They way I see it is a follows:
Each word can represent up to 1024 x 0.02 mm = 20.48 mm of travel
A word is sent every 40 ms or 25 times a second so
25 x 20.48mm = 512 mm/sec
That is much faster than the retraction speed.
As a suggestion - any filament with additives like wood, stone or (what I am going to use) carbon fiber would DEFINITELY block incoming IR and as they will have a rougher surface should help to eliminate reflections. A small square of black paper above the sensor would also probably help with reflected light.
It would be really nice if there was less of the “may” “might” etc in this article as regards reflections, filament height and design. After all your design and testing surely you could be a bit more specific? It would also help if the author actually specified WHAT TYPES OF FILAMENT would absorb 850 nm wavelengths - I have seen a lot of spec sheets for filament and I have NEVER seen IR absorbance listed as a parameter! As 850 nm is a non visible wavelength colour is actually not much of a guide as dark blue might actually be better than black for example.
A big problem with this company is they are highly knowledgeable engineers, enthusiasts and hobbyists and forget that many people are not and just want to be able to buy something, plug it in and have it work without lots of redesigns and tweaking.
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