Z moves up when uc100 disconnects

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Z moves up when uc100 disconnects

Postby flyforever » Sat Jan 12, 2019 5:26 am

Occasionally, my machine comes to a stop due to UC100 "disconnect error". If I disconnect the USB cable from the pc, the z axis starts moving up. When I reconnect the cable, the z axis stops. This is a safety issue, and I am not sure if it's UC100 related.
Once I reboot the pc, everything works normally again.

thanks
tc
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Re: Z moves up when uc100 disconnects

Postby cncdrive » Sat Jan 12, 2019 12:17 pm

No, it is not UC100 related. When the UC100 has no USB cable connected then it has no power and so it cannot send commands (signals) to your motor drives, so ofcourse the UC100 cannot generate that motion.
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Re: Z moves up when uc100 disconnects

Postby cncdrive » Sat Jan 12, 2019 12:55 pm

What I think that causing the issue is that you using a cheap chinese breakout board which has TTL buffer ICs on the inputs and requires separate power on the primary side (e.g. a USB connection or external 5volts).
And the designer of that board put TTL buffer ICs on the outputs for the step/dir signals to the drives, but did not place any pullup or pulldown resistors on them.
So, what happens is that if you unplug the UC100 then the primary side of the outputs on the BOB goes into an undefined voltage state, because it is connected nowhere and so the output of the buffer will randomly move 010101 etc., this gives the step signals to the drives. And this is a problem with cheap chinese BOBs and not with the UC100. The UC100 can not solve design issues of the BOB, if you will disconnect the UC100 totally then this issue will likely still happen, so you will see that it is not a UC100 problem. :)
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Re: Z moves up when uc100 disconnects

Postby flyforever » Sun Jan 13, 2019 5:33 am

Your explanation make perfect sense. The bob is cnc4pc c10, so I am not sure about its quality. I will look into it to determine if, in fact, one of the output pins is floating.
thank you for your assistance.
tc
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