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Author Topic: Motor changing direction at random  (Read 682 times)

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Motor changing direction at random
« on: January 08, 2021, 09:48:53 PM »
I have recently connected my 3 axis CNC to Mach3 via 3 TB6600 drivers and a ST-V2 BOB. Everything is wired up correctly and Mach3 Config has been entered as per BOB installation instructions.

However, the Y axis motor changes direction at random with each activation of the jog command, either by hot key or from within Mach3. i.e when I press the Y+ command, the motor will start in any direction; Y+ or Y-. The next time I hit the Y+ command again, the motor might run in the opposite direction. The DRO however will continue to clock as if the motor is running in the Y+ direction. The same occurs with the Y- command but the DRO will continue clocking in the Y- direction. This problem initially happened only to the Z axis motor, but that seems to have resolved itself mysteriously and now occurs only to the Y axis. Both X and Z axes' motion are stable.

I have ruled out the TB6600s and the BOB by interchanging the Drivers and BOB axes pin connections, and changing the Motor Outputs pin values in Mach3 Config accordingly. It does not matter what channel I establish between Mach3 and the motors, the Y axis jog commands can not assure direction.

My computer's O/S (Vista) was reinstalled + memoryoveride.zip, as was Mach 3 (R3.043.062) and I also addressed the blue question mark after the Mach3 driver in 'Device Manager' with the fix in https://www.machsupport.com/forum/index.php?topic=38269.0. The blue question mark remains.

I've attached the xml file.

Do any of you have any suggestions?

Offline Tweakie.CNC

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Re: Motor changing direction at random
« Reply #1 on: January 09, 2021, 01:38:09 AM »
Check that your PC parallel port outputs are 5 Volt TTL logic and not 3.3 Volt TTL. This thread may be helpful; https://www.machsupport.com/forum/index.php?topic=34848.0

Tweakie.
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Re: Motor changing direction at random
« Reply #2 on: January 09, 2021, 03:38:15 AM »
Thanks Tweakie, I'll check that in the a.m.

Offline MN300

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Re: Motor changing direction at random
« Reply #3 on: January 09, 2021, 07:17:21 AM »
If the problem is 3.3V on the parallel port when the signal level is high it would barely meet the minimum value for the BOB board's input. However the direction represented by 0 volts should run reliably. Sherwood reports that the system fails in both directions.

Offline TPS

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Re: Motor changing direction at random
« Reply #4 on: January 09, 2021, 11:39:40 AM »
had a look to the BOB shematic, i think this only can happen, if USB is not connected or something is wrong with the 5V of the USB supply.
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: Motor changing direction at random
« Reply #5 on: January 09, 2021, 07:56:44 PM »
I'll send the pics first
Re: Motor changing direction at random
« Reply #6 on: January 09, 2021, 08:27:58 PM »
The parallel port is integral to the motherboard and not 5V I think. The slot I can use is 3.3V. Pls see the previously attached pics. Can I insert a universal PCI card into the 3.3V slot to supply 5V?.
If yes, I purchase a universal card to resolve the 5V BOB board supply before considering the next.
If no, what are the options; updated computer?

The BOB is not connected to a USB for its 5V supply but to a dedicated 5V 3A transformer. Pic of activated BOB attached.

Offline MN300

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Re: Motor changing direction at random
« Reply #7 on: January 09, 2021, 09:46:15 PM »
I have labeled the step and direction pins on your photo.
The top pins are the signals from the parallel port. The bottom pins, one to the left, are the outputs to the stepper drivers.
To measure the voltages connect the negative lead of the meter to PC GND and probe the pin you want to check with the positive lead.
This will eliminate any doubt as to what the port voltage level is.
Re: Motor changing direction at random
« Reply #8 on: January 09, 2021, 10:46:40 PM »
OK, without jog command: Voltage between GND and each (X,Y,Z and A axis) DIR parallel port input = 108.6 mV. GND to all DIR Driver outputs = 0.29 V. Voltage between GND - STEP //port inputs = 4.5 V; GND - STEP Driver outputs = 5.1 V.
When jog command, for positive direction GND - X or Y DIR input = 4.5 V, for neg direction = 108.6 mV

The voltage does not change despite a change in direction for the Y motor.
Re: Motor changing direction at random
« Reply #9 on: January 09, 2021, 10:53:58 PM »
What is IC2 used for?