Wicked Awesome!
Small motors need to breathe, if only a little bit. They have fans on the electrical connection end that force air out, which causes air to be drawn in at the mechanical mounting end. That's why there is a pattern of "breathing slots" just outside of the mounting pilot.
By letting the motors breathe a little, you extend the time they take to heat up. Without through-ventilation, hot air is trapped inside. Trapped air is a pretty good thermal insulator, so the windings on the motor's armature heat up much faster than the motor's case -- that means that by the time the case gets too hot to touch, the windings are probably hot enough to burn insulation, releasing the familiar magic smoke.
Conclusion -- by letting the motor breathe, you are relieving thermal stress on the windings MUCH more than can be detected just by sensing the case temperature. If you plan to run a small motor continuously, it is essential to let it breathe.
To see another example of breathing holes in a face-mounting plate for small motors, look closely at the twin-FP gearbox in
this picture.
__________________
Richard Wallace
Mentor since 2011 for FRC 3620 Average Joes (St. Joseph, Michigan)
Mentor 2002-10 for FRC 931 Perpetual Chaos (St. Louis, Missouri)
since 2003
I believe in intuition and inspiration. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.
(Cosmic Religion : With Other Opinions and Aphorisms (1931) by Albert Einstein, p. 97)