Chapter 9&10: Feedback & Wait for it!

Chapter 9 and 10 are all about sensors. In the first part, we learn what a condition is. A condition is something the sensor can detect such as the color on a traffic light. The Next part talked about each of the sensors: the touch sensor, sound sensor, light sensor, ultrasonic, and rotation sensors. The touch sensor is activated by the button on the front being pressed or released. In the program block for this sensor, you can choose to activate it when the sensor is bumped, released or pressed. This is useful to make the NXT look for walls and prevent damage. If the NXT has a stop block after the button is pressed, the robot will stop before the robot can damage itself. The sound sensor detects sound. In a previous investigation done last week, we found that the sensor looks for the amplitude (volume). This sensor can be programmed to respond after the sound goes above a certain level or after the sound goes below a certain level. This sensor can be used like in the drag race where we programmed it to start on a clap. The next sensor is the light sensor. The light sensor detects the amount of light. Programming it is like the sound sensor in which you can look for light greater than a certain value or less than a certain value. This is useful in applications where you must follow a line that is darker of lighter than the rest of the surface. The ultra sonic sensor sends out a signal from the sensor and it has a receiver that looks for the signal that bounces back and based on the amount of time, it can tell you how far the sensor is from a wall. making it useful in dark applications and telling your robot to stop before it gets to an obstacle. To program it, you can once again select it to wait til the value gets greater than a certain value or less than a certain value. Finally there is the forgotten rotation sensor. Most people dont realize it is there because it is built into the motor. To program this sensor, you can choose the number of degrees or rotations to wait for the motor to turn either forwards or backwards. We have used this sensor in the circuit race challenge. In this challenge, we had to calculate the number of degrees that the motors should turn so that it would go around the track without going to the inside. Wait blocks stop waiting when a command is met. All of the above applications use wait blocks

Frequency & Amplitude

Last week, we learned about the sound sensor on the NXT and how to set thresholds and we also did an investigation about whether the NXT picks up frequency, amplitude, or both. In the first investigation, we learned that to find the threshold to use in a program, you must take the minimum sound value the sound sensor reads on the nxt, add the maximum value the sound sensor reads and divide by two. You are in essence taking the average of the two values. In the next investigation, we looked at the sensors response to frequency and its response to amplitude. Frequency is the pitch the sound is and amplitude is the volume. In the end, we found that amplitude is much more reliable in getting a reading. Also, as the amplitude increases, the value on the sound sensor increases. For frequency, the values were all over the place which was not much help in a program. In conclusion, frequency is not a good thing to measure using the NXT sound sensor.

Chapter 6: Building stragegies

The topics discussed in chapter 6 are Studless Building Techniques, maximizing Modularity, loading the structure, putting it all together: chassis modularity and load, and hybrid robots: using studless and studded lego pieces. With the new lego parts, studless bricks are now taking over studded bricks. Studless bricks are more flexible but that doesnt mean weaker. Four different beam arrangements are given. Arrangement A is the straight beam. Arrangement B is the L shaped beam. Arrancement C is the is a multiple beams hooked together in a way so there are beams facing every direction. Finally arrangement D is where there are two beams connected by a rod. Arrangement A alone isnt very useful but when hooked to something else, it can provide stability. Arrangement B is used to make a more rigid assembly. Arrangement C can connect two white beams. Arrangement D is useful to like the two beams in option A but it will not work under tension. Combining these four configurations can give you a light and sturdy robot. An important note was also given about the pegs. It says that the black and blue pegs are better to use when connecting beams because they fit tighter. The gray and tan ones are better suited for moving parts. The next section was about modularity which is where you build the robot in sections that can be removed and used for other projects and can also be removed without having to deconstruct the whole robot. Sometimes you have to give up a little modularity to get the robot more compact but the more modular the robot, the easier it will be to handle. Loading the structure was the next section. To start off, the book says to keep the wheel close to the supporting beam because it acts as a lever the further out it goes. The gears also need to be close to supporting beams to ensure that there is minimal friction in the system. If there are two gears, it is a good idea to connect the two axles with a beam. In the next section, all of these concepts are put together. It goes on to say how it is good to separate the left and right drive assemblies which provides better modularity. Also, it mentions that you should put the load of the NXT to where it shares the load equally throughout the robot. Chapter 6 has helped me finish the drag race challenge and the tractor challenge by making it easier to make modifications and increase the strength of my robot while making it lighter at the same time.

Drag Race & Tractor Pull

To finish up the unit on gears, we had two team challenges. A drag race (test of speed) and a tractor pull (test of power). The first team challenge for the gears unit was the drag race. In this challenge, we had to make the robot that would go 3 meters in the least amount of time. To design the robot for the challenge, I first went with a 1:25 gear ratio with the standard task bot but found that the robot didn't have enough power to get started. I decided to not use a gear train and stick to a 1:5 ratio which would give me quick acceleration for the very short race. I also decided to add another motor which gave more power. I geared it the same as the others to prevent any problems from unbalance of power. The program I used was a very simple one. It had a sound sensor block in the beginning and then a forward for 3 seconds block with the coast button selected. To run the race, everyone had their program start on sound so we ran all the programs and played the beginning of a metallica song. This ensured that all the robots would start at the same time. My robot ended up getting across the line the fastest but it was very very close between me and Kenny. The next day we had the tractor pull. In this challenge, we had to build a robot that would pull or push the most weight 50 cm. in under a minute. To design the robot, I needed more torque and less speed. In this challenge, I made a gear train which gave my robot a gear ratio of 25. To get more friction between the robot and the ground, I put some weight on the front and back of the robot and I added extra wheels. My program was even more simple than the drag race. I consisted of a move block with the time box set for 60 seconds. For the first trial in the tractor pull, I decided to push 2 kg. My robot did this without even the slightest hint of it putting much effort in. After this, I decided I better do some testing to find out how much my robot was capable of pushing. It was able to push 7 kg with just a little bit of trouble so I decided that was the best weight to push for my final trial. My robot did it in 45 seconds. 7 Kg was also the highest in the class. All in all, these challenges helped us apply what we have learned about gears to something practical.

Chapter 2: Gears

Gears serve many purposes on a robot. they can make your robot go fast, they can make your robot have a lot of torque (power), or you can make it go somewhere in between. The terminology used is driven gear and driving gear. the driving gear is the one attached to the motor. The driven gear is gear attached to the wheel. to find the gear ratio, you must divide the number of teeth on the driven gear by the number of teeth on the driving gear. If the gear ratio is below one, the robot will go faster with less power than if it had a gear ratio of one. If the gear ratio is above one, the robot will go slower than a ratio of 1 but it will have more power. Also, if you need a lot of power or a lot of speed, you can make a geartrain which connects different gears. If a geartrian is used, it multiplies the ratio of the first gear by the ratio of the second set of gears. There are gears called bevel gears which are helpful in changing the direction of the force. This is good if you dont have room for the wheel but you do in another spot. Another topic discussed in this chapter is pulleys. Pulleys can be used to lift an object and they can work the same way as gears. You can get more power or more speed dependent on the size. This is what was discussed in Chapter 2.