Final Class Blog

The robotics semester has come to an end and this will be my last entry. In the robotics unit we covered the main areas of robot construction, NXT programming and NXT sensor usage.

When it comes to robot construction we have learned the basic and finer points to creating a well constructed and fine tuned robot. We have learned how to properly support different kinds of structures with various types of supports, for example using cross beams to properly support a rectangular or cubular shape. In addition to this we learned how to properly add on and support other parts of our robots such as the gear attachments and the wheels. The wheels should favorably, not be directly attached to the motor, however on an axle that is connected through the use of gears; also that gears, axles and wheels should all be as close to the core of a robot as possible as it reduces the amounts of friction and pressure upon them. Finally we also learned how to properly balance the loads on our robots so that the robot has a center of gravity that is as low and stable as possible.

During the robotics course we learned how to use the NXT programming software to allow us to control what we wanted our robots to do. The NXT programming software consisted of two main palettes that allowed us to control most all of the robot's actions. On the robotics palletes where blocks programmed to make the robot perform actions such as moving, sensor blocks such as the sound sensor block and math/logic blocks which allowed the robot to compare data it had collected to make a decision based upon it. The NXT programming software would then be downloaded onto the NXT brick and the program could then be run.

Upon conclusion of the course we researched, studied the capabilities of and used almost all, if not all of the NXT sensors included in the kit. The sensors we focused on included: the rotation sensor, sound sensor, ultrasonic sensor, light sensor and touch sensor. The rotation sensor was built into the motor's and allowed us to calculate the distance the robot would travel based upon the wheel size and distance/rotation the robot travelled. With the sound sensor (measuring soud levels), we created thresholds of sound that allowed us to program our robots to perform actions upon that threshold being reached, however prevent it from acting prematurely upon sounds that were too quiet/loud. The ultrasonic sensor worked by calculating distance of objects based upon sending and recieving sound waves. We used the ultrasonic sensor to help us navigate an obstacle course. The light sensor emitted a red light and measured the amount of reflected light it recieved. We used the light sensor to allow our robots to track lines and stop at certain points. Finally, the touch sensor was triggered based upon if the sensor was pushed, tapped, or released, at which point the robot would perform a certain action. We used the touch sensor to stop our robots whenever it hit an object so that the motors would not keep moving and possibly damage the robot.

Throughout the course we were constantly working with calculating different algebraic formulas in order to measure and predict distance, speed and gear ratios. During our investigations of each sensor we also compared different hypotheses in order to prove which was most right/correct. Throughout the course we also had to constantly work with different partners so collaboration was a must in order to achieve our tasks. Thus effective collaboration and communication were important concepts throughout the course.

Challenges: Drag Race and Tractor Pull

We have been assigned a new challenge, and this time around its less about using the sensors and all about the speed. We have to design a robot that will be able to cover the distance of a 3 meter straight track in the shortest amount of time. This challenge comes after we finished the gear worksheets, so obviously we will need to find a gear combination that will be optimum for speed.

At first we planned to create a robot with a gear train of two 40t gears and two 8 t gears...(even three at a point in time...that machine would truly have been monstrous) however my partner, Hakyoon, and I soon came to realize that with the minimal time allotted us, our robot simply wouldn't be able to support all of that extra weight on the wheel axles...a true shame. In the end we opted for a simple 1:5 gear ratio added a wheelie bar...In the first drag race our robot went berserk and 'unintentionally' using little lego 'spikes' protruding from its wheels rammed into the opponent and flipped it...even though we had to re-run the drag race (surprisingly beating the competitor's robot with the same gearing) our robot...truly was demonstrating its inner beastliness.




The tractor pull challenge works much in the opposite direction. We will have to design a robot that can push/pull the greatest amount of weight across 50cm in the shortest amount of time.
The gearing for this robot will be hard to balance between losing too much speed while still giving the robot lots of torque.

In addition to the modified gearing, our robot will most likely need a slight revamp to its actual structure in order to push large amounts of weight. The weight of the robot shouldn't be much of a problem, so my partner and I will most likely try to place additional weight on the driving wheels of our robot so that it has more traction and won't slip when pushing the weights. Some other attachments such as 'steering rods' may be placed out in front of the robot so that the object being pushed doesn't slip away.

Gears and Speed Investigation

In this investigation we explored the relationship between gearing up or gearing down and speed.
We were testing two hypotheses used to predict this relationship; the first being:

A: Speed One/Gear Ratio One = Speed Two/Gear Ratio Two
and the second being:

B: Speed 1 * Gear Ratio 1 = Speed 2 * Gear Ratio 2

We then setup our taskbot to run for 3 seconds and recorded the distance the robot moved each time with three different gear ratio configurations, 1:1, 3:5, and 5:3. Following this we used each formula to predict the speed at which the robot would travel at each speed, later comparing this to the actual angular velocity at which the robot moved by dividing the distance by the time (3 seconds). After comparing all of the results we found that hypothesis B was very accurate in predicting the actual speed the robot would go. Looking at the values produced by our experiment we found that the relationship between gear ratios and speed is inverse. Inverse meaning that as the gear ratio decreases, the speed increases, and as the the gear ratio increases, the speed decreases. This relationship is the opposite of a direct relationship such as that between wheel size and distance.

Playing With Gears

This chapter in the LEGO robotics book overviews the importance of using gears to improve the functionality of your robot and to ensure proper usage of gears.
First off, the main theory behind a gear is that by using a gear to turn another gear of a different size, you can either multiply the force behind that second gear, or greatly accelerate the speed at which that gear travels. In the above example, the gear being used to turn the other gear is known as the driving gear, and the gear being turned is known as the driven gear. The forces being outlined in the above example are essentially torque, and what is known as angular velocity, or 'speed'. Torque is a product of force and distance and basically is the amount of kick or driving power behind a gear. Angular velocity is the rate at which your robot will cover distances.
When wanting to increase torque on a robot, the driving gear would have to be smaller (have fewer teeth, ie. little pegs) than the driven gear and vice versa for the driven gear. So based upon this concept one would think that you should just add as many gears as possible to magnify your robots capabilities. However, this is where another catch is met: a force called friction. Friction is the amount of force being transferred between the teeth of your gears; and consquently, having more gears means more teeth and thus more friction. Having too much friction can damage the robot, gears, and whatever motors are driving it; thus a proper balance must be found.

There are also many types of gears that can be used for several different situations. For example, a gear known as a knob wheel (four rounded teeth) is a gear that is specialized in providing more torque as its larger surface area on the teeth allows more energy to be transferred. Another type of gear, known as a clutch gear is essentially a 'safety' gear that locks down when too much force is applied to it. This gear is useful in protecting the rest of your gears and robot in case too much force is exerted.

In addition to just connecting gears to gears; gears can be connected using pulleys and chains. Using pulleys and chains allows you to connect gears that would normally be too far away to just stick in a bunch of other gears to connect. Pulleys also have the advantage of being much quieter than gear connections. The difference between pulleys and chains lies in the forces they are better suited to dealing with. Pulleys, using belts tend to have very little grip on the gears and as a result produce very little torque, which is good if you are going to for angular velocity. Chains however are composed of individual links and have the most amount of grip on the cogs on the gears. This means that they produce the most torque and are relatively poor for use when trying to achieve high angular velocity.

Getting in Gear Investigation

Today we started to work with gears and experimenting with gear ratios.

We experimented with making both the driven and driving gears larger. We did this be switching which gear (24t/8t) was attached to the motor. The driving gear is the gear attached to the axle attached directly to the motor, the driven gear is the gear that is attached to the axle attached to the wheel (turned by driving gear). We found that making the driving gear larger than the driven gear speeds up the robot based on the ratio of the teeth on the wheels. However by making the driving gear smaller than the driven gear means that the gear has to rotate multiple times to turn the other gear once. This slows down the robot however adds considerable torque to the robot (torque is basically the power/driving strength behind a motor) .

The highest speed we would be able to achieve with the taskbot NXT model without using gear trains would be with using a gear ratio of 40t to 8t with 8cm diameter wheels.

However, as we came to realize, having a setup with high gear ratios and high angular velocity creates a potentially hazardous situation for the NXT motor and gears. If for whatever reason the robot hits an obstacle and doesn't stop, then the motors multiplied driving force of the gears can bend or mangle parts of the NXT. Having some sort of PANIC! button here would be useful...or perhaps just adding a touch sensor to the front of the robot underneath some sort of ramming shield.

Classic Projects

This chapter basically summarizes two projects that are often undertaken and are an ample introduction into the fun yet complex world of programming and constructing effective robots.
The first project concerns the navigation of your room. The robot to be constructed for this project will require at least one touch sensor and ultrasonic sensor to be successful in this task. A robot optimized for this task however would probably incorporate the use of at least two touch sensors, the ultrasonic sensor as well as a bumper design and special gearing. The bumper would probably be split into two sections as it allows for more coverage and allow the robot to turn based upon which touch sensor was hit, in relation to which bumper was pressed. The only limitations with this kind of bumper however are that it increases the likelihood of the robot being too wide and getting stuck on awkward inward facing angles such as where walls meet. The gearing (1:3, meaning that for every rotation of the motor, the wheel would turn a third of its normal capacity) would be used to slow down the robot so that a more cautious approach could be used to explore your room in case the robot falls into dangerous pitfalls that would be harmful to the robot (stairs...). These additions are what differentiate a robot that is optimized for a project, and those that simply 'work.'

The second project involves line tracking and covers several methods to both increasing tracking speed, accuracy and design more efficient robots. When line tracking the important to remember is the amount of hysteresis your robot creates. Hysteresis is the amount of 'sway' the robot has as it travels over the line; more sway means less control and less speed in this case. It is also suggested to place the light sensor 5mm-10mm to the ground to maximize the amount of reflected light and reduce the chance of the robot veering off of the line (If it has too much speed).

The Course Robot

The key points from chapter six to remember when building are:

• Modularity
• Balance - low center of gravity = stability
  
• lightweight and strong as possible
• Proper structural support

Of these points, as my partner and I are planning to create a robot that is both slim, low to the ground and light-weight; we will use the concepts of balance, lightweight structural support and keeping the robot low to the ground. These will keep the robot from flipping over during the various obstacle course challenges as well as reduce unneeded weight which could slow down the robot. More to come...

...Today we worked on programming the robot to make the first leg of the course. This included setting up a light sensor and touch sensor as well as getting the robot to run straight. For the most part the program was successful, however the robot had difficulties in keeping a straight path. For the challenge this will be our main concern.

For Monday we will have to setup the program for the ultrasonic sensor as well as create the evasion program for our ultrasonic sensor on the last leg of the course.

After COUNTLESS on-course tests and the never ending re-balancing of the our course-bot...and admittedly due to calculating the angles at which the robot generally steered off of course...Hakyoon and I finally managed to navigate the obstacle course, scoring perfect 10's across the course with the exception of the last leg where the robot skimmed the can and earned us a lowly 7 :S