An Abbreviated Glossary of Terms
Autonomous Robots
Autonomous means “Not controlled by outside forces”. In the case of autonomous robots, it means that they can “think” for them selves. Of course what really happens is that they follow instructions that have previously been given to them, and the limited “thinking” is most likely making decisions as to which instruction to execute based on what feedback they are getting from the various sensors that they employ. This could be as simple as an statement.
Power Supplies
A device to convert the available electricity to a specific type/value eg. you may have a 6volt DC battery but need 24 volts AC to power a motor. The power supply would be needed to make this conversion.
Voltage Regulator
A voltage regulator is able to reduce or limit the amount of voltage that is available in a part of a circuit despite variations in load . eg. If you had a 12 volt battery powering 12 volt motors and a processor that cannot operate on any more than 5 volts, then a 5 volt voltage regulator would be placed in the circuit to supply the processor. Whether the processor needed 20ma or 300ma the voltage would remain the same at 5 volts.
Regulated Power Supply
A power supply that will supply a given voltage output regardless of load conditions (within the range of the device).
Motors
A device to convert electrical energy into rotary motion. Small motors may be of several basic designs including DC motors, AC motors, Stepper motors, some motors can also be divided into Shaded Pole or Permanent Split Capacitor types which refers to method used to initiate motion.
DC Motors
Generally high speed and low starting torque. Ideal for continuous duty applications such as race track cars, clocks, motorized store displays.
Stepper Motors
Easily controlled by processors, stepper motors are constructed with many separate windings so that one pulse will cause the armature to rotate to the next winding thus pulsing the supply will cause the motor to turn is small “steps” typically 1 1/2° to 7 1/2°
Controlling Motor Speed
The method used to control motor speed depends on the type of motor used and must be balanced with the torque requirements. eg for continuous applications a simple DC motor can be used and the speed can be controlled simply by reducing the voltage level. But don’t expect to reduce it by more than about 50% as the motor may stall at this lower voltage. Stepper motors can be controlled simply by the frequency of the pulses supplied to the windings while the voltage and the amount of torque available will both remain constant. Another way to reduce or increase speed is to let the motor operate at its most efficient level but adjust the output speed by connecting through a gearbox. This method usually limits the output to a single speed but may be the answer to convert a high speed/low torque motor to a low speed/ moderate torque application. The most efficient method though is achieved by using a PWM circuit. PWM refers to Pulse Width Modulation. Imagine switching the power to a motor(or an LED) on and off very fast so that the motor gets either full power or nothing. If drawn on a graph paper the the result would be a square wave. If the length of the ‘on’ state and the ‘off’ state are equal lengths then the motor would be running at approximately half speed. Thus the speed can be accurately controlled by changing the length of the ‘on’ to ‘off’ parts of the cycle. the longer the ‘on’ part of the cycle the faster the motor will spin. There is a limit though and most motors cannot operate with less than 10% of ‘on’ time.
Muscle Wires
Made of a metal called “Nitinol”, the wires have the special property of having a memory that can be activated. Thus they can be deformed then with the addition of a small amount of current the wire’s resistance creates heat which causes it to regain its memory and attempt to return to its non-deformed state. Useful for small, delicate movement where size limits the use of other mechanical means.
An Illuminating Idea! Using LED’s
The ubiquitous L.E.D., a Light Emitting Diode. Guaranteed for a minimum of 100,000 hrs. and costing from 10 cents to a couple of dollars. Can be made to produce light in a specific band width therefore they can be paired with a photo diode of the same frequency and used as the coupling system for an optical transmitter/receiver combo (your TV/VCR control?).
LED’s are voltage and current sensitive. Too much and they pop! You will need to calculate the right sized resistor to use in series with the LED to limit the current.
Sensors
Humans have eyes, ears, nose, touch and taste, all of which operate in very narrow and specific bands of sensitivity. But sensors are available that can “see” frequencies in the far infra red and ultra violet bandwidths that are far beyond the sensitivities of our eyes, in fact with the exception of taste and smell, many modern electronic sensors are capable of being far more sensitive to our environment than humans are.
Of course sensors are only the first part, the information from the sensors then has to be processed and acted upon. Generally human still have the edge on machines here, although the gap between humans and technology is constantly getting smaller.
Sensing Light
PhotoDiodes and PhotoTransistors both act somewhat like switches that allow either voltage or a current to flow when a certain frequency of light strikes the lens. A PhotoResistor changes its resistance with the change of light intensity striking its lens. A PhotoCell will produce voltage when sufficient light strikes the lens. Therefore photodiodes and phototransistors lend themselves to on/off applications while photoresistors and photocells are more suited to applications where a variation is to be sensed
Sensing Heat
A Thermistor varies its resistance as its jacket temperature changes where as a Thermocouple is two dissimilar pieces of metal that will produce a corresponding electron flow (voltage) as the temperature at the junction is increased. There are several combinations of metals that are sensitive to different temperature ranges (K type is generally used for room temperature applications). Bimetallic strips use the notion that metals expand at different rates, thus a simple switch can be incorporated into the structure. Bimetallic strips are most often used to switch applications that involve a temperature variation greater than 100°.
Sensing Pressure
Mechanically activated switches that use “whiskers” are still the cheapest way to sense a known pressure difference however there are an increasing number of pressure transducers finding their way on to the market in the last few years. Many use piezo-electric crystals that produce a small voltage when under pressure. The package and method of manufacture can make them sensitive to changes as little as 100th of a gram for use in medicinal gram scales, to increments of 100 grams but in the range of 100’s of tonnes that are used in heavy machinery.
Sensing Speed
The automotive industry favours Hall Effect Transistors to sense rotational speed. A Hall-Effect will switch when in the presence of a magnetic field so a small magnet placed on the outer edge of a rotating disc will activate a hall effect that is positioned close to the edge of the disc. Every time the magnet passes, the transistor opens briefly to allow a pulse of electricity to pass. In another circuit these pulses are counted and compared to a clock of known speed and the results converted to a usable output such as a numerical LED display (digital speedometer). A similar arrangement is available which used an LED and a light sensor. The light is shone through a perforated border on the edge of the rotating disc. The light pulses are counted and compared as with the hall effect.
Sensing linear speed is more complex but if you ask nicely, the local police may show you an example of a method that is in common use, called Radar. This used the Doppler effect. In essence an ultrasonic sound is transmitted in waves of a known frequency and amplitude. As the waves travel further out from the transmitter they loose their integrity at a fixed rate of decay. As waves tend to bounce off of solid objects, they will eventually hit something solid and bounce back toward the transmitter. Here they are received and compared to the signal that went out. The difference is calculated and converted to a value that we can relate to – “You were recorded travelling at 33 Kph. above the speed limit Sir!”
Sensing Sound
Sound, like light, travels in waves but sound is actually compressions in the air around us. These variations in air pressure can be very slight like the gentle rustling of the leaves on a tree or extreme as in the deafening roar that you would experience standing next to a runway when a big jet takes off. When you hear these sounds a thin membrane in your ear is pushed and pulled by the pressure variations in the air. This movement is then passed through several parts in your inner ear finally to become an electrical signal that is sent to your brain . This can be mimicked with a microphone. As the diaphragm of the microphone is pushed and pulled by the variations in the air pressure four possible things can happen on the other side depending on how the microphone is made.
One of the first mic’s used carbon particles behind a metal diaphragm as the disc was pushed in, the carbon was squeezed and so the resistance was reduced through the carbon thus a variation in voltage was the outcome relative to the pressure on the diaphragm. Similarly pressure on a piezo-electric crystal will cause electrons to flow and so produce voltage. Another system uses the proximity of another plate parallel and very close to the metallic diaphragm but with no electrical contact between them. As the diaphragm changes its position relative to the second plate, so the capacitance between them is changed. The fourth method causes a magnet attached to the diaphragm to move within a coil. This movement of the magnetic field induces current in the coil. These microphones share some commonalities, all are sensitive to sound waves, all produce corresponding variations in their respective electronic outputs, and their outputs (being very small) all need to be amplified to be of any use to us.
Sensing Location
Proximity sensors may be of the contact, or non-contact type. Contact proximity sensors are the least expensive and usually comprise a tiny micro switch that is activated by a whisker, roller, lever, or in the case of sensing air flow, a sail. Two conductive strips connected to a circuit which senses a change in resistance can be used to sense levels of non-flamable liquids.
Non-contact proximity sensors will use either ultrasonics (sound beyond the human hearing range), ultrasonics, infrared sensors (if the object to be sensed is known to be of a higher temperature that its surroundings) or for close range non-contact sensing, optics are most commonly used. This device is usually comprised of an LED and a PhotoDiode. A narrow beam of light is shone at a fixed angle to the location where the object to be sensed should be. When the object comes exactly into place the light is reflected back down a short tube within the sensor body or a collimating lens onto the photodiode which switches allowing a signal to the next part of the circuit.
Batteries
There are several kinds of batteries available, both rechargeable and non-rechargable.
Non-rechargables, or “dry cells”, tend to pack a pretty good punch when new but then gradually loose power at a steadily increasing pace. Alkaline batteries flatten this curve somewhat and therefore are best used with motorized equipment.
Rechargeable batteries come in many shapes sizes and chemical groups. Other than Lead Acid, which are not allowed in most Robot competitions due to their tendency to spill highly acidic contents if not vertical. The current breed of rechargeable batteries include nickel cadmium (NiCd), nickel metal hydride (NiMH), and lithium ion polymer (LiPo), lithium Iron Phosphate (LiFe).
The most popular types of rechargeable batteries, Lithium ion(Li) and NiMH are very popular now because they can be made with similar characteristics and packaged the same way as dry cells. LiPo and NiMH can be charged at any time but Ni-Cads need to be almost fully discharged then fully charged otherwise they loose their capacity to fully charge. Note that Alkali and Ni-Cd cells are a nominal 1.5 volts, whereas the Li and NiMH are 1.2 volts. However, at this time, LiPo and LiFe are not allowed in our competitions due to the dangers inherent in their design.
Links and Other Resources
http://www.robotbooks.com/ Possibly the largest collection of books on robotics anywhere and with books suitable for all reader levels.
Electronic Parts and Supplies – New and Surplus (http://www.allelectronics.com/)
Mondo-Tronics’ Robot Store at http://www.jameco.com/Jameco/robot/robotstore.html
Robotic Components, Robots, Future-Bot Components (http://www.futurebots.com/)
Solarbotics formerly HVW Technologies: Microcontrollers & Robotics. BASIC Stamps, PICs, Serial LCDs, Motor Control, & More (https://solarbotics.com/) – this is a Canadian supplier.
Western Canada Robot Games. Calgary, AB.
And our friends at Digi-key – this is a “Canada friendly” supplier.
Robotic Components, Motors, Gear Motors, Arduino, Baby Orangutang and much more (http://www.pololu.com)
For precision Sonar try MaxBotix
Be sure to shop around as prices can vary greatly from one store to another.
If you have any ideas or information that can be added to this page please email Ian Elwood-Oates
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