Coilguns 101

        Over the past few months, I've been doing quite a bit of research into coilguns and how the work, so I thought I'd do a write-up on them.

      When a conductive wire, such as copper wire, is rolled up into a coil, and an electric charge is applied to it, it creates an electromagnetic field. The higher voltage applied to it, the larger the field. This means that a metal object will be pulled towards the coil with more force if more voltage is put through the coil.

       

        A coilgun operates with this basic principle. The copper coil is wrapped around a plastic barrel(it doesn't have to be plastic, just a material that doesn't conduct electricity). Then, a very large charge is released into the barrel over a very short period of time, creating a quick but extremely powerful magnetic field. When a bullet is placed in the barrel, a short length behind the coil, the magnetic field pulls it towards the coil with great force, causing the bullet to fly down the barrel with great speed. 

        The large burst of energy required for the coil is generated with the use of a capacitor. a capacitor is much like a battery, in that it stores energy. However, a capacitor can release it's energy much faster than a battery. So if a high voltage capacitor fully charged, then connected to a coil, it will release all the energy into the coil very quickly. 

        When talking about coilguns, you may hear the term 3 stage, or sometimes 3 phase. This simply means that multiple coils are used to keep the bullet at constant acceleration down the barrel.       

Testing the Analog Inputs

        The 4 inputs on the SSC-32 card can be used in 2 different ways: Digital and Analog. We have already used the first in the last post and now we will try using them in Analog mode.

       To do this, we need a Potentiometer (or “Pot”) as shown in the diagram from the SSC-32 manual.

        A potentiometer is basically an adjustable resistor, so the as you turn the dial on it, the resistance acting on the electricity moving through it increases or decreases.

        We used the ohmeter to check the resistance of the pot by measuring across the two outside connectors. The meter showed that this was a 25K ohm pot and when we adjusted it, the reading didn't change, confirming we had the correct leads.

        We then tried reading the resistance across the center and outside leads and found it varied as we turned the handle.

        We then connected up the three leads of the pot to the “+” (5 volts), “-” (ground) and “A” (the first analog input) pins of the SSC-32 card using the breadboard. We also connected leads to the “A” and “-” pins so that we could monitor the voltage being given to the “A” input as we adjusted the potentiometer. The connections are shown below:

        With the pot adjusted to 5 Volts we used the terminal program to send a “VA” command to check the value of the “A” input which came back with “FF” or 255 in decimal. Note that the first 3 bytes (56 41 0D) are the “V”, “A” and carriage return we typed in.

        Note that the initial “VA” command did not give the correct value because one dummy command at the beginning is required to change the input from digital to analog mode. We then adjusted the pot to 0 Volts and tried the command again:

        This time the response was “00” or 0 decimal.

        We then calculated what the response should be if the voltage was set to 3 volts:

        If measuring the value correctly, the response to the “VA” command should be 3 volt/ 5 volt * 255 or 153 decimal which is “99” in hex. When we tried it we got the correct result!

        We also tested the other 4 inputs pins by tying them to either Ground or 5V. They can all be queried at the same time using the “VA VB VC VD” command which returns 4 bytes instead of 1.

                   Now that we know they work, we can connect the compound eye to these inputs. The eye is actually connects to 4 input pins, one for each direction around it(up, down, left, right). It also has two other pins, one to power the receivers, and one to power the emitters. 

New Parts

        After a bit of a delay, the parts we ordered from Robot Shop have finally arrived! We received a new servo motor for the grabber on the arm to replace the old one that is not working correctly (the internal gears are worn and it has a greatly reduced range of movement), a collection of wires to connect the SSC-32 inputs and the Raspberry Pi to the breadboard, and two circuit boards so we can connect them together and to the sensors.

        The circuit on the left is a Logic Level converter. The main purpose of it is to take signals from one voltage, and convert them to another. This is vital, as the infra-red sensor operates at a different voltage than the SSC-32 and Raspberry Pi.

        The board on the right is Dagu Compound Infrared Sensor. The bulbs in the middle emit rays of infra-red light, and the black sensors measure the response time.  If something is in front of the sensor, the rays will reflect off of it, and the response time will be quicker. This allows the sensor to detect objects up to 20cm away. We can use this on our robot to follow a person, detect obstacles, or help to position the arm when picking up an object.

Lift kits 101

      Currently, I've been doing some research into buying a lift kit for my truck, and I've noticed a lot of confusion among people in the same situation. I'd thought I'd help by writing down everything I've learned so far.

      First and foremost, there are two basic types of mainstream lift kits:

Body Lifts

      Body lifts lift up a vehicle by simply using blocks to lift the body of the vehicle off the frame. This makes body lifts incredibly cheap, simple, and easy to install. However, they offer almost no performance improvements.

This means that body lifts are really designed for people looking to get a slightly lifted look, or to make room for bigger tires, without spending lots of money. It would be extremely uncommon to find a body lift kit bigger than 3 or 4 inches.

An example of a body lift kit.

Suspension lifts

      Suspension lifts are the real deal. Anyone serious about off road performance should get a suspension lift. They lift a vehicle by replacing and adding key parts of a vehicles factory suspension system. These new parts lower down the wheels from the frame, and allow bigger shocks. This allows the addition of bigger tires, and more wheel travel, which is how much the wheel can move up and down.

An example of a suspension lift kit. Note the bigger shocks.

       The suspension lift kit that I am planning to buy is produced by a company called Race Car Dynamics, and offers 5" of lift. The main reason I'm interested in it is that it has received extremely positive reviews from many people, and it adds additional equipment that other kits don't, such as traction bars, which act as a brace between the rear axle and the frame, and high quality Bilstein shocks. 

What the RCD 5" Lift looks like installed.

The S-Motorworks Centurion

       This is a model I made over the course of several months, during my design class. Being the only student taking grade 12 design during that semester, my teacher basically gave me a carte-blanche for my course outline. My task was to simply research a sector of design(architecture, automotive, aircraft, etc) and design a product. I chose automotive, and decided to try designing a rugged, heavy duty, off road cargo hauler vehicle, which I dubbed the Centurion.

      I started by designing the wheels, along with a simple driveline system and frame. After much research, I discerned that the best suspension set up for all-terrain travel is that of the Mercedes-Benz Unimog. The Unimog uses a portal axle system, where the axle meets the wheel hub at a higher point than the wheel's center, then turns a gear which turns the wheels. This gives the vehicle a very large ride height, without endangering stability. 

        After that, I attempted to build the body. My first try was to give it very modern styling, but to my disappointment, I soon realized that it was far beyond my skill level. Here's a picture showing what it looked like when I gave up on modern styling.

       As you can see, it began to get very messy, and I realized that it would have taken me far too long to have a presentable product. So I decided to go for something a little more outlandish. I felt like doing something vintage, yet still somewhat advanced. Basically, I smashed together a 1920's truck with a 1960's bulldozer, then threw in some elements of an armored car. 

      I was fairly pleased with this, but sadly, I had to stop working on it, because our teacher went on a leave of absence for the the remaining months of the semester, and a substitute tech teacher was put in place. As a result, I had to work on a different project instead, so it would be easier for the new teacher to mark. My hope is to one day finish this, or possibly even return to the original modern body style.

My Grade 12 Design Project

       I just thought I'd share the presentation I recently made for a design course I took last semester. We were told to imagine that the year is 2025, and the town of Orangeville has expanded to 3 times it's current size (2013). We were told to predict how it would expand, and then design 3 different public transit systems that could be used in Orangeville. We were also told to make our systems as environmentally friendly as possible. To make all of the 3D models, I used Google Sketchup.

       If you would like to view it, just click here. I'm not the kind of person to brag, but my teacher told me it was the best presentation he'd ever seen.