We've come a long way since we started the FIRST Tech Challenge: From coming up with various solutions for the different tasks the robot should be able to do to finally building the robot itself. A lot of hours have gone into this project and finally we can reap the reward: L.U.I.G.I.
While we have a lot of freedom in designing the robot, there were a few restrictions. The main restrictions are: a limit to size, a limited amount of motors and no pneumatic parts. These restrictions immediately reduced the amount of ideas we had, but in the end we came up with a few concepts.
The main task the robot had to accomplish was stack blocks in a column of four blocks high. For this task we designed two systems: a method based on a forklift, and one based on a bulldozer. The main difference between the two being the method of vertical displacement.
The Forklift Method
In this method we used the property of a forklift truck. This consists of being able to lift a block vertically with no horizontal movement. The abscence of vertical movement makes the robot more stable during, grappling, lifting and releasing a block.
This method also has the benefit of being able to place the blocks in the column (see The Challenge) without having to move the robot. Furthermore there is a lot more room for vertical movement using the forklift method than there is with, for example, the bulldozer method.
In our system a central beam is moved up and down by wheels, fixed to the frame of the robot, on either side. The grappling system (see below: Grappling System) is mounted to that central beam now also gaining the ability to move vertically up and down.
Although this concept does leave a lot of room for vertical movement, it does have a few disadvantages. Because the system has to be at the front of the robot, thus outside of the wheelbase, there is some instability. This results in the point of mass being moved to the front of the robot causing a slight inclination to the front of the robot.
We countered this effect by placing our components, battery and motors (which will be mentioned later on in weight distribution) as far to the rear of the robot as possible.
The Bulldozer Method
In this method we used the property of bulldozers. This method consists of a beam rotating from a fixed at the end one of the sides of the beam which is mounted to the center of the truck.
Though this method is more stable when the block is higher in the air, a very long beam is necessary to reach to the same heights as the forklift method. This is due to the mathematical way circular movement works.
You can see that the forklift method only needs to have a beam of length 'x' to travel 'x' distance in height.
For the bulldozer we need a lot longer beam to cover the same distance vertically, while keeping the block in front of the robot, as the robot cannot block the path of the block (excuse the pun) while placing it in the column (see The Challenge).
By using the sine we discover that for travelling a distance 'x' while keeping the distance from the front of the robot to the block >0 we need a beam with a length exceding the total restricted length of the robot, thus making the bulldozer method non-viable.
To be able to move a block, we have to grip it first. For this task we again devised two methods to do so.
The first method we developed, mainly, for the bulldozer method (see above in Concepts). This system is based on two plates, rotating from their respective points at a distance a little greater than that of the block, as to apply pressure on two sides of a block. The two plates spanning less than the area of the sides of block ensure there is enough pressure on the block to counteract the force of gravity so as not to slip away. The small plates also have the advantage of being able to be implemented in small spaces.
The second method we developed specifically for the forklift method as it is not feaseble in combination with the bulldozer method.
This system consists of two long plates with a total height of two times the size of the blocks. By using the characteristics of the forklift method, being vertical movement without horizontal displacement, we are able to move to blocks at a time. This leads to a dramatic improvement in the speed the task is completed as we can move two times the amount of block in the same time the former method takes to move one.
To increase the pressure on the sides of the block, as the plates put pressure on the entire side of the block thus reducing the overall pressure, we put strips of a special material to concentrate pressure on specific points and to increase grip. Therefore making it very hard for the block to slip.
Wheelbase and Weight Distribution
For maximum stability, a wide and long wheelbase is desirable. This is to reduce the chances of the point of mass falling outside the wheelbase resulting in the robot toppling over. While we tried to make the wheelbase as long and wide as possible, we had to keep the different methods of moving a block into account. This means leaving enough space for the grappling and movement system. In the end we settled for a design with a maximum wheelbase area, leaving just enough space for the other systems.
To further assure that the point of mass stays within the wheelbase, we placed our components, battery and motors in the middle of the wheelbase as much as possible. This resulted in a system with gears and chains to move motors placed at the top of the robot, operating various tasks, to the bottom of the robot.
To further diminish the chances of the robot toppling, it is desirable to keep the wheelbase as low to the ground as possible. To do this we choose small wheels to keep the axle holding the wheels as close to the ground as possible, ergo, keeping the wheelbase close to the ground.
Programming and Sensors
Coming Soon ...