This is a battery powered motor for a small rowing boat. The motor used is from an electric wheelchair which ran from 24V. The motor has a built in reduction gearbox to provide a large torque to the wheels on the wheelchair. This gearing ratio was far to high for the propeller. The prop needs to turn much faster in order to generate the right amount of thrust to move the boat.

Fortunately the motor used had a small part of the main rotor protruding from the opposite end to the gearbox which was sufficient to attach a sprocket. This sprocket was linked with a chain to another sprocket on the main axle. This axle was then connected to a 90 degree 2:1 gearbox from a cheap angle grinder which was then attached to the propeller.

The propeller is from an old barge and is a little larger than necessary, but the motor provides just enough power to compensate.

The control system uses a pulse width modulation system for a smooth speed control and efficiency. The circuit used is based on the power pulse modulator but with the high voltage MOSFET being replaced by an array of lower voltage high current bipolar transistors so that the huge currents demanded by the motor could be tolerated.

The other switches on the control box are for forward/stop/reverse and to choose between 12V and 24V operation. These are simply large power switches that are used to directly switch the power as necessary.

A Homemade Magnetohydrodynamic Thruster (MHDT)

Based on the image on the left, it is possible to make a simple MHD thruster, just powerful enough to propel a toy boat.

This type of thruster generates magnetic fields by passing an electric current through a liquid conductor, such as sea water. Using another magnetic field, the liquid can be pushed in a chosen direction, therefore generating thrust. You can easily make one of these devices from household materials and a couple of neodymium magnets. In the diagram below the small arrows represent the intersecting electric and magnetic fields. the large blue arrow represents the flow of water.

Two opposing inner faces of a rectangular plastic tube are covered by metal strips. These are the main electrodes and should have a connection for a battery. Magnets are attached on the outside of the tube so that they are attracting each other, and are at 90° to the electrodes.

The metal strips here are cut from a thin Aluminium sheet, but you can just use foil although it wont last as long. The electrolysis and salt water corrosion soon eats away at the metal, but foil should last just long enough to see it working. The best sort of electrode would possibly be made from carbon. A good power source for this device would be a pulse width modulated supply such as our power pulse modulator. This would allow you to adjust the frequency and width of electical pulses so that you could get the optimum thrust from your design.

To learn how a MagnetoHydroDynamic thruster works, see the Propulsion section.

This setup shows the electrodes closer together than the magnets. The combination of magnets used in this device were not strong enough to move the electrified water with any decent force. At only 1.5V in salty water, large amounts of electrolysis occurs, but the water does generally flow in one direction.

The key to getting the best performance it to have the strongest magnetic field you can get across the gap between the electrodes.

Also make sure the magnets are behind the plastic or insulated somehow. You don’t want them shorting out the electric current in the water.

The valveless pulse jet engine or pulse detonation engine is the most simple type of jet and is therefore popular among hobbyists as a DIY project. it is often referred to as a ‘tuned pipe’ because its operation depends upon making the parts the right size and shape so that it fires, or resonates at the engines natural, fundamental frequency. This type of jet propulsion does not need any type of turbine, turbofan, or propeller, making it much less complex than a typical turbojet. In a turbojet the turbine or turbofan is used to compress the fuel/air mixture in the combustion chamber so that it is more efficient and powerful.

This jet engine has absolutely no moving parts and it relies on the simple shape of the combustion chamber and exhaust for it to function. The fuel to the jet is provided at a constant rate, but it is detonated in pulses. After each explosion there remains a lower pressure area inside the combustion chamber. This is immediately filled as air rushes back in and mixes with the fuel feed ready for detonation again.

This example of a homemade jet engine is about as simple as it gets, but it could not be used for propulsion purposes because it is only safe to operate for a short time. The main body of the pulse jet engine is made from copper pipes and various adaptors. The combustion chamber is made from two copper adaptors that have been cut and soldered together. Copper is an excellent thermal conductor which helps to spread the heat throughout the jet, but solder melts very easily so if the jet engine were allowed to run for more than a few seconds this part could come apart. This was enough to demonstrate the principles of operation which is all this DIY jet engine was designed for. If you wanted a working model for providing thrust, it would be necessary to consider different materials as a running jet will get very hot.

These images show the basic ‘tuned pipe’ without the spark plug and gas supply. Tuning was achieved by altering the length and width of the parts used. This was quite simple as there are wide range of plumbing parts that will easily fit together.

The fuel was provided from a cheap blow torch and was injected into the combustion chamber using fine brass tubes bought from a local hobby shop. This chamber also contained a tiny homemade spark plug. The spark rate could be controlled by varying the power to a HV capacitor connected in parallel with the spark plug.

The power supply for the tiny spark plug was made from a mini cold cathode PSU connected to a HV diode and capacitor. An alternative is to use an ignition coil and an ignition coil driver circuit.

The spark plug its self was just a single wire inside a small glass fuse. This wire was connected to one capacitor terminal (live) and the body of the jet engine was connected to the other terminal (earth). The spark would jump from the tip of the wire to the inside of the combustion chamber to ignite the fuel mixture.

The simple design and adjustability of this jet means that a wide variety of fuels can be used. The most common fuel used is kerosene and propane, but common lighter gas will work for this basic demonstration. Click here for More information on Jet Engines.

DIY Sensor Multiplexer

This device was created to allow more analogue sensors to be added to a homemade robot. It is simply a 8 port switcher for analogue or digital signals. The device is controlled by a PIC 12F675 microcontroler, and gives eight analogue outputs from one analogue input, and one digital input.

The K8000 computer interface board, used on the robot, is limited to four analogue inputs. A multiplexer was essential in order to capture more sensor data. The multiplexer can allow the computer to capture data from several sensors using a single analogue input on the K8000.

To do this it was necessary to create a device that could switch eight digital outputs one at a time and be controlled by 1 digital input from K8000. This is very similar to ‘running lights’ where several LED’s run in sequence and start again. To keep the multiplexer small it was decided that a PIC microcontroler would be used, as this would greatly reduce the number of required components. The chosen PIC was the 12F675 because of its small size (8 pin) and the low cost of the chip programmer. This PIC has only four digital outputs so these also needed to be multiplexed. The digital outputs when low can be used like a ground connection, allowing LEDs to be connected directly across two outputs as shown below.

The diagram above shows how four outputs of a PIC can be used to control 8 LEDs. If these LEDs are inside an optoisolator then they can be used to trigger transistors, allowing a sensor to pass data to the computer. The diagram below is intended to show the connections of the sensor multiplexer. This diagram does not show some components such as resistors and capacitors, and is intended only as a guide.

To capture sensor data from the multiplexer a subroutine named ‘GetPlexer’ was created in the robots main code. This loop can read the value of the analogue input on the K8000, store it in an array, and then switch the digital output to the multiplexer on and then off again. This process will loop until all 8 sensors have been read.

When power is connected the first sensor in the array will be active. It would be as if it were connected directly to the analogue input of the K8000. When the signal from the digital output of the K8000 goes from low to high the power to the first sensor is disconnected and the next sensor is activated. This process repeats until the last sensor is activated and then it starts again from the beginning. This was housed in a plastic box and jack sockets added to allow easy connection and removal of sensors.

A DIY Robot – PC or Laptop Controlled

This robot was developed as a final year project for Bradford University Cybernetics Department in 2003/2004. This page is a shortened version of the final project report. The full report is available by clicking the link at the bottom of this page.

Project MIRC

MIRC, which stands for Mechanized Interface for Robots and Computers – it is not a robot in itself, but a mechanism for interfacing robotic hardware with standard computer systems (MIRC + Computer = Robot).

This project aimed to develop a modular system (MIRC) for interfacing already commonly available hardware for conducting household or industrial tasks, with standard computers. Ultimately, it was designed to link to an already established infrastructure to develop new and more effective ways of utilizing it.

The MIRC could ultimately enable the technology of the PC to become mobile, thus minimising the need to carry out mundane or repetitive activities and to enable long distance completion of tasks. In the proposed approach, the MIRC was operated by command from a laptop which had been programmed using fuzzy algorithms to carry out basic object avoidance and wheel tracking. By using fuzzy algorithms rather than the more standard IF/THEN statements currently used in programming the MIRC has increased flexibility and potential for adaptation for a range of uses.

Currently most advanced robots are custom made for a particular task and expensive to produce. Other robots are designed simplistically as toys or gadgets, and as such are mass produced and relatively cheap to produce. The MIRC which has been produced as a result of this project combines these factors by using mass produced components to create a technically advanced robotic system which has the additional capacity for customisation, giving endless flexibility. Ultimately it could allow the consumer to purchase a MIRC and then to create a robot custom built for their needs from standard components without the need for extensive knowledge of robotics or expensive outlay.

PCs today are much faster than they used to be. So much so, that the average computer has enough processing power to adequately analyse sensor data such as stereo video images in real time. Due to the PCs huge variety of applications and its popularity across the world it seemed clear that a robot could be based on this technology. This would allow for USB devices and component upgrades to come from the same sources as normal PC equipment. The same manufacturers could also make the products, allowing it to reach world markets very quickly. The versatility of the PC in part comes from the variety of IO ports it is able to use. This allows it to connect to many different types of hardware, and with ever growing processor power the bandwidth capabilities of the ports grows too. The most important part of the MIRC was the sensors, so a good interface for these was essential. It needed to have the capability of capturing analogue and digital sensor data and also outputting in the same way. A fully constructed model could be capable of many things. If many different manufacturers created USB and FireWire upgrades, the robots could have a huge range of functions. Devices like robot arms, vacuum cleaners, paint sprayers, even robotic legs could be added simply by attaching them in the correct place and installing the software. Wireless networking would enable robots to communicate with each other from almost anywhere and the owner to control them all via the internet.

Objectives

The aim of this project was to create a prototype MIRC to show how a PC based robot could be developed. The objective was to produce a basic model with four wheels, standard sensors and a web cam forming the centre around which an individual could create their own custom robot with extra USB devices.

It was intended that the structure of the robot should be simple to facilitate easy adaptation and upgrading. The housing was designed to create three distinct layers within the MIRC to separate elements of the robot, thus leaving room to add more devices and a laptop computer when complete. The bottom layer would be designed for battery housing and mechanical hardware, such as wheels and sprockets, the middle layer to contain the main interface electronics, and the top layer to be for the external devices.

The MIRC was developed over a period of eight months. Initially research was conducted into robotic control systems, pc interfaces, sensors and actuators. A K8000 interface board formed the basis of the project, as it allowed for the connection of analogue sensors and actuators to the pc. The PC was chosen rather than built in micro processor because it was far more powerful and customisable.

Sensors

The first type of sensors needed was proximity detectors. The sensors chosen for this were simple photo reflective IR devices. These sensors consist of an infra red LED and phototransistor in a plastic case; they would output a voltage that was dependant on the amount of IR light hitting the detector. Using analogue sensors enabled development of fuzzy logic to control how the robot avoided objects. These sensors worked well at short range as long as there was no ambient sunlight. It wasn’t until the weather got sunnier that it was realised how much the sunlight would affect operation. Sunshine affected the photo reflective sensors outputs by increasing output to about ¾ of maximum. Adding sunshine sensor and adjusting the other sensor values relative to it stopped the sunshine from making the outputs go too high but it reduced the range so much that they were useless.

A much better type of sensor is the Sharp GPD-12 Infra red range finder. It is much larger in size than the photo reflective sensors but is much more accurate as it measures the angle of the reflected light as well as the intensity. On board signal processing then converts this to an analogue output voltage. The downside to this sensor is that it costs over £10. The GPD-12 is one in a range of infra red range finders by Sharp. They come with various output types and ranges.

The head module on the MIRC contains several sensors, one of which is an ultrasonic range finder by Milford instruments [21]. This sensor uses the Polaroid transducer system, which has a single transducer for sending and receiving echoes. This is mounted on a servo for panning and is controlled by a board connected to the computers serial port. Another sensor in the head is a USB webcam of 640*480 pixels. Currently this has not been used in the project as the laptop being used does not support USB. With a more modern laptop this camera could be utilized for many functions, such as object recognition, motion tracking and remote avatar web conferencing.

One sensor on the MIRC is an ultrasonic proximity detector. This is the Velleman K3502 parking radar kit. This kit usually sounds a buzzer when an object passes a preset distance from the sensor. To connect this sensor to the K8000 the buzzer was removed and the buzzer output was connected to a digital input on the K8000. There was no need to alter the voltage or the buzzer output, as the K8000 can tolerate a wide range of voltages (5-20V DC).

Actuators

The main actuators of the MIRC are the two drive motors. Each motor drives one wheel independently. The original design involved using a four wheel drive system. Steering was done using he ‘tank drive’ method. This allows for a zero turning circle and therefore greater manoeuvrability in a small space. This method was found to be insufficient due to large amounts of slippage and torque requirements. The current method employs two large back drive wheels and castors at the front. The steering is done in the same way as the ‘tank drive’, but as the wheels are on the back the turning circle is increased to twice the length of the MIRC. The great reduction in slippage with this method meant that less torque was required and therefore better performance was achieved. The speed and direction of the motors can be controlled via the K8000 and H-Bridge driver board [22]. The motors are fitted with a 148:1 gear box to give greater torque, but this was still insufficient for the ‘tank drive’.
The other actuators are the pan and tilt servos for the head assembly. The panning servo is controlled by the same board that controls the Polaroid transducer range finder. The tilt servo is controlled by a separate board [21] which is capable of controlling up to 8 servos. This board is not currently connected due to the lack of ports on the laptop used in development.

Robot Body (chasis)

The body of the MIRC consists of three layers. The bottom layer is for the drive mechanics and batteries, the middle layer is for the interface electronics and the top layer for the computer and room for expansion. The base was initially made from an aluminium sheet with aluminium shelving brackets along the sides for strength. This eventually had to be changed as the original base did not prove sturdy once the heavy batteries were added. Rapid acceleration and turning caused the whole base to flex, which eventually caused the chains between the motors and wheels to slip, and one of the gearboxes to break. This was one of the main obstacles that was overcome as it slowed progress and wasted funds. The new base is made from a piece of thick MDF with wooden supports for the bearings, and performs much more effectively.

Software

The software currently being used to control the MIRC is written in QBASIC. This language is neither modern nor powerful, but it is relevant to the dated laptop used. At the beginning of the project it was difficult trying to get java programs to work adequately on the laptop. Finally it was realised that the laptops slow processor could not handle all the computation required by this platform independent code. Although QBASIC could not be used to produce an adequate final working program with a GUI, it was sufficient to control the majority of hardware. If a more modern computer had been available to work with better quality programs could have been produced and more advance hardware added. C++ was the preferred language but the editor and compiler were too complex for the laptop used. Editing on a PC and transferring compiled programs to the laptop was not practical due to it having faulty disk drives and communication ports.

Fuzzy Logic Control Software

In order for a robot to function effectively in the home, it must be able to adapt to circumstances that the programmer may not have considered. If the program was not able to learn and adapt, the user would soon find that the robots abilities were quite limited. No matter how many situations and tasks it was programmed to deal with, there would always be something it would fail to ‘understand’. This is why software developed for the MIRC uses fuzzy algorithms.

The current software does not involve fuzzy learning as this will take considerable time to develop, but example programs were created to demonstrate this. The first example does not involve learning but uses fuzzy logic to determine how the MIRC moves. This program (Appendix H) causes the MIRC to act like a finite state machine. [23] The program simply captures data from analogue range sensors on the front and sides of the MIRC. This data is then combined and converted to a value for the speed of each motor. If the MIRC approached an object that was on its left side, the right motor will slow down causing it to move away. The closer the MIRC is to the object the more the wheel will slow down, causing it to turn sharper. The outcome of this is that the MIRC behaves more like an animal than a machine. The QBASIC code for combining the sensor values and changing the motor speed is shown in figure 6 below.

Figure 6. Changing speed of the motor, relative to all sensor readings

This is one line of code. LTemp is eventually used as the speed value for the left motor. The other variables are the sensor values. This applied to both motors, causes the effect mentioned previously and also will cause the MIRC to slow down if passing through a small space.

Another example program created was a fuzzy line follower (Appendix I). This program uses similar algorithms to the object avoider program. Two photo reflective sensors are mounted on the front of the MIRC for detecting lines. Different types and colours of lines were tried and the relevant programs created for them, but it was found that slow polling of the sensors would only allow for gently bending lines to be followed. If a faster computer was available, sensor data could be captured faster and therefore sharper bends could be followed.

To demonstrate fuzzy learning, a program was created that simulated evolution. (see A.I.) The program creates a type of predator and prey environment where one species hunts another for food. The prey are just simple circles which move around randomly on the computer screen. Each one has its own set of parameters which define how fast it moves and how erratically it behaves. The predators are the evolving species which eat the prey, move around and breed. Each one has its own unique set of variables which governs behaviour. This is their simulated DNA. When the program starts several prey are generated and one just predator. The ‘DNA’ for this initial predator is randomly generated. It is attracted to the prey so it chases them until it is close enough to eat. Once the predator has eaten enough food it will make a copy of its self but with some slight mutations in its ‘DNA’. The mutations may have positive or negative effects, such as being able to survive longer without food, or becoming less agile. At first the majority of predators will group together, but by the time several generations have lived and died, distinct groups can be seen. Using this method, a robot could be the predator, and the prey could be its charging station or tasks it meant to perform.

Conclusions

The resultant MIRC combined with a laptop appears in presentation as a robot. It has achieved its original objective of mobilisation of which can perform a range of simple tasks determined by the software used. Whilst the project has achieved its aims, there is limitless capacity to develop further to reach its full potential. With funding and further experimentation this humble foundation could prove a stepping stone to real functional usage of this type of technology. The production of an advanced MIRC is possible at a reasonable cost with mass production and as such could impact on everyday life. 
Currently there is no main program or OS. Eventually it will be a mainly fuzzy controlled system. It appears rather pointless trying to create a precise, accurate system as it would cost large amounts of money and time to make it work. The intended outcome is to create a kind of fuzzy logic based cyber pet. This would mean that a MIRC based robot would act more like an animal than a sophisticated machine. Learning algorithms could enable you to teach it tricks just like you do with a dog, rewarding good behaviour and punishing it if it does something wrong. 
Throughout this project a great deal of knowledge has been gained in various areas of cybernetics, and a significant project achievement has been reached. Images of the competed MIRC are available on the attached CD. The MIRC created for this project will continue to provide learning opportunities as it continues to develop and improve. A point to stress is how difficult turning theory into practice actually is. Testing very often showed unexpected results. A lot of time can be used getting things to work the way they were intended to, and very often a compromise is necessary.

Further Work

There is much more work that can be carried out on this project: – Once the oddometry is working effectively, a charging station for the robot could be built to locate when in need of recharging. Armed with a modern laptop, the next step will be to incorporate the webcam and wireless networking. With image processing a robot could recognise objects, rooms or even faces. Another thing to add is a robot arm. There are already robot arms available for purchase that can plug into a USB port, although a custom design may prove more effective. Eventually the entire MIRC will be connectable to a laptop by one single USB cable as this would make connection simple. Also a USB hub could be built in to the MIRC for simple addition of hardware such as robot arms or a barcode reader.

The ability of modern computers to connect to wireless networks is an important factor to the potential success of the MIRC. Being connected to the internet not only gives the MIRC access to large amounts of data. It also means that it could be connected to other networks such as mobile telephone networks. This opens the doors for a whole new interactive system. A person wishing to make a MIRC based security robot could monitor it from anywhere. Data and images could be sent to a multimedia telephone or instructions sent back to it. The most popular use of this is expected to be web conferencing. A person could use the MIRC like a remote avatar, allowing them to ‘step inside’ it and drive it around.

Laptop controlled MIRCs could be networked together, enabling them to work as a team to complete the same objective. This could even be done with the robots in different parts of the world. Groups of robots could be simultaneously controlled by a single user. Using the fuzzy style of programming described earlier, several robots could share all their sensor data and process it between them. This could act like a shared ‘conciseness’ making each individual robot more like a single part of one machine, rather than individual robots communicating and working as a team.

This article is a short version taken from the main project report.
To see the full documentation for Project MIRC, click here.

THere is a new version of this project using moder electronics and software. See the DIY Robot II

A DIY Mechanical Puppet Animator

This is very simple device that uses a simple mechanism to animate some small puppets to make them look like they are dancing.

The mechanism converts the rotary motion of a motor into a linear motion that oscillates with simple harmonic motion (SHM). This means if the velocity of the rod was plotted on a graph, it would look like a typical sine wave. It is just a simple push-pull type device that is used to move a long rod back and forth. The moving rod will be used to transfer the motion to two puppets, side by side.

The images below show the mechanisms used to transfer motion to the puppets. The wooden ‘T’ piece tilts left to right repeatedly. It is linked to the main rod by a short length of silicon tubing which stretches ant the end of each stroke. The stretching of the tubing at the end of the stroke means that the motion of the puppets is more rhythmic because they stop briefly before changing direction. This helps to randomise the movements of the freely swinging arms and legs.

The mechanism is installed in a custom wooden box. The puppets are suspended from the ‘T’ piece by nylon strings attached to the hands and feet, and the main body is suspended from a fixed point to carry the weight.

To reduce the noise output from the device, the mechanism is boxed in with foam lined walls, and the joints are greased to reduce friction. The strings pass through small holes in the lower section so that the puppets are suspended in an independent cavity.

The speed of the motion is controlled using a simple pulse width modulator circuit based on a 555 timer IC. When powered by 6V DC the speed can be varied between stationary and ‘crazy’ where the puppets are moving very erratically. This allow the device to be used for longer periods because if the battery level falls the speed controller can be turned up to accommodate it.

These dancers are also able to demonstrate resonance! When the speed is adjusted just right, it is possible to ‘tune in’ to a part of the puppet which makes the movement suddenly become erratic and more significant.