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Old 2nd Jul 2019, 11:09 pm   #77
Lucien Nunes
Rest in Peace
 
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
Default Re: Bell and Howell TQII 1652 16mm projector

Quote:
B&H projectors could be supplied to special order with a 3 blade shutter for showing silent films,
A few 16mm machines, the Siemens 2000 certainly, possibly a Hortson model, had adjustable shutters. A dial within the inching knob of the Siemens rotates parts of the blades relative to the mainshaft. That projector also has infinitely variable speed, so you can adjust both the flicker and jerkiness to your own preference.

If you'll permit me a digression for the purposes of comparison, the projectors I am working with here in Estonia, have two different electronic methods of speed control. The Philips DP75 70mm mech has a 3-phase motor driven by a digital inverter, therefore theoretically programmable to any speed (although the sound follower, being digital, expects SMPTE timecode at a recognised frame rate). The Sondor Nova 35mm has a microcontroller-driven movement with separate stepper motors for all sprockets including the intermittent, also the shutter, allowing it to project forward and reverse up to 60fps and fast wind to 200fps without unlacing. Its timebase only generates certain integer frame rates so it is not infintely variable like the DP75. The significant difference compared to the OP's DC motor is that no actual tacho feedback is needed in either case since the drives are synchronous. The steppers are salient i.e. they have preferred positions that they take up with each cycle, while the 3-phase motor is hysteresis-synchronous - it runs up as an induction motor and when the slip is small enough, the magnetic poles in the rotor stop moving relative to the iron and it rotates with the flux vector (which, to be fair, the inverter does watch via the main windings).

How many other speed control / change methods have been used? Centrifugal governors, resistances, gearboxes (Dad's Victor sound-on-disc machine has two gearchange knobs, one for the film and one for the record), disc and idler, belt and stepped pulley... the B&H PWM seems rather sensible compared to some of them.

Last edited by Lucien Nunes; 2nd Jul 2019 at 11:15 pm.
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