McGraw-Hill - The Robot Builder''''s Bonanza Part 5 pps

hands. Especially with metal, the bit can snag as it’s cutting and yank the piece out of your hands. If you can’t place the work in the vise, use a pair of Vise-Grips or other suitable locking pliers. FINISHING Cutting and drilling often leaves rough edges, called flashing, in the metal. These edges must be filed down using a medium- or fine-pitch metal file, or else the pieces won’t fit together properly. Aluminum flash comes off quickly and easily; you need to work a little harder when removing the flash in steel or zinc stock. Build the Buggybot The Buggybot is a small robot built from a single 6-by-12-inch sheet of 1/16-inch thick aluminum, nuts and bolts, and a few other odds and ends. You can use the Buggybot as the foundation and running gear for a very sophisticated petlike robot. As with the robots built with plastic and wood we discussed in the previous two chapters, the basic design of the all-metal Buggybot can be enhanced just about any way you see fit. This chapter details the construction of the framework, locomotion, and power systems for a wired remote con- trol robot. Future chapters will focus on adding more sophisticated features, such as wire- less remote control, automatic navigation, and collision avoidance and detection. Refer to Table 10.1 for a list of the parts needed to build the Buggybot. 126 BUILDING A METAL PLATFORM TABLE 10.1 PARTS LIST FOR BUGGYBOT Frame: 1 6-by-12-inch sheet of 1/16-inch thick aluminum Motor and Mount: 2 Tamiya high-power gearbox motors (from kit); see text 2 3-inch-diameter “Lite Flight” foam wheels 2 5/56 nuts (should be included with the motors) 2 3/16-inch collars with setscrews 1 Two-cell “D” battery holder Misc 1-inch-by-6/32 stove bolts, nuts, flat washers Support Caster: 1 1 1/2-inch swivel caster Misc 1/2-inch-by-6/32 stove bolts, nuts, tooth lock washers, flat washers (as spacers) See parts list in Table 8.3 of Chapter 8 for motor control switch Ch10_McComb 8/18/00 2:09 PM Page 126 FRAMEWORK Build the frame of the Buggybot from a single sheet of 1/16-inch thick aluminum sheet. This sheet, measuring 6 by 12 inches, is commonly found at hobby stores. As this is a standard size, there’s no need to cut it. Follow the drill-cutting template shown in Fig. 10.1. After drilling, use a large shop vise or woodblock to bend the aluminum sheet as shown in Fig. 10.2. Accuracy is not all that important. The angled bends are provided to give the Buggybot its unique appearance. BUILD THE BUGGYBOT 127 6" by 12" aluminum sheet 1 1/2" 1 7/8" 3/8" (Same) Drill holes for caster plate 5 1/2" FIGURE 10.1 Drilling diagram for the Buggybot frame. Ch10_McComb 8/18/00 2:09 PM Page 127 MOTORS AND MOTOR MOUNT The prototype Buggybot uses two high-power gearbox motor kits from Tamiya, which come in kit form and are available at many hobby stores (as well as Internet sites, such as TowerHobbies.com). These motors come with their own gearbox; choose the 1:64.8 gear ratio. An assembled motor is shown in Fig. 10.3. Note that the output shaft of the motor can be made to protrude a variable distance from the body of the motor. Secure the shaft (using the Allen setscrew that is included) so that only a small portion of the opposite end of the shaft sticks out of the gear box on the other side, as shown in Fig 10.3. You should secure the gearboxes and motors to the aluminum frame of the Buggybot as depicted in Fig. 10.4. Use 6/32 bolts, flat washers, and nuts. Be sure that the motors are aligned as shown in the figure. Note that the shaft of each motor protrudes from the side of the Buggybot. Figure 10.5 illustrates how to attach the wheels to the shafts of the motors. The wheels used in the prototype were 3-inch-diameter foam “Lite Flight” tires, commonly avail- able at hobby stores. Secure the wheels in place by first threading a 3/16-inch collar (available at hobby stores) over the shaft of the motor. Tighten the collar in place using its Allen setscrew. Then cinch the wheel onto the shaft by tightening a 5/56 threaded nut to the end of the motor shaft (the nut should be included with the gearbox motor kit). Be sure to tighten down on the nut so the wheel won’t slip. SUPPORT CASTER The Buggybot uses the two-wheel drive tripod arrangement. You need a caster on the other end of the frame to balance the robot and provide a steering swivel. The 1 1/2-inch swivel caster is not driven and doesn’t do the actual steering. Driving and steering are taken care of by the drive motors. Refer to Fig. 10.6 on p. 131. Attach the caster using two 6/32 by 1/2-inch bolts and nuts. Note that the mechanical style of the caster, and indeed the diameter of the caster wheel, is dependent on the diameter of the drive wheels. Larger drive wheels will require either a 128 BUILDING A METAL PLATFORM 6" 4 1/2" 1 1/2" FIGURE 10.2 Bend the aluminum sheet at the approximate angles shown here. Ch10_McComb 8/18/00 2:09 PM Page 128 different mounting or a larger caster. Small drive wheels will likewise require you to adjust the caster mounting and possibly use a smaller-diameter caster wheel. BATTERY HOLDER The motors require an appreciable amount of current, so the Buggybot really should be powered by heavy-duty “C”- or “D”-size cells. The prototype Buggybot used a two-cell “D” battery holder. The holder fits nicely toward the front end of the robot and acts as a BUILD THE BUGGYBOT 129 Tire Nut Motor and gearbox Coupler (with setscrew) Output gear (with setscrew) Motor shaft FIGURE 10.3 Secure the output shaft of the motor so that almost all of the shaft sticks out on one side of the motor. Nut Base 1/2" x 6/32 Bolt Motor gearbox Mounting flange FIGURE 10.4 The gearboxes and motors are attached to the frame of the Buggybot using ordinary hardware. Ch10_McComb 8/18/00 2:09 PM Page 129 good counterweight. You can secure the battery holder to the robot using double-sided tape or hook-and-loop (Velcro) fabric. WIRING DIAGRAM The basic Buggybot uses a manual wired switch control. The control is the same one used in the plastic Minibot detailed in Chapter 8, “Building a Plastic Robot Platform.” Refer to the wiring diagram in Fig. 8.4 of that chapter for information on powering the Buggybot. To prevent the control wire from interfering with the robot’s operation, attach a piece of heavy wire (the bottom rail of a coat hanger will do) to the caster plate and lead the wire up it. Use nylon wire ties to secure the wire. The completed Buggybot is shown in Fig. 10.7. Test Run You’ll find that the Buggybot is an amazingly agile robot. The distance it needs to turn is only a little longer than its length, and it has plenty of power to spare. There is room on the robot’s front and back to mount additional control circuitry. You can also add control cir- cuits and other enhancements over the battery holder. Just be sure that you can remove the circuit(s) when it comes time to change or recharge the batteries. 130 BUILDING A METAL PLATFORM FIGURE 10.5 Attach the foam wheels (with plastic hubs) for the Buggybot onto the shafts of the motors. Ch10_McComb 8/18/00 2:09 PM Page 130 TEST RUN 131 Nut Tooth Lockwasher Base Caster 1/2" x 6/32 Bolt FIGURE 10.6 Mounting the caster to the Buggybot. FIGURE 10.7 The completed Buggybot. Ch10_McComb 8/18/00 2:09 PM Page 131 From Here To learn more about Read Plastic robots Chapter 8, “Building a Plastic Robot Platform” Metal robots Chapter 9, “Building a Basic Wooden Platform” Using batteries Chapter 15, “All about Batteries and Robot Power Supplies” Selecting the right motor Chapter 17, “Choosing the Right Motor for the Job” Using a computer or microcontroller Chapter 28, “An Overview of Robot ‘Brains’” 132 BUILDING A METAL PLATFORM Ch10_McComb 8/18/00 2:09 PM Page 132 Ready-made toys can be used as the basis for more complex homebrew hobby robots. The toy industry is robot crazy, and you can buy a basic motorized or unmotorized robot for parts, building on it and adding sophistication and features. Snap or screw- together kits, such as the venerable Erector Set, let you use premachined parts for your own creations. And some kits, like LEGO and Robotix, are even designed to create futuristic motorized robots and vehicles. You can use the parts in the kits as is or can- nibalize them, modifying them in any way you see fit. Because the parts already come in the exact or approximate shape you need, the construction of your own robots is greatly simplified. About the only disadvantage to using toys as the basis for more advanced robots is that the plastic and lightweight metal used in the kits and finished products are not suitable for a homemade robot of any significant size or strength. You are pretty much confined to building small Minibot or Scooterbot-type robots from toy parts. Even so, you can some- times apply toy parts to robot subsystems, such as a light-duty arm-gripper mechanism installed on a larger automaton. Let’s take a closer look at using toys in your robot designs in this chapter, and examine several simple, cost-effective designs using readily available toy construction kits. 11 CONSTRUCTING HIGH-TECH ROBOTS FROM TOYS 133 Ch11_McComb 8/18/00 2:09 PM Page 133 Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use. Erector Set Erector Set, now sold by Meccano, has been around since the Dawn of Time—or so it seems. The kits, once made entirely of metal but now commonly including many plas- tic pieces, come in various sizes and are generally designed to build a number of dif- ferent projects. Many kits are engineered for a specific design with perhaps provisions for moderate variations. I’ve found the general-purpose sets to be the best bets. Among the useful components of the kits are prepunched metal girders, plastic and metal plates, tires, wheels, shafts, and plastic mounting panels. You can use any as you see fit, assembling your robots with the hardware supplied with the kit or with 6/32 or 8/32 nuts and bolts. Several Erector Sets, such as those in the Action Troopers collection, come with wheels, construction beams, and other assorted parts that you can use to construct a robot base. Motors are typically not included in these kits, but you can readily supply your own. Because Erector Set packages regularly come and go, what follows is a general guide to building a robot base. You’ll need to adapt and reconfigure based on the Erector Set parts you have on hand. The prepunched metal girders included in the typical Erector Set make excellent motor mounts. They are lightweight enough that they can be bent, using a vise, into a U-shaped motor holder. Bend the girder at the ends to create tabs for the bolts, or use the angle stock provided in an Erector Set kit. The basic platform is designed for four or more wheels, but the wheel arrangement makes it difficult to steer the robot. The design presented in Fig. 11.1 uses only two wheels. The platform is stabilized using a miniature swivel caster at one end. You’ll need to purchase the caster at the hardware store. Note that the shafts of the motors are not directly linked to the wheels. The shaft of the wheels connect to the baseplate as originally designed in the kit. The drive motors are equipped with rollers, which engage against the top of the wheels for traction. You can use a metal or rubber roller, but rubber is better. The pinch roller from a discarded cassette tape player is a good choice, as is a 3/8-inch beveled bibb washer, which can be found in the plumbing section of the hardware store. You can easily mount a battery holder on the top of the platform. Position the battery holder in the center of the platform, toward the caster end. This will help distribute the weight of the robot. The basic platform is now complete. You can attach a dual-switch remote control, as described in Chapter 8, “Building a Plastic Robot Platform,” or connect automatic control circuitry as detailed in Part 5 of this book, “Computers and Electronic Control.” Do note that over the years the Erector Set brand has gone through many owners. Parts from old Erector Sets are unlikely to fit well with new parts. This includes but is not lim- ited to differences in the threads used for the nuts and bolts. If you have a very old Erector Set (such as those made and sold by Gilbert), you’re probably better off keeping them as collector’s items rather than raiding them for robotic parts. The very old Erector Sets of the 1930s through 1950s fetch top dollar on the collector’s market (when the sets are in good, complete condition, of course). Similarly, today’s Meccano sets are only passably compatible with the English-made Meccano sets sold decades ago. Hole spacing and sizes have varied over the years, and “mixing and matching” is neither practical nor desirable. 134 CONSTRUCTING HIGH-TECH ROBOTS FROM TOYS Ch11_McComb 8/18/00 2:09 PM Page 134 Robotix The Robotix kits, originally manufactured by Milton-Bradley and now sold by Learning Curve, are specially designed to make snap-together walking and rolling robots. Various kits are available, and many of them include at least one motor (additional motors are avail- able separately). You control the motors using a central switch pad. Pushing the switch for- ward turns the motor in one direction; pushing the switch back turns the motor in the other direction. The output speed of the motors is about six rpm, which makes them a bit slow for moving a robot across the room but perfect for arm-gripper designs. ROBOTIX 135 Wheel Base Drive motor Motor clamp Rubber roller Swivel Side view Caster Drive wheels A B FIGURE 11.1 Constructing the motorized base for a robot using Erector Set (Meccano) parts. a. Attaching the motor and drive roller over the wheel; b. Drive wheel-caster arrangement. Ch11_McComb 8/18/00 2:09 PM Page 135 [...]... (HOOK-AND-LOOP) You can attach non-LEGO things to LEGO pieces with Velcro (otherwise known by the generic term “hook-and-loop”) Get the kind with self-sticking adhesive backing Put the hook material on one piece and the loop on the other Press them together for a very strong—but not permanent—bond Build the LEGO Pepbot The Pepbot is a small, two-wheeled robot constructed from an assortment of LEGO parts... 12.4d 5 Attach a 2u-by-6u plate down the centerline to the top of the chassis, as shown in Fig 12.4e 6 Attach a round pad with a 2u-by-2u round brick, then press this assembly into the ends of the centerline beams, on the bottom of the frame (Fig 12.4f) Side blocks 1 Create four sets of three 2u-by-4u bricks, stacked on top of one another (Figure 12.5a) 2 Attach the assembled side blocks to the frame,... hot-melt glue to affix two 2u-by-6u plates to the side of each servo casing, as shown in Fig 12.6 Use only a moderate amount of epoxy or hot-melt glue, as you may need to remove the plate from the servo casing For one servo, glue the plate to the right side (looking at the servo top down, with the output shaft on the top) For the other servo, glue the plate to the left side Be careful to align the. .. and download the program in Listing 12.1 You may need to depress the reset button on the OOPic microcontroller board to prevent the Pepbot from activating prematurely Place the robot on the floor, then release the reset button The Pepbot robot should come to life, first going forward, then spinning both to the left and right It should then turn right, then left, and then finally back up The program... use epoxy or hot-melt glue (hot-melt glue is preferred) to secure the hub of the wheel to the plate that is connected to the servo Be absolutely sure that the wheel hub is exactly centered over the servo plate; if it is not, the robot will not travel in a straight line ATTACHING THE DECK The “deck” is where you place the Pepbot’s batteries and control circuitry The deck is simply an 8u-by-16u LEGO building... the Pepbot Use the following steps Frame 1 Begin by assembling the frame as shown in Fig 12.4a Attach two 16u beams to two 2u-by-12u plates, forming a rectangle 2 On the underside of the frame attach the two 2u-by-16u plates lengthwise (see Fig 12.4b) 3 Connect two additional 16u beams down the centerline of the bottom of the frame (Fig 12.4c) 4 Attach two 2u-by-12u plates to the top of the frame, as... Fig 12.7, using two 2u-by-12u plates ATTACHING THE WHEELS The wheels of the Pepbot are lightweight foam tires, which are used in model R/C airplanes I selected wheels with a 3-inch diameter, which makes the Pepbot travel fairly fast across the floor (hence the name Pepbot) You can use smaller wheels if you wish, but consider the following: I The smaller the wheel, the slower the robot R/C servo motors... wheels will make Pepbot travel faster I The smaller the wheel, the less clearance there is between the bottom of the robot and the floor Conversely, the larger the wheel, the more clearance there will be This can be helpful if you run Pepbot over thick carpet or want it to travel over small bumps, like the threshold between a carpeted and a tile room I The design of the Pepbot will not allow tires smaller... “motor 3,” to the large connector on the opposite end of the beam arm Position this motor so the drive spindle is on the other end of the beam arm Attach a double plug and an elbow between the drive spindle of motor 3 and the connector opposite the drive spindle of the fourth motor, “motor 4.” The two claw levers directly attach to the drive spindle of motor 4 Motorize the joints by plugging in the yellow... LEGO, or see the LEGO Web site for more information on LEGO parts FIGURE 12.3 Use LEGO wheels, pulleys, and gears to enable your robot creations to scoot around the floor Ch12_McComb 8/18/00 2:08 PM Page 150 150 BUILD CUSTOM LEGO-BASED ROBOTS Securing Parts LEGO parts are made to snap together When properly constructed, the snap-together system provides for relatively strong joints However, the active . that the shaft of each motor protrudes from the side of the Buggybot. Figure 10 .5 illustrates how to attach the wheels to the shafts of the motors. The wheels used in the prototype were 3-inch-diameter. setscrew. Then cinch the wheel onto the shaft by tightening a 5/ 56 threaded nut to the end of the motor shaft (the nut should be included with the gearbox motor kit). Be sure to tighten down on the. create futuristic motorized robots and vehicles. You can use the parts in the kits as is or can- nibalize them, modifying them in any way you see fit. Because the parts already come in the exact or approximate