[Arm-netbook] SPI-based LCDs, 3D printing, RISC-V

[Luke Kenneth Casson Leighton]

On Thu, Apr 27, 2017 at 1:00 PM, Christian Kellermann
<ckeen at pestilenz.org> wrote:

> As the current issue is time in producing them I would also scratch
> the printed parts order myself, maybe in exchange for a discount on
> future designs done by Luke and print them myself. People with access
> to a maker lab could consider doing the same...
>
> I am not capable to promise good quality printing for 3rd parties as I
> have been starting getting into this for a rather short while now...

 well, a 200x200 basic reprap will do the job, with a 0.4mm nozzle and
a layer height of between 0.15 and 0.2mm is absolutely fine.  it's not
hugely difficult.  i've just ordered this ($140!!) 3D printer from a
taobao seller, it's arriving in a couple of days:

 https://world.taobao.com/item/526287577504.htm

now, at $140 i am quite happy to get up to 10 of those (if the first
one checks out fine) - it looks *really* sturdy: 20x20 aluminium
box-section: my only concern about rigidity being that it uses
L-brackets which go *into* the frame rather than triangle-corners
which are bolted outside and lock the box-section absolutely solid.
but, we'll see what happens.

 also it looks like it has a clone of the E3Dv6 hot-end (which is
really good), it has trapezoidal z-axis lead screws with proper brass
nuts, borosilicate glass plate (to be confirmed).

 the one thing i have told the guy (and he's happy to give a RMB 70
discount): i do NOT want the f*****-s***-for-brains RAMPS 1.4
controller.  if you're familiar with 3D printing for f***'s sake STAY
AWAY from ANYTHING that uses the brain-dead "Polulu" driver "modules".
RAMPS, RUMBA, Lerdge, Megatronics - just don't f*****g well do it.

 the reason is really really simple: those QFN ICs are designed
SPECIFICALLY, as outlined CLEARLY IN THE DATASHEET, for the heat to be
dissipated THROUGH THE PCB.  there is a ceramic insulator on the TOP
OF THE CHIP which ACTIVELY PREVENTS HEAT DISSIPATING THROUGH THE TOP.
if you put a heat sink on top of the chip it does... nothing.

 now, when the first reprap was created, in order to save time and
development cost they bought some PROTOTYPING boards with the stepper
drivers pre-mounted, which came with SPECIFIC instructions "under no
circumstances use these in production".

 so what happens?

 well, they (a) burn out (b) overheat (c) stop working for a couple of
seconds at a time in the middle of a print...

 ... you get the general idea.

so anyway i ordered a Melzi 2.0 from here:

 https://www.aliexpress.com/store/group/Melzi-board/1757194_500507171.html

and it turns out that on the reprap wiki there's a mod to them which
allows for the connection of a BT UART.  it would have been handy if
those pins had been brought out on a header but hey, what's wrong with
a bit of soldering.

if you don't want to do soldering then you can just put the Melzi 2.0
into "auto-load" mode, drop a file in a FAT32 filesystem on a MicroSD
card and power it up.

i like the Melzi 2.  it's simple, relatively low-cost compared to some
of the other options, no-nonsense and straightforward.

l.