Page 156 - Anatomy of a Robot

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RELIABILITY, SAFETY, AND COMPLIANCE 141
Linear Power Supplies
If the design can put up with some inefficiency, consider using linear power supplies.
Switching power supplies can generate a considerable amount of interference emitted
both as RF and through the power line.
Isolate Noisy Circuitry

Keep very high frequency circuits well away from input/output (I/O) circuitry that leads
to the outside of the robot. Interference can move right through PCBs to neighboring
circuits. Try to isolate I/O circuitry as much as possible from all other sources of inter-
ference on the PCB board.

Quiet Motors

Beware of motors with brushes that create sparks. Some motors are more quiet than oth-
ers. It’s a good bet that if sparks are visible when looking from the edge of the motor, it
is generating a significant amount of interference. If no qualitative way to evaluate a
motor is available, try using the detuned radio method mentioned earlier. A noisy motor
will make a radio crackle and pop.

Use Pretested Components

It is possible to buy pretested components, such as power supplies, that have already
been tested for emissions. The manufacturers can provide profiles showing the emis-
sions at various frequencies. The testing agencies will often take these profiles into
account. If they feel the tests have already been run, they may skip some tests. However,
from experience, it seems to be the case that pretested components don’t always live up
to their reputation. A power supply that has already been tested and certified will actu-
ally fail to meet emission specs in a new robot. It’s always wise to repeat all the tests
from scratch.

SHIELDING
So how do we keep interference inside the robot (and interference from entering)? First
of all, we cannot prevent it completely. All packages for electrical systems will allow
interference to leak through. The trick is to keep it well below the tolerable levels pre-
scribed by the governmental groups that regulate it. Many techniques exist for limiting
the amount of electrical emissions that escape a robot.