RE:heatsink flexing was: chopper max voltage

<orig msgs below>

Kevin,

The L298 "legs" are bent in a "Z" shape to accomodate this thermal
expansion.

I HAVE to disagree with your statement that hanging a heatsink in the
air will do less damage than fixing the heatsink as securely as
possible. And, Flexing of the pc bd should definitely be avoided!

Success in electronics is the sum of lots of little choices, and
OFTEN the decisions involve conflicting needs! It is pretty easy to
get something electronic to work, but can be VERY difficult to get it
to work WELL! Especially this mixed analog/digital (relatively)hi-
current stuff we call CNC.

Net result is we have lots of "OK" choices, but very few "REALLY GOOD"
ones. Look at the response when someone "gets it right".(Geckodrives)

Ballendo

>the heatsink is mechanically mounted to the PCB with alloys spacers
>to reduce mechanical stress on the driver legs etc.

>Although this may reduce the stress caused by vibration (i.e. it
>steadies that huge resonant springy mass hanging off those poor
>little terminals), it can also *cause* stress as the heat sink and
>the device's leads undergo differential thermal expansion. I suspect
>that the latter stresses, which would typically be relieved through
>flexing of the PCB, easily exceed the stresses caused by vibration
>and the weight of the heat sink.
>Kevin Martin