August update - assembly tips and a few issues September Update - working well, thoughts on changes October Update - moving motors and magnetic carriage mod
In case anyone isn't aware Richard Horn of richrap fame has a BigBox and is giving feedback. Most interestingly he's making his own magnetic quick change carriage system which hopefully he'll share the files for once it's done. So by the time it ships you'll already have some mods to try. I'm keeping my fingers crossed Richard hacks in a filament detector as well.
May I - in all due modesty - mention my auto leveling solution for the Ordbot Hadron? You can find some pictures here. The description is in german there, if needed, I'll post a translation. In short: The extruder is mounted on a second level plate. That moves around a hinge made up from two spherical magnets that rest in appropriate shells. Thus, the hinge axis (y) and the lateral degrees of freedom in x and y are defined. The other side of the plate is held down by a spring with a mechanical limitation. The plate also rests on an Allen(?)-screw that presses on an FSR (Force Sensitive Resistor). That is part of a potentiometer circuit, generating a voltage that is below the trigger level of a Schmitt trigger. During the initialisation, the carriage holding the plate moves down onto the heated bed. At a given point, the nozzle touches the glass, rests there and presses the whole plate upwards. Sometime then, the force onto the FSR becomes so small (increasing its resistance) that the Schmitt trigger does its job - Z-zero reached (with some very good reproducible offset that has to be included in the overall configuration), this signal is fed to the controller then where the lower Z-limit switch normally goes. The Carriage moves away from the HB again, force on the FSR returns, Schmitt trigger falls back asleep. Z-0 defined. Same sequence for the auto leveling. I take 9 sample points evenly spread over the heat bed. The tremendous advantage: any change on the hotend geometry has no influence on the retrieval of the Z-position. The key point is always the nozzle tip. When time allows, I'll make a video of it somewhen. Slightly dejusted heatbeds need no attention - the geometry is completely corrected in the Marlin firmware. You may ask and argue, why not a mechanical switch? That always implies some way to operate, whereas the FSR acts practically motionless, just reacting to a pressure change. And it is very reproducible. I like magnetic couplings too. Inspiration came from Johann Rocholl's Delta printers where he used these magnetic ball joints (no pun intended) for the beams carrying the extruder holder, and the FSRs he uses under the print bed. The transformation into the above described constellation grew in my basement. Oooops, that was more than short now, more a nearly complete description in englisch. FWIW... Cheers, U. (aka 'Chattermark', shhhhhh ! )
