APEX Robot Rabbit. Tel:

Transcription

1 APEX Robot Rabbit

2 Television programmes such as Robot Wars and Techno Games have inspired many people to have a go at building their own robots. Some of these robots are fantastically complicated, and expensive, using the very latest digital microprocessors and control circuitry. Some of the competitors, however, have taken a much simpler and cheaper approach to designing their robots. It is perfectly possible to create a robot that is both fun, and a great learning experience, for a few pounds with limited technical knowledge. At the most basic, a robot needs only contain a few components such as batteries, wires and motors to allow it to move. This datasheet has gone a little step further and shows you how you can build something a bit more adventurous, but without requiring many years of robotics experience to create it! Introducing the Robot Rabbit! Our Robot Rabbit, like all rabbits, is nocturnal. During the day, he hides away, but at night, he can come out to run around. On his own, or with other Robot Rabbits in the dark, he will run around until his batteries run down. As with all rabbits though, he is always wary of predators. In particular, our rabbit hates light, and will try to run away from it! If he sees a torch, or a car headlight, he will turn to run in a different direction. If you manage to catch him fully in torch light, he will freeze completely, hoping that if he stays still, you won't see him! The next few pages will show you how you can make a Robot Rabbit of your own. They will show you how to make the electronics, and even tell you where you can buy the parts. They will also give you some suggestions as to how you can make the Robot Body and the moving mechanical parts such as the wheels and gears, however most of this will be left to your imagination so that you can create a robot that really is your own!

3 Robot Electronics The circuit show below has been designed to drive two motors which are connected by some gears to the left and right wheels of your robot. The motors are controlled by the amount of light falling on two 'eyes'. The robot eyes are Light Dependant Resistors, LDRs. In the dark, these LDRs have a high electrical resistance. The LDRs are electrically connected to the input to a transistor. In the dark, the high electrical resistance will allow the transistor to turn on, and the wheel motor will turn. In the light, however, the resistance of the LDR drops, which turns the transistor off and stops the motor. The variable resistor is included to allow the circuit to be fine tuned to react to different light levels. Since we want to robot to turn away from light, the Left LDR 'eye' is connected to the right wheel motor and vice-versa. This means that if the left eye sees light, the right motor will stop, but the left motor will continue to run, so the robot will turn to the right, away from the light. If both eyes see light, both motors will stop and the robot will freeze. In the dark, both motors will run, so the robot will move in a straight line. Robot Rabbit Circuit Diagram

4 The circuit shown needs the following parts: Part Quantity needed Available from for one Robot BSS295 Transistor 2 RS (Order Code ) Farnell (Order Code ) 1N4001 Diode 2 RS (Order Code ) Farnell (Order Code ) 10k Variable 2 RS (Order Code ) Resistor Farnell (Order Code ) NORP12 LDR 2 RS (Order Code ) Farnell (Order Code ) Motor, 3V D.C. 2 RS (Order Code ) Farnell (Order Code ) These parts are available from most good electronics suppliers such as RS ( or Farnell ( In some cases, the suppliers may have a minimum order quantity for some components which may be larger than the number that you need for a single robot. In addition to these parts, you will need either a PCB, or some Veroboard on which to assemble the circuit. A suitable PCB is available from APEX Electronics, and Veroboard is available from most good electronics suppliers (for example RS, order code , or Farnell, order code , either of which should be enough for at least 10 robots). You will also require some wire, a soldering iron, and some solder in order to assemble the circuit, and a suitable battery and a battery holder. The circuit has been designed to run from any suitable battery between 3V and 12V D.C. If the motors are geared down sufficiently (see the mechanical construction pages), it is possible to run the motors from 2 x AA batteries, though it is more likely that, unless the mechanical gearing is very well designed, you will need to run the circuit from 4 x AA batteries to give the motors extra power. Batteries and a battery holder are also available from the suppliers listed above. It is also possible to use different motors if you have any suitable ones available, however you need to ensure that the battery voltage is suitable for the motor, and that the motor will not need too much power for the circuit to drive it. The circuit should be capable of driving almost any small D.C. motor which takes a current of no more than 1A. A complete kit of parts for the electronics, including all components, motors, wires, a 2 x AA battery holder and a PCB is available from APEX Electronics. Alternatively we can also supply the PCB on it's own, pre-drilled and ready for assembly, or we can supply the electronics fully assembled. An order form is attached to the back of this leaflet. The following two pages show how the circuit can be assembled either using Veroboard, or using a PCB.

5 Printed Circuit Board Assembly - apex@empyrion.demon.co.uk PCB Component Side PCB Track Side (Not to Scale)

6 Veroboard Assembly Veroboard Component Side Veroboard Track Side

7 Robot Mechanics Once you have assembled the electronics for the robot, you will need to design and build a suitable robot body to mount them on. You will also need to design a system of gears to connect the motor to the wheels. The basic robot body can be made easily from a piece of wood. You only need to make sure that it is large enough to mount the motors, gears, batteries, eyes and the circuit board. It is important, however that the robot is not too heavy, since this could prevent it from moving around properly. The two eyes need to be positioned so that they are looking forwards, and angled apart so that they are looking in different directions. More difficult is the gearing arrangement which is required for the wheels and motors. The electric motors run at a fairly high speed, but with very little power. If a wheel were connected directly to the motor shaft, the motor would be unable to turn the wheel round once it is placed on the floor. The motor needs to be geared down so that for several revolutions of the motor shaft, the wheel will only turn round once. This could be done using gear wheels from a set of toy building bricks, or using gear wheels available from electronic or mechanical suppliers, or from model shops. Ideally, a gear ratio of at least 6.5 to 1 is required, although a ratio of 10 to 1 or more would be better (i.e. for every 10 revolutions of the motor shaft, the wheel turns once). The example show uses a gear ratio of approximately 5 to 1, which is only just sufficient to allow the motors to drive the wheels! A suitable arrangement of gears could be produced from gear wheels available from RS. It may also be possible to design a suitable gearing system using pulleys and belts, such as elastic bands. A more expensive, but easier solution would be to buy motors with a gearbox already attached. In this case, the motors suggested on the previous pages will not be required. Again, these are available from model shops, and electronics suppliers. Gear Wheels available from RS: 12 Teeth Part Number Teeth Part Number (Together these would give a gear ratio of 6.7 to 1) Pre-Geared Motors (30 to 1 ratio) are also available from RS, Part Number

8 Setting Up the Robot Finally, now that you have completed building the Robot Rabbit, you will need to set up the eyes so that they are correctly adjusted for the light level in which you are going to be working. This is a relatively simple procedure if you follow the simple steps below. 1. Find yourself a torch that you will be using with the robot. A bright torch is better. 2. You will need to find a suitable way of keeping the robot wheels off the floor while you set it up so that it doesn t try to run away during the procedure. You could try propping it up on a small block of wood or a book. 3. Turn both of the variable resistors fully anti-clockwise using a small screwdriver. 4. Connect the batteries to your robot. At this point, both of the wheel motors should be stopped. 5. Switch on your torch and point it at the left eye of your robot. 6. Turn the variable resistor connected to the left eye slowly clockwise until the right wheel motor starts to turn. You now need to slowly turn the resistor back anticlockwise again until the motor just stops again. 7. Check that when you remove the torch, the wheel turns. The wheel should turn in a direction that would move the Robot Rabbit forwards. If you find that the wheel is turning in the wrong direction, you will need to swap over the two leads that go from the circuit board to the motor at the motor end to make the motor turn the other way. 8. Repeat the procedure with the other eye. Your robot is now fully set-up and ready to go. You will probably find that the robot needs a smooth surface to run on such as a large wooden floor. Carpets and grass are difficult terrain for our Robot Rabbit, and it may not be able to move. Once your robot has finished, you could try playing a game with it. Put the robot in a large darkened hall so that it has plenty of room to run around. You can then try to catch the Rabbit by chasing after it with a torch. It will try to turn away from the torch light and go in a different direction, but if you manage to shine the torch in both of the eyes at the same time, it will freeze! Good luck with your Robot Rabbit, and enjoy your first robotic adventure!

9 Order Form Complete Kit of parts comprises: 2 x 3V D.C. Motors 2 x NORP12 LDRs 2 x BSS295 Transistors 2 x 1N4001 Diodes 2 x 10kW Preset Variable Resistors 8 x 200mm Lengths Solid Core Wire 1 x 2 AA Battery Holder 1 x PCB, Pre-Drilled Assembled Electronics includes all of the above, pre-assembled and tested. Neither kit includes any mechanical components other than the motors. Item Price Each Number Required Total Price Robot Rabbit PCB 2.00 Complete Robot Rabbit Kit of Parts Robot Rabbit Electronics (Assembled) Postage & Packing, per Kit (Not Required for Bare PCBs only) 4.00 Total: Please send a cheque for the total amount, in Sterling, with your order, payable to Alan Platt to the address given below. Alan Platt APEX Electronics 2 Icknield Walk Royston Hertfordshire SG8 7JG Kits will normally be delivered within 14 days. We apologise that we can only supply kits to customers within the UK.