Chapter 2 Gears

Gears are very important elements in a robot. They don't work by itself; in fact we need at least 2 of them. What they basically do is to transform one force into another effectively like a pulley or a chain. Beyond that, however the chapter discusses some properties of gears, relating to important aspects of physics. First of all, every gear has a certain number of teeth. This number of teeth simply tells us a lot of things. It determines the size of a gear. The more teeth a gear has, the bigger it is. Furthermore, when two or more gears are combined together, the number of teeth on each gear affects the speed of a robot. For instance, suppose a robot has two gears on its motor. One is a driving gear, which has 12 teeth and the other, a driven gear, which has 36 teeth. The time for the driving gear to rotate once is equal to the one for the driven gear to rotate 3 times. Therefore, the robot can speed up 3 times than an ordinary robot with the same number of teeth of a driving gear and a driven gear. This acceleration is called angular velcocity. However, we can't simply speed up the robot without losing anything. In fact, angular velocity decreases torque. The torque is strength of gears, which is used in such a way to go up tilt. The larger gears are, the more torque they have, because larger gears have a further distance from the centre. In order to make an extremely big torque, sacrificing the angular velocity, we can use geartrains. Here, we use more than 2 gears connected. However, it's important to set up carefully, because if torque is too big, than LEGO parts may get damaged.
There are other types of gear too. First, we have a work gear block. It looks like a stick and can connect it to types of gears mentioned eariler. It can't be turned by other gears thus create friction a lot. This friction isn't always bad as it allows very compact assembly solutions. The other gear is clutch gear. It helps to limit the strength we can get from a geared system and preserve our motors and parts. It usually accompanys geartrain.

Get in Gear (Investigation)

Mr. Inskeep gave us two questions to work on.

1. What would happen if you made your driving gear bigger and your driven gear smaller ?

If my driving gear is bigger than my driven gear, what would happen is that when the driving gear rotates a certain number of time, the driven gear rotates more, proportional to the number of time. This can speed up the robot. For instance, suppose the driving gear has 36 teeth and the driven gear 12. Then time taken for the driving gear to rotate once is equal to the one for the driven gear to rotate 3 times. The robot with this setting is 3 times faster than the robot with the same number of teeth of a driving gear and a driven gear. However, if the driving gear is bigger than the driven gear, torque decreases. This small torque causes the robot to struggle when it climbs up inclined surface.

2. What would happen if you made your driven gear bigger and your driving gear smaller ?

If my driven gear is bigger than my driving gear, what would happen is that when the driving gear rotates a certain number of time, the driven gear rotates less, proportional to the number of time. This can slow down the robot. For example, suppose the driving gear has 12 teeth and the driven gear 36. Then time taken for the driving gear to rotate 3 times is euql to the one for the driven gear to rotate once. The robot with this setting is 3 times slower than the robot with the same number of teeth of a driving gear and a driven gear. However, if the driving gear is smaller than the driven gear, torque increases. This big torque causes the robot not to struggle when it climbs up inclined surface.

Just for your information, the left gear is the driving gear and the right the driven gear.

Chapter 14 Classic Projects

Just like Chapter 6, the purpose of this chapter is to pay a special attention to examples given in Chapter 14 and apply them to other various situations. The first example is how to design a program to explore our room. Mainly, we are using a touch sensor for this case. Letting the robot go straight for the most of time, we make lots of swing turns when the robot collides with obstacles. However, it's important to use a gear ratio 1:9 to slow the robot down for the first trial. This is because if it moves very fast, it might hurt when it collides with hard obstacles such as wall. Once the program is well designed, we can speed up by using a gear ratio 1:3. In case our room has a flight of staris going down, we can use an ultrasonic sensor facing the floor to sense the edge so that we can avoid a bad fall. The second example is to follow a line. In this case, we use a light sensor as a main sensor. First of all, it's very important to lower the attach point for the light sensor so that the sensor is much closer to the ground. In other words, the distance between the light sensor and the ground should be in the range of 5mm to 10mm. The reason why we do is that otherwise light reflected from the ground won't be effective enough for the light sensor to see. For the programming, we can make robot turn right when the light sensor sees the line and to turn left when it sees the surface out of the line. As the robot tracks the line, we may notice that robot is moving too slow. The main cause is the robot's gear. If the robot is moving too slow, we can find a bigger gear that is able to make robot move the fastest by trying out many times.

Obstacle Course Detection (Official trial)

We had two official trials. For the first tiral, we couldn't get a good score on the last part of the challenge. Since our robot didn't have a free port to include a missile shooting nor did we have a billiant idea to improve the last part, actually we deserved the bad score. However, Woosik and I dared to make another trial. The second trial was just fine before the last part. However, as the robot got closer to the finish line, it seemed to collide with the cans again. In fact, it eventually touch the cans slightly !! Therefore, I never expected a full score on this again. Nevertheless, when Mr. Inskeep asked the class if he should give us 9 or 10 for this, you guys kindly shouted '10' at the same time !! Thank you guys. I really appreciate your shouting(?) As a person who has finished the challenge though, please come up with a brilliant idea to avoid the cans. Depending on the luck like us is too risky...

Obstacle Course Detection (Process 3)

Today, we finally had an attempt to test our robot !! We had expected very good result, but our first attempt turned out to be really bad. The primiary cause of this bad result was that the robot was curving a lot instead of going straight, which massed up the entirle program. Therefore, we made robot go, curving in opposite direction to the curve that had been created in the first attempt. Eventually, our second attempt appeared to be really good. The robot, instead of curving, went straight. Furthermore, the program we had designed was effective too. In other words, now Woosik and I are ready for the actual trial !!

Obstacle Course Detection (Process 2)

As I said, I will show you our robot !!

It looks very simple but the wires are really COMPLICATED.

Today, Woosik and I worked on the programming.

The reason why the robot didn't stop in the box in the previous class was that we had a problem with setting the threshold of the light sensor. It was too LOW (approximately 16) Thus, we set a high value. If I am not mistaken, the value was about 50. Then, we made the robot stop in the box for 5 seconds by using the time sensor.

After prgramming for the box obstacle, we designed the program for the 2 walls. We made a swing turn (turning right) right after the touch sensor hit the first wall. Then, we made the robot go straight, sensing the second wall with the ultrasonic sensor. As we made the robot get close to the second wall, we made another swing turn (turning right again) After that, fianlly, we set to go straight until the light sensor sensed the white line at the end of the race. To be honest, we just hoped the robot would aviod the cans.

Chapter 6 Building Strategies

The main purpose of this chapter is to completely perceive basic techniques with the studless beam and design our own robots. To begin, the first technique is to make a best assembly of the beams. This technique is connecting two or more beams. Depending on the situations, we can use more rigid assembly instead of simply connecting two straight beams. However, we need to consider tension and compression to make more rigid assembly. These are forces that can act upon objects. Tension is a force that attempts to stretch or lengthen an object while compression to shorten or compact an object. These two forces are significant elements, because we can make a stronger robot by perfectly understanding them. There is another important element, which is weight. Weight determines the magnitude of inertia, which is the tendency that objects have to resist changes when in a state of motion or rest. For instance, when the bus suddenly starts to move, passengers may fall down, because they tend to be stationary but the bus makes them move forward. This inertia is important because as the magnitude of the inertia increases (in other words, as the weight increases) it’s very hard for robot to change its motion from the previous. Obviously we don’t want to design a robot that has a single motion. The second technique is modularity. While building our robot, we will likely have to dismantle and rebuild it, or parts of it. Therefore, it’s best to make our model by maximizing modularity. In other words, we should make it as easy to take apart as possible. The last technique is hybrid. It isn’t always necessary to make an assembly with the beams only. We can utilize the LEGO TECHNIC pieces too in order to make innovative and interesting creations. In my opinion, understanding this hybrid is very important, because this is the one that encourages us to design our own robot, which is the purpose of this chapter.

Obstacle Course Detection (Process 1)

Today, Woosik and I finishned constructing a robot to be used in the challenge. We didn't modify a lot from the original structure. Instead, we just kept it, because we thought it was stable enough to do the challenge. Therefore, what we basically did was installing sensors. I will post the picture of it later on. (So look forward to seeing how complicated it is !!) Furthermore, we had some time to create a program. When we tried out our program at the very end of the class, we succeeded going forward by clapping but failed to stop in the box. Therefore, in the next class, we will probably work on how to stop in the box and sucessive steps too.

Obstacle Course Challenge

First of all, we need every sensor we have learnt so far : Sound sensor, Light sensor, Touch sensor and Ultrasonic Sensor. The robot starts by hearing a clap. It goes straight and meets the first obstacle which is stopping inside a box drawn on the ground. At this point, we can clap again to turn off the sound sensor and turn on the light sensor. As the light sensor sees the blue color, the robot stops and by using wait sensor (time) we can stop the robot for 5 seconds. Then the robot goes straight again. When it collides with the first wall, it turns right. As soon as it turns right, the ultrasonic sensor senses the second wall and the robot approaches it. Then the robot stops in front of walls and make a right turn and ultrasonic sensor senses the cans. Some of you might worry that the robot might hit the cans. However, the robot can avoid them by setting the robot to go straight. Lastly, by using light sensor, we can make the robot stops when it sees the white tape.

Chapter 1 Understanding LEGO® Geometry

In order to enjoy every aspect of LEGO robotics, it's very important to understand basic geometric properties of the LEGO bricks and beams. Measurement of LEGO bricks are based on the metric system. However, although they are based this system, it's important to keep in mind that a brick's height and length don't have equal values but a constant ratio. One of the most important bricks in LEGO is a TECHNIC brick, or a beam. This brick has some holes inside a beam which enable other beams to be connected to each other via pegs. Therefore, it's very significant to utilize it well, because we can construct a light and strong robot. To fit a diagonal beam, we need to use Pythagorean theorem. This theorem is that in a right triangle, square of hypotenuse have to be equal to sum of length squared and base squared. When we apply the theorem into our fitting a diagonal beam, number of holes inside a beam represents square root of any sides. For instance, if a beam of base has 3 holes and a beam of height has 4 holes, we can use a beam that has 5 holes as a diagonal beam, because 3 square (9) + 4 square (16) is equal to 5 square (25)

Additional information about Liftarms
Liftarms are beams that come in many shapes and sizes to connect parts at dffering angles. These are helpful when we need to construct the robot's grabbers, fingers, ball casters and etc.

Johnny's Field of View Experiment

For what do we do this experiment ?


The purpose of this experiment is to figure out how widely can the ultrasonic sensor sense.


Procedure

1. In front of the robot, stick a piece of long tape on the ground.

2. Randomly place the can ON the tape to figure out the longest distance that the robot can sense. It's very important to eliminate every obstacle between the can and the robot.

3. Once you have found the distance, draw a circle on the tape to mark it with a maker

4. Using the marker, draw a line on the tape every 10cm wide. Make sure lines not to exceed the circle.

5. Place the can out of the tape (in other words, on the white board) You must check if the robot shows distance in cm instead of ??????? If you find difficulty to put the can at the right place, try putting the can closer to the tape.

6. Draw a circle where the center of the can was at.

7. Repeat 5-6 until you get 15 points. It's good to get a circle at a different distance from before.

8. Deem of the place where the robot is the origin (0,0) of x and y axes. Find x and y coordinates of every circle.

9. On the recording paper, draw every circle according to its coordinates you've obtained. Keep in mind that the ratio of the actual distance and paper is 5 to 1. In other words, 1 cm on the recording paper is equal to 5 cm in reality)

This copying to the paper enables us to manage the data very easily !!!