- Fit the O-ring around one of the skateboard bearings. This will be the rear caster’s wheel. Mount it between the axle holders, with a large acrylic washer on either side, on a 5/16"×1" bolt secured with a matching nut.
- For the caster’s swivel mount, run four #4 screws through 4 small metal washers, then through the 4 mounting holes around the rear caster hole in the large acrylic base piece. Drop the bearing holder (the acrylic square with the larger center hole) over the 4 screws. Drop the bearing into the holder, then drop 4 small acrylic washers onto the screws. Finally, drop the bearing retainer (the square with the smaller hole) onto the screws and over the bearing. Secure with nuts.
- The metal washers provide clearance; without them, the caster will hit the screws.
- Attach the side pieces to the top of the base by fitting 4 nut/bolt pairs into its cross-slots, as in Step 1. Use 2 more nuts and bolts to join the tops of the side pieces to the crossbar piece.
- Tweezers help to hold the nut in place while you start the screw.
- Assemble the sensor tray from the sensor shelf, sensor shelf riser, 2 sensor shelf brackets, and 6 nut, screw, and washer sets. As with the other acrylic pieces, fit the tabs into the slots and secure by twisting the nuts down on the bolts in their cross-slots. The sensor shelf will act as a base for attaching the robot’s sensors.
- Attach the sensor tray to the front of the chassis with 2 screws.
- Attach the caster holder to the caster swivel mount with the remaining 5/16" bolt and matching nut. Fit 2 large acrylic washers over the bolt between the underside of the swivel mount and the top of the caster holder, so the caster can turn without mounting hardware getting in the way. The inner race of the horizontal bearing should be clamped between the large bolt head and the 2 acrylic washers.
- You may have to temporarily loosen the screws to get the bolt to fit through the caster assembly so that the bolt’s head is captured by the wheel supports.
- Use the seam ripper to slit the joint area, making the slit continuous. Starting with the joint, place the tire onto the wheel, working it around the rim a little bit at a time.
- Place a pencil through the center of the wheel and roll it on a table to seat the tire. Use fine sandpaper to lightly sand the glue joint. Be careful — you only want to remove excess glue.
- With each circular servo horn, center it under a wheel with the horn hub protruding through. Rotate the horn until you see 2 of its 4 injection-mold marks through each of the wheel’s slots. Mark the horn through the 2 slots with a sharp pencil. Drill two 7/64" holes into the horn where the mold marks intercept your lines.
- Use two #4 screws and nuts to attach a horn to each wheel, and mount the wheels on the servo axles using the small screw that comes with the servos.
- Separate the PCB into 3 boards — the controller board and 2 sensor boards — by splitting it along its 2 scribe lines. You may need to deepen the scribe line between boards with a utility knife before separating them.
- Cut the 8-pin female header into two 3-pin headers by cutting through the fourth and fifth pins. Sand the cut edges smooth.
- Populate the board with the components as marked, starting with the shortest ones (resistors and diode) and working up to the tallest. Route the battery holder’s leads through the strain relief holes before attaching. Make sure the large capacitor’s polarity is correct, with the lead near the band marked with negative signs (–) opposite the hole marked (+). The female headers go into the locations marked “Sensor R” and “Sensor L.” Do not place the chip into the socket yet.
- Use a multimeter to check all connections, following the wiring-check tables at http://makeprojects.com/v/29. If everything checks out, plug in the chip with its pin 1 near the switch, and its notch next to capacitor C1.
- The wiring tables list all the pairs of points on the board that should have continuity or a specified resistance.
- After any work on the circuit board, perform the checks again before you plug in the chip. Before checking, disconnect the servos and sensors from the controller board and turn the power switch off.
- Cut the 3-wire ribbon cable in half. Strip and tin all ends of both pieces. For each, solder one end to a 3-pin male header and the other to a sensor board, with the red wire in the location marked “1.”
- Plug the cables into the female sockets on the controller board, connecting the red wire to the sides marked “1.”
- There are several tool chain options for programming AVR chips, but a good choice for beginners is to combine Atmel’s AVR Studio 4 with the open-source WinAVR.
- Download and install WinAVR and AVR Studio 4 (search “AVR Studio 4” at http://www2.atmel.com/) and install with all defaults. You will need to register on the Atmel website before downloading the AVR Studio 4 installer.
- Some have reported an issue of AVR Studio 4 installer freezing after selecting “Install”. A proposed work-around is to open Task Manager and end the task “Rundll32.exe.” The author has not experienced this issue.
- Atmel now recommends their newer AVR Studio 5, which has some nice features, but is larger and more complex than version 4.
- Launch AVR Studio 4. Click the “New Project” button at the top of the Welcome screen, then select “AVR GCC” for the Project Type, to specify the gcc compiler, for project code written in C. Give the project a name (“TW_tabletop” here), then uncheck “Create initial file” and check “Create folder.”
- Create a new folder named “AVR” in My Documents, select that location, and click “Next.” In the next popup, select “AVR Simulator 2” as the Debug platform and ATtiny85 as the Device. Click Finish.
- Download the Tiny Wanderer code examples from http://makeprojects.com/v/29, or else use your own code. Each program will consist of a .c and .h file, for the C source and headers. Copy or move these files to the project directory created in step 7c. For example use tinywanderer_edgeDetect_version2b.c and tinywanderer_edgeDetect_version2b.h, for the tabletop edge detection program.
- Each project that you program into the Tiny Wanderer will have different .c and .h files. Be sure to use the appropriate .c and .h files for your project.
- Open the project AVR GCC pane, right-click the “Source Files” folder, select “Add Existing Source File(s)” and specify the project’s .c file. Do the same for the project’s .h file after right-clicking on the “Header Files” folder.
- Double-click both project files in the AVR GCC pane to open them up in the editor. Right-click Project → Configuration options menu item, select “Custom Options” at the left of the popup, In the Custom Options pane, uncheck “Use AVR Toolchain” box and add the locations for avr-gcc.exe and make.exe. The default locations for these will be C:WinAVR-20101001bin and C:WinAVR-20101001utilsbin, respectively. Click “OK”.
- This is where you connect AVR Studio 4 to WinAVR, installed earlier. These instructions apply to AVR Studio 4.19 (build 760). This final version differs from previous versions of AVR Studio 4.
- Now you can edit your program. To build the project for uploading to the ATTiny85 chip, select the “Build Active Configuration” icon on the tool bar or push F7. You will either see a successful build message or a list of errors for debugging.
- After a successful build, connect your programmer to the Tiny Wanderer PCB board and click the “Display the Connect Dialog” icon on the toolbar. Turn the power switch on and make sure the robot has batteries. Select your programmer and click “Connect…”
- Click the small “Connect to the Selected AVR Programmer” icon in AVR Studio’s toolbar. Click “Read Signature” in the resulting popup and wait for the “Leaving Programming Mode” message at the bottom.
- Click the Program tab at the top, and wait for the path of the compiled HEX file to appear under the “Flash” subheading. Once it appears, click “Program” to upload it to the ATTiny.
- If you change projects, the HEX file path will not change. You must change this path to the new project’s file.
- Turn off the power to the board, unplug the programmer, and re-plug the servos.
- Congratulations! You have reprogrammed your AVR microprocessor.
Print out and glue pattern to piece of acrylic.
- Drill out holes in pattern using a 9/64” drill bit for the small holes, and a 5/16” drill bit for the larger hole. To form the two slots, drill two 9/64" holes next to each other and use the small file to join the two adjacent holes.
- Acrylic can be drilled with less chance of cracking by using a drill bit with a more acute angle at the tip. One way to make this type of drill bit is to chuck a normal drill bit into a drill, and run it backwards against a grinding wheel.
After the bend the bumper support should look like the image to the right.
Install the 1” #6 screws into the bumper and lock them into place using a nut on each screw. Unscrew the nut and washer that comes with the switch and insert the switch into the 5/16” hole. If the fit is too tight use the round file to enlarge the hole. Re-install the washer and nut on the switch.
Adjust the nuts on the bumper support screws so that the switch plunger is about to engage. Add a second nut to each bumper support screw to lock the adjustment. Re-check the smoothness of the bumper action, and the switch’s operation.
Cut two pieces of small multi-strand wire. Strip the insulation from all four ends and tin the ends of the wire. Connect one end of each wire to a different terminal on the switch.
Disconnect the servos and program the robot with the example program.
