Introduction to Robotics experience

This robotics class was really interesting. I even enjoyed doing homework. From the experience I have been in this class, constructing robot is very significant. This is because it's linked to every aspect of both science and math. For instance, if the robot has bigger wheels in circumference, it can move further than the one has smaller wheels with a same number of rotations. Programming the NXT is important too. Although the robot is well constructed for a certain situation, if programming is wrong, the robot won't work effectively. For example, we need to be very careful of making the program related to a sound sesnor. We should make two wait blocks to avoid two actions to simultaneously happen. Finally, utilizing every sensor is also pivotal. Without using sensors, we can't apply the robot to many situations. For example, without any sensors, what the robot can do is just moving as soon as it starts to run. Nevertheless, with a light sensor for instance, we can track a line with a specific color.

This class teached me a lot of scientific and mathmatic asepcts as I read the robotics book. With basic knowledges I gained by reading the book, I could effectively not only program NXT but also construct the robot. Then I could check if my applying was right by running the robot. Furthermore, this class required me to communicate and collaborate with people. Because this class was lacking the robots and books in number, it was very important to discuss with people and come up with a good plan. Also while doing some challenges, I needed to share the ideas well.

Tractor Pull - Test of Strength

This challenge is to construct a robot that will push or pull the most weight 50 cm in the fastest time. Since we are considering both of the strength and the time, it's very important to find out the gear ratio which torque and angular velocity are well balanced. If the torque is too high, then the robot won't be able to push the weight quickly. In contrast, if the angular velocity is too high, then the robot won't be able to push the weight effectively. It may not even push the weight. I really wonder which group will find the best gear ratio. In my opinion, this time, small gears won't work.

Today, the combination of the smallet gear and the biggest one, which made the gear ratio 5 was the most effective to pull or push the most weight.

Drag Race - Test of Speed

This challenge is to construct a robot that will be the fastest in a 3 meter race. Technically this challenge is a matter of designing a good set of gears. In fact, I saw many groups use the biggest gear on the motor and the smallest one on the wheel. However, very competitive, our group tried to use the combination of 4 gears (2 of the biggest ones and 2 of the smallest ones) Impressively, in the air the wheels rotated crazily. It was like a fan to cool people down. Unfortunately, however, when the robot was on the surface, it didn't even go. Therefore, we modified. This time, we used 2 of the medium size gears and 2 of the smallest ones. However, again, the robot didn't go. Thus, we just used the biggest gear and the smallest one only. I hope it will make a good start. A good start is the only way to be the first, because most robots' speed is the same as mine.

Am I depending on the luck too much ? :)

Gears and Speed (investigation)

To check which Hypothesis is more effective, you measure teeth on a driving gear, teeth on a driven gear and gear ratio. You set the robot to go for only 3 seconds. Then you measure how far the robot goes for 3 times and average the distances. Averaging is important, because it reduces the error created during the experiment. With the average, you get the speed by diving it by time, which is 3 seconds. Having got every data for all conditions and using both of the Hypotheses A and B, you predict speed. After that, you compare the predicted values to the actual value. The Hypothesis which gives you a similar value to the actual one is consequently B. This is simply because the actual value and the predicted one are close. Accodring to my data, for the setting that gave me 49.3cm/s in reality, Hypothesis A gave me 18.1cm/s whereas Hypothesis B 50.3cm/s.

Another aspect we need closely look at is that speed and the gear ratio has a inversely proportional relationship. In other words, if one decreases, the other increases. Also if one increases, the other decreases. According to my data, gear ratio 1 gave me the speed 30.2cm/s. However, gear ratio 3/5 gave me the speed 49.3cm/s

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.