CHAPTER 4: Structures and Construction
Robotics from http://www.thefreedictionary.com
ro·bot·ics
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Engineering from http://www.thefreedictionary.com
en·gi·neer·ing
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con·struct
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I heard this saying:
I heard a construction worker say this, "Measure once, and then you measure twice, and you measure once more before cutting". This applies to cutting, building, constructing, fabricating a part, or whatever your job is. It's always good to go back and check just to make sure you got it just right. "You can't cut the wood longer, but you sure can cut it shorter."
Structures: Watch carefully, these are very short films.
Tall structure on wheels - see what happens to a tall and short base structure.
http://www.mumbai-central.com/misc/pic02305.gif
Yes, it is a set of buildings. Look at how each is made and what similarities they all have. What makes them strong and not fall over?
http://sportsfigures.espn.com/sportsfigures/enhanced/images/centergravity.gif
Nice little example of Center of Gravity but a nice way to show what happens to tall structures if the Center of Gravity and weight is not in the right place.
Tall structure with long body on wheels - see what happens to a tall and wide base structure.
http://www.wma-minelife.com/coal/graphics/Truck004.JPG
Tall, wide, and long. This is a vehicle that is well planned.
Low structure on wheels - see what happens to a low structure.
http://www.brightland.com/sourcePages/johnAtBondurant2.jpg
This is a vehicle that is low in height and low to the ground. Why would something be so low to the ground? What are the benefits and what are the problems? Think common sense wise.
Patterns, structures, and math:
As builders, you want to look at the below sites to see how things are built. You will notice that I concentrate on squares and triangles and the combination of the two. It is important to learn how to build for stability, with support, and how to form shapes with straight beams, triangles, and squares. You could probably figure out how to build circles based on squares and triangles. These are very important, not only in math, but in engineering. There are sites listed below to help you on your journey of understanding. You may even want to invite a math teacher to help.
Easy:
Syngress.com - A great way to learn brick geometry. Look at the Pythagoras' Theorem section.
virtualatdp.berkeley.edu - Nice site to learn about brick geometry.
Intermediate:
Clever Quilter.com - This pattern has triangles in squares.
Geoaustralia.com - This has triangles in squares in familiar shapes.
Adavanced:
Principals of Nature.net - Triangles in squares and structures.
Math pages.com - Double equations from triangles in squares.
Turns:
If you plan to use 4 wheels for your vehicle/robot do these suggestions:
1. One motor for two back wheels for forward and backward movement. This is in conjunction with having another motor for controlling a rack and pinion. This allows your vehicle a way to turn based on wheel that have turning wheels. Think of what a car does.
http://www.rqriley.com/images/fig-1.gif, look at this example. It shows 4 wheels and 3 wheeled vehicles. Both use a rack and pinion steering system.
http://driversed.com/CO-DMV-Handbook/images/wheel_turn_cars.gif
Parallel parking. This is a tough one. Can you create a robot to do exactly this kind of complex move?
meineke.com - Beautiful look at rack and pinion. It also covers other parts of vehicles.
philohome.com - LEGO car steering.
Steering from badlink.com - Ok, the five builds above this is on this site as well as other builds.
2. If the above is not an option, then try building a wide base, but short front to back distance. Place front and back wheels close together. Click on bottom link labeled, "Good turn ..." to see what the vehicle could look like. Essentially you are imitating a tank tread kind of vehicle. You'll also want to gear both front and back wheels to turn in the same direction, with either side having its own independant motor. You can apply this to a vehicle with more than 4 wheels. Think in terms of a circle. Make the circle to encompass your robot. The four wheels should be on the edge of the circle and not extend out of the circle. It will look wide and short.
http://www.dancingcows.co.uk/images/t34tank.jpg
The 4 wheeled turn concept is like turning with a tank. One side goes one way, while the other goes the other. You'll notice the tight turns, but also notice that having a wide base is important.
Good turn with four wheels - it is possible to get a 4 wheeled vehicle to turn with a wide base.
mindstorms.lego.com - 4 wheeled vehicle and 4WD
If you plan to have 2 wheels and a turn base third wheel:
1. Make sure the two powered wheels are independant motors. The third turn base wheel should freely turn in 360 degrees. This allows for a pin point turns. The third turn base wheel will allow for the turning of the whole vehicle and give balance to the vehicle.
From Seatle Robotics.org, notice the small wheels in the front of the vehicle. That is a turn base wheel. This can also go in the back if you choose.
If you plan to have a 2 wheeled vehicle and with sliders:
1. Again, two powered wheels will have independant motors. Be sure you are doing this on smooth ground. Warning: DO NOT DO THIS ON ROUGH GROUND UNLESS YOU PLAN TO RUIN YOUR PARTS. To give balance, you would place sliders or something that can slide in the front or back. This vehicle will do pin point turns as well.
There are many examples of what I've mentioned already coming up.
Point out all important points that you've just seen.
1. Tall structures with a wide and long base works. Think of a cone with the wide area on the bottom and point on the top.
2. Low structures work well.
3. Turning with four wheels are best when the wheels are close from back to front or front to back, and wide apart.
4. If you have the opportunity to use tank treads, use those instead for pin point turns.
Measuring a turn:
Measuring a turn can be done by printing or drawing a large protractor and then using the "View" on your NXT or RCX to view the amount of rotation or degrees the wheel turns based on pivot point and amount of turn (this is based on degrees according to the protractor as a measuring tool).
The bigger your wheels the less degrees/rotations it takes to do a turn. The smaller your wheels, the more degrees/rotations it takes to do a turn. Make sure your pivot point is exactly where it should be. Look at pictures below. The wider your base, the more your wheel needs to spin (more degrees/rotations) to complete a turn.
View the pictures below to get an idea on how to do this. Click on picture to make it bigger.
Take the two front wheels, draw an imaginary line between one wheel to the next. Then mark the middle point of that. The middle point between the two wheels is considered the PIVOT POINT. The PIVOT POINT is the point where your robot spins around. You can also see that I've centered that point on the middle of my made up GIANT PROTRACTOR.
I marked, with liquid paper (white out), the bottom start point of the wheel. I will be measuring the degrees in which my wheel will turn. Today, I am measuring 90 degrees.
I go to the VIEW option in the menu.
Then I choose MOTOR DEGREES and the correct port in which my motor is plugged in. In our case I am testing MOTOR on PORT C.
I carefully turn the vehicle on the pivot point (one wheel goes backward - Motor A, while the other goes forward - Motor C). I make the 90 degree turn and observe the WHITE MARK I made earlier with the LIQUID PAPER.
My display read, "192" degrees. The wheel went over a half turn, of a full rotation, to complete 90 degrees. With different wheel sizes you'll get different results. You'll want to measure in MOTOR DEGREES if you are measuring a turn from 0 to 180 degrees. If you are going beyond 180 degrees you can start measuring rotations instead, for a turn.
Be sure to do three or four tests to make sure you are getting similar results each time. You will have to worry about wheel slippage.
COG (center of gravity) and balance:
- Keep weight low to the ground.
- Balance weight through out robot, from front to back, and side to side.
http://www.cdc.gov/niosh/images/fig1-11.gif
Very good example of COG, but also a good example of tall and short structures.
Easy:
http://www.wikihow.com/Calculate-Center-of-Gravity
Intermediate:
center of gravity from http://www.thefreedictionary.com
Advanced:
http://www.phys.hawaii.edu/~teb/java/ntnujava/block/block.html
http://theory.uwinnipeg.ca/physics/rot/node4.html
Something about engineering:
The median of a trapezoid:
Weirdrichard.com has a great lesson on figuring out mathematically the median of a trapezoid. Click here to access the site
Before you build, be aware of these things!
- Please design your robots on paper before actually building. Show all functioning parts and indicate with an arrow the direction in which these items move.
- Know where all your sensors are ported. On the RCX, the grey area is the input ports labeled 1,2, and 3. Know the direction of your wires as well.
- Know where all your motors and lamp(s) are ported. On the RCX, the black area is the output ports labeled A,B, and C. Know the direction of your wires as well.
- Your RCX has a Program button where you can choose from 5 programs to uplaod your program to. You must download the firmware from your computer to the RCX before doing anything with ROBOLAB.
- Your RCX has a View button that allows you to access each port (you can see an arrow pointing to the port it is accessing). If you plug-in a sensor in port 1, press the power (to power the unit) and then press the view button to access port 1. Notice what the display reads as you play with the sensor.
- The run button will only work if a program, from ROBOLAB, was uploaded to a program slot, from 1 - 5 (one of those represents one program slot).
- Use the LEGO Constructopedia to learn a little bit more about your RIS system.
Setup tips and hints - Make sure you have setup your classroom for the next activities.
Remember these: Have this read to you. Click here.
- Know the problem and have at least three solutions.
- Have an educational guess about your best solution you want to try.
- Always create a building plan (blue print) that shows how it functions (use arrows to show movement).
- Testing your creation, adjusting your program and build, recording results, and doing these things over and over until the results are to your expectations are all part of robotics.
- Do a historical documentation of each step up to solving the problem. Always take pictures and document all results and adjusted solutions.
- Make sure your teacher always views each step as a way to demonstrate your true results. Ask for help, but not the answers.
Design on CAD:
CAD (abbr.) = computer-aided design - from http://www.answers.com
MLCAD is a free Windows CAD application. You will have to download all components including parts. If you have never used a CAD program then you may have to decide whether to pursue this or not. It's kind of like building but on a computer. I can't say that it's easy, but once you get the hang of it, it isn't bad. The good part is that you can snapshot pictures of each step as you build so that you can create a building guide for later.
The reason one would build with CAD first is to see if the model design would work (strictly to see if pieces fit right). This also gives the students the opportunity to keep track of how many of each piece they are using.
Download MLCAD here: click here for Windows
Download LDraw here: click here for Mac
Because of the amount of time needed to design, depending on how complex your robot, the use of CAD would not be good for a class that requires time to build, program, and test under time constraints.
Lets look at LEGO's Constructopedia for RCX (NXT please to next page): (these are all available on other websites as well)
Page 1 to 7 - basic understanding of the RIS system
http://www.javaranch.com/journal/200407/images/rcx.jpg
Page 10 to 25 - Roverbot (Very first project with 4 wheels. Use Robolab, instructions below in green, to do training mission.)
Page 26 to 29 - bumper
Page 30 to 33 - double bumper
Page 34 to 35 - light sensor
Page 36 to 45 - Acrobot
Page 46 to 48 - pivot wheel
Page 49 to 54 - single bumper
Page 55 - light sensor
Page 56 to 73 - Inventorbot
Page 74 to 77 - hat arm
Page 78 to 80 - slap arm
Page 81 to 83 - squeeze arm
Page 84 to 85 - thrower arm
Page 86 to 87 - light sensor
Page 88 to 97 - special features
Page 98 to 101 - tips and tricks
Page 102 - light sensor/test pad
Last page - parts ID
Robolab stuff:
ROBOLAB has a tutorial. When you start up ROBOLAB, hopefully version 2.5.4, one of the menu options is "Training Mission". Have your RCX, tower already plugged in (before you start up your computer),
http://www.active-robots.com/products/lego/lego-spares/legotower-750.jpg
(Have a box ready to cover your creation and RCX tower at the same time to program your robot)
batteries in your RCX,
http://www.kipr.org/curriculum/Sensor_Photos/change_batt.jpeg
and mind ready to learn. Turn up the volume as the audio must be heard in order to understand the "Training Mission". You won't regret this.
Learning link:
Ask questions, look for ideas, or find troubleshooting tips:
ask Robohi <--- visit "For Educators" and look up topics (posts). There is more than one page of stuff. Make sure you are registered before trying to post something.
Work on this for day 10, 11, 12, 13, 14, and 15 ... (Build one robot at a time and get it ready for programming. Come back to this section again to build new robots after completing the other. Completion means that you have not only built the robot, but also programmed it properly and got it to function as intended.)
Other things you can build: These are available on other websites.
RCX, attachments, and NXT construction plans
Build the different robots and figure out exactly what they are all suppose to do. Then you will want to figure out how they can be programmed through robolab.
1. Map out how the robot functions, or how you think it functions. What is it's purpose? How does it function with each sensor? For example, a Tankbot with a Light sensor will allow this vehicle to track a line and follow it. Look on the previous page for the Line follower program to see how to program your bot. That line follower follows a black line on a white board.
2. Once you map it out, write a pseudo code of your program.
3. Set your RCX box to program 3 and on robolab, press your download program button and program your RCX box.
4. Test, test, and test.
5. See if you have to fix your program and/or robot.
6. Test, test, and test.
7. Repeat steps 5 and 6 as many times as needed.
Try these steps with all robots you build.
Ideas:
1. Light sensor = line follower (different shades), can help robot to sense something, and then either move a certain way or do something else. Example of use, avoid line or follow line.
2. Touch sensor = allows for sensor to be pressed, depressed, bumped and then do something or move a certain way. Example of use, avoid wall or falling off a table.
3. Rotation sensor = allows for sensor to sense how many rotations it's going through. Example of use, to measure out length of one part of a maze.
4. Ultrasonic sensor = allows for sensor to send out an ultrasonic sound, bounce back, and for sensor to receive bounce and calculate distance through RCX program. Example of use, to help robot avoid or go closer to an object it detects.
Activity (revisiting gears and wheels):
Large wheels cover a large surface area, meaning this could make a vehicle fast. Smaller wheels does not cover a large surface area thereby would make a vehicle very slow. Thin wheels do not give good grip because of the lack of surface area, while wide wheels would cover a larger surface area. Mix this with big gears and small gears. Which would make the best combination for torque? Which would make the best combination for speed? Make a chart to seperate big gear and small gear (going across) and the different kinds of wheels (going downwards). Build a basic four wheel vehicle with the different kinds of gears and fit it with different wheels and jot down all findings. Teachers please guide your students. In a spreadsheet you will be able to create a bar chart to see the results. For torque, drag a set of keys. For speed, mark start and end then race the different vehicles. Again, record your results. Take notice of the different kinds of threading on the wheels, you may want to expand your experiment by going on different kinds of terrain. What wheels do well on rough ground? What wheels do well on smooth surfaces?Extra intermediate activity:
In order to come up with something that works effeciently whether its wheeled or not, you'll have to consider some of these factors; pressure, drag, friction, external forces, external conditions, gravity, dynamics (if applicable), program, condition of parts, condition of motor, battery power, weight, balance, time of day, lighting, weather, temperature, and, moisture. Ok, some terms bleed into others, but the idea is to think of these as individual factors. Some may or may not apply depending on what the situation is. See how you can factor in these things to make a more efficient and effective robot.
Trials and Challenges (Activities to do in class):
The following is a Power Point Show that allows the user to view the different trials and challenges and teaches how to create some of the "Trial & Challenges" boards for your classroom. There are pictures and PDFs that were linked to this that won't work on this slide show. The pictures are not available on the internet (originals created by author). The PDFs are availble through LEGO. If you have attended the author's workshops, you will be able to ask the author for a copy of this with all links that work on a CD.
These are standard activities done in classroom all around the world. These are also known as "Battery Killers".
Trialschallenges.pps - click here to download and view
Don't forget: Have this read to you. Click here.
- Know the problem and have at least three solutions.
- Have an educational guess about your best solution you want to try.
- Always create a building plan (blue print) that shows how it functions (use arrows to show movement).
- Testing your creation, adjusting your program and build, recording results, and doing these things over and over until the results are to your expectations are all part of robotics.
- Do a historical documentation of each step up to solving the problem. Always take pictures and document all results and adjusted solutions.
- Make sure your teacher always views each step as a way to demonstrate your true results. Ask for help, but not the answers.
Questions (Try answering these questions again. Are you answering differently from last time? Why or why not?):
1. What parts should we really memorize?
2. Why are friction and non-friction pins in their different lengths important?
3. Why are bushings of any length important?
4. Why are bricks with studs important?
5. Why are beams without studs (just holes) important?
6. Why are axles and flexible axles important?
7. Why are plates with studs important?
8. What's so important about sensors?
9. What's so important about the programming brick (RCX or NXT)?
10.What's so important about each gear?
Ask questions, look for ideas, or find troubleshooting tips:
ask Robohi <--- visit "For Educators" and look up topics (posts). There is more than one page of stuff. Make sure you are registered before trying to post something.
Work on this for day 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, and 30 ... (Build one robot at a time and get it ready for programming. Come back to this section again to build new robots after completing the other. Completion means that you have not only built the robot, but also programmed it properly and got it to function as intended.)
Extra Credit "Fun" activties:
Blind as a bat - Use only an ultrasonic sensor corded to your RCX or NXT. You will have to program your sensor to respond to close objects. If you are too close to an object (object avoidance) it should warn you with a beep or sound. Then, with your partner, one will be blind folded and using your device will have to navigate the room with your partner helping. You should then switch places.
Mouse - Create a vehicle that is sensitive to light and dark. You will want to test light and dark settings around the room. Your vehicle will have to move toward the light or the dark. It will have to be able to navigate around. Not just follow a straight line.
Bumper car - Be very careful in this one. Build good bumpers and do not play sumo with this. The carts have to avoid each other after one bump. this will require a front and back bumper. You should also allow for a new direction (turn) as it drives backward.
I want to know if you don't yell first - Create a robot with a sound sensor and it will represent a worm in a house. When the sound sensor picks up a whisper, it will put its head out as if to listen. When the sound sensor picks up a loud noise, the worm will go back in the house.
Stop by my house and sing a tune - Use the rotation sensor and sound coming from your RCX or NXT. Your creature or vehicle has to travel a certain distance and play a tune. Plot out where each house will be and use your RCX or NXT with the rotation sensor to measure out each distance to put into the programming. The objective is to stop in front of each house and play a turn.
Racing with crawlers - Build the crawler bot from the Constructopedia (first bot with legs). You will have to program this to move forward. Race this forward and then race it back. Is it possible to make the robot turn? Is it possible to make it go forward, turn, and then make its way back and then stop?
Build this:
I'm only kidding. Don't build this, build it better. Kidding.
Ask questions, look for ideas, or find troubleshooting tips:
ask Robohi <--- visit "For Educators" and look up topics (posts). There is more than one page of stuff. Make sure you are registered before trying to post something.
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Extra credit:
Remote control bot:
Using 2 touch sensors and two long cords you can create independent motor controls. You can even program a third to do backward motion. The challenge is to have one touch sensor to allow the robot to be able to drive around and still not get trapped in a corner (in other words, back itself out of a situation where if were to move only forward it would get stuck.