Page 142 - Anatomy of a Robot

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RELIABILITY, SAFETY, AND COMPLIANCE 127
Shock
Sway and shock can tear wires out of connectors.
Bad design Contacts are one of the hardest components for an electrical engi-
neer to master. They always take contacts for granted. The truth is, contacts require
quite a bit of experience to use correctly. If a designer puts too much current
through them, they can burn out. If the designer does not have sufficient voltage
across them, contacts can fail to make true contact. The failures occur well after
shipment.

Cabling

Wires and cables can fail for several reasons listed below.
Abrasion Wires and cables will rub up against surfaces and abrade the insula-
tion away. In a robot, this could be a real problem. Cables should be well insulated
and run far away from sharp internal surfaces. Most PCBs are full of sharp
objects.
Flexing Wires and cables will flex repeatedly inside a moving robot. Eventually,
one or more wires may break. Flexible cables are a discipline unto themselves in
the electronics world. It takes great experience to build them properly. If a cable
is not designed to flex repeatedly, see to it that it does not!

Transistors
Even though a processor may contain 4 million transistors, it may be more reliable than
a single transistor! In particular, power transistors can be a problem. Many engineers
are not well versed in keeping them safe and happy. As a general rule, try to avoid using
too many discrete transistors. If the design calls for a power transistor, make sure it’s
used well within its specifications.

Batteries
Batteries are basically canisters of chemical soup destined to leak, die, explode, and fail.
If we are lucky, they will not do all of these things at once. We’ll get more into safety
later. Most robots probably will have batteries in them. If batteries are going to be in the
robot, better study the technologies very well. If the batteries can be replaced periodi-
cally, preventive maintenance might even be warranted. Some batteries are more reli-
able than others. If the robot is designed for long-term autonomous operation, then
study spacecraft technology and the batteries used in satellites.