Re: [Emc-users] 3D Printed L Type Timing Pulleys

[marcus . bowman]

On 2021-01-02 06:53, John Dammeyer wrote:

I have noticed the 3D
printed pulleys are noisier than the metal ones.


I wonder whether that is because the surface of the teeth will 
inevitably be rougher than if they had been die-cast or machined?



But the noisy grind
of the stepper motor is also gone.


Got to be a bonus.


More when it's wired up to LinuxCNC.


Looking forward to that. Following this topic with interest.

Marcus



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Re: [Emc-users] Chinese VFDs with good reputations

[Dave Cole]

Thanks for the tip on HuanYang!

Dave

On 12/30/2020 2:49 PM, Eric Keller wrote:

On Wed, Dec 30, 2020 at 1:20 AM Gene Heskett  wrote:


Most are HuanYang, and decent, reliable stuff. I'm using 2 of them.


 From what I can tell, most of the HuanYang vfd's on ebay are copies.
HuanYang uses a module for the high power stage, most of the cheap ones are
using discretes.

They have a store on Amazon, but don't list the models that have a braking
resistor for some reason.  I guess it's better go go direct with them.
Eric Keller
Boalsburg, Pennsylvania

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Re: [Emc-users] hy_vfd vs crc errors running at 38400 baud

[Gene Heskett]

On Friday 01 January 2021 12:24:55 John Dammeyer wrote:

> > -Original Message-
> > From: nk@nksb.online [mailto:nk@nksb.online]
> > Den Fredag, Januari 01, 2021 06:03 CET, skrev Chris Albertson
> > : �I don't know much about RS485 but I
> > did read that the current return path is required. You should be
> > able to send and about 100K up to 4000 feet.
> >
> > RS-485 use differential signals, currents flowing in differention
> > directions so return path is in the other conductors. A termination
> > is needed, should be easy to find how it should be made ib internet
> > once you know it's needed.
>
> As Dan stated RS485 changes the polarity of the signal so current
> flows from Pin A to Pin B for one logic level and from Pin B to Pin A
> for the other.  Unlike CAN bus, a ground is _not_ needed.
>
> But there are several rules to follow.  One of them is the impedance
> of the cable should be in the neighborhood of 100 Ohms.  Using 50 Ohm
> cable is pushing it.
>
> The cable, with twisted pair is a transmission line and as such needs
> to be terminated across the A,B pins with a resistor that matches the
> cable impedance.  So a 50 ohm cable needs a 50 Ohm resistor at each
> end.  That's a parallel combination of 25 Ohms load plus the 2x 12K
> receiver input impedance.  For now forget the input.
>
> Differential output from the TI SN75176 data sheet at 54 Ohms is
> Typically 2.4V.  So 2.4/54=44mA.
>
> Now use two 50 Ohm resistors and 2.4V/25 Ohms = 96mA which exceeds the
> maximum drive current.  Assume the low output voltage of 1.7V/25 Ohms
> and you get 68 mA which is still 8mA above max.
>
> If you don't use 50 ohm resistors on 50 Ohm impedance cable then you
> get reflections from the edges of the data signals.  Again, might not
> be a big deal on a short cable or even a long one.  But the right
> combination of 1's and zero's might well create a travelling wave that
> randomly distorts the signal with no repeatability or possibility of
> testing.
>
> I suggest finding a piece of cable that is rated at 100 Ohm or 120 Ohm
> impedance (twisted pair) and using that with proper resistors at each
> end.
>
> Say you google "shielded twisted pair cables" and chose the link for
> the Beldon 9451.  Seems pretty good from the Digikey spec list except
> they interestingly don't list the impedance.  For that you need to
> download the Beldon data sheet and there you find the characteristic
> impedance is 45 Ohms.  That' pretty typical.
And TBT, shielding is not required for such a twisted pair, PARTICULARLY 
when the shielding over-wrap is calculated into the cable impedance 
because the added capacitance can easily cut the impedance by at least 
50%.  Commmon flat ribbon cable is a good example, with every alternate 
wire a ground, its impedance for the ire between those grounds is in the 
130+ ohm range. Put the 9451, which essentially twists and shields the 
same 2 wire pair, and you get that 45 ohms. In a broadcast facility with 
audio buses extended from the DA output, looking at the usual 600 ohms 
load each devices audio input is terminated with, and you've just 
designed a heck of a good lowpass filter. We like to keep stuff up to 15 
kilohertz in our tv audio.  But due to the missmatch, 200 feet of 9451 
cable is down over 12 db at 15 kilohertz at the other end of that cable.  
So I designed an audio DA with a high power output swing of the + and - 
15 volt supplies, and source terminated it with 47 ohm resistors and had 
one of my more technical operators build it. Sounded noticeably better, 
but 22 such cards in a 4 unit high rack sure made a good control room 
heater. And since the control room was in the middle of the building, I 
had a hell of a time convincing the AC service techs that I could care 
less if it was 20F below outside, that air conditioner absolutely HAD to 
run 100% of the time. I found one tech that knew how to fix it, he 
ordered special fan motors that could be speed controlled, and found a 
modulator that turned the outside condenser fans down to about 30 rpm in 
really cold weather. That kept the condenser coils hot enough that it 
worked just fine. But he went to greener pastures, and the next guy was 
a ducking fummy and tore it all out when I wasn't looking. I taught my 
replacement about those finer details, and retired in 2002. Then came 
digital and a brand new tech room was built, sharing an outside wall 
with the building. And that simplified the air conditioning needs.

> Now add 100 Ohm to the search "shielded twisted pair 100 Ohm cables"
> First hit is for 9501.  You have to look carefully to see it's 75 Ohm.

That 75 ohms means its still shielded, you did specify it. This stuff on 
the amazon usb-485 cable is not, no foil or drain wire in sight so I'd 
hazard a SWAG at 90+ ohms, maybe even 100+ ohms, not too bad IOW.   In 
other words, twisted is good, but get rid of the shielded requirement in 
your cabling search. Take a lesson from ma Bell and let the 

[Emc-users] Logging AXIS messages.

[John]

Are the pop up messages at the bottom RH side of AXIS display logged anywhere?

Sent from John's iPhone 4S

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Re: [Emc-users] hy_vfd vs crc errors running at 38400 baud

[John Dammeyer]

> -Original Message-
> From: nk@nksb.online [mailto:nk@nksb.online]
> Den Fredag, Januari 01, 2021 06:03 CET, skrev Chris Albertson 
> :
> �I don't know much about RS485 but I did read that the current return path
> is required. You should be able to send and about 100K up to 4000 feet.
> 
> RS-485 use differential signals, currents flowing in differention directions 
> so return path is in the other conductors. A termination is
> needed, should be easy to find how it should be made ib internet once you 
> know it's needed.
> 

As Dan stated RS485 changes the polarity of the signal so current flows from 
Pin A to Pin B for one logic level and from Pin B to Pin A for the other.  
Unlike CAN bus, a ground is _not_ needed.

But there are several rules to follow.  One of them is the impedance of the 
cable should be in the neighborhood of 100 Ohms.  Using 50 Ohm cable is pushing 
it.  

The cable, with twisted pair is a transmission line and as such needs to be 
terminated across the A,B pins with a resistor that matches the cable 
impedance.  So a 50 ohm cable needs a 50 Ohm resistor at each end.  That's a 
parallel combination of 25 Ohms load plus the 2x 12K receiver input impedance.  
For now forget the input.

Differential output from the TI SN75176 data sheet at 54 Ohms is Typically 
2.4V.  So 2.4/54=44mA.  

Now use two 50 Ohm resistors and 2.4V/25 Ohms = 96mA which exceeds the maximum 
drive current.  Assume the low output voltage of 1.7V/25 Ohms and you get 68 mA 
which is still 8mA above max.

If you don't use 50 ohm resistors on 50 Ohm impedance cable then you get 
reflections from the edges of the data signals.  Again, might not be a big deal 
on a short cable or even a long one.  But the right combination of 1's and 
zero's might well create a travelling wave that randomly distorts the signal 
with no repeatability or possibility of testing.

I suggest finding a piece of cable that is rated at 100 Ohm or 120 Ohm 
impedance (twisted pair) and using that with proper resistors at each end.

Say you google "shielded twisted pair cables" and chose the link for the Beldon 
9451.  Seems pretty good from the Digikey spec list except they interestingly 
don't list the impedance.  For that you need to download the Beldon data sheet 
and there you find the characteristic impedance is 45 Ohms.  That' pretty 
typical.

Now add 100 Ohm to the search "shielded twisted pair 100 Ohm cables"
First hit is for 9501.  You have to look carefully to see it's 75 Ohm.  

There are other brands.  

John Dammeyer




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Re: [Emc-users] hy_vfd vs crc errors running at 38400 baud

[nk@nksb.online]

Den Fredag, Januari 01, 2021 06:03 CET, skrev Chris Albertson 
:
 I don't know much about RS485 but I did read that the current return path
is required. You should be able to send and about 100K up to 4000 feet.

RS-485 use differential signals, currents flowing in differention directions so 
return path is in the other conductors. A termination is needed, should be easy 
to find how it should be made ib internet once you know it's needed.

I'd use a section of Eithernet cable because I know it is twisted inside.
I don't know the best way to provide a "return path for all voltages"

Pretty sure it's a very good cable, just make sure the differential signal 
pairs are twisted. Used a PLC with RJ-45 connectors for RS-485 communication, 
there might be a standard way to assign pins then using RJ-45 connectorts, I 
know there is for other connectors.

If this is going through optical isolators,I see a problem the signal
voltages are like RS232 −7V to +12V. The optos are going to do 0 to 5
volts with is usually very marginal.

Your isolators are builtin into som hardware you use? Otherwise I might be able 
to recommend other isolator technology I found worked well, do not manufacture 
semiconductors and have no interest to sell them.

On Thu, Dec 31, 2020 at 8:05 PM Gene Heskett  wrote:

> On Thursday 31 December 2020 20:10:35 Chris Albertson wrote:
>
> > Now is the time to connect the digital scope and see what is actually
> > on the wire. Is the data bad or is the receiver unable to read good
> > quality 38400b data?
> >
> > This is differential data, it should be able to go half a kilometer or
> > something like that. Is it actuary using a twisted pair of wires and
> > is there a good logic ground?
> >
> That I doubt. Its a 2 wire cable, so any logic ground is coming thru
> other cable from the 5i25, thru the interfaceing and back to the ACM
> terminal. DCM could be grounded but is not, and everything on that
> circuit isvia the opto's isolating the spindle outputs of the 7i76D.
>
> That stuff is still hooked up, but could be disconnected as its no longer
> actually controlling the motor. There does not appear to be a ground
> reference for the rs485 signals called out in the sample wiring diagram.
> There is an earth ground in addition to the 2 wire single phase input,
> and its connected back to the static ground in the service box.
>
> > It's easy to see if the cable is the cause. look at the bits on the
> > cable end, then remove the cable and look at them in the output port.
>
> The only way I can access that would be to back the pins out of the term
> strip far enough to put the scope probe hook onto the Hilitchi pin. The
> scope is plugged into a different circuit entirely, so its ground
> reference is bound to have some noise on it. I can set the scope to
> combine the 2 signal wires into a differential, but having done that,
> the serialization of the samples quantizations can easily be seen. I
> should probably do that, if for no other reason than to confirm the baud
> rate matches going both ways. I have previously caught the pc lying
> about the actual baud rate its generating. Depending on the individual
> driver, it might be fixeable but haven't tried. From an lsmod:
> usbserial 31410 3 ftdi_sio
> and I've not had previous experience with the ftdi_sio being off.
>
> Since the lags can be gotten used to, I might just leave it at the slower
> speed as that seems to be bulletproof so far.
>
> Thanks Chris. And a Happier New Year to all.
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> If we desire respect for the law, we must first make the law respectable.
> - Louis D. Brandeis
> Genes Web page 
>
>
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--

Chris Albertson
Redondo Beach, California

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