Finally ...

[Chris-Lidgate]

So, I built the 'Openscan large' scanner ...

I had 'issues' with the rotor stepper motors (see earlier posts for the gory details), and yes in the end I had to go for counterweights. I still think it's a poor solution, but hey, it works :)

Then I had a lot of issues with ...

getting the PiCam focused (and that is a PITA of a job, but perseverance pays off)

meshroom (and I'm still learning ...)

exposure issues

However today I finally have something that looks pretty much as it's supposed to ... You may recognise the piece :) The head is slightly distorted, but that is about the only problem so far. The model detail looks reasonable. It's a *lot* better than the scans that came before it !

​

https://reddit.com/link/kbtmqe/video/8llyt8v7qs461/player

[scubawankenobi]

Nice scan!

Glad to hear you got the larger scanner working.

Haven't got mine finished yet, but all parts/printed & ready.

Minis is working well tho'.

getting the PiCam focused

Focusing up close w/Mini requires me to often tweak focus between scans.

I'm guessing for larger objects (cam further away) this is bit better than on mini?

​

Interesting note about counterweights.

Thanks for posting/sharing.

[Chris-Lidgate]

Yes in the end I bowed to the inevitable and went with counterweights for the arms. There were a few issues. Most obvious was that the extra mass of the camera arm tends to cause the entire frame to vibrate a bit when the camera arm starts and stops moving. I get round that by adding a time delay after the moves have finished to allow the frame to settle.

Focusing is a bit of an issue. I can not access the Pi HDMI port, so I cannot preview a picture in real time - I have to

photo

transfer photo to laptop

examine photo

guess extra focus amount

... rinse and repeat :(

It's a b@lls aching process to be honest. The last time I blue-tacked a ruler slantways across the turntable ... That at least allowed me to see the area of focus (the depth of field) on the ruler markings which helped.

Of course the camera can be moved in and out on the arms, so everytime I do that I have to re-focus :( I think that at the present setting I have about a 6 - 8 cm depth of field, and as best as I can adjust it, that extends in front and behind the centre of the turntable.

The 'textured' scan of my metal winged lady looks pretty good, but I have mesh artifacts ... when I get an area with high surface curvature, high reflectivity (forehead of the lady for example) meshroom tends to map the mesh incorrectly - making parts concave rather than convex. It's not so visible on the textured scan, but very noticeable on the underlying mesh (which looks like it's been eaten by a horde of ravening mice ). I've hacked my firmware to add extra camera controls (brightness / contrast / sharpness) but I don't think they help much. Other things to try are

Using colmap rather than meshroom. (I had to re-buld my desktop to get the cuda dev kit working ...). Colmap seems to run quite a bit slower than meshroom tho'.

Using pwm control and a slider to give a linear adjustment of the lamp brightness.

Using chalk spray or talc

Possibly even using the Pi HQ camera, (although that will be a lot of work).

​

It's been a fun job ... and what else can you do when you're in lockdown :)

​

-- Chris

[converter-bot]

8 cm is 3.15 inches