Talk:Step rates
Imho the whole discussion about what maximum step rates are achievable with each firmware makes very little sense (and it looks like a pissing contest). :-(
This page should begin with a honest discussion about RepRap printer mechanics and kinematics, kinetic energy, vibrations, tolerances and finally, realistic expectations about print quality and how it relates to print speed.
Then we could talk about print speed and stepper rates.
Also this page only mentions en passant the most obvious, immediately quantifiable spec that has a direct relation with maximum step rates: the MCU clock. Yes, whatever firmware one is using, doubling the MHz doubles the maximum step rate, all other things remaining constant. This is why anything running on an ARM processor at 80MHz or more will result in faster maximum step rates than anything else running on an AVR 16MHz processor. And indeed the BeagleBone Black with its 1GHz ARM Cortex-A8 and two 200MHz Programmable Realtime Units (PRUs) has been reported to be able to generate step pulses in the MHz range.
Finally, there are two more obvious facts that this page fails to mention:
- A firmware that is able to achieve a faster maximum step rate is not going to give you better quality prints. Actually, even for reasonable print quality, you'll be printing well below the maximum step rate of even the slowest firmware listed here.
- Two different firmwares printing at reasonable speeds (i.e. with step rates below the maximum step rates of the slower one) will give you exactly the same result: the same object printed with the same amount of material in exactly the same amount of time with the exact same quality.
Now, what is a reasonable maximum printing speed? From my own experience on a P3Steel (a particularly rigid Prusa i3 variant), around 50mm/s. Yes, the Prusa i3 and the P3Steel are Cartesian printers with a heavy moving print bed and print head. So I'll quote Andy Cart, the designer of the Cherry Pi series of linear delta printers (derived from the Kossel by Johann C. Rocholl):
- I normally use 0.3mm @ 25mm/s as my first layer speed and height and have it slightly 'squished' on the bed. I just use kapton tape wiped with acetone at 60 degrees C as my print surface. Subsequent layer heights are really dependent on the model and your preference. I normally print at 80mm/s, 50mm/s for higher quality prints.
(from his post in the forum: http://forums.reprap.org/read.php?178,361141,500088#msg-500088 )
