On Tue, 23 May 2017 02:27:24 +0100 Luke Kenneth Casson Leighton lkcl@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
On Tue, May 30, 2017 at 10:05 PM, David Niklas doark@mail.com wrote:
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.
but you don't print at the time when z-axis motors are in motion: they're there purely to move the bed up (or down) for the next layer. thus the important thing to have for z-axes is precision and fine tolerances. fine tolerances can be achieved on lead screws with double nuts and a spring to prevent backlash.
ok so on to the next issue:
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.
so you're advocating 3 lead screws instead of 4 i considered this as well, however i realised that if the printbed has even the slightest amount of twist it becomes impossible to correct that: you literally have to throw out whatever metal plate is being used and replace it.
if you have 4 lead screws, they may be used to place a twist on the plate to return it to dead-flat.
l.
arm-netbook@lists.phcomp.co.uk
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David Niklas -
Luke Kenneth Casson Leighton