Hello,
thank You for Your replies.

Yes, I was believing that I would get maximum force when fully activated,
but here's an example (one of the many) data sheet that is confusing me:
http://www.guardian-electric.com/pdf/TP12x13PushDCTubular.pdf

There's no graph but a table, but as You can see for strokes near zero it
reports big forces, for strokes extended to the full length it reports small
forces. It's a push type solenoid, so the full stroke is supposed to happen
when electrically actuated.

Yes, the linear actuator (DC motor) was the best candidate until now, but
I haven't found anything satisfactory. Moreover, although as I said I need
to actuate a motorbike brake pump, the application is different (I've to
push a plate and there are springs on it) so the force needed increases with
displacement.. seemed a good/natural thing to use a solenoid, and to simplify
the design (at first I wanted to use a DC motor with gearbox and a cam to
optimize maximum force generation only towards the end of the stroke, but
without a CNC machine all of this looks overkill.. and a solenoid looks so
simple!).

Of course electrical/mechanical efficiency is an issue.. I can get about 50%
efficiency with DC motors I think, but what about solenoids (used near the
full stroke)?

Cheers,
Mario

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