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noel shelley06/11/2021 11:39:07
1278 forum posts
21 photos

Time moves on and so now we have the the VFD with all it's features and faults. But before that, back in the early 70s was the TASC unit made by PYE electric. It was a coupling unit, the motor would run at it's rated speed, the unit did the rest ! You could control the output speed or the output torque and countless combinations of the two. So for example machining a piece on the lathe, as the diameter reduced the speed would increase to maintain surface or cutting speed. The electronics were quite clever but simple. Has anybody seen one or got one ? Noel.

Andrew Johnston06/11/2021 12:00:49
6574 forum posts
701 photos

Never heard of them, but a quick search shows that they are still for sale in the US. It seems that they don't control the motor directly, but add an eddy current clutch on the motor output which can be controlled for speed or torque. So not as flexible as a VFD but presumably intended to maintain speed/torque on varying loads such as pumps and fans.


Michael Gilligan06/11/2021 12:04:26
20057 forum posts
1040 photos

A quick search on Espacenet gives two very promising results:



Bo'sun06/11/2021 13:29:06
602 forum posts
2 photos

Not sure if I've got the spelling right, but I seem to remember from my days in manufacturing, something called a "Kopp Variator" that did a similar thing. If I recall, it was to synchronize conveyor speeds.

Howard Lewis06/11/2021 14:29:56
6005 forum posts
14 photos

A variator sounds like the purely mechanical set up where there is a belt carrying the drive between two cone pulleys, with interleaved faces, whee one was adjusted to give the required output speed.

One such application was on Hartridge Majestic Injection pump test machines.

The Dafmatic car transmission worked on the same principle.


noel shelley06/11/2021 14:53:52
1278 forum posts
21 photos

I was briefly employed in this department in 1970, I was taken on I fancy as a favor to our apprentice officer. After 3 months of boredom I left ! The basic unit is as Andrew has said, the clever bit was the application. One was the application of spooling nylon thread, where the thread was fed through an eye on a lever that controlled a pot, IF the lever dropped due to the thread being slack the spool would speed up, If the lever was to high it would slow down to avoid breaking the thread. As the spool filled it would slow down the RPM. About 6 months after I left the department closed down. Noel.

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