Help with gantry machine. Dual motor setup

Hello Linuxcnc Forum,I have been using my router now with linuxcnc for about 6 years or so and mostly without a problem.

It's a XYYZ gantry machine and I have until yesterday been manually squaring the gantry (hard stops with power off).I recently decided to implement gantry squaring in the homing sequence, which took a bit of figuring out but it works like it should. The problem that I can't seem to work out now is the gantry motors wont reach full speed without stalling or missing steps! Obviously bad for a gantry!

The only thing different (that I can tell) is both Y motors are getting different step and direction signals. Before I changed things over both Y drivers were sharing parport pins, one step and direction for both drivers.I feel like it has something to do with timing or latency but maybe I missed a critical step? Do I need to sync the motors some other way after homing? I mean if it jogs like it should after homing it should be right, right? 

I really tried to avoid starting a new thread on gantry/dual motor problems but I have been sitting here all day searching through old posts, reading about double-steps and going through the documentation but I can't seem to find it out. If anyone can point me to the right information I would greatly appreciate it. 

Thanks,

Jeremy



 
 

Looks like none of your joints have the following critical settings

Don't assume my values are correct. They are just a bit of a guess.

Hi, thanks for looking over it. 

All joints have:

Wait...
From your hal file: Change the reset time to 5000 or start at 10000 and lower gradually till you are OK with it.

Okay, so I had a few hours to play around and changing the reset time but alas to no avail.

I'll have a look at some more timing things but the problem still exists.

I need to get some more work done so I'll probably have to revert the changes I've made for gantry squaring for now but any help would be greatly appreciated!

SOLVED.

For anybody in the future who happens to have the same problem, the issue was the choice of parallel port pins.

I have a rotary axis so pins 2-9 were in use and when I gave my Y2 motor it's own step and direction pins I just used the next free output pins, 16 and 17.

It worked just fine, until I sped things up and then one motor would lose steps and rack the gantry.

By moving Y2 to pin-02 and 03 and the rotary axis to 16 and 17 has fixed the problem on the gantry at least.

Is this a known problem? Or should that have worked just fine? Is it maybe a wire shielding issue?

At least it's working now anyway.

It is not a problem, it is just how the parallel port works, there are 8 data pins 2-9, "service" pins 1,14,16,17,, and "i do not know" pins 10,11,12,13,15.
Pins 2-9 can be used as inputs or outputs, same with 1,14,16,17, but pins 10,11,12,13,15 can only be inputs.
There are also electrical differences between them, pins 2-9 are better at sinking than sourcing current, pins 1,14,16,17 when used as inputs require more current than pins 2-9 or 10,11,12,13,15, etc, etc.
It has 3 modes of operation:
-OUT = 12 outputs +5 inputs
-IN = 4 outputs +13 inputs / data pins 2-9 are inputs
-X = 8 outputs +9 inputs / only data pins are outputs

Strobe, one group of those pins is called strobe, or a pin, a bit fuzzy ...

Wow, fantastic explanation, thank you.

But I guess this means the rotary axis shouldn't be on pins 16 and 17?

I mean, it works but I can't see if it's not keeping up like the obvious signs of a racking gantry.

I do have a second parallel port but that is not supposed be used for step and direction signals?

Pins 16 and 17 can be used, it is just that they might not work as the data pins, or might not meet the drive requirements at higher speeds. Probably more to do with the drives, but i never investigated it thoroughly.
I know for sure some encoders will not work with pins 1,14,16,17 when used as inputs as they do require more current than the pins 10,11,12,13,15.
And yes, second parallel port can be used for everything, there is just one issue that might crop up, address change after a reboot, and that could be remedied by entering BIOS and seting the resourse assignment to manual. Most new boards/PC's do not have that option though.
Even if this happens, checking the address and changing it in the hal file takes about a minute of time.