FPGA Robotics Projects - Rapid Prototyping of Digital Systems - page 266

short jumpers are used to connect the two servo signal wires, and other jumpers are used
to any connect sensor boards.

16. Four, 1-inch hex spacers with 4-40 threads or use the shorter spacers that come
with the board. These are used to mount the UP3 board to the Plexiglas base using the
holes in the UP3 board.

• Parts Available from a Hardware Store

17. 3/16-inch thick Plexiglas cut into a 10.5-inch diameter circle . This part is the base of
the robot. Colored Plexiglas such as opaque white, will not show scratches as easy as
clear. Holes to cutout and drill are shown in Figure 13.11. If a band saw, jig saw, or
other machine tool is not available, a local plastics fabricator can cut this out. When
using a number of very large sensors or a DE2 board, it may be necessary to increase the
size slightly or add another circular deck for sensor mounting. A larger robot requires
more space for maneuvering. To prevent scratches on the Plexiglas, keep the paper
backing on the plastic until all of the holes have been marked and drilled out. The size
of the wheel slots may need to change depending on the wheels you select.

18. One 8-inch long strip of 2-inch wide sticky-back Velcro . Two 8-inch long strips, 1
inch wide can also be used. The Velcro is used to attach the battery to the bottom of the
Plexiglas base. Since the battery is attached with Velcro and a connector, it can be
quickly replaced and removed for charging.

19. Approximately 8 inches of 1-inch wide double-sided 3M foam tape . This is used to
attach servos, skids, and optional sensor boards to the base. Be sure to clean surfaces to
remove any grease or oil prior to application of the tape for better adhesion. For a more
durable servo mount, Lynxmotion has aluminum servo mounting brackets that can be
used instead of the double sided tape.

20. Four 4-40 Screws 5/16-inch or slightly longer . The screws are used to attach the UP3
board to Plexiglas. The screws thread into the hex spacers attached to the UP3 board.

21. Blue Loctite, Cyanoacrylate (CA) Glue, and Clear Silicone RTV. These adhesives
and glues are useful to secure screws, servos, and wheels. The mechanical vibration on
moving robots tends to shake parts loose over time. These items can also be found at
most hobby shops. Only a few drops are needed for a single robot. A single tube or
container will build several robots.

13.7 I/O Connections to the board's Expansion Headers
Most servos and sensor I/O signals will need to be attached to an expansion
header. Many FPGA pins are now 3.3V. R/C Servos and most sensors use 5V,
but be sure to check the device's datasheet. Don't forget to connect a ground
signal between the device and the FPGA board, even if the device has it's own
power supply or a direct connection to a battery. Several ground and power pins