Re: Through the mount USB3.0 on Mach2 trouble unrelated to temp


Howdy Micheal,

I gave your video a watch. What you are seeing is essentially data dropping in the USB cable. This is because the cable length is simply too long for such high speed communication. To put it simply, you are right on the verge of a perfectly working connection, so the data is intermittent. 

I saw this a lot in testing, whenever I used only cable between my laptop and hard drive or camera. If I linked three unpowered, passive cables together the setup would only work properly when the cable length was below 2 meters. As is, your cable length is nearly 3 meters. While USB 3.0 technically has no length limit spec, it almost never reaches more than 3 meters without some kind of repeater. 

To make your setup work, you need to either:

  1. Get shorter cables between the camera, mount and computer
  2. Use an active cable between the computer and mount
  3. Use a powered, USB hub at the base or top of the mount along with shorter cables. 
Otherwise, your setup will keep giving you these errors. I promise that this error is not caused by a mechanical issue in the cable, because if there was any kind of problem you wouldn't have been able to recognize the device in the first place. USB 3.0 is too finicky to work on damaged cables. 

Liam Plybon

From: <> on behalf of Micheal Fields Jr via <mpfjr@...>
Sent: Wednesday, January 13, 2021 12:16 PM
Subject: Re: [ap-gto] Through the mount USB3.0 on Mach2 trouble unrelated to temp
HI Terri,

Not sure if you just skimmed my post and didn't watch the video but I went through all of that in my testing point for point.  There should be two contact points in the Mach2.  One at the base of the mount and one up near the saddle plate.  Roland says the length of that cable is about 18 inches.   I bought a 3 foot female/female cable to duplicate the mount cable but on the outside.  This cable also has two contact points.   Simply swapping that "pretend" internal cable solves the problem completely.  I also have a computer that sits currently on the eyepiece tray of my tripod and has a short cable going to the mount.   I also tried to put a powered industrial USB hub between that computer and the mount just in case the USB port on the PC was weak.  Made no difference.  Then at the saddle I have a 3 foot cable going to the hub which is another industrial powered 4  port hub.  
There is no getting around it.  The internal cable has something wrong.  Not wrong enough that some devices won't work but wrong enough that when reaching to a higher point it can't remain reliable. If I had found that it must be flaky drivers for the camera or under powered hubs etc, then that is one thing but if I just swap the cable and it works as it should then it is not signal loss related to what I am doing.  Give my video a look if you have time.

On Wed, Jan 13, 2021 at 06:44 AM, Terri Zittritsch wrote:
Michael, I dealt with this, being one of the first Mach2 users, and evidently the first one to try usb3.   The issue is likely all of the signal loss due to the number of connectors between your computer and hub, especially including those inside of the mount.     I identified the initial USB3 issue (turned out to be crossed USB3 wiring) and had to send the mount back for rewiring. Given I'm an EE in the custom semiconductor business, I have some peripheral knowledge of the limitations of USB3, so it makes sense to me.   
This was solved with an active repeater cable (it was for me) and I tested all kinds of cable lengths and ultimately I was limited to a 3' cable between the mount and my computer plus 1' cable between dec axis output and hub for reliable operation (which isn't acceptable for me).   I now have a 15' repeater cable with a small 8" cable from the repeater head (which is female) to the mount (male-male usb3 cable).    Then I use a short cable on the DEC head USB port to my cheapo hub.   My cheapo hub works fine to 0F and doesn't miss a beat.  While some vendors specify all kinds of industrial specifications for various expensive hubs, they likely have the same silicon inside of them.  They may have some better environmental sealing so if that gives some peace of mind, which is ok if you need it.   My hub is so cheap I've just purchased a spare and bring it when traveling.    So this works for me and I use several ZWO cameras, although I have a new 60MP camera that I've not tested yet.  But it works for an ASI071, ASI290, ASI1600MM.    I also confirmed that none of this had anything to do with the hub itself, because the same results could be had when bypassing the hub entirely as well as bypassing the mount pass through.    


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