[Arm-netbook] Existential 3D Printing Moments

[Luke Kenneth Casson Leighton]

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crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68


On Mon, May 29, 2017 at 3:44 PM,  <doark at mail.com> wrote:
> On Fri, 19 May 2017 01:42:52 +0100
> Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>>
>> On Fri, May 19, 2017 at 12:35 AM, Neil Jansen <njansen1 at gmail.com>
>> wrote:
> <snip>
>> now, neil, this is the kind of speed at which an arduino 2560 *cannot
>> cope*, and, also, where the design flaws inherent in RAMPS - using
>> prototyping Evaluation Boards (polulu-style drivers) - start to show
>> up.
> Could you be more specific? Why can't the arduino cope?

 there are more experienced people who know the precise details.
bottom line: an 8-bit 16 mhz processor is simply not fast enough to be
able to send the data to the stepper motors in a way that they will
remain properly synchronised.

 example: X axis gets changed direction/speed, and Y needs to be
changed at the exact same time.  but because it takes e.g. 50uS (0.05
ms) to get round the "compute" loop, the print head has moved on (say)
0.2mm in that time, it's going so fast, so X and Y are no longer
properly synchronised.

 only by going to a 32-bit processor running at say 100mhz can you get
the timing synchronisation back.




>> david crocket (dc42) has specifically designed the duet series so that
>> you can consider exceeding PWM rates of 150 khz, which is what you
>> need if you want to sustain 500mm/sec for example (and do not want
>> problems to occur at speeds well below that).
> Link?

 google it please.

>> also i forgot to mention that i've been using the E3Dv6 "volcano"
>> which, when you use a 0.5 to 0.8mm nozzle can easily do flow rates of
>> something mad like.... 200c^3/min - particularly when combined with
>> the huge 40:1 gearing of the flex3drive which can *accurately* deliver
>> the kinds of torque needed.  the volcano basically turns the heat
>> chamber round, so that the heat area is 20mm long instead of the usual
>> 10mm.
> Torque for what?
> Again, maybe a link would help us stay on the same page.

 google them, please.  i have a lot else to take care of.

>> none of this stuff i knew about, the 18 months before i began
>> designing the laptop's parts.  oh well.
>
> I researched 3D printers thoroughly before I bought mine. I even started
> asking questions at a forum, and I'm still not too certain if I got what
> I sought.
> According to this list, I did worse when looking for hacker boards.

 well, if you are only looking to print a few trinkets at below 50 mm
/ sec then whatever you have is perfectly fine.

 if on the other hand you're looking for something that you intend to
take seriously, then yes you have been through an important learning
experience.

 actually after looking at the design of TMC2100 postage-stamp-sized
driver boards, i believe these may actually be okay.  in these
particular boards they've put the TMC2100 *ON THE OTHER SIDE OF THE
PCB*.  what that means is that you can put a heatsink on the TOP of
the PCB, where it will actually be effective at taking heat away.

l.