cassette deck mechanism with large diameter flywheel
 

Attached are the photos of a tape drive mechanism that was widely used in the middle-class Soviet tape decks. It seems quite unusual, using a heavy large-diameter flywheel (implying a 220V motor taken from a reel-to-reel machine). The only idler is used for playback mode; in forward/rewind mode, corresponding pulleys are pulled a little bit back and come into direct contact with the flywheel, resulting in a very noisy (and sometimes tape-tearing) but rapid rewind. My sources claim that this is not an own development and that it was hugely inspired by one of the SONY decks; however, I was not able to find anything like it. Has anyone seen a similar mechanism? I would be very grateful to see an original implementation of this idea.

Re: cassette deck mechanism with large diameter flywheel
 

I think various companies used AC motors for their earlier mains only powered decks: Sony, Akai and Pioneer to name three.

An interesting feature in this one is that what looks like a metal take up spool idler seems to gain its traction by riding directly on the rubber flywheel belt. I've not seen that before.

Re: cassette deck mechanism with large diameter flywheel
 

Clarification: the idler seems to connect with the belt as the belt is wrapped around the flywheel. Not necessarily the best way as there would be only a small surface area of contact between idler and belt. More common for the belt to "wrap" around the idler for better grip.

Re: cassette deck mechanism with large diameter flywheel
 

The Wollensak mechanism had a large flywheel, AC motor and rewind by idler pressing against flywheel. Used in Wollensak, Advent and NEAL decks amongst others. Actually works very well, if rather "agricultural".

Re: cassette deck mechanism with large diameter flywheel
 

Probably a similar heavy duty setup was used in their high speed cassette AV 2770 duplicators. Unfortunately a good overall design marred by the reel tables with their integral felt and plastic clutches which tended to increase in torque over time, leading to damaged tapes.

Re: cassette deck mechanism with large diameter flywheel
 

As Tim says, synchronous AC motors were used in most early Japanese HiFi decks. DC motors only became common in about 1977.