LEGO MINDSTORMS - Building Robots Part 10 ppt

Unconventional Vehicles • Chapter 16 321with a single central motor: transport motion to the bogies through theirsupporting axles, and to the front and rear wheels with a system similar

Trang 1

320 Chapter 16 • Unconventional Vehicles

The RCX stays on the top, just behind the point where the bogies connect

to the body (see Figure 16.11)

■ Universal joints Those that power the wheels are easily avoidable with adifferent construction For example, our setup for the front wheel doesn’tuse them, and you can replicate this for all the wheels In Figure 16.12, weshow a wheel with no universal joints and no gearbox

■ Polarity switches You can use the free port of the RCX to controlone bogie, and connect the other to the same port that drives the frontand rear wheels No polarity switches are needed for this configuration,but your SHRIMP would only turn in one direction

■ Motors A nonsteering SHRIMP also saves one motor.We didn’t try,but we are sure it’s possible to use a single motor instead of two in eachbogie In theory, with a lot of gearing, you can power your SHRIMP

www.syngress.com

Figure 16.11The SHRIMP Top View

Trang 2

Unconventional Vehicles • Chapter 16 321

with a single central motor: transport motion to the bogies through theirsupporting axles, and to the front and rear wheels with a system similar

to the one we used for the steering setup Such a SHRIMP will sufferfrom a lack of power and therefore climbing ability, due to the reducednumber of motors and increased friction

Creating a Skier

What we find most interesting in this project is not just the fact that this “skibot”

robot can be used in the snow, but that without propulsion it descends snowy

slopes like a true skier (well, almost!) It uses a technique known as snowplowing,

due to the V-shape of the skis, often used by human skiers In snowplowing ofthe human variety, the skier angles his toes inward in order to put the tips of hisskis together and simultaneously dig the inside edges of the skis into the snow.To

www.syngress.com Figure 16.12A Wheel Assembly

Trang 3

reduce speed, the skier pushes out the tails of his skis, increasing their angle tomake a wider V; to increase speed, the skier draws the tails nearer, making the

V narrower

Our robotic skier is based on the same principle It mounts onto a pair ofskis, and while descending a slope, it varies the angle of the skis to increase ordecrease the resistance and maintain a roughly constant speed It uses only onemotor and one sensor:The motor is on the back and operates the legs, makingthem more or less convergent, thus keeping the speed in the desired range; thesensor is a rotation, attached to a wheel at the end of the left ski pole, and serves

to measure the speed

Another interesting feature of this robot is that its geometry and the position

of its center of gravity make it always point toward the direction of the imum slope.There’s no need to shift weight to control direction, this happensautomatically because the motion along the longitudinal axis of the robot is theone that offers the lower resistance

max-A general view of our skier can be seen in Figure 16.13

Figure 16.13The Skier

Trang 4

To build the skis you need some extra beams and, more important, many tiles(see Figure 16.14).We used 36 2 x 2 and two 1 x 4 tiles (available as spare parts atthe LEGO Online Shop) If you are open to employing non-LEGO parts, you canbuild the skis from other materials, like strips of plastic available in hobby shops

The legs are not vertical, but rather are inclined outward.This is very tant For a human skier, it’s what keeps the skis resting on their inner edges andproducing the necessary resistance to gravity when in the convergent (snowplow)position (see Figure 16.15)

impor-We achieved this effect by using some hinges and forming the legs from thediagonal of a perfect right triangle If you don’t have hinges, other possible solu-tions exist, like the one shown in Figure 16.16

Each leg is rigidly attached to a 40t gear.The pictures don’t show them, but

we used the extra crossed holes of the gears to place pin-axle connectors into

The two gears meet a worm gear in the middle of the assembly, which receivemotion from the motor and controls the convergence of the legs (Figure 16.17)

Looking at the bottom, you notice a longitudinal beam that locks the tures, and a transverse axle and beam that serve as boundaries to the movement

struc-of the legs (Figure 16.18).There are no limit switches If the RCX tries to close

or open the legs more than what’s allowed, the belt will slip on the pulley

www.syngress.com Figure 16.14Side View of the Skier

Trang 5

Figure 16.15Front View of the Skier

Figure 16.16Alternative Leg Geometry

Trang 6

What’s peculiar about this robot is that it has beams with all the possible entations.The skis are studs down, the legs studs front, the body partly studs front,partly studs right, and partly studs up (see Figure 16.19)

ori-www.syngress.com Figure 16.17Rear View of the Skier

Figure 16.18Bottom View of the Skier

Trang 7

There’s not much to say about the ski poles.The right one is just decorative,placed there for the sake of symmetry.The left one, meanwhile, incorporates arotation sensor that’s directly connected to a wheel (see Figure 16.20)

Figure 16.19Skier Top View (RCX Removed)

Figure 16.20Detail of the Left Ski Pole

Trang 8

Programming this robot is so simple that the topic deserves only a few words

Inside the main program cycle, test the increment in the rotation sensor counts: Ifthis falls in the range that represents the desired speed you chose, switch themotor off; if it’s above the range, start the motor in the direction that closes theskis, and vice versa if it’s below the range.This will speed up or slow down theskibot as needed

If you test your skibot in the snow, try to find or create well-packed powder,like those normally found on ski runs It’s not able to ski on black diamond runs

or in loose powder!

How Did We Test the Skibot without Snow?

Suppose you want to build this robot and test it, but currently there’s

no snow outside This book was written during the hot Italian summer,

so we faced that very question ourselves

Well, we admit we had thought of going to the Alps to visit a glacier where some of the winter snow had survived Unfortunately, we had to settle for a less expensive and time-consuming solution We placed four large ice-packs, the kind used in portable camping refriger- ators, on an inclined board Then we covered them with frost taken from the freezer, gently pressing it down It didn’t make for a particularly long run, but it was enough to verify that our robot actually skied A positive side effect of this experiment was that Mario’s wife, coming back home, exclaimed: “You defrosted the freezer—bravo!”

What else could you improvise with to simulate a snowy run?

Prepare an inclined plane (a table top would do the trick), and cover it with some fabric like a blanket, a sheet, a tablecloth or anything else you have handy You have to adjust the slope depending on the kind of fabric you use, and the top will likely need to be steeper that the snowy slopes your robot can actually descend, because real snow produces much less friction.

Inventing…

Trang 9

Creating Other Vehicles

Here we present you with a list of suggestions for possible projects, their

common denominator being that all of them are, at least in part, vehicles.They’remeant just as starting points

Elevator

We briefly discussed an elevator project in Chapter 4, in which we explained that

a single touch sensor, placed in the elevator car, can control the positioning at anunlimited number of floors.We said also that a second touch sensor could servethe purpose of addressing the car to the proper level, using a simple system wherethe RCX counts the number of clicks on the sensor

A variation on this theme is the car park elevator, where you emulate one ofthose automatic storing systems It would be nice if your robotic parking coulddecode a sort of ticket, maybe using colors or shapes, so it can return the corre-sponding vehicle

Train

The RCX is almost a natural extension to the LEGO 9v electric train system.They share the same voltage and the same connectors, and in fact many train fanscurrently use one or more RCXs to introduce automation in their layouts.Thistopic is so vast it would require a dedicated book, so we will provide only somebasic tips

There are two basic approaches to control a train with the RCX: a) the RCX

is on the train; b) it supplies power to the tracks

In case a), you put the RCX in the locomotive or in one car and connect anout port to the train motor.The train motor is also wired to the wheels, whichnormally draw current from the tracks, so it will happen that your RCX willsupply power to the tracks, too Nothing bad happens, but DON’T connect thetrain speed regulator to the tracks as well; you could damage your RCX

If you are the kind of person who likes customizing things, you can open thetrain motor and interrupt the connection to the wheels, so your train will betotally independent from external sources.This way you can run many RCX-controlled trains on the same track.You can create some external references toread with sensors, so your train knows when to slow down or stop, or place aproximity sensor on the locomotive to avoid collisions

Trang 10

In the second approach, b), you substitute the train speed regulator with theRCX and power the tracks from one out port.You can control three indepen-dent tracks or segments with a single RCX, and use the input ports, for example,

to detect the arrival of the train at the station

There are many other devices you can automate in your layout: switchingpoints, level crossings, decouplers, semaphores, swing or draw bridges, and so on

Cable Railway or Gondola

In a real cable railway, there are two pairs of cables: two supporting ones and twopulling ones.The supporting cables are more or less rigidly attached to the lowerand upper stations, and work as railways for the cabs that have their pulleys run-ning over them.The pulling cables transfer motion to the cabs: one cable goesfrom the first cab to the second across the upper station, while the second con-nects the two across the lower station

You can place the motor either in the upper or the lower station If you usethe upper station, you can avoid the second pulling cable Use touch sensors tocontrol when the cab enters the station so you can stop the motor, possibly after

a short slow down

Boat

LEGO inventory includes different kinds of propellers, so one might wonder ifit’s possible to make a robotic boat It is indeed possible, but it’s not easy to pro-vide the necessary flotation lift using only LEGO parts.The two solutions thatcome to our mind require uncommon parts, either single mould boats comingfrom the System product line, or a bunch of TECHNIC air tanks.The idea is tobuild a sort of catamaran, with both hulls made of two System boats or a row ofair tanks

A simple, cheap, and handy non-LEGO alternative for the hulls is to usecommon soft drink plastic bottles and attach them to long beams with rubberbands or duct tape

The RCX will stay on the deck, together with the motor that drives the peller and the other that controls direction.You can place bumpers on the front

pro-to make your robotic boat change direction when hitting an obstacle

Trang 11

To minimize the risk of damages in case of an accidental bath, put the RCX into a small transparent plastic bag, with just the wires coming out from the opening, and seal the bag with a rubber band Run your robot in a controlled environment with calm waters, like a pool with no people in it

Sailing Tricycle

We are both fans of sailing, and in the wake of the great success of Luna Rossa,the Italian sailboat that won the Luis Vitton Cup 2000, we decided to build arobotic sailing tricycle or land yacht.We named it Duna Rossa (Red Dune) tomimic the original Luna Rossa (Red Moon)

Though building that tricycle has been a lot fun, we must admit that the formances were less than exciting.With a strong wind and a favorable slope itmoved!

per-See if you’re able to do better: keep the structure as lightweight as possible,use a very large sail, and reinforce the mast with shrouds, forestays, and backstays(ropes)

The RCX controls two motors, one to steer the rudder and the other tooperate the winch for the mainsail.You can detect the wind direction through avane on the masthead connected to a rotation sensor Monitor the position of theboom with a second rotation sensor to adjust it for the proper angle with theelectric winch Finally, you’ll need a third sensor (a touch is enough) to controlthe position of the rudder

You can program your robotic sailing tricycle for two basic behaviors: adjustthe mainsail to keep with the desired course, or adjust the course to maintain aspecific sailing point

Trang 12

Summary

If there’s a lesson you can draw from this chapter, it is that any problem in roboticsrequires a custom-tailored solution After having long talked of standard mobilityconfigurations, we described some situations where none of them applies

You’re not necessarily required to invent new solutions any time, more oftenyou can just look around you, or on the net, and find something that helps you

or points you in the right direction SHRIMP was designed to move on bumpyterrains, but there are obviously other possible configurations For example, therobotic vehicles designed for planetary exploration are a good source of inspira-tion, and there’s a large quantity of documentation available in the publicdomain

We must confess that our skier was born more for purposes of fun than todemonstrate some general principle Nevertheless, this small and simple robot has itsmerits, helping us picture the wide range of applications robotics can be used for

Trang 15

334 Chapter 17 • Robotic Animals

Introduction

Trying to emulate animals in designing and constructing a LEGO robot is a funand instructive experience.You can approach the problem from different view-points—for example, concentrating your attention on the behavior of the animal,

or on its shape; you can even create a pure fantasy animal or develop your pretation of some mythological creature

inter-In the following pages, we will show you two projects: a mouse and a turtle.The mouse is probably the simplest project of the book, using just one motorand two touch sensors, and it’s easy to replicate using only the parts contained inthe Robotic Invention System.The turtle, on the contrary, is a bit more sophisti-cated and requires a few additional parts

Once again, the robots of this chapter offer us the opportunity to revise andapply some of the concepts stated in the first part of the book.You will discover anew use for caster wheels—through which we will implement a sort of auto-matic steering feature for our robotic mouse—and a leg geometry for the turtlewith a design not shown in Chapter 15 Both the robots employ touch sensors todetect collisions, but we’ll also suggest other techniques that result in more intel-ligent behavior from your robotic animals

The last section of the chapter contains a list of proposals intended as startingpoints for new projects inspired by the world of animals: squirrel, mole, ostrich,kangaroo, crab—take your pick!

Creating a Mouse

Our LEGO mouse doesn’t claim to look very similar to a real one, instead itresembles one of those simple mechanical mice seen in cartoons, which drive catscrazy.The programmed behavior is very simple, too: the mouse goes straight until

it hits an obstacle, then goes back for a while, changes direction and goes forwardagain If someone pulls its tail, it stops for a few seconds, then restarts.Very youngchildren love to run after it trying to catch its tail, and in case you have a dog or

a cat at home they very likely will love it, too—maybe even too much!

In this project, we used the Scout, the younger brother of the RCX found inthe Robotics Discovery Set, but you can obviously build yours around the RCX(Figure 17.1)

We thought that size was a very important factor for a robotic mouse:Wewanted ours to look like an adorable mouse and not a large rat! For this reason, indesigning this robot we put a lot of attention into restraining its dimension.This

Trang 16

goal affected our choices regarding the driving system, which employs a techniquenot yet described in the book: a variation of a steering drive that requires onlyone motor In fact, the motor is used to power the drive wheels, while thesteering capability comes from the unconventional use of a caster wheel

Looking at the bottom, you can see the very simple mechanics: a motor drivesthe differential gear with a 1:1 ratio (Figure 17.2) Combined with the large diam-eter of the wheels, this makes our mouse very fast Exactly what we wanted

The front caster wheel is the key to the turning ability of the mouse All oting wheels tend to follow the direction of the body they are attached to, butthis has its range limited by mechanical constraints In fact, the liftarm attached tothe pivoting axles cannot go further than the two left and right plates that block

piv-it (Figure 17.3).When the robot goes backward, the caster turns until the liftarmhits the blocking plate, and with the caster in that position, the robot turns

Resuming forward motion, the robot will go straight again.To make the castereven more reactive, we built it asymmetrical

When describing the steering-drive configuration in Chapter 8, we explainedhow the distance of a steering wheel from its pivoting axle affects positively itstendency to self-center: the greater the distance, the more effective the self-cen-tering.This applies to caster wheels, too, and it is the reason why we used thatparticular connector to attach the front wheel: It’s the one that keeps the wheelfarthest from its pivoting axle

Robotic Animals • Chapter 17 335

Figure 17.1The LEGO Mouse

Trang 17

Figure 17.2Bottom View of the Mouse

Figure 17.3The Caster Wheel Turns the Mouse

Trang 18

Removing the RCX, you see the two touch sensors that control the headand tail (Figure 17.4).The rear one is normally kept closed by two rubber bandsattached to the tail assembly Pulling the tail opens the switch and the softwarestops the mouse

The entire head is a bumper that detects hits through its nose, whiskers, orany other part (Figure 17.5).The short tubes we used as whiskers are the onlyparts you won’t find in the MINDSTORMS kit.We are not suggesting you cutthe longer one in two, however! You can use axles in place of tubes

The head is what actually makes this robot a mouse instead of any other sible creature (Figure 17.6).This demonstrates how a few parts can deeply affectthe “personality” of a robot! We leave to you the exercise of converting thismouse into a different animal by changing some of its decorative elements

pos-www.syngress.com Figure 17.4Top View of the Mouse (Scout Removed)

Trang 19

Improvements Upon the Mouse’s Construction

We explained that one of our goals was limiting the size of the robot, and weachieved it through a single motor steering drive.The limitation of this setup isthat it doesn’t allow you to control the direction of the robot, which results in amouse whose movements are very predictable Using a second motor to controlthe front steering wheel you can enrich the behavior of the mouse with somerandom changes in direction.You should redesign and enlarge the body of therobot to make room for the second motor

Figure 17.6The Head of the Mouse

Figure 17.5The Front Bumper of the Mouse (Head Removed)

Trang 20

You can also add legs to the mouse to make it more realistic Some of the legsshown in Chapter 15 will suit this model, but with working legs it will be defi-nitely much slower.We wanted a fast mouse, and this is the reason we chosewheels An intermediate solution comes from attaching legs to the wheels so thatthey move and give the illusion they are propelling the robot (Figure 17.7)

When the programmable brick faces the direction of motion, you can use the

IR message emitter of the RCX and a light sensor in the nose to implement theproximity detection technique described in Chapter 4, thus saving your mousefrom too many collisions

Creating a Turtle

The LEGO turtle project is a bit more ambitious than the mouse project, as wereally tried to mimic the size, shape, and way of walking (as well as other basicbehaviors) of a real turtle Our robotic version walks around, and when it hitssomething, retracts its head and waits a few seconds.Then it goes backward awhile, trying to avoid the obstacle, eventually resuming straight motion

We used a few extra parts, the most important ones being four universaljoints and four #3 angle connectors.You can save the third motor and the tiles ifyou eliminate the retractable head

Figure 17.8 shows a general view of the turtle.We made a strong effort to fit allthe components into a design not too different from the shape of an actual turtle

The most relevant parts are the legs In contrast to what we made for themouse, this turtle walks on feet and uses a leg geometry not shown in Chapter

15 In fact, all the legs shown in Chapter 15 tend to produce tall robots In thiscase, however, we needed a compact design suitable for a short creature.You canunderstand the principle behind our mechanism by way of a simple experiment

www.syngress.com Figure 17.7A Pseudo-Leg

Tiêu đề	Building Robots Part 10
Trường học	Syngress
Chuyên ngành	Robotics and Unconventional Vehicles
Thể loại	PPT
Năm xuất bản	2001

Định dạng
Số trang	40
Dung lượng	1,15 MB