"Larry" wrote in message
Oops....I forgot to mention a problem with DC motor driving with this
latch. DC commutator motors don't draw current through the whole
rotation, just when the commutators make contact. So, you'll be feeding
pulsating DC to the SCR, which WILL ASSUREDLY make it unlatch!

Actually, most (maybe all) DC, conventionally commutated motors have
brushes wide enough, and commutator segment spacing narrow enough that that
they work, as some say, "make before break". Otherwise,
there would be many rotor positions where the motor would not start. (we all
have experienced that with burned commutators, no?)
My newest DC pump motor has no shaft, no armature, no brushes, no shaft
seals (and not much power). Fellow in Florida makes them. Rotating magnetic
field coupled to a floating magnetic impeller inside a bronze housing. Pumps
solar heated water in my experimental mini-greenhouse up here in the Pacific
Northwest. Rain, rain, go away!
Old Chief Lynn