Kevin DeMarco is an Electrical Engineer in Atlanta, GA. In addition to Electronic Theory & Design, Kevin is interested in guitar, Ultimate Frisbee, and raising his two pet rats.
A brief update on my DIY RC plane design. I have finished the proof of concept for using a PIC18F to convert receiver pulse widths into motor controller pulse widths. Currently, I’m only using four AA batteries as a power supply. I’ll be needing higher current batteries. My next course of action is to create a PCB for the RC plane circuit. I’ll be using KiCAD for the PCB design as it is open-source and free! I’ll provide circuit schematics and board layout in the future. Here is a brief video of my electronic motor controller.
My current addiction to RC planes has led me to constructing my first balsa wood glider plane. Here’s my first version in all its glory…
Balsa Wood RC Plane - Version 1.0
I built the plane’s fuselage and wing structure from a free balsa wood plane I found online at: RC plane advisor. However, I slightly deviated from the plane with the internal supports and the outer frames.
I adjusted the wing placement until the plane’s center of gravity was centered about the wings. Then I tested gliding the plane onto my bed. Unfortunately, the results were not what I had expected. The plane would glide forward for about 5 feet, slow in speed, stall, and the tail would drag the plane down first. Not good. I did some more research online using the website, RC powers, as a reference and found some useful information. First of all, the RC powers guy noted that his planes flew best when the center of gravity was shifted slightly towards the nose. This makes sense for gliders because it uses gravity to aid in forward motion; thus, providing lift to the wing structure.
My next course of action is finding appropriately sized actuators, a motor, a receiver, and a battery to fit into my glider, so that is no longer a glider. Here is a video my roommate helped me record of some testing in action.
My good friend, Mike Galdos, gave me an iRobot Create for the pleasure of having me be one of his groomsman in his wedding. Thank you, Michael. You are very welcome indeed, sir. *tips hat*
The iRobot Create comes with some pretty nice documentation about its serial communication protocol. I was able to communicate with the iRobot using a serial terminal on my PC and the included iRobot serial communication cable which has some level shifters in it.
However, the iRobot is kind of useless unless you can control it without being connected to a computer; thus, you are supposed to purchase their iRobot Command module for about $60. But that’s not fun…
ENTER… the Microchip PIC microcontroller. I plopped a pic18f2550 I had hanging around onto a breadboard, wired up the programming interface, and added a 5V voltage regulator attached to a 9V battery. Thus far, I’ve been able to program the PIC from my computer and my next step is to actually control the iRobot with my PIC. Here is a close up of the PIC on the breadboard.
PIC on Breadboard
The back payload area on the iRobot is a great place to be! Work hard and work well little PIC.
Of course, there will be more posts concerning future developments.
I’ve been thinking of a method for releasing miniature parachuters and “bomb” payloads from my RC plane lately. I’ve looked into simple servos, but they weigh too much for the simple action that I want to perform (a bit overkill). I’ve looked into muscle wire, but I don’t have any muscle wire with me RIGHT NOW. Finally, I looked into electromagnets. Here is my simple experiment below…
Basic Electromagnet Theory
Current flowing through a wire induces a magnetic field around the wire
Induced Magnetic Field
If we tightly wrap the wire in a cylindrical fashion, we can amplify the effect of the magnetic field.
If we tightly wrap the wire around an iron core, the magnetic field will induce a north and a south pole in the iron core that will attract or repel other materials that are affected by magnetic fields.
Naturally, much more information on electromagnets can be found on Wikipedia.
1.) Obtain the materials:
Battery (AA)
Wire - light gauge is better because when you wrap the wires you can get them closer together
Something that is made of IRON (FE) (ie. a nail)
Rubber band (it will help keep the wires on the battery’s terminals without burning your fingers)
Nail and Wire
2.) Next, I tightly wrapped the wire around the nail. Always in the same direction. Your electromagnet will be more effective if you can make each wire turn as parallel to the previous turn as possible. See below…
Wire wrapped around nail
3.) Finally, I attached the wire to the terminals of a battery. I used a very weak AA battery for this task, but it still worked.
The Completed Electromagnet
Now, you just have to find something else that can be affected by a magnetic field. Being the creative person that I am, I chose another nail. I included a short video of my demonstration below…
In conclusion, my electromagnet worked and I plan on implementing it on my RC plane as a “payload drop” actuator. There will be follow up posts.
Notes:
Be careful when you are attaching the wires to the battery because you are essentially shorting the battery out. This creates a lot of heat in the wire and the battery. You will probably burn yourself. To be safe, I first tried this with oven mitts.
Listen to gangsta rap when you are working with electronics. It’s a great reminder for the dangers involved when working with current.
EcoCar: The neXt Challenge
Fall 2008 Workshop Trip Report
Last Wednesday, 9/24/2008, through Sunday, 9/28/2008, I travelled to Detroit, Michigan to attend the EcoCar Fall Workshop. EcoCar is a General Motors (GM) and Department of Energy (DoE) sponsored international collegiate vehicle engineering competition that will take place over a period of three years. EcoCAR seeks to advance the level of vehicle technology capable of reducing petroleum consumption and greenhouse gas (GHG) emissions while demonstrating the real-world performance of a range of technology options. The Georgia Tech EcoCar team is composed of faculty, undergraduates, and graduates from the College of Engineering.
During the workshop, the Georgia Tech team was introduced to concepts and technologies involving Hybrid & Electric Vehicles, safety critical systems on automobiles, embedded design of automobile controls, automobile modeling with Matlab & Simulink, hydrogen cell battery design, Lithium-Ion battery design/control, and common automobile communication protocols.
As a Systems & Control team advisor, I have to help the team decide between two hardware technologies to implement the hybrid vehicle control strategy: National Instruments’ cRIO with LabVIEW and dSPACE’s MicroAutoBox with Matlab & Simulink. While dSPACE’s hardware is designed specifically for automobile control design, National Instruments’ system is more versatile and will also be used for various testing procedures.
By the end of the workshop, the Georgia Tech team decided that the our preferred architecture for the vehicle will be a parallel hybrid-electric with Lithium-Ion battery cells. The term “parallel” means that both the gas-powered engine and the electric motor can independently supply power to the vehicle’s powertrain.
Currently, the College of Engineering is working to convert part of the Techway building (located next to GTRI’s Food Technology Building) to be used by the Georgia Tech EcoCar team. Also, Georgia Tech is allowing undergraduate students to obtain course credit for participating in the project. One of the challenges with this project will be partitioning the tasks and workload such that undergraduate students can accomplish a specific yet significant task during the course of one semester.
More information about Georgia Tech’s EcoCar progress can be found at www.ecocar.gatech.edu. The EcoCar competition’s website is located at www.ecocarchallenge.org. If you have any desire to help the Georgia Tech EcoCar team, contact Kevin DeMarco at Kevin.DeMarco@gtri.gatech.edu.
I built my first functioning sine wave generator this weekend. The schematic for my design is shown in the figure above. It was created using Orcad’s PSPICE. I used the classic “Wien-Bridge Oscillator” design that I had learned in my Analog Electronics class taught by Dr. Leach. Funny side-note about Professor Leach… when he was explaining the history of oscillators and how a fundamental problem with oscillators is actually starting the oscillation…
Well, when they were designing the first oscillator, no one knew how to start the oscillator oscillating. Does anyone know how they did it? …. crickets chirp … they turned on the lights!
Yep, we still don’t really know what he meant by that exactly. (there must have been some stray voltage from the AC power lines that creeped into the oscillator circuit that triggered the oscillation when the lights turned on.)
Back to my design… I was surprised that the oscillator actually worked because I designed it on a breadboard, which includes all sorts of weird capacitances and poor grounding. Also, I didn’t have the exact capacitance values I had calculated so I had to settle with 104 nF (nano-Farads) caps instead of 80 nF caps, but that just resulted in a different frequency. Here is a photo of the circuit on the breadboard.
Wien Bridge on a Breadboard
The different cap values did result in a change in the predicted sine wave frequency. I had calculated a sine wave of 2000 Hz, but due to the lack of the appropriate cap values, I adjusted the frequency to 1530 Hz. Thus, in the circuit, now R1= R2 = R3 = 1k Ohms, RF = 2k Ohms, C2 =C4 = 0.104 uF. The output frequency on my oscilloscope looked like…
Wien Bridge Sine Wave Output
When the volts/division and time/division were counted, the output frequency measured 1515 Hz and the sine wave had an amplitude of 12.5 V (ie. Peak-to-Peak Voltage of 25 V). Pretty good if I don’t say so myself. However, if you look closely at the oscilloscope capture you can see some slight distortion on the lower portion of the sine wave. This could be partly due to imperfections in the Op-Amp, the capacitance values, or poor ground planes in the breadboard; I can’t tell yet. A good way of checking will be to order some surface mount components and test/design the circuit on a printed-circuit-board!
Cool Notes:
The op-amp was powered by the bipolar power supply (+/- 15 V) I designed a week ago. A post will be coming on that soon.
I have an analog oscilloscope (Tektronix 465) that doesn’t have any built-in screen capture or computer communication. Thus, in order to obtain the sine wave screen shot, I took a photo with a camera. Here were the shutter settings…
When it comes to lugging my guitar equipment around, I am severely concerned with portability and a quick setup. In the past, I had nine or ten guitar effects pedals hooked up to each other, with wall warts attached to each one. Some were even running on batteries that lasted only a week or two. I needed a solution to my portability problems.
The first step was to find a high-quality modeling amp. My choice was the Line 6 Flextone III (2×12 version). I chose this amp due to its versatility and the fact that I didn’t need a truck to move it. I spent a lot of time in guitar stores trying out all the different amps and I am still very happy with my decision. Instead of purchasing the overpriced foot controller for the Flextone III, I opted to control my new amp with the Behringer FCB1010 Midi Foot Controller. I am not a fan of Behringer products in general due to the so-called, “Classic Behringer Hum.” However, since this pedal is only outputing digital Midi signals, I could deal with it. Also, since I bought it from my good friend, Matt Waldron, for $90, it was a great deal. Programming the Behringer Midi controller is interesting, but will be reserved for another post.
Finally… the culmination of years of optimizing show setup times… the Guitar Effects Briefcase. It’s a really simple idea!
Procedure:
Find medium quality briefcase (Walmart, Ross, Garbage can)
Remove excess materials from inside of briefcase (ie. useless extra pockets)
Buy Velcro from a craft store. Line the bottom of the briefcase with the Velcro as well as each guitar pedal.
Briefcase Lined with Velcro
Pedals with Velcro
Insert guitar pedals however you wish, connect pedals with short 1/4″ guitar cables, and attach pedals to the DC Brick Power supply.
Types of cords and connectors used.
Put it all together and you get…
Completed Guitar Effects Briefcase
Tips:
Use right angle 1/4″ guitar connectors for the input and output of the briefcase
Consider how your foot will fit in the briefcase when you are hitting the on/off switches of each pedal
Use the Dunlop DC Brick Power Supply… for now at least… I am designing my own power supply
I purchased my first RC Plane this past weekend. The Super Cub is a trainer that has some automatic flight control to help the beginner. However, I didn’t find the automatic flight control that helpful. Like a fool, I chose a small grass area on Georgia Tech campus for the initial flights. I used a sidewalk for a take off runway, which proved impossible to land back on.
I haven’t taken the plane apart yet, but I think the automatic flight control consists of two light sensors: one on the top looking for the bright sky, and one on the bottom looking for the darker ground. The instruction manual says that if automatic flight control (ACT) is turned on, the plane will be able to recover from dives; however, the plane has to be at least 200 feet in the air for proper functionality. Nevertheless, I flew my plane at an average of 40 feet off the ground…. there were some accidents… I got better though…
I thank my girlfriend, Mira, for being an excellent videographer and capturing the brilliance of the flight.
I hope to develop some of my own sensors and add-ons to this RC plane. An absolute “must” is the G.I. Joe parachute drop.
Tonight! I started my blog site that will focus on do-it-yourself technology and other software/hardware open source ventures. I will post projects and I ideas I come up with, as well as original ideas I find elsewhere. However, I will try not to just repeat what all the other DIY blogs post. The shameless copying and posting between various blogs when one person comes up with a good idea is amazing.
The name for this blog is derived from the term “Mixed-Signal Design,” where Mixed-Signal Design is in reference to systems that utilize both Analog and Digital signals. (ie. amplifiers, transceivers, microcontrollers, everything.)
I try to be efficient in design, life, and writing.
