RepRap: Blog

I've been unwinding my maths, and I've redone the outer flexure of the XY Table. Note how all the flexures are now the same length:

 

Of course, the inner flexures use totally different maths, so I can't just apply the same trick for the inner table flexure. Blast. Do that another day and upload both fixes then.

Thinking of being dragged into the '20s. You might have noticed that I've been using Arduino/RAMPS to control the GRBL CNC side of things. Old hardware, but reasonably cheap and I have some kicking around.

Eventually the world will move to FluidNC on the ESP32, but there's a bit of a hardware shortage as all the compatible boards seem to sell out and never get a second run. I have a cunning plan (adding tail and calling it a weasel optional): Get an Arduino-format ESP32 WROOM board and stick one of those nasty, cheap CNC shields on top of it.

 

In theory, that'll allow me to run the new hotness and get ready for the changeover. FluidNC will also provide a built-in web control interface. One advantage of that is that I might be able to stick the game controller jog pad into my laptop, and use that to push gcode into the FluidNC machine over the USB port without having to disconnect my GUI interface.

Guess what popped up in my news feed today?

https://all3dp.com/4/reprap-pioneer-returns-with-a-diy-3d-printer-that-hits-micro-level-precision/

That's Josef Prusa watching me demonstrate μRepRap in his chateau. A handful of Maker notables were also present, and we had an excellent brain melding session there while emptying Josef's wine cellar. 

To quote von Braun "Research is what I'm doing when I don't know what I'm doing." Which is why the XY Table flexure arms aren't all the same length. Damn. Well, we'll get a few microns of vertical resolution back in V0.04, and we'll need it as the working volume increases.

That'll take just a little bit longer though because my laptop SSD has keeled over after being worked hard for 8 years. I have an up to date backup. Just need a working machine...

The problem with the previous reducing pantograph design was that it is damned hard to print as some of the beams cross over each other. It occurred to me that by making the design symmetrical it could be made fully constrained to 1DoF without "crossing the beams."

True, it makes it much larger - in a practical version the main beams would be around 100mm long. But this would still fit on a standard Prusa Mk3 bed.

Again, a parallel linear flexure (not shown) would be needed to fully constrain the driven end. I'll play around and see what the flex angles are and what we can get away with to form a 10mm working area using a reduction of 2.5:1 - shorter beams mean less unwanted flexing in the mechanism

Oh, and if we move the anchored block (on the green line) up and down the Y axis, we can uniformly displace on that too.

To give the μRepRap Axis Driver true linear motion (as opposed to the current very-flat-arc motion) I've suggested using a pantograph mechanism to do the movement reduction. The point of this is to allow common CNC or 3D Printer software to drive μRepRap without having to do maths to get the absolute positioning right.

To create a pantograph using flexures I need two things: First, there can be no shared pivot points; basically every pivot only has one moving arm sticking out of it. Second, the areas where the drive screw and stage attach must have a level land - I cannot directly attach the drive screw or a stage to a pivot point.

So I noodled around with FreeCAD and came up with this 1 DOF-constrained concept, based on having the drive screw on the left flat, stage attached to the middle, and the right flat firmly anchored:

As you can see, this functions as a 3:1 reducing linear pantograph, and you'll note the flats at the bottom remain parallel to the X axis. Printable design left as an exercise to the enthusiast...

Those understanding constraints might notice it relies on the drive screw being linearly constrained, but that can be handled with the same sort of parallel flexure as the Maus C stage uses, so I've cheated and left that off for clarity.

The PEGDA has arrived. For those catching up, this is the main component of a UV curable resin that polymerizes as a stable ionic gel. What this gets us is a way of creating electronic devices using μRepRap's fabrication abilities. These devices won't be the super fast silicon sort of things, but rely on migrating ions into or out of gel structures to change their electrical characteristics.

These structures should be stable in themselves, but for long term use I'll probably encapsulate them in standard UV resin to isolate them. There are though a few other chemicals needed to do these tricks, some of which can be re-purposed from more readily available pharmaceuticals, and others which might need a bit of kitchen chemistry.