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From: KevinJ93 <kevin_es@whitedigs.com>
Newsgroups: sci.electronics.design
Subject: Re: Motor Speed Control
Date: Sat, 9 Mar 2024 14:56:43 -0800
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On 3/8/24 8:42 PM, Bill Sloman wrote:
> On 9/03/2024 5:49 am, KevinJ93 wrote:
>> On 3/7/24 8:48 PM, Bill Sloman wrote:
>>> On 8/03/2024 7:13 am, KevinJ93 wrote:
>> ...
>>>>
>>>> Not in 1970. Even after that time they did not possess any advantage 
>>>> over DC motor drive with speed stabilization based on back-emf.
>>>
>>> Don't be silly. Back-emf depends on the strenght of the magnetic 
>>> field generating the basck-emf, and that is temperature dependent.
>>
>> At about 0.2% per deg the magnetic field strength stability was 
>> adequate for the speed accuracy required under the required 
>> environmental conditions.
> 
> Motors run hotter than their environment

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

>>> Synchronous motors rotate at a rate that reflects the stability of 
>>> the frequency source that determines the drive frequency, and 
>>> reasonably stable frequency source - watch crystals have been around 
>>> for ages.
>>
>>>> Even for AC powered units where power was not an issue stepper 
>>>> motors were never used. Synchronous motors with synthesized drive 
>>>> were occasionally a feature but many/most used back-emf 
>>>> stabilization with DC motors.
>>>>
>>>> ICs were available to integrate that circuitry:
>>>>
>>>> eg https://www.precisionmicrodrives.com/ab-026
>>>>
>>>>>> Even implementing the discrete drive electronics would be more 
>>>>>> costly than necessary at a time where individual transistors were 
>>>>>> a significant cost; Philips' solution used two transistors - 
>>>>>> creating a divide by 4 plus driver transistors plus an oscillator 
>>>>>> would probably require about ten transistors plus numerous other 
>>>>>> components.
>>>>>
>>>>> Which you could could buy in an integrated circuit. Most of mine 
>>>>> were in a chunk of PROM.
>>>>
>>>> Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all 
>>>> your power budget.
>>>
>>> It didn't - and it wasn't bipolar.
>>
>> MOS EPROMS such as the 1702 were cumbersome to use with multiple 
>> supplies required. 
> 
> It was one-time programmable, not an EPROM.

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

>> The logic to drive them would have been TTL consuming significant 
>> amounts of power as well as expensive.
> 
> 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 first EPROMS that were easy to use, such as the 2708 weren't 
>> widely available till the late 70's.
> 
> The stepper motor circuit that I worked on was developed in 1978.
> 
> <snip>
>