Losing Communication

[derekgirven]

Hi,
Just a though we have had a lot of problems with our machines loosing contact to the port . try split the power lines going to your spinal and box to separate isolater on your db board. some how I was getting feed back (don't as me how). i.e plug one into another socket. may work for you too.

[dana_swift]

Bob- sorry I just noticed your question regarding "what is a USB isolator?"

I will start out with what is USB?

USB is a bi-directional serial data system with several capacities, the system automatically adapts to the slowest capacity device. It also provides some limited power to run things that dont need much- like thumb drives, small hubs, etc.

Now what is an isolator?

An isolator acts like "wire" with no physical electrical connection from one side to the other. So anyone would reasonably ask- how do you send power across such a thing? Answer: good old transformers. Well really modern high-tech transformers, RF transformers instead of 60hz transformers. The power capacity of an isolator is approximately 95% of the original capacity of the computer it is plugged into. In a nutshell - plug it in and dont worry about it.

So- how does data get across the "gap"? - optical isolation. Data going each direction drives LED's that get connected to photo-detectors on the other side. No electrical connection.

Since power is transferred from one side to the other, the isolator only works when the power source is on one side (the male usb plug) and can only provide power on the other side (the female usb plug).

And that last little thing- signaling the capability of each side to the other- that is done with optical isolation also.

What you end up with is a USB cable that can tolerate very high voltages from one side to the other. Usually over 1000 volts before the system fails catastrophically. Some isolators are over 3000 volts, then I wouldnt want to be working on a computer with 3000 volts on the other side of that little cable would you? I dont even want 50 volts..

How much differential ground voltage can USB take with standard cables? Conceptually none, but in reality about 0.75 volts. How much can old fashioned RS232 serial tolerate? About 7 volts. Thats a factor of 10 difference, where the "new and improved" serial system is not as tolerant as the old serial system. Both of which were designed based on the assumption that there was no ground differential voltage between the sender and the receiver.

When I was at Tim's shop, I measured the ground differential voltage - which was usually around 0.005 volts, with a maximum of 0.025 volts or so during air cuts. We did not cut anything so no dust was going through the ductwork which can change that 0.025 to a much higher number.

What I was checking for is ground loops, that was clearly eliminated as a problem source. That leaves two suspects- Windows 8 and dust collection static. Tim has tried another computer without any change in reliability so that leaves us with dust collection static buildup.

An isolator might help with that problem, but its a shot in the dark.

Good news is USB isolators can be purchased for under $50 on Amazon.

Now to deal with the real problem- static charge in the dust collector. For that, I am devising a meter to read how much static we have. Then I intend to try different things to lower it, and rather than just guess how effective each possible solution is, I intend to measure it and remove the guesswork.

Hopefully that is a full answer on USB isolators, and how it pertains to this installation.

I will now rotate my hat back from "electrical engineer" to "woodworker".

D

[Joe Porter]

My head hurts, I think I'll go lie down....joe

[Ken Sully]

Tim,
I have been following the forum for a while and looking forward to my first shopbot next spring. I was in the x-ray business for many years and chased grounding issues and ground loops. I have attached an article you may find useful.
Ken

[CantologyLLC]

First post - been lurking for too long. Seems a good place to pipe in. Been running my Desktop hard for over a year with intermittent comm problems. Followed all the usual advice and problems have become much less frequent. But last Saturday morning I had three nasty glitches - all the same: caused bot to lose track of X axis, shut off the router, but kept driving! Tore the material off my vac table pulling 24"hg! Not pretty. Couldn't think of anything else to do to combat this ambush of my day. So I installed the latest beta, which I had heard has more robust comm. No problems since. And I love the new interface. But I don't see the beta discussed anywhere on the forum. Am I missing something?
-Will

[Bob Eustace]

Thanks for the excellent explanation Dana. Does going optical reduce the speed at all do you know? If isolated USB only has one port what do you do with the spindle USB? Sorry for all the questions! Cant wait for you to perfect your static measuring gadget.

[dana_swift]

Bob- the speed of opto-electronices "can" be extremely fast. There is nothing inherently speed limiting about the optical isolation technique.

The person designing the isolator must choose appropriate parts to avoid speed issues, and to achieve efficient power transmission, etc. Nothing is automatic. As consumers, all we can do is buy something and hope the designer did their homework.

Fiber-optic communication is just a long distance form of optical isolation. The speeds they achieve with fiber optic data are just amazing. USB does not run anywhere near that fast, so the presence of the isolator "should" be transparent. I dont recommend blindly putting them in the system, but its worth a try if a problem shows up. They just plug in, so its real easy to unplug and remove them.

For what its worth, I am presuming the hub is next to the computer, and the isolator would be inserted in the cable from the shopbot that plugs into the hub.

If several people try isolators, it will be interesting to post some info on how it is affecting their USB speed test, and any other results they may be noticing. Any takers?

D

[adrianm]

First post - been lurking for too long. Seems a good place to pipe in. Been running my Desktop hard for over a year with intermittent comm problems. Followed all the usual advice and problems have become much less frequent. But last Saturday morning I had three nasty glitches - all the same: caused bot to lose track of X axis, shut off the router, but kept driving! Tore the material off my vac table pulling 24"hg! Not pretty. Couldn't think of anything else to do to combat this ambush of my day. So I installed the latest beta, which I had heard has more robust comm. No problems since. And I love the new interface. But I don't see the beta discussed anywhere on the forum. Am I missing something?
-Will

You have to apply to join the beta forum. Discussing the beta releases on the main forum is not encouraged.

See the beta notes on the page you downloaded the beta from.

[Brady Watson]

So I installed the latest beta, which I had heard has more robust comm. No problems since. And I love the new interface. But I don't see the beta discussed anywhere on the forum. Am I missing something?

Will - Welcome to the forum & thanks for joining in. The beta control software doesn't get as much attention and interest for the average user. The latest beta certainly brings a lot of new functionality and a revised look to the interface. There are a number of specialized enhancements that you can read about when you install it or via the SB main site beta section.

There is no secret handshake or special beta forum area for discussing the beta version of SB3. So feel free to talk about it all you want. I'm afraid the SB3 beta isn't quite as anticipated as the Vectric releases

You have to apply to join the beta forum. Discussing the beta releases on the main forum is not encouraged.

See the beta notes on the page you downloaded the beta from.

You are on the ShopBot Forum. The Tardis is translating for you. Do you know many fingers am I holding up?

-B

[Bob Eustace]

Brady this is a fascinating thread! This problem seems to affect all model Shopbots, so to the layman, (read - dumbell) the problem would appear to be the computer driving them? Does the answer lay in sticking a USB stick directly into the bot bypassing all the unknowns? Could this be made a retrofit option? Have been comms error free until I read this topic yesterday - first time we had ever cut blackwood. Weird how it always happens on jobs where you havent used C3 and have been tooooooooo lazy to write down the start co-ordinates!

A wonderful winter pastime for Dana could be to write a little routine that plonks this info in a separate file?????