You can add pads to the fingers by using the corner braces included in most Erector Set kits and then attaching weather stripping or rubber feet to the brace. The finished gripper should look like the one depicted in Fig. 27.5. ADVANCED MODEL NUMBER 1 You can use a readily available plastic toy and convert it into a useful two-pincher gripper for your robot arm. The toy is a plastic “extension arm” with the pincher claw on one end and a hand gripper on the other (see Fig. 27.6). To close the pincher, you pull on the hand gripper. The contraption is inexpensive—usually under $10—and it is available at many toy stores. 406 EXPERIMENTING WITH GRIPPER DESIGNS FIGURE 27.2 An assortment of girders from an Erector Set toy construction kit. TABLE 27.2 PARTS LIST FOR TWO-FINGER ERECTOR SET GRIPPER. 2 4 1/2-inch Erector Set girder 1 3 1/2-inch-length Erector Set girder 4 1/2-inch-by-6/32 stove bolts, fender washer, tooth lock washer, nuts Misc 14- to 16-gauge insulated wire ring lugs, aircraft cable, rubber tabs, 1/2 by 1/2-inch corner angle brackets (galvanized or from Erector Set) Ch27_McComb 8/29/00 8:35 AM Page 406 Chop off the gripper three inches below the wrist. You’ll cut through an aluminum cable. Now cut off another 1 1/2 inches of tubing—just the arm, but not the cable. File off the arm tube until it’s straight, then fashion a 1 1/2-inch length of 3/4-inch-diameter dowel to fit into the rectangular arm. Drill a hole for the cable to go through. The cable is off- centered because it attaches to the pull mechanism in the gripper, so allow for this in the hole. Place the cable through the hole, push the dowel at least 1/2 inch into the arm, and then drill two small mounting holes to keep the dowel in place (see Fig. 27.7). Use 6/32 by 3/4-inch bolts and nuts to secure the pieces. You can now use the dowel to mount the gripper on an arm assembly. You can use a small 3/4-inch U-bolt or flatten one end of the dowel and attach it directly to the arm. The gripper opens and closes with only a 7/16-inch pull. Attach the end of the cable to a heavy- duty solenoid that has a stroke of at least 7/16 inch. You can also attach the gripper cable to a 1/8-inch round aircraft cable. Use a crimp-on connector designed for 14- to 16-gauge electrical wire to connect them end to end, as shown in Fig. 27.8. Attach the aircraft cable TWO-PINCHER GRIPPER 407 4 1/2" 3 1/2" 3" Pivot bar Finger FIGURE 27.3 Construction detail of the basic two-pincher gripper, made with Erector set parts. 1/2" x 6/32 bolt Fender washer Pivot bar Finger Tooth lock washer Nut Gap between finger and pivot bar A B FIGURE 27.4 Hardware assembly detail of the pivot bar and fingers of the two-pincher gripper. a. Assembled sliding joint; b. Exploded view. Ch27_McComb 8/29/00 8:35 AM Page 407 to a motor or rotary solenoid shaft and activate the motor or solenoid to pull the gripper closed. The spring built into the toy arm opens the gripper when power is removed from the solenoid or motor. ADVANCED MODEL NUMBER 2 This gripper design uses a novel worm gear approach, without requiring a hard-to-find (and expensive) worm gear. The worm is a length of 1/4-inch 20 bolt; the gears are 408 EXPERIMENTING WITH GRIPPER DESIGNS 3" FIGURE 27.5 The finished two-pincher gripper, with fin- gertip pads and actuating cables. FIGURE 27.6 A commercially available plastic two-pincher robot arm and claw toy. The gripper can be salvaged for use in your own designs. Ch27_McComb 8/29/00 8:35 AM Page 408 standard 1-inch-diameter 64-pitch aluminum spur gears (hobby stores have these for about $1 apiece). Turning the bolt opens and closes the two fingers of the gripper. Refer to the parts list in Table 27.3. Construct the gripper by cutting two 3-inch lengths of 41/64-inch-by-1/2-inch-by-1/16- inch aluminum channel stock. Using a 3-inch flat mending “T” plate as a base, attach the fingers and gears to the “T” as shown in Fig. 27.9. The distance of the holes is critical and depends entirely on the diameter of the gears you have. You may have to experiment with different spacing if you use another gear diameter. Be sure the fingers rotate freely on the base but that the play is not excessive. Too much play will cause the gear mechanism to bind or skip. Secure the shaft using a 1 1/2-inch-by-1/2-inch corner angle bracket. Mount it to the stem of the “T” using an 8/32 by 1-inch bolt and nut. Add a #10 flat washer between the “T” and the bracket to increase the height of the bolt shaft. Mount a 3 1/2-inch-long 1/4- inch 20 machine bolt through the bracket. Use double nuts or locking nuts to form a free- spinning shaft. Reduce the play as much as possible without locking the bolt to the bracket. Align the finger gears to the bolt so they open and close at the same angle. TWO-PINCHER GRIPPER 409 Arm tube Dowel Set screw Hole for cable End view FIGURE 27.7 Assembly detail for the claw gripper and wooden dowel. Drill a hole for the actuat- ing cable to pass through. Coupling Cable to claw (spring loaded inside claw) Steel aircraft cable Motor spindle FIGURE 27.8 One method for actuating the gripper: Attach the solid aluminum cable from the claw to a length of flexible steel aircraft cable. Anchor the cable to a motor or rotary solenoid. Actuate the motor or solenoid and the gripper closes. The spring in the gripper opens the claw when power to the motor or solenoid is removed. Ch27_McComb 8/29/00 8:35 AM Page 409 To actuate the fingers, attach a motor to the base of the bolt shaft. The prototype gripper used a 1/2-inch-diameter 48-pitch spur gear and a matching 1-inch 48-pitch spur gear on the drive motor. Operate the motor in one direction and the fingers close. Operate the motor in the other direction and the fingers open. Apply small rubber feet pads to the inside ends of the grippers to facilitate grasping objects. The finished gripper is shown in Fig. 27.10. Figs. 27.11 through 27.14 show another approach to constructing two-pincher grippers. By adding a second rail to the fingers and allowing a pivot for both, the fingertips remain 410 EXPERIMENTING WITH GRIPPER DESIGNS TABLE 27.3 PARTS LIST FOR WORM DRIVE GRIPPER. 2 3-inch lengths 41/64-inch-by-1/2-inch-by-1/16-inch aluminum channel 2 1-inch-diameter 64-pitch plastic or aluminum spur gear 1 2-inch flat mending “T” 1 1 1/2-inch-by-1/2-inch corner angle iron 1 3 1/2-inch-by-1/4-inch 20 stove bolt 2 1/4-inch 20 locking nuts, nuts, washers, tooth lock washers 2 1/2-inch-by-8/32 stove bolts, nuts, washers 1 1-inch-diameter 48-pitch spur gear (to mate with gear on driving motor shaft) 1 1 /2" x 1 /2" corner angle iron Locking nut Nut Nut Tooth lock washer 3 1 /2" x 1 /4"-20 bolt 48 pitch spur gear 3" "T" Gears 3" A B FIGURE 27.9 A two-pincher gripper based on a homemade work drive system. a. Assembled gripper; b. Worm shaft assembly detail. Ch27_McComb 8/29/00 8:35 AM Page 410 TWO-PINCHER GRIPPER 411 FIGURE 27.10 The finished two-pincher worm drive gripper. FIGURE 27.11 Adding a second rail to the fingers and allowing the points to freely pivot caus- es the fingertips to remain parallel to one another. Ch27_McComb 8/29/00 8:35 AM Page 411 412 EXPERIMENTING WITH GRIPPER DESIGNS Pivot points Palm Gripper FIGURE 27.12 Close-up detail of the dual-rail fin- ger system. Note the pivot points. Pull cables to close FIGURE 27.13 A way to actuate the gripper. Attach cables to the fingers and pull the cables with a motor or solenoid. Fit a torsion spring along the fingers and palm to open the fin- gers when power is removed from the motor or solenoid. Ch27_McComb 8/29/00 8:35 AM Page 412 Torsion spring Gripper (closed position) Pulley gear Drive Tension spring Torsion spring FIGURE 27.14 Actuation detail of a basic two-pincher gripper using a motor. The tension spring prevents undo pressure on the object being grasped. Note the torsion springs in the palm of the gripper. 413 Ch27_McComb 8/29/00 8:35 AM Page 413 parallel to one another as the fingers open and close. You can employ several actuation techniques with such a gripper. Fig. 27.15 shows the gripping mechanism of the still- popular Radio Shack/Tomy Armatron. Note that it uses double rails to effect parallel clo- sure of the fingers. You can model your own gripper using the design of the Armatron or amputate an Armatron and use its gripper for your own robot. Flexible Finger Grippers Clapper and two-pincher grippers are not like human fingers. One thing they lack is a com- pliant grip: the capacity to contour the grasp to match the object. The digits in our fingers can wrap around just about any oddly shaped object, which is one of the reasons we are able to use tools successfully. You can approximate the compliant grip by making articulated fingers for your robot. At least one toy is available that uses this technique; you can use it as a design base. The plastic toy arm described earlier is available with a handlike gripper instead of a claw grip- per. Pulling on the handgrip causes the four fingers to close around an object, as shown in Fig. 27.16. The opposing thumb is not articulated, but you can make a thumb that moves in a compliant gripper of your own design. 414 EXPERIMENTING WITH GRIPPER DESIGNS FIGURE 27.15 A close-up view of the Armatron toy gripper. Note the use of the dual-rail finger system to keep the fingertips parallel. The gripper is moderately adaptable to your own designs. Ch27_McComb 8/29/00 8:35 AM Page 414 Make the fingers from hollow tube stock cut at the knuckles. The mitered cuts allow the fingers to fold inward. The fingers are hinged by the remaining plastic on the topside of the tube. Inside the tube fingers is semiflexible plastic, which is attached to the fingertips. Pulling on the handgrip exerts inward force on the fingertips. The result? the fingers col- lapse at the cut joints. You can use the ready-made plastic hand for your projects. Mount it as detailed in the previous section on the two-pincher claw arm. You can make your own fingers from a vari- ety of materials. One approach is to use the plastic pieces from some of the toy construc- tion kits. Cut notches into the plastic to make the joints. Attach a length of 20- or 22-gauge stove wire to the fingertip and keep it pressed against the finger using nylon wire ties. Do not make the ties too tight, or the wire won’t be able to move. An experimental plastic fin- ger is shown in Fig. 27.17. You can mount three of four such fingers on a plastic or metal “palm” and connect all the cables from the fingers to a central pull rod. The pull rod is activated by a solenoid or motor. Note that it takes a considerable pull to close the fingers, so the actuating solenoid or motor should be fairly powerful. The finger opens again when the wire is pushed back out as well as by the natural spring action of the plastic. This springiness may not last forever, and it may vary if you use other materials. One way to guarantee that the fingers open is to attach an expansion spring, or a strip of flexible spring metal, to the tip and base of the finger, on the back side. The spring should give under the inward force of the solenoid or motor, but adequately return the finger to the open position when power is cut. Wrist Rotation The human wrist has three degrees of freedom: it can twist on the forearm, it can rock up and down, and it can rock from side to side. You can add some or all of these degrees of freedom to a robotic hand. A basic schematic of a three-degree-of-freedom wrist is shown in Fig. 27.18. WRIST ROTATION 415 FIGURE 27.16 Commercially available plastic robotic arm and hand toy. The gripper can be salvaged for use in your own designs. The opposing thumb is not articulated, but the fingers have a semi- compliant grip. Ch27_McComb 8/29/00 8:35 AM Page 415 [...]... could make the robot stop when it sees a bright light By using two sensors, each connected to separate motors (much like the line-tracers of Chapter 38 ), you could make the robot follow a bright light source as it moves By simply reversing the sensor connections to the motors, you can make the robot behave in the oppo- +V M1 Ground +5V D1 1N40 03 R1 10K R2 1K c Q1 2N 222 2 b Q1 RL1 e FIGURE 28 .1 Only a... from the board +V M1 Ground +5V D1 1N40 03 Q1 R2 1K c Q1 2N 222 2 b R1 10K RL1 e FIGURE 28 .2 By connecting the sensors and control electronics differently, a robot can be made to “behave” in different ways Ch28_McComb 8 /21 /00 4:04 PM Page 424 424 AN OVERVIEW OF ROBOT “BRAINS” You can “rewire” a robot controlled by a computer simply by changing the software running on the computer For example, if your robot. .. chapter we’ll review the different kinds of “brains” found on the typical hobby or amateur robot, including the latest microcontrollers—computers that are specially made to interact with (control) hardware Endowing your robot with smarts is a big topic, so 421 Copyright 20 01 The McGraw-Hill Companies, Inc Click Here for Terms of Use Ch28_McComb 8 /21 /00 4:04 PM Page 422 422 AN OVERVIEW OF ROBOT “BRAINS”... probably use the laptop as is, without removing its parts and mounting them on the robot That way, you can still access the keyboard and display Use the parallel and/or serial ports on the laptop to connect to the robot While these ports don’t provide the same flexibility as a direct connection to the motherboard’s system bus, they should function admirably for most robotic applications You can use the unit’s... form; the cartridges plugged into the back of the computer The Commodore 64 is no longer manufactured, but it can still be found at swap meets and other used markets The keyboard enclosure of the Commodore 64 holds the computer The power supply for the Commodore 64 is external to the computer You’ll want to replace it with regulated power from your robot, using a 6- to 1 2- volt battery source The power... Chapter 33 , “Using the OOPic Microcontroller” Ch29_McComb 8/18/00 2: 16 PM Page 435 29 INTERFACING WITH COMPUTERS AND MICROCONTROLLERS T he brains of a robot don’t operate in a vacuum They need to be connected to motors to make the robot move and to sensors to make the robot perceive its surroundings In most cases, these outside devices cannot be directly connected to the computer or microcontroller of a robot. .. often ϩ5 and sometimes ϩ 12 A few, like the IBM PC compatible, require negative reference voltages of -1 2 and -5 (However, some IBM PC-compatible motherboards will still function if the -1 2 and -5 voltages are absent.) Accessibility to the microprocessor system bus or an input/output port The computer won’t do you much good if you can’t access the data, address, and control lines The IBM PC architecture... 419 PART 5 COMPUTERS AND ELECTRONIC CONTROL Copyright 20 01 The McGraw-Hill Companies, Inc Click Here for Terms of Use This page intentionally left blank Ch28_McComb 8 /21 /00 4:04 PM Page 421 28 AN OVERVIEW OF ROBOT “BRAINS” “Brain, brain, what is brain?” If you’re a Trekker, you know this is a line from one of the original Star Trek episodes of the 1960s, entitled “Spock’s Brain.” The quality of the. .. removed, the motor, et al, stops Ch29_McComb 8/18/00 2: 16 PM Page 438 438 INTERFACING WITH COMPUTERS AND MICROCONTROLLERS OTHER COMMON TYPES OF OUTPUTS Other types of outputs are used for the following purposes: I Sound The robot may use sound to warn you of some impending danger (“Danger, Will Robinson, danger!”) or to scare away intruders If you’ve built an R2-D2 like robot (from Star Wars fame), your robot. .. board logic The ϩ5 vdc is high-current demand; some early PC motherboards may draw an amp or more I ϩ 12 and Ϫ 12 volts, used for powering disk drives and, in the case of Ϫ 12 volts, for RS- 23 2 serial communications For serial communications the current demand for the ± 12 volts is low: 100 mA or less Additional current capacity is needed for the ϩ 12 volt source if you use a floppy or hard disk I Ϫ5 volts, . 1 / 2- inch-by-1 / 2- inch corner angle iron 1 3 1 / 2- inch-by-1/4-inch 20 stove bolt 2 1/4-inch 20 locking nuts, nuts, washers, tooth lock washers 2 1 / 2- inch-by-8/ 32 stove bolts, nuts, washers 1 1-inch-diameter. DESIGNS TABLE 27 .3 PARTS LIST FOR WORM DRIVE GRIPPER. 2 3- inch lengths 41/64-inch-by-1 / 2- inch-by-1/16-inch aluminum channel 2 1-inch-diameter 64-pitch plastic or aluminum spur gear 1 2- inch flat. gripper. Refer to the parts list in Table 27 .3. Construct the gripper by cutting two 3- inch lengths of 41/64-inch-by-1 / 2- inch-by-1/1 6- inch aluminum channel stock. Using a 3- inch flat mending