Re: [time-nuts] Control Systems (was: uC ADC resolution)

[Bob kb8tq]

Hi

> On Jun 11, 2017, at 2:21 PM, Chris Albertson  
> wrote:
> 
> On Sun, Jun 11, 2017 at 9:28 AM, Attila Kinali  wrote:
> 
>> Hi,
>> 
> 
> 
>> 
>> You are asking a lot of question regarding control systems.
>> But, there are no easy answers there. Especially if you want
>> to build it cheap. The cheaper you want to be the more you
>> need to know and understand the problem.
>> 
> 
> This has been my opinion for a LONG time.  It is easy to come up with good
> solutions if to just throw money at the problem.So you see here people
> proposing just going top of the line all across but an engineer earns his
> money
> by comping up with cost effective solutions that meet all the stated
> requirements.
> 
> This is my interest in mechanics too.  Can a $200 3D printed plastic robot
> arm
> with poor absolute repeatability place an M6 screw into an M6 nut?
> Certainly
> not if it runs open loop.  But what if you add visual feedback?
> Yes everything requires more expertise if you reduce the budget
> 
> So you understand my questions are all like this:  "If you back down from
> top of the line solution how does that effect real world performance?"
> No one answers.
> 

Would it help if each and every time we answered “that depends”. This is always
the real answer to any real world engineering problem. Quantifying and 
qualifying 
*all*  the dependencies is what people get paid to do for a living. There is 
*always* 
both theoretical and experimental work involved. There is never a simple one 
line 
answer. If you want the more detailed answer, start digging into it. Try this 
and that.
Measure what you see. Report your results and we’ll help you analyze them. 

Often this spirals instead into a game of liars poker. I can do it for $100, he 
can do 
it for $10, somebody else can do it for $1, the next guy is at $0.10 and we are 
at
$0.01 in no time. There is no data, not qualification of anything, just a bunch 
of random
cost numbers. That’s not how things work on any real design I’ve ever seen. Raw 
cost per unit, 
time / cost to implement, margin requirements,  volume of production, and 
performance 
are all tightly related  to each other. Until you nail all that down, talking 
about a price 
per unit does not make any sense.  

As an example, we are talking here about OCXO’s. Can you build a ten cent OCXO? 
Sure 
you can. It only takes a well stocked junk box of “free” parts. Can you spend a 
few years 
tweaking the one uint for performance, indeed yes again. Is it still a ten cent 
OCXO after you 
spend a year of your time tweaking it?  Would you sell someone a year of your 
time for ten cents? 
Would you build, test, and sell somebody a thousand of them for ten cents each? 
 

Bob


> 
>> 
>> I suggest you reading an introductory text into control systems
>> like e.g. "Feedback Control of Dynamic Systems", by Franklin, Powell,
>> Emami-Naeini.
> 
> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] Control Systems (was: uC ADC resolution)

[Attila Kinali]

On Sun, 11 Jun 2017 11:21:15 -0700
Chris Albertson  wrote:

> This has been my opinion for a LONG time.  It is easy to come up with good
> solutions if to just throw money at the problem.So you see here people
> proposing just going top of the line all across but an engineer earns his
> money
> by comping up with cost effective solutions that meet all the stated
> requirements.

Yes, I have done plenty of that. If the production run will be >100k
then it's well worth spending a month or two to shave off 1€.
But on a small volume project, or even worse a one-off project,
I am not going to try save 10€ if I that would cost me a day of reading
and doing calculations.

> So you understand my questions are all like this:  "If you back down from
> top of the line solution how does that effect real world performance?"
> No one answers.

Because there are no easy answers. What you are asking requires
someone sitting down and do the math (or simulations) and figure
out what the limiting parameters are, when restricting the design
in this or that way.

To give this a little perspective:
For one of my many side-projects, I do need an DAC with a very
high resolution (>23bit). It took me a few days to figure out that I
really need this resolution and cannot do with anything lower. I have
probably poured another 3-4 (man)weeks just calculating and simulating
different designs that looked promising enough to deliver the needed
performance. I have settled on two designs I want to try, but I am
still reading up on different issues and refining the design for those.
I guess it will take me another (man)month or two until I a can say
with confidence that the design is good, will with high probability
deliver the performance I need and there are no easy ways to improve it.
And then I will start the implementation (ie schematics, layout and software).

Like you asked for your temperature control loop, I could have asked
how to build such a DAC. But I would not have gotten any answer.
Because there simply isn't anyone who knows the answer. At least not for
a design with my constraints. If you read carefully what I have asked
on time-nuts and volt-nuts in the last half year or year, you will find
quite a few of my questions relate to this project in some way or other.
Questions on how to do this or that. Questions on whether X is possible
or not and if yes, under what conditions. To some questions I got answers,
to others I didn't. If I didn't get an answer, I knew that the question
is difficult and tried to read up on it as much as I could manage.

I do not know, whether it does look like answering questions on time-nuts
is easy. At least for me it isn't. I came here 10 or 11 years ago.
For over a year I didn't write anything, but just read. Then I ventured
my opinion on things I thought I knew and started asking small questions
here and there (if you want to have some fun, go back and read what I
wrote 8-9 years ago... I was sooo naive...). In the meantime I continued
reading up on different things as time allowed. It really took me full
10 years to reach the level I am at now, but I still do not know anything.
My knowledge is full of holes and things I think I understood but didn't
(the construction of the E1938 is a nice recent example of that). There
are whole areas I have no clue about at all (e.g. how to build low noise
oscillators, or how ADEV, MDEV & co actually work) and I know it will take
me years to gain a sufficient understanding of those. Answering, even simple
questions, can take me easily half an hour. I often have to go back to my
documents and paper collection to check things, as I am unable to remember
everything in detail. Then writing a (hopefully) intelligeble answer is
also something that shouldn't be underestimated.

Hmm.. this ended being up longer than I intended it to be. Sorry about that.
But I hope I made my point clear. If not:

TL;DR: Some questions are just difficult and need someone to sit down
and think hard before they can be answered.

Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Control Systems (was: uC ADC resolution)

[Chris Albertson]

On Sun, Jun 11, 2017 at 9:28 AM, Attila Kinali  wrote:

> Hi,
>


>
> You are asking a lot of question regarding control systems.
> But, there are no easy answers there. Especially if you want
> to build it cheap. The cheaper you want to be the more you
> need to know and understand the problem.
>

This has been my opinion for a LONG time.  It is easy to come up with good
solutions if to just throw money at the problem.So you see here people
proposing just going top of the line all across but an engineer earns his
money
by comping up with cost effective solutions that meet all the stated
requirements.

This is my interest in mechanics too.  Can a $200 3D printed plastic robot
arm
with poor absolute repeatability place an M6 screw into an M6 nut?
Certainly
not if it runs open loop.  But what if you add visual feedback?
Yes everything requires more expertise if you reduce the budget

So you understand my questions are all like this:  "If you back down from
top of the line solution how does that effect real world performance?"
No one answers.


>
> I suggest you reading an introductory text into control systems
> like e.g. "Feedback Control of Dynamic Systems", by Franklin, Powell,
> Emami-Naeini.




-- 

Chris Albertson
Redondo Beach, California
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