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Motor Speed Control

My phase-shifted 60 Hz tape drive thing worked pretty well, for the time. I used a few triacs to get stop/fwd/reverse. One phase of the stepper was raw 60 Hz from a transformer, and the other phase had a series R+C to get a 90 degree phase shift. We tweaked the RC to get the smoothest rotation.

I've done a fair number of stepper drivers, like the ones to tune the superconductive cavities at CEBAF, but I've never driven, or seen, a VR type.

Aerospace people like to use "torque motors", which are basically big VR steppers.

Reply to
john larkin
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Nonsense. The cheap way of making an approximation to a sine wave is pulse width modulation.

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That document is from 1997, but the idea has been around for a lot longer. I used it in 1975 - if not to make sine waves - and it is cheap and efficient. The "modified square wave" - which has no third harmonic content - is equally old.

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Reply to
Bill Sloman

Motors run hotter than their environment

It was one-time programmable, not an EPROM.

CMOS was around and cheap. I'd first used it around 1975, and the price fell by a factor of three as I was developing the 1975 circuit.

The stepper motor circuit that I worked on was developed in 1978.

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Reply to
Bill Sloman

With only 50-100mW being consumed by the motor (10's of mA at 3-6V) the temperature differential was small.

If it was NMOS it was almost certainly an EPROM in a cheaper package without the quartz window.

Reply to
KevinJ93

But it was lot bigger inside the motor than you could detect from outside it.

Perhaps. It was 46 years ago.

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Reply to
Bill Sloman

Are EPROMs obsolete now? I assume they must be or we wouldn't have USB drives and SD cards etc.

Reply to
Cursitor Doom

EPROMs are obsolete, but they were replaced by electrically erasable PROM.

USB cards and SD cards do the same job, but they cost more and take up more space on the board - if you don't need much programmable memory an EEPROM can be big enough.

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Reply to
Bill Sloman

I know, that's why I said that the 2708 series were the first convenient to use ones with a single power supply.

Although an EPROM, some equivalent parts were available in a cheaper package without a window - they were one-time programmable.

kw

Reply to
KJW93

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