Wednesday, August 31, 2011

REMOTE CONTROLLED LAND ROVER without Microcontroller

Robotics is a fascinating subject— more so, if you have to fabricate a robot yourself. The field of robotics encompasses a number of engineering disciplines such as electronics (including electrical), structural, pneumatics and mechanical. The structural part involves use of frames, beams, linkages, axles, etc. The mechanical parts/accessories comprise  various types of gears (spurs, crowns, bevels, worms and differential gear systems), pulleys and belts, drive systems (differentials, castors, wheels and steering), etc. Pneumatics plays a vital role in generating specific pushing and pulling movements such as those simulating arms or leg movements. Pneumatic grippers are also used with advantage in robotics because of their simplicity and cost-effectiveness. The electrical items include DC and stepper motors, actuators, electrical grips, clutches and their control. The electronics part involves remote control, sensors (touch sensor, right sensor, collision sensor, etc), their interface circuitry and a microcontroller for overall control function.

Project overview
What we present here is an elementary robotic land rover that can be controlled remotely using primarily the RF mode. The RF remote control has the advantage of adequate range (up to 200 metres with proper antennae) besides being omnidirectional. On the other hand, an IR remote would function over a limited range of about 5 metres and the remote transmitter has to be oriented towards the receiver module quite precisely. However, the cost involved in using RF modules is much higher than of IR components and as such, we have included the replacement alternative of RF modules with their IR counterparts for using the IR remote control. The proposed land  rover can move in forward and reverse directions. You would also be able to steer it towards left and right directions. While being turned to left or right, the corresponding blinking LEDs would blink to indicate the direction of its turning. Similarly,during reverse movement, reversing LEDs would be lit. Front and rear bumpers are provided using long operating lever of micro switches to switch off the drive motors during any collision. The decoder being used for the project has latched outputs and as such you do not have to keep the buttons on remote control pressed for more than a few milliseconds. This helps prolong the battery life for remote. The entire project is split into sections and each section is explained in sufficient detail to enable you not only to fabricate the present design but also exploit these principles for evolving your own design with added functions/ features.

Forward and reverse movement. To keep our design as simple as possible, we have coupled a 30-rpm geared 6V DC motor to the left front wheel and another identical motor to the right front wheel. Both these front motors are mounted side-by-side facing in opposite directions. Wheel rims (5cm diameter) along with rubber wheels are directly coupled to each of the motor shafts. This arrangement does not require separate axles.

During forward (or reverse) movement  of the vehicle, the two wheel shafts, as viewed from the motor ends, would move in opposite directions (one clockwise and the other anticlockwise). For reversing the direction (forward and backward), you simply have to reverse the DC supply polarity of the two motors driving the respective wheels.

Steering control. There are different methods available for steering a robotic vehicle. The commonly used ones are:
1. Front wheels are used for steering, while rear wheels are used for driving; e.g., in tractors.
2. Front wheels are used for steering as well as driving; e.g., in most light vehicles. In these vehicles (such as cars), the front wheels are coupled using a differential gear arrangement. It comes into play only when one wheel needs to rotate differentially with respect to its counterpart. When the car is moving in a straight line, the differential gears do not rotate with respect to their axes. However, whenthe car negotiates a turn, the differential allows the two wheels to rotate differentially with respect to each other.
3. All the four wheels are used for driving as well as steering. Examples are Kyosho (USA) 4-wheel drive/4- wheel steering electric powered monster truck chassis. 4. Single front wheel is used for driving as well as steering; e.g., in a tricycle.
5. Two driving wheels that are independently controlled to turn; e.g., in a tank.

In our project, to keep the things simple, we have used Method-5 with some modification. For the rear wheels, we have made use of a single 5cm dia. plastic castor wheel, entical to the ones used in revolving chairs. Such a wheel turns by 180° when you try to reverse the direction of the vehicle’s motion. This way the movement of the rover becomes stable in both the forward and reverse directions. The steer ing (clockwise or anticlockwise) motion is achieved by driving only one wheel at a time. To turn the vehicle towards left (as perceived by the driver) we energise only the righthand- side motor, and to turn it towards right we energise only the lefthand- side motor during turning. Drive circuit for the motors. Here is a typical circuit for driving one of the motors, in forward or reverse direction, coupled to, say, the left-hand front wheel. Simultaneously, the righthand motor has to rotate in the reverse direction (w.r.t the left-hand motor) for moving the vehicle in the same direction. It means that input terminals of the motor drive circuit for the righthand motor have to be fed with reverse- polarity control signals compared to those of the left-hand motor drive circuit. In the H-bridge motor drive circuit (see Fig. 2) when A1 input is made high and A2 is made low, transistor T1 (npn) is forward biased and driven into saturation, while transistor T2 (pnp), being reverse-biased, is cut-off. This extends the battery’s positive rail to terminal-1 of the motor.Simultaneously, with input A2 at ground potential, transistor T3 (npn) is cut-off, while T4 (pnp) is forward biased and driven into saturation. This results in ground being extended to terminal-2 of the motor. Thus the motor rotates in one direction. Now, if the two inputs are logically complemented, the motor will run in the opposite direction. When both the inputs are at the same logic level (Gnd or Vcc), the motor is at rest. Thus we can control the movement (forward, reverse and stop) as well as the direction of rotation of the motor with the help of logic level of the two control input signals to the motor.


1 comment:

  1. These automated vehicle concepts are amazing. I am in awe of the circuitry. Yet their principle is quite the same with the most simplest remote control like roller shutters perth.