Page 126 - Anatomy of a Robot

03_200256_CH03/Bergren 4/17/03 12:27 PM Page 111
COMPUTER HARDWARE 111
out www.acnc.com/04_01_00.html and www.pdl.cs.cmu.edu/RAIDtutorial/ for
RAID technology info. For both URLs, follow the links; they have multiple
parts.
Removable media The robot design may call for the addition of removable
media. Floppy disks, CD-ROMS, or memory cards can be used to add or remove
data from the robot. This sort of communication link works if the data does not
have to go through immediately. It’s called Sneaker Net because the operator walks
around and carries the data. The only extra considerations to keep in mind are
Removable media may be less reliable than permanent media.
Removable media can be stolen or misplaced.
Removable media can jar loose with shock.
Removable media drives leave an extra hole in the side of the robot that can
admit dirt and RF interference (to be discussed later).
Connections and cable integrity HDs have many connections. In any portable
robot application, connections can be an unreliable component. If the HD con-
nects directly to a robot PCB, then the number of connections is minimized. If the
HD is connected to the robot using a flexible cable, then the number of connec-
tions is doubled (decreasing reliability) and another component is introduced into
the system. A flexible cable will truly live up to its name; it will flex. If the robot
moves about quite a bit, all components will be subject to accelerative forces.
Most flexible cables are not meant to withstand continuous flexing. They are only
made flexible so the cable can bend around and make a proper connection.
Specially made flexible cables can be designed for repeated flexing in mobile
applications, but they must be specified for such use, and most are not. Flexible
cables may ultimately break.

Tape Drives
It seems clear that all the considerations we’ve discussed about HDs also apply to tape
drives. To reiterate these considerations, let’s list the topics from the previous dis-
cussion:

Vibration
Shock
Temperature
Gyroscopic torque
Spin-up time
Longevity
Error rates