[Noisebridge-discuss] getting that goddamned mill to work

Mon Oct 5 02:37:30 UTC 2009

Latest on the MaxNC mill. Today I verified that quadrature signals
work, by the simple expedient of hooking up a quadrature encoder:
turning the shaft moves the axis.

The entire thing needs to be disassembled, cleaned, and relubed
because the grease is gummy and sticks.
The Z axis is stiff, the Y axis is frozen; both pop the breaker
sometimes.  I didn't test the X or the rotation.

We also (still!) need a Linux box. Jonathan M. and I found a Thinkpad
laptop that looked fine save it didn't have a power supply (16V at
4.5A if you see one). Specs are really not important as the mill
driver board handles the critical timing.

I will go ahead and build a step->quadrature converter box just
because it would be fun. (No micros: jellybean TTL FTW! )  Need some
7486 XORs but couldn't find them -- do we have any? Also, if anyone
sees a parallel port A/B box in the hack pile, that would make an
ideal enclosure.

I could use some help on the mill TLC and the linux box if people are
keen on this!

On Fri, Oct 2, 2009 at 12:10 PM, Michael Wright <mike at smallip.com> wrote:
> I think Jon pretty much summed it up.
>
> We've got it to work as well as can be done using the UI on EMC2.  It
> looks like the EMC2 HAL (hardware abstraction layer) allows for making
> pretty significant changes to the motor signaling (Seph basically
> changed everything of how EMC2 talks to make it use 4 pins per motor
> to control the MaxNC10OL), we have the MaxNC10CL (closed loop) so we'd
> have to do slightly less work to make it do quadrature on 2 pins per
> motor.  This would be a pure software hacking adventure, probably most
> of the work could be done using EMC2 on a VM on a laptop, with final
> testing requiring a real machine and the mill.
>
> I've downloaded and played with Mach3 demo-ware in a VM.  It actually
> has a menu option for MaxNC CL mode.  This along with the other things
> I've read makes me think it will work.  If it's possible to believe,
> it actually looks more esoteric and harder to use than EMC2 (at least
> for someone who doesn't know CAM yet).  That said if it makes the mill
> work, someone can make an instructable on how to do CAM.  The demo of
> Mach3 allows 500 lines of Gcode, the licensed version allows 10,000
> and costs $175.  My plan is to arrive with a windows 2k hard drive and
> put it in one of the three boxes (2 compaqs from Dr. J plus one from
> Jonathan L).  If that works, then it works and other hacking can be
> done for fun rather than "necessity".
>
> In terms of other hacking for fun, I'm thinking it would be pretty
> easy to make an Arduino/Sanguino based 4 knob control box that
> converts the perfectly good CNC mill into a functional power-feed only
> manual mill.  For the kinds of one-off things I tend to do, having
> direct control is nice (plus the learning curve is lower).
>
> The important things we learned in EMC2:
>
> If you have the enable pins set correctly the mill humms at about 10
> khz (actually all 3 stepper motors)
> If you have the enable pins set correctly any one of the steppers will
> resist externally applied torque
> If the steppers don't behave closed loop (hum and resist torque),
> something's not enable and no other testing has any chance of success
> Spindle is pin 1, inverted, it pwm's fine (if not set inverted it runs
> by default, which I don't recommend)
> The spindle may not be affected by the enable pins (needs more testing)
>
> Here's the pin config that made the most sense (and made controllable
> noise)
>
> outputs:
> 1 Spindle PWM  Invert Checked
> 2 A Step
> 3 A Dir
> 4 Y Step
> 5 Y Dir
> 6 X Step
> 7 X Dir
> 8 Z Step
> 9 Z Dir
> 14 ESTOP Out  Invert Checked
> 16 ESTOP Out
> 17 ESTOP Out  Invert Checked
>
> Inputs
> 10 All Limits
> 11 Unused
> 12 Unused
> 13 Unused
> 15 Unused
>
> On Oct 2, 2009, at 10:48 AM, Jonathan Foote wrote:
>
>> I don't think jitter is an issue. On the worst machine last night it
>> was less than 25 us. Mike's borrowed machine got it down to less than
>> 5 (thanks for bringing that in, Mike!)
>>
>> Seeing as how the actual stepper pulses are generated by 4 Mhz PICs, I
>> think we are, if anything running too fast.
>>
>> But we made some progress, we got the spindle motor PWM working, and
>> found magic enable pins. We can enable the stepper feedback so they
>> will fight you if you try turning them out of position, and I'm pretty
>> sure we're giving them drive signals because we can hear them whine.
>> But they still don't move.
>>
>> I think the final hurdle is generating true quadrature drive signals
>> rather than step + direction. This is an easy hardware hack (two
>> flip-flops and some logic should do it), or we could improve the
>> open-source EMC2 code to generate the signals we need. The hardware
>> solution strikes me as much easier than mucking about in the guts of
>> that Linux port driver, but I could be convinced otherwise, especially
>> if there's anyone else on the planet with a similar problem. (Is
>> anyone on the EMC2 list/forum/IRC that could ask?)
>>
>> I think the next step is testing that hypothesis by feeding one axis
>> some true quadrature signals from hardware. I have some AVR code to do
>> just that.
>>
>>
>> OK, enough hacking, back to the drama.
>>
>> -J
>>
>>
>> On Fri, Oct 2, 2009 at 10:13 AM, Andy Isaacson <adi at hexapodia.org>
>> wrote:
>>> On Thu, Oct 01, 2009 at 11:56:29PM -0700, Jesse Welz wrote:
>>>> 2009/10/1 dpc <weasel at meer.net>:
>>>>> Michael Wright <mike at smallip.com> writes:
>>>>>
>>>>>> After running the Jitter-Test program on the computer I have the
>>>>>> sinking suspicion that the machine we're trying to use isn't good
>>>>>> enough to send step and direction commands.
>>>>>
>>>>> hmmm.... i never got around to schleping down the machine for the
>>>>> reversing stuff but just noticed it has a prallel port. how good is
>>>>> good enough?
>>>
>>>
>>> The problem is that some low-end computers from about 1998 to 2003
>>> (and
>>> some up to the current day) use SMI mode (System Management
>>> Interrupt)
>>> to do stuff on the CPU without letting the OS know about it.  This
>>> means
>>> that at any moment your code may stop executing for up to a few
>>> hundred
>>> microseconds -- plenty long enough to totally hose a PWM or stepper
>>> motor pulse sequence.
>>>
>>> The motherboard I last saw being used for the mill was a Via Eden
>>> CPU,
>>> which is known to potentially have such issues.
>>>
>>> Most "real" AMD or Intel CPUs' motherboards don't have these issues,
>>> although it's not guaranteed (it depends on the BIOS and system
>>> vendor,
>>> and laptops are also known for having such problems), so check for a
>>> better mobo -- I know I saw a few in the E-Waste pile.
>>>
>>> -andy
>>> _______________________________________________
>>> Noisebridge-discuss mailing list
>>> Noisebridge-discuss at lists.noisebridge.net
>>> https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss
>>>
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