. The Alias was fine. The new frame, however, was not.
The crash illuminated a fatal flaw in our design. The holes drilled through the cardboard for the dowel weakened them too far to be useful. We would undoubtedly crash several more times even before we go to the "tough" parts, so we needed something more resilient.
Back to the drawing board.
* Dealing with the weights in grams is easier than dealing with fractions of ounces, so from here on out, all of our measurements will be in metric.
Before we can start our relatively-still-secret quadcopter-project in earnest, we needed to find out how much extra weight could the Alias really handle. I drilled holes in a small plastic storage container, and rigged it up as a basket that could be carried by the copter.
The basket and the harness for the Alias weighed in at a combined 1oz (our scale was accurate to about an eighth of an ounce).
We rigged up the Alias in the basement again, and then started loading it up with washers.
We found that the Alias could lift about 1.5oz of washers in the basket, or 2.5oz total being hauled by the copter. Of course, we had to run the motors at full power to get off the ground.
Switching the Alias from Basic to Expert mode gained us another quarter of an ounce, but as the name suggests, it becomes a lot more challenging to fly. For one, it doesn’t auto-level itself when we let off of the stick – it will just keep going in the direction we last had it pointed.
We decided that 2.5oz was our effective limit. That required a full battery and we’d only have 1-2 minutes of flight time, but for what we want to do that should be enough.
The next step will be to build the frame to attach to the Alias to hold the real load.
Lucy joined the ranks of SETI@Home yesterday.
For those of you who aren’t familiar with this program, SETI stands for the Search for Extraterrestrial Life. The project collects radio signals from space in the hopes of finding signals that denote intelligent life. The processing for those signals, though, requires a computer. In fact, a LOT of computers. But buying and maintaining a “lot” of computers requires a LOT of money. In 1995, David Gedye proposed a different approach. There are already a “lot” of computers in the world, and much of the time those computers aren’t doing anything useful except running a screensaver. Could we build a screensaver that analyzed SETI radio data, and looked cool doing it?
SETI@Home was born.
Lucy saw the screensaver running on my computer earlier this week, and when I explained what it was doing, she was REALLY interested in helping, so we added it to her machine.
You gotta start somewhere, right?
For the last year, one of our CD players has been acting up – skipping in the middle of a song, taking a really long time to start playing the first song, that sort of thing. In the last month or so, it stopped playing CDs at all – it would just spin and spin, and eventually give up. We decided to retire it. CJ asked if I wanted to take it apart with the girls as a project.
Like you had to ask!
Lucy was thrilled at the idea of taking it apart, so we decided that would be our next project. We wanted to do it on a weekend, when we wouldn’t be as rushed as on a weeknight, but weekends are a precious commodity around here. Lucy’s people and my people had a heck of a time finding one that worked for both of us. Ahem. As it turned out, this past weekend worked for both of us.
I told Lucy to head down to the workshop, and I’d be there in a minute. I joined her a minute later, only to find this waiting for me on the workbench:
What the?! You’re looking at the head from our first robot project, sitting on top of the CD player, with my safety glasses on. Lucy just giggled.
Anyway, the CD player.
My first question to Lucy was, where do we start? Lucy responded, "I have no idea." Well, take a look at it, turn it around, see how we can get into it. She did, and after a minute responded, "I think we need a screwdriver." Ok, which one? I have several. "One that looks like a diamond." Ah, that’s called a "Phillips" screwdriver. I always thought it looked like a "plus" sign. "Oh yeah. We need a Phillips screwdriver."
And we were off.
8 screws later, we had the bottom case off.
Our next task was to cut the wires leading to the battery compartment and the transformer for the AC jack. I took a moment to describe what the latter did.
Next we needed to cut a couple of other wires that were in our way of the main circuit board.
Now we could focus on getting that board up and out, and see what the innards of this CD player looked like.
Another 5 screws later, and we got it.
We spent a while going around the board, pointing out the white knobs used to adjust the volume and radio tuning, the resistors, the capacitors, the digital display (shown in the far bottom), and some of the other components. I also pointed out that the lines on the bottom of the board were really wires that connected everything together.
Next, we extracted the laser that actually reads the discs (well, ok, "read" – past tense – the discs):
I showed Lucy that there were two motors – one that spun the discs, and one that moved the laser reader back and forth to read them.
While she was playing with the laser reader, I extracted the circuit board that held the buttons for play, fast forward, etc.
I explained that these were "momentary" switches, because they would only turn on while you pushing down on them – only on for a "moment".
And then we extracted the speakers, and we had lots of fun playing with the embedded magnets.
Lucy thought they looked like flying saucers, but they needed guns to do battle. Muhahahahaha!
So she "armed" them with some of my small screwdrivers:
Several days later, I realized that had a really fun, and unplanned, consequence. The screwdrivers had become partially magnetized, so we had some fun seeing that in action.
Overall, this teardown was most excellent, and time well-spent.
In this episode, Mark and Lucy build a programmable rover based on the Raspberry Pi 2.
Here are a couple of the key components that we used on this rover:
I’ll be posting a detailed account of what went into configuring the Raspberry Pi 2 and getting it to work with the motor drivers on my technical blog, http://mark-gilbert.com in the next week or so.
Not too long ago, Lucy and I built a SnapCircuits rover and then rebuilt it. It was a fun project, and it was easy to drive, but even before we started building it, Lucy expressed her interest in actually being able to build a rover that she could program. I wanted to use the SnapCircuits rover as a starting point, to see if this would really capture her interest for more than one project. It did. Katherine also really wanted to get in on programming a rover, so I began to piece out what a "programmable" rover would look like.
I wanted to build something that not only could be programmed, but also have a camera that could send back real-time video. That would allow us to set up an obstacle course in our living room, and crudely simulate the Mars rovers.
I’m happy to report that most of the pieces for "Rover Version 2" arrived today:
This is Dagu 4WD Chassis from RobotShop, a Raspberry Pi 2 and a USB WiFi module from AdaFruit.com. The only thing missing are the motor drivers, which should arrive later this week. These were the minimum-required parts for the next Rover. Once we get this one put together and working, then we’ll add the camera.
Come Saturday, Lucy and I will start to build the chassis. Between now and then, I need to get comfortable with the Raspberry Pi (since this will be my first time with one). With an insane amount of luck, we’ll be able to take it for the first test drive this weekend.
Stay tuned for our next Science and Technology podcast!