[Arm-netbook] a designing a low-cost decent 3d printing board

[David Niklas]

On Tue, 23 May 2017 02:27:24 +0100
Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
<snip>
> in particular i would very much like to "stack" the steppers because i
> have a design where it is going to use *four* z-axes.  in a first
> iteration those may be wired up as 2x 2-serial in parallel, however it
> would be very *very* nice to be able to just add a second "stack" of 4
> z-axis steppers and use them to do automatic bed-levelling.  so to do
> that it would mean having on-board jumpers that could select
> alternative GPIO pins... or maybe to use an I2C-based or SPI-based
> GPIO expander in order to reduce the amount of GPIO needed.
<snip>

Remember that as the weight and speed of the hot end increases the load
on the z-axis motors and gears also increases (if temporarily), leading to
(temporary), inaccuracies when using multi motor setups.
If I were to use multiple motors I'd not do it like this:
M == motor
H == Hot end

TOP       SIDE
M----M    +-----+
|    |    |H    |
|H   | -> |     |
M----M    M-----M 

But rather like this:


TOP       SIDE
+----+    M----+
|    |    H    |
|    | -> |    |
M----+    M----+

Assuming I understand you rightly.

Sincerely,
David