This is an answer to a question calberts asked in a thread on FS2 controllers . I Thought it better to open a new thread to answer.

Hi Chris,

USB hubs (or rather USB as such) are a major and most annoying topic. You will find an number of concerning topics in this forum

Only recently we tested 7 different powered USB hubs (USB2 as well as USB3) connected to the controlling PC of our public observatory and than connected to two different Fujitsu laptops, all running KStars/EKOS/INDI
.
The hubs were connected to the PC/laptops by high qualitiy "active" 3m USB2 and USB3 cables which had been tested successfully separately with every single device. The hubs then were step-wise "loaded" with a Canon 750D, a QHY5LII mono, a MGen autoguider, and a SonyA7II - no mount controller was attached since that worked over a RS232 serial connection. But I found mount controllers are a minor issue on hubs.

Result of our tests: only 3 out of 7 hubs worked at all with all devices attached (one USB3 hub, the two others were USB2) - but only one of the USB2 hubs worked satisfying when connected to the laptops as well!
Connected to the laptops one or another hub would work with more or less devices attached. Some hubs worked part-time with only some of the devices connected, some combinations of hub and devices failed completely. Different USB cables between hub and devices were tested and these obviously come in different qualities as well. Starting streaming from the QHY also seemed to degrade the stability of the connections. And to some extent bugs or some kind of sensitivity on the side of the INDI drivers might as well interfere and stop devices from working at all.

Our results which, i am afraid, will differ from those of others with different setups, are as follows:
USB2 tends to be more stable/reliable with most devices; hub power should be at least 3,5A at 5V. Use high quality cables as well. The male connectors should fit firmly and not shaky. And make sure not to use a mere charging USB cable! (Happened to us while testing) Streaming devices should connect directly to an USB port at the PC. We believe one has to try out combining material until it works reliable - and that may change with an additional device.

I still wonder how people get these USB devices to work, especially cameras, connected to a RasPi?!

PS: At our observatory we changed to a compact € 300 PC with 10 USB ports that are connected to two internal hubs (USB2 and USB3) and use long (>= 2m) USB cables to connect to the devices. (OK, one USB hub is used to power some cross-hair LEDs).

CS
Michael

This resembles my experience with USB hubs. Just like Michael, I decided to put a decent "veteran" PC (2x USB3 + 10x USB2) to work at the telescope, run indiserver there and connect all devices directly. From that moment all USB issues were solved.

I agree that some hub work better than other and there is probably a hardware implementation reason for that.
But we must also remember some basic plumbing rules: it is not possible to connect two camera that use 100% of the usb bandwidth and try to put the two flux in one cable.

Personally I always use separate direct cable from the computer to the camera and guide camera. But the hub is OK for the mount, the focuser, the filter wheel and probably other low bandwidth devices.
This meant you need at least 3 usb port on the computer and be sure it not use an internal hub for the two camera ports.

Watch out also "active" USB cables. They have a 1 to 1 hub embeded in order to extend length, but can be troublesome.

USB has a limit of hubs in cascade it can handle and I think the best practice is to limit using a "computer <-> hub <-> devices" configuration.

Some years ago I tried to use 2 active USB cables to comunicate my computer to my telescope, camera, etc. It had a random behavior.
Now I has the configuration "computer <-> ethernet <-> old laptop <-> hub <-> 4 devices (ST8, FS2, MaxDome, Robofocus)" working ok.

so would most agree that best practice is to have a powered hub connected to the pi and the devices connected only to the powered hub ??

Hi all,

I am not expert in linux what so ever. Try this " Adding dwc_otg.speed=1 to /boot/cmdline.txt" then reboot your RPI3. Plug every of your devices into your 7-ports powered USB hub and try it out. Hope can save the day.

Tom

from my experience i use the usb ports of a pc to run my imaging camera, mount cable and guide camera everything else goes to the hub, but one issue i have is with my atik EFW2 with rpi. The only way the pi can recognize the filter wheel is to connect it at my pi and the imaging camera at my D-link hub. Another issue i had a few days ago is that my dmfc and mount would conflict with each other when my hub was not powered. I have ordered a 10 usb 12v powered startech hub in order to try it and also have an extra usb port for future equipment

DSLR's dont count they provided their own power so are quite happy being plugged in to RPI USB port - just make the cable as short as possible and best quality for signal strength. For the UK Lindy cables are very good. Never had problems using DSLR with this method - hence using Remote Indiserver is ideal on different RPI's IMO

stash is correct about the power consumption of DSLRs as well as all separately powered devices draw hardly any current from the hub.
However beware that non-powered USB2 devices can draw up to 0.5 A and USB3 devices up to 0.9A per port. Using a 10 port hub with a 2.5A power supply might be on the low side.
To complicate things even more the USB-C connector (which I have not seen on astro devices yet but only on cell phones and tablets) may draw up to 3A per port. So don't charge Your cell phone from the same hub when using it for internet connections

And to top all this: USB-PD (USB Power Delivery) may request 5V, 12V or even 20V and up to 5A (= 100W max power) from the charging device! These values are considered for USB connected displays for example. But it will take some time before we see devices like these at our telescopes.

Unfortunately a lot of hubs on the market use cheap components that can be very sensitive to environmental factors, particularly temperature. There are plenty of industrial grade hubs on the market for top dollar, but I have had good success when I switched to this 7 port USB3 hub from StarTech. (3 charge, 4 Data)
www.amazon.ca/gp/product/B00HNWY9SW
I have operated with this in the dead of winter under -25°C without a hitch. It powers my RPi3, and up to 2 USB dew heaters. Plus it controls my Guide Cam, DSLR, and memory stick with one port to spare. My Pi's USB ports are occupied with the Hub, Mount, WiFi and USB extension cable to a tablet and keyboard via another powered hub at my table.

You're right about the quality of USB hubs. I have success with this USB2 hub from coolgear:

www.coolgear.com/product/usb-2-0-over-ip...e-over-tcpip-network

I have had this in my obs for about 6 years powered up and temperature ranging from -40C to +40C. So far so good ... These are a little more expensive, but you can save on gray hair tonics.

jmh

I would like to add a point to this topic concerning the mixture of USB 2 and USB 3 devices connected to a same hub.
Remember to connect FIRST the USB 3 devices (cameras in my case) to the hub, and THEN the additional USB 2 devices (scope in my case).
The first device you plug in will configure the port, so always connect USB 3-capable hubs or devices first.
If you plug in a USB 2 hub first, all devices connected or "daisy-chained" to that hub will operate up to the maximum transfer rate of USB 2 speed (480 Mbps).
If you are on Apple, check connections with System Information (Apple () menu > About This Mac > System Report, then select : Hardware / USB, use ⌘R Refresh Information)
THEN power up the devices and start the astronomy software.