The Hexababy Robot

When I dream up hacks I usually think about them for a day or so first. I had an idea this week for another cat toy and I thought I had it pretty well worked out. Once I got into the build though, a mechanical problem reared it’s head which required an entire redesign and brought the project to a screeching halt!

So there I sat on a Friday night with a busy weekend ahead and no project to post… hmmmm.

As I looked around my workbench some things suddenly came together. I had this Spider robot from Hexbug.com that I bought at Radio Shack and a silly doll head that I chopped off from a doll I found at thrift store. Yes, I buy weird stuff from the thrift store. Hey, ya never know when you’ll need some doll parts right? I had already stuck the doll head on the spider one evening when I was at the bench goofing around live on ustream. I figured I needed to do some sort of hack to it though in order to post it up as a project. I decided to add some LEDs to the eyes and one inside the head and feed them the same power that drives the motors in the bot. Since they’re diodes already it would be easy to make the red ones light up in forward and the green one light up in reverse simply by their orientation to the power.

Follow along with the video as the mad scientist in me performs plastic surgery and hacks up a The Hexababy!

Next week we’ll get back to some electronics but until then, keep on hackin!

The Murray Riding Mower Restoration

When I started this whole Hack A Week thing I posted an introductory video in which I stated I would be doing all kinds of projects. While most of them have been centered around electronics I have deviated into such things as Chicken Tractors and a workbench build.

This week I decided to share a project I’ve been working on for a few weeks. My landlord gave me a free riding mower a while back that had quit running. It had a list of things wrong with it. It needed a new battery, two tires had gone flat, the charging system didn’t work, the seat was falling off, the drive belts were cracked and most importantly, the engine would no longer start up and run.

Being as the engine is the heart of the machine I decided to tackle this problem first. The most common problem with a mower that won’t start is a dirty carburetor and the easiest way to check the condition inside is to remove the float bowl. It’s usually held on with a single brass bolt which also holds the main jet which meters the fuel. When I removed this one I found a lot of dirt and a faulty float and needle valve assembly. I ordered up the new parts directly from Briggs & Stratton online and received them in a few days time. After installing them on the engine it still wouldn’t run which meant something had failed mechanically. It did indeed crank over as if it had no compression, which meant that something had gone wrong with the valves. Time to pull the valve cover.

After removing the valve cover the problem quickly revealed itself. The rocker arms were both loose and out of alignment with the valves, which meant that the engine could not breath properly. This misalignment had also bent one of the push rods which was easily straightened. After a little tightening and realigning the valve train was back in working order. I re-installed the valve cover and gave it a crank. As you’ll see in the video it fired right up and ran fine! There’s more things that I fixed and I’ve documented them in the video along with the “hack” part of the project which is revealed at the very end.

So get comfy and enjoy 22 minutes of mower restoration… and as always, keep on hackin!

The FM Transmitter Bug

Building an FM transmitter is fun! This kit was very easy to build so it would be a good first time kit if you’re just getting started in electronics. If you can understand how to read capacitor and resistor values and you can solder, you can build this kit. If you’d like to build one they can be purchased from these vendors:
http://www.hobbyengineering.com/H1481.html
http://www.hobbytron.com/Mini-FM-transmitter-3-Volt-FM-Transmitter-bug-kit.html.

My Friend John S. gave this kit to me recently and I thought it would be a good Hack A Week project. There’s some good electronics to learn about here: class C amplifiers, FM transmission, VHF antennas, positive and negative feedback, stray capacitance, and induction.

The circuit is basically an audio amplifier that modulates a radio frequency oscillator tuned around 100 MHz. Output from the collector of the amplifier transistor is fed into the base of the second transistor where it modulates the resonant frequency of the “tank” circuit (the 5 turn coil and trim capacitor) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. The tank circuit is connected to a Hartley oscillator circuit.

I was able to receive transmissions out to 30 meters and that was going through a metal garage door. The range can be greatly extended by using a dipole antenna rather than the half wave antenna. Connect the dipole to the circuit with a 50 ohm coaxial cable. Connect the center lead to the antenna point on the circuit and the outer shield to earth ground. I’ll be experimenting more with this.

Have fun building this and keep on hackin!

Component list:

Resistors: (carbon, 0.25 W, 5%)
1 – 1Megohm
1 – 47K ohm
1 – 22K ohm
1 – 10K ohm
1 – 470 ohm

Capacitors:
1 – 1n ceramic #102
1 – 5pf ceramic
2 – 22n #223
1 – 27pf ceramic
1- 100n monoblock

Other stuff:
2 – BC547 transistors
1 – 5 turn coil (make sure you separate the windings so they don’t touch each other)
1- Electret microphone
1 – tripcap, yellow (6 – 45 pf)
165 cm antenna wire
Battery holder, 3v – 9v.

The 1994 Five String Electric Bass Guitar

This weeks project is a retro look at a five string electric bass guitar I built in 1994. I documented the project in photos and put them into an album. I thought it would be interesting to make a Ken Burns style video with these photos using the two axis camera dolly from hack #7.

Back in 1994 I was living in Hawaii on the island of Maui. I was into RC airplanes and woodworking at the time, and I had just started playing the bass guitar. I wanted my own bass and, being the DIY person that I am, decided to build my own. I chose to make it a five string because that extra low B note is big and round, and it allowed bass lines below E.

The first order of business was to find some wood. I found a local man that had a sawmill and he sold local grown woods already cut into cured planks. I chose Monkey Pod for the front body wings, Tropical Almond for the back body wings and Golden Ponsiena for the neck. I chose Purple Heart for the fingerboard because of its hardness and density which closely resembled Ebony.

Now that I had a selection of wood, it was time to start designing my new bass. I did a few sketches and then went to work on a scale drawing in pencil on drafting paper, old school style. I didn’t have a PC or internet access back then. I still use pencil and paper a lot to this day to draw up plans and shop drawings. I like it’s simplicity. After about a week of drawing and design changes I had a final plan. The next step would be to do a full scale color rendering of my new bass to see how the woods would look together. I used some water color markers for this and soon had a nice full color picture to hang on the wall and look at. I liked it. Now it was time to get started with the build.

At this point I’ll let the video and photos tell you the rest of the story about the construction. I love this instrument! It’s become a part of me, an extension of my musical expression and I plan on playing it for years to come.

Enjoy the video, and keep on hackin!

The Propeller Development Robot

This week I decided it was time to do a project with the Parallax Propeller chip. I’d heard all kinds of good things about this MCU and since I have all these Roomba parts laying around my shop I figured it was time to build another robot. I wanted a robot platform that I could experiment with. One that could easily have other sensors added in the future. I had a Propeller MSR1 control board on hand which is perfectly suited to this purpose with it’s 24 IO pins and on board h-bridge. I also had an extra Parallax PING sensor to mount on my robot and a couple of those wonderful Roomba drive motors to move the thing. Next I needed a chassis to mount everything to. I had a plastic enclosure leftover from the Laser Ranger Finder project that was perfect. Now that all my parts were gathered together, it was time to get building.

When I build a thing I usually just sit down with my parts and brainstorm for a while. I come up with ideas, think them through and change them as the design comes forth. Being willing to change the path you’re on with design is important. I try to let the function dictate the form. So, after some time I came up with a way to mount the motors to the enclosure and use the enclosure’s top to mount the control board and sensors to. This would allow easy access for future mods to be added. My choice for batteries was eight AA rechargeables simply because I had them on hand. They would go inside the enclosure and help keep the center of gravity down low which would add stability. At the rear I installed a tail wheel from a Roomba which is designed with two wheel tank steering in mind.

Once everything was together it was time to get some code and upload it. After a crash course in SPIN from my friend Roy Eltham, I had some standard motor drive and sensor code going. It was time to test. There was, of course, a bug. There’s always something to troubleshoot… that’s hackin! The problem was in the sensor part of the robot. It would seem to trigger a turn in direction even though there wasn’t an object in the way. Strange. I checked code, wiring, connectors, I even raised the PING sensor up on the bolt that you see in the final design, but none of this worked. I decided to look at the specs for the PING and noticed that an example schematic had a 1K resistor in series on the signal wire! Aha! I installed this resistor and suddenly, the robot was working perfectly. It was an impedance matching issue.

This was my first time using the Propeller chip and I have to say that I love it! It’s a very powerful MCU. I’m very pleased with the ease of use of the programming language to alter the robot’s behavior. I’m sure you’ll be seeing more projects from me that put it to use.

Until then… keep on hackin!