Hi,
Under some circumstances this effect can be produced by one
motor winding connection not being good at the driver end of the motor
cable. Usually with a long (2 mtr) cable. Can also be due to one output of
the driver unit being bad. With power off, use an ohmmeter to check the
winding resistance at the motor end off the cable, then look for similar
resistance at the output pins of the driver unit, and the output pins of the
driver ICs. If that looks good, with power on and the motor running look
with a scope at the waveforms on all four driver outputs. The two outputs
for one winding are different, but one output on one winding should be the
same as one output on the other winding, and the other two should also
match.
Also an open circuit Direction signal, with the open at the breakout board
end of the cable can produce similar effects as suggested below.
----- Original Message -----
From: "Slavko Kocjancic" <[email protected]>
To: "Enhanced Machine Controller (EMC)" <[email protected]>
Sent: Tuesday, March 30, 2010 2:23 AM
Subject: Re: [Emc-users] Random Direction Changes
> [email protected] pravi:
>> Hi all,
>>
>> I am experiencing some odd direction changes on a home-brew CNC
>> machine that I have on loan.
>> The machine was apparently purchased off ebay, and all the settings I
>> dug out from data sheets for the driver chips and motors.
>>
>> X and Y are working well, but Z (which has a similarly spec'ed but
>> different motor from the other two) decides to change direction at
>> random.
>> The basic behavior is that when you push the jog button in a certain
>> direction you don't know which direction it will go.
>> It will maintain it's course in that direction, but when releasing the
>> button and pressing it again, it will again choose a random direction.
>> Thus the problem it is very easy to reproduce.
>>
>> I am interested to hear what you think this problem may be caused by?
>> I have yet to pull out the oscilloscope, but being a relative newcomer
>> I wanted to ask for advise on how best to debug this problem.
>>
>> I should add that I did have this CNC set up briefly on Mach3, and
>> encountered the same issue.
>>
>> Thanks in advance,
>>
> Just check the wires again. That can be caused by bad connection of DIR
> signal or even replaced dir/step signal or shorted together. If you
> don't have scope then just use earphone. Connect earphone trought 10k
> resistor to direction signal and ground. You should hear nothing when
> motor moves. But must hear click when you change direction. On the step
> pin you should hear clear tone without clicking. That's works even
> betterthan scope!. As all interrupts are heard as clicking in steady
> signal. On scope is very easy to miss that glitch.
>
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