Code 42

Note: It's been about 2 months since I've posted the part 3 of this article. Sorry for being late with this part. I hope you have read my earlier articles on Li-Po batteries (Li-Po Batteries Explained Part 1 , Part 2 and Part 3 ). Now let's look at the most important part - charging and maintenance. First of all, why is this so important? Well, just watch the following video on what happens when you mistreat a Li-Po battery. So....., now that you've seen the dangers of Li-Po batteries, it should be clear that they should be handled with care. Li-Po's are very different from conventional rechargeable batteries, so you should only use a charger specifically designed for Li-Po's. Doing so will increase the life span of the Li-Po battery pack and yours as well.

If you have studied about brushless motors, you'll probably know that they need a electronic controller (ESC) to run. Since the ESC can't actually see how the motor is running,  it needs to somehow detect the orientation of the rotor (moving part) relative to the stator (stationary part) of the motor. The two most popular ways of doing this is to use a Hall Effect Sensor or to measure the Back EMF of the undriven coils. The Back EMF method does not require any additional sensors, but it's implementation is complicated and has to overcome several issues. The Hall Effect method is much simpler than that, but requires a Hall Effect Sensor near the rotor of the motor to operate. So, how does a Hall Effect sensor work? Simply put, it is a device that varies its output voltage based on changes on a magnetic field. The operation of the sensor is based on the Hall Effect which was discovered by Edwin Hall in 1879. The theory is explained as follows,  The Hall Effect

If you've read my previous posts about Li-Po batteries (Li-Po Batteries Explained Part 1 and Part 2 ), you'll now understand the basics of Li-Po's. Now let's look at some standard ratings of Li-Po's that you'll need to consider when you buy them. Voltage A single Li-Po cell is rated at 3.7V. This however doesn't mean that the fully charged voltage of a Li-Po cell is 3.7V. Actually, Li-Po cells have a minimum voltage of 2.7V (fully discharged) and a maximum of 4.23V (fully charged). The 3.7V is just the average operating voltage of a single cell. Many Li-Po battery packs have two or more cells connected in series to provide higher voltages. The cell count of the battery pack is denoted by the 'S' number. A 2S battery pack means that there are 2 cells connected in series, thus providing 7.4V. Here are some examples of standard size battery packs: 1S = 1 cell x 3.7V = 3.7V 2S = 2 cells x 3.7V = 7.4V 3S = 3 cells x 3.7V = 11.1V and so on....

I explained about Li-ion batteries (the predecessor of Li-Po) in my earlier post ( Li-Po Batteries Explained - Part 1 ). Now let's see what these 'Lithium Polymers' are. Lithium-Polymer Batteries - The real ones Li-Po batteries - also known as Li-Poly, Pi-Pol, PLI and PLI - are a type of rechargeable batteries that uses same types of electrodes as the Li-ion batteries. The difference is with the electrolyte it uses. Instead of the liquid solvent used in Li-ions, Li-Po uses a polymer electrolyte. In the original design, which dates back to the 1970's, the electrolyte is a dry, plastic-like, thin film. It doesn't conduct electricity, but allows the exchange of ions between the electrodes. Theoretically, with this design, batteries could be made very thin (less than 1 millimeter) and to a variety of form factors. And because of the electrolyte being dry, the manufacturing process can be simplified and the safety of the battery will be higher because of no risk in...

If you are interested in radio controlled aircrafts and stuff, you've probably heard about Li-Po batteries. They are very common in RC planes, cars, boats etc. because they have several advantages over other batteries like less weight, variety of form factors, high discharge rates etc. So what are these "Lithium Polymer" battries? How are they different  from the common Li-ion batteries (which are found on mobile phones etc.)? And most importantly, are they really "Lithium Polymer"? To understand these, we must first look at the more common Li-ion battery, and then move on to Li-Po batteries. Lithium-ion Batteries - The predecessor of Li-Po Lithium-ion batteries - also known as Li-ion or LIBs - is one of the most common types of rechargeable batteries used in consumer electronics. They are especially popular in portable electronic devices such as mobile phones. This is because they offer several advantages like high energy density, no memory effect, low se...

Here's a quick post about a few things I learned about laser 3-D scanners. In the classification of 3-D scanners, laser scanners fall in to the category of 'Non-Contact Active'. There several types of scanners in this category, but the most common type used is the Laser Triangulation scanner. These are used in scanning relatively small objects with high accuracy. How does it work? A triangulation scanner shines a laser dot to the object and uses a camera to look for the location of the laser dot. Depending of the distance from the laser emitter to the surface of the object, the dot appears at different places on the camera's field of view, as seen on the following diagram. Operating principle of a triangulation laser scanner

We talked about the basics of IR ( Part 1 ) and the SIRC protocol ( Part 2 ). Now let's see how RC 5 protocol works. RC 5 RC 5 was introduces by Philips. It uses IR pulses modulated to 36 KHz. The logic level encoding is simpler than in SIRC. RC 5 Logic Levels Logic '0' is represented by an IR pulse of 0.9ms and then waiting 0.9ms. Logic '1' is the complete opposite, 0.9ms waiting and then 0.9ms pulse. Therefore, both '0' and '1' have a similar 1.8ms pulse width. As in SIRC, a command in RC 5 is also sent as a data packet. Its structure is as follows. RC 5 Data Packet As you can see, RC 5 has 2 start bits, which are always '1'. The address part and the command part are 5 bits and 6 bits respectively. Their function is similar to those of SIRC. The bit marked as 'T' has a special purpose. If you press the same button of the remote several times, the 'T' bit will toggle between 0 and 1. If you press and hold the...

In the last post ( Understanding IR Remote Controls ) I explained what IR is and why it is commonly used in remote controls. Now let's see some common encoding methods used in IR remotes. As you know by now, the IR signals emitted by remote controls are modulated to a frequency between 30 KHz and 60 KHz. In order to send a command, it has to be encoded in to this signal. There are several encoding protocols of which the SIRC protocol introduced by SONY and the RC 5 protocol introduced by Philips are used more commonly. SIRC SIRC stands for 'SONY Infrared Remote Control Code'. It used 40 KHz modulated IR signals. The logic levels (0 and 1) are represented by the width of the IR pulse. SIRC Logic Levels As you can see, the logic '1' is sent by a pulse of 1.2ms and then waiting 0.6ms. Similarly, logic '0' is sent by a pulse of a 0.6ms and then waiting 0.6ms. Those who are familiar will identify this as a sort of a pulse width modulation (I'll be ...

When hearing the word 'Remote Control', the first thing that comes to most people’s mind would be the TV remote control. They have become so common that other devices - CD/DVD players, Fans, Air-conditioners, Refrigerators, Washing machines etc. - are also getting the same sort of remote controls. These days it's easy to find that almost all consumer electronic devices have a remote control. Almost all of these are IR remote controls. What is IR? IR, or Infrared, is an electromagnetic radiation that has a wavelength between 0.7 and 300 micrometers (frequency range between 1 THz and 430 THz). The Electromagnetic Spectrum There are several advantages in choosing IR for remote controls, such as: Low power requirements Low circuitry costs Simple circuitry Portability Few international regulatory constraints High noise immunity  However, there are a few disadvantages like requiring line of sight, blocked by common materials, short range and light and weather ...

I hope you've read my earlier posts on helicopter gyro (RC Helicopter Gyro Explained - Part 1 and Part 2 ). Now let’s see how gyros are categorized by how they respond to yaw movements. Yaw Rate Gyros Yaw rate gyros (sometimes known as Standard Rate Gyros) are the simplest form of helicopter gyros. They work as a dampener to any yaw movements. This limits the amount of yaw movement because of torque variations from the main rotor, gusts of wind trying to turn the helicopter or even commands from the transmitter. A yaw rate gyro doesn't stop a heli turning because of external forces; it just limits them to a controllable amount. For an example, if a helicopter with a yaw rate gyro is hit by a sudden crosswind, it will slowly turn in that direction rather than a sudden spin, making it easier to keep it under control. Almost all the old mechanical gyros and few of the new piezo gyros are yaw rate type. They are mostly being replaced by the new Heading Hold Gyros. Headi...

Now that we know what a gyro is (from the previous post) lets see how it applies to RC helicopters. Why does a helicopter need a gyro? The answer is - for stability. As you might know, in a helicopter the main rotor generates both the lift and the trust. Therefore the engine (or the main motor) has to provide a lot of torque to the rotor. Unfortunately, this torque not only spins the rotor but also spins the fuselage of the helicopter in the opposite direction. That's why a helicopter needs a Tail Rotor or a similar 'anti-torque' mechanism to cancel out the torque on the fuselage. To keep the helicopter stable the anti-torque mechanism must respond quickly to any changes in torque. But the problem is, the torque is always changing. Changes in the engine or motor speed, changing the pitch of the rotor or even gusts of wind change the torque and will try to spin the helicopter out of control. In a RC helicopter, manually adjusting the tail rotor for these constant ch...

I recently bought a RC Helicopter - a Falcon 8911 4-Channel  RC with a built-in Gyroscope (Gyro for short). It's the first time I've seen a 4-Channel RC helicopter, let alone a one with a gyro, in the Sri Lankan market. The heli was pretty good, although I still need more 'flight training'. I will do a separate post on my heli ;) The thing that interested me most is the gyroscope. I knew the basic concept of a gyroscope but didn't know how it applied to helicopters. So I did a little research on the internet and found out a lot about gyros. To others who are interested, here's what I've learned. First of all, what is a gyro? A gyroscope is a device for measuring or maintaining orientation (a.k.a. angular position). The most basic is the mechanical gyro. A mechanical gyro is essentially a wheel spinning at a high rated speed and whose axle is free to take any orientation. Based on the principles of conservation of angular momentum, the orientation of ...