How to Build with the Mindstorm Kit

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Jonathan Ellis
6 years ago
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1 How to Build with the Mindstorm Kit There are many resources available Constructopedias Example Robots YouTube Etc. The best way to learn, is to do Remember rule #1: don't be afraid to fail New Rule: don't be afraid to back up and try something else Note: some images and content adapted from High Teck Kids, Building LEGO Robots for FIRST LEGO

2 What to Expect With this presentation we are going to highlight some techniques and theory Hands on!! You have already built some robots and you've probably played with LEGOs before. Certainly, you get the basic idea I want to introduce to you some new techniques and hopefully talk about what all those weird pieces in this kit are actually good for.

3 Index LEGO Construction Basics Gears and Pulleys Wheels Robot Drives

4 1. Lego Construction Basics 1. Bricks 2. Plates 3. Beams 4. Pins and Connectors 5. Half Pins and Axles 6. Frames 1. Cross Bracing 2. Compression/Sheer/Tension 3. Super Frame

5 Let's Begin at the Beginning The Brick Dimensions are given in terms of studs Length x Width x Height Example 2 x 4 x 1

6 Plates Plates are 1/3 the height of a Brick Some plates (called technic plates) have holes which allow pins and axles to pass through

Beams Beams are 1x bricks with holes in the side The holes are placed at 1 stud intervals, between the studs on top Connector pins allow the beams to

7 Beams Beams are 1x bricks with holes in the side The holes are placed at 1 stud intervals, between the studs on top Connector pins allow the beams to be connected together side by side (instead of just one on top of the other, like with regular bricks) Beams are CRUCIAL for sturdy robot construction.

8 Pins The black Technic pin with friction (friction pin) is the most commonly used The gray Technic pin has a slightly looser fit

9 Half Pins and Axles The gray pin (really short) can be used on the side of a beam to mimic studs Axles come in different lengths measured in studs How can you tell how long an axle is? Look at them next to a beam Use the stud ruler Note: Even stud length axles are black and odd stud length axles are gray (most of the time)

Basically, all the other pieces are meant for connecting axles, plates, bricks and beams together in various ways (parallel, perpindicular, at a fixed

10 Basically, all the other pieces are meant for connecting axles, plates, bricks and beams together in various ways (parallel, perpindicular, at a fixed angle, at a variable angle, rotating freely, or not.) Note: some connectors pictured don't come in our kit and not all of our connectors are pictured here

11 Frames Your robot needs a strong backbone, just like you do. Your robot's backbone is it's frame Often, when designing a robot, you might start with it's frame It's important to consider the forces that are going to be trying to tear your robot apart

12 An EVEN BETTER frame Using Cross Bracing To cross brace you need to use 1 beam and 2 plates!

13 Forces on Brick Connections Try This: Stack two beams on top of one another Apply these three forces using your fingers Which force is most likely to take the two beams apart? So, why do we need cross bracing then?

14 Super Frame (1 beam, 2 plates, 1 beam) You do NOT HAVE to use this frame In fact, many people don't start with the frame, instead they start with the motors (big and bulky). Regardless, make your robot sturdy and resistant to the three types of forces (compression, sheer, tension)

15 2. Gears and Pulleys 1. Gear Basics 2. Spur Gears 3. Gear Ratios, Torque and Gear Trains 4. Crown Gears 5. Bevel Gears 6. Worm Gears 7. LEGO Gear Rack and Pinion 8. Pulleys

16 1. Gear Basics: Why Use Gears? To transmit torque (rotation) from one axle to another. To increase or decrease the speed of rotation To reverse the direction of rotation To move rotational motion to a different axis (x axis to the y axis) To change rotary motion to linear motion To keep the rotation of two axles synchronized (together)

17 2. Spur Gears Most Common Gears Gears are referenced by their size (the number of teeth they have) All LEGO Spur Gears have the same size teeth so they can all mesh properly (no matter the size of the gear, or the number of teeth)

18 Spur Gear Spacing

19 Half stud Spacing Vertical Gear Spacing

3. Gear Ratio If you have two different sized gears, the gear ratio is how far the first gear turns vs how far the second gear turns. This is exactly how your 18 speed (or any speed) bicycle works.

20 3. Gear Ratio If you have two different sized gears, the gear ratio is how far the first gear turns vs how far the second gear turns. This is exactly how your 18 speed (or any speed) bicycle works. If the first (little) gear turns 1 time then 8 teeth go by Also, 8 teeth go by for the large gear; BUT the large gear has 24 teeth total so it will only turn 1/3 of a revolution In other words the first gear must turn 3 TIMES before the second gear turns all the way around Thus, we say this is a 3:1 gear ratio and this is called gearing down If you switched the gear around you'd get a 1:3 ratio gearing up

22 Torque A force that tends to rotate things. For example, you generate a torque any time you apply a force using a wrench. When you use a wrench, you apply a force to the handle. This force creates a torque on the nut, which tends to turn the nut. A force applied to the teeth of a large gear will generate more torque than the same force applied to the teeth of a small gear. This also means that for a given torque, a larger gear will transmit less force than a smaller gear Formula: Torque = Force * Distance

23 Rule: Gear down to get more torque BUT less speed Rule: Gear up to get more speed BUT less torque Choose One: Strong and Slow Or Fast and Weak

24 Gear Trains: Multiplying Torque

25 4. Crown Gears The crown gear has teeth that are raised on one side and rounded off on the other to give it a crown like appearance. Used when the shafts to be turned meet at an angle. It can be meshed to spur gears and worm gears, but it doesn't mesh well with other crown gears.

26 5. Bevel Gears The bevel gear has teeth that slope along one surface of the disc. It is also used when the shafts to be turned meet at an angle. It has less friction than the crown gear, but can only mesh with another bevel gear.

27 LEGO Differential What is a differential? YouTube Video A differential is a device takes a torque applied to its housing, and evenly distributes it to two output shafts, allowing each output to spin at a different speed.

28 6. Worm Gears A worm gear is a screw which usually turns along a spur gear. Works with gears on axles that are at right angles. Can create very high gear ratio as each time the shaft spins one revolution, the spur gear moves one tooth forward.

29 Worm Gears are Self Locking You can turn the input shaft to drive the output shaft, but you cannot turn the output shaft to drive the input shaft. This is very useful for arms as no torque is required to keep it in place.

30 7. LEGO Gear Rack and Pinion The gear rack looks like a spur gear laid out flat. It is usually used in conjunction with a spur gear (which is referred to as the pinion). Converts rotation into linear motion (left or right). YouTube Video Note: this is also how the steering in your car works.

8. Pulleys The theory behind pulleys is exactly the same as for gears, but pulleys don't have to directly touch Instead, they are connected via belts (usually

31 8. Pulleys The theory behind pulleys is exactly the same as for gears, but pulleys don't have to directly touch Instead, they are connected via belts (usually different sized rubber bands for LEGO) LEGO belts are color coded; small (white), medium (blue) and large (yellow) It's still possible to gear up and gear down

32 3. Wheels Wheels affect your robot's speed, power, accuracy and ability to handle variations in terrain.

33 How are Wheels like Gears? Big wheels equals more speed Big wheels equals less torgue (less ability to climb over obstacles, etc) Can't get more of one without losing some of the other.

34 Instead of wheels, you can use tracks Advantages (like a tank) Good traction on rough surfaces Stable Agile (turns in small space) Disadvantages Slips on smooth surfaces A lot of power loss due to bending of tread, etc.

is inside the wheel base The closer the center of gravity

35 Wheel Base and Robot Balance Wheel Base Balance In order to be balanced you need to make sure the center of gravity is inside the wheel base The closer the center of gravity is to the wheel base the better Finding the Center of Gravity

36 Why is balance important? For your robot to move in a predictable and repeatable manner all wheels must be in contact with the ground at all times, and the weight carried by each wheel must be consistent. It's nearly impossible to program a robot if you can't trust that it will behave the same way on consecutive attempts Keep in Mind: Momentum and sloping surfaces shift the center of gravity When jerking a robot really fast in one direction it takes a while for the COG to catch up (can cause the robot to fall over, even) Also, the further from center the COG is, the more likely a robot is to tip over on an incline

37 4. Robot Drives A.K.A. Drive Mechanisms 1. Differential Drive 2. Steering Drive

38 1. Differential Drive The Tri bot (the first robot we built) IS a Differential Drive Robot All differential drive robots use two motors to drive two wheels, and then have a third unpowered swivel caster wheel. These are very common types of robots Things to Consider: Where should the Center of Gravity be? How do I get the differential drive robot to go straight? Do I HAVE to have a caster wheel?

39 Where should the center of gravity be for differential drive robots? Rule: the less weight that has to be supported by the third wheel the better That's why the third wheel is usually WAY in the back

40 How can differential drive robots go straight? First, going exactly straight is REALLY HARD NO MATTER WHAT!! Think about how hard it can be to make a shopping cart go exactly straight! It's better to build and program robots so they don't have to rely very much on being able to go straight Go straight enough Use sensors, etc. to know where you are Lucky for us, our motors can be synchronized via software; but the problem is when one wheel slips and the other doesn't There are two mechanical solutions on the next slide

41 Purple piece is a connecting piece of flexible hose. It's SO MUCH easier to not have to worry about going exactly straight!! You need to figure out a way to stop lock the differential in place (keep it from turning). If it can't turn, then the wheels MUST turn at the same time (and thus go straight.

42 Do I HAVE to have a caster wheel? NO, actually! You can use Skid Steer Remember the tank! It was differential drive too! It's also possible to have multiple wheels on each side (usually 3 or 4) that are all conrolled by the same motor (one motor per side)

43 2. Steering Drive Just like your car One motor drives the two back (usually) wheels Use a differential for letting you get around curves OR power only ONE back wheel (not as good) One motor is used to turn the front wheels Use a rack and pinion set up OR use one motor for EACH front wheel (not as good you ONLY HAVE 3 motors)

44 Turning Comparison Differential drive robots are more popular because they don't have to move forward to rotate and steering drive robots do Think parallel parking!

LEGO Parts Guide. Naming and Building with LEGO parts. Version 1.3 4/12/10

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