Really, the printer is terrific, but the calibration I did initially wasn't so hot, so the results were a little erratic.
The secret sauce to consistent printing? A dead-level print bed, and an exactly correct first layer height.
Printing PLA on green painters tape (it's what I had handy) on a cold bed works incredibly well; much better than the mixed results I was getting on glass, although I might give glass another shot now that it's dialed in.
Here are a few other things that went wrong along the way:
- Slightly loose set screws = strange repeating patterns in the prints
- Totally loose set screws = loss of pulley / axis = 1.5 dimensional artwork (loss of print)
- Current set slightly high = hot stepper motors = skipped steps (layer misalignment)
- Heat creep (heating in the upper extruder barrel) = extruder jams, incomplete prints
- Whacky temperatures = poor print adhesion to the bed, and gooey extrusions (loss of print)
- Broken end-stop wires = total meltdown of print
- Poor calibration = non-square prints
I also did a lot of learning about what makes a 3D object printable, and the secret here is 'simple'. Not because it's hard to print, but it's hard to get the design right in the first place, including matching measurements up to the real world, so it can waste a lot of time and filament.
But when it does work well it turns out pretty good:
These are the steering controllers, which drive the four corner wheels +/- 45 degrees. These are mounted to 3D printed carriers, and the carriers mount to the smaller 3D printed connecting blocks that fit inside Actobotics aluminum channels and brackets.
The carriers have built-in stand-offs and screw holes, and a vent under the L293D, although I don't expect much heating. Although these are the versions I'll use the rest of the year, I could see a half-dozen design tweaks I could make... sometimes good enough is... good enough.
The smaller connecting blocks are more interesting. They hold the carriers down near the corner wheels, and keep the metal walls from deforming (this bit of aluminum isn't 3 sided channel). Because the stresses might be large / dynamic, I decided that with screw holes the object would never be totally solid, and with delamination a possibility I needed a way to keep the metal walls apart... like hex nuts on a screw that runs the width of the channel. Because the nuts are captive they can't move together, and the distance between the walls can't decrease. We'll see if they stand up to rough terrain in about a month from now, weather permitting...