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Learning how to build Lotus Seven replicas...together!
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PostPosted: December 15, 2016, 11:48 am 
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seattletom wrote:
This is pretty cool stuff! 8)

mjalaly wrote:
Still trying to figure out how to make it usable after scanning....
Can you add accurate dimensionality to the model once it is in Solidworks? For instance, add a known dimension between two points on the mesh model and have it scale all dimensions proportionally for the rest of the model? I purchased some "factory" drawings of the LS3 several years ago, so could provide specific dimensions for the motor model shown in your post. Alternatively, one could measure between two exhaust manifold bolt holes on a real motor and use those. Or between two points on any object being scanned.

If a dimensioned model was accurate enough for 3D prototyping, it should work well enough for Locost design.


The engine model and transmission are very accurate. The LS3 model came from the web and the transmission was lazer scanned. The issue is that solidworks doesn't like these models so i would need to scale them before coming into solidworks. the other issue is actually using the model. I bring it into solidworks as a STL file (no i really cant output it to a different format) as an STL solid model but it still as all of the cloud points etc. The model is also really hard to modify, like you cant cut extrude it (well you sort of can with surface cut tool) and every change takes like 7min.

I have been trying to change as much as i can in meshmixer before saving as a reduced mesh stl. From what i understand, a lot of people take the mesh model and remodel the whole thing in solidworks.

where did you find factory drawings??

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PostPosted: December 17, 2016, 1:50 am 
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asmasm wrote:
Miata engine scan:
Image

I'll do another scan on a junk block painted white- The areas that show a lot of errors are shiny surfaces (compare the cast iron to the powder coated engine stand).

As far as the workflow goes, to do this kind of scanning you need a decent camera, software, and a relatively power computer. For software I like reality capture. I'm shooting the photos under controlled lighting with a nikon d800E, a good lens, a tripod, and a cable release. The mesh this generates is 14 million triangles, which is super overkill mocking up parts so you can get away with a much lower resolution camera. The main thing is keeping as much in focus as possible, making tack sharp images, treating shiny surfaces with paint or scan spray, and shooting around the object in circles with only a few inches of movement each time. The software looks at the photos to find marker points. If it can find a point on several photos taken at different angles, it can generate a 3d position for that point. Do that a few million times and you have a lot of detailed 3d information.


I actually changed the mesh to one with much less resolution because it was faster to manipulate. I am just building models to cut from foam. Scanning a whole engine is a project, I think I am going to scan individual components next.


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PostPosted: December 17, 2016, 2:51 am 
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mjalaly wrote:
where did you find factory drawings??
I got them from an online outfit called DataDrawings.com They are full scale, dimensioned, black on white drawings of good quality. I purchased right side, top and rear views of the LS3. Should have purchased front and left side at the same time. As I recall, they had a list of other engine and transmission drawings available for sale as well. However, their web site is gone and it looks like they no longer exist. Nothing came up on a quick web search, not even old images.

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PostPosted: December 18, 2016, 9:20 pm 
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I did some testing for how accurate I can get the dimensions. Neither my method for measuring off of the 3d model or my cheap HF calipers are very precise. The scale factor looks to be somewhere in the range of 0.1% to 0.06%. I'm getting a block that threw a rod from a friend. I'll paint that one and upload the result.


Image

Image


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PostPosted: December 19, 2016, 10:13 am 
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@ asmasm, I assume you are using a lazer scanner?

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PostPosted: December 19, 2016, 10:42 am 
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Nope. Really careful photogrammetry:
Image


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PostPosted: December 19, 2016, 11:14 am 
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asmasm wrote:
Nope. Really careful photogrammetry.


hummm.... i tired 123D catch and got some funky geometry. Good but not great This was 70 photos. Shown below with and without texture.


Attachments:
Capture2.JPG
Capture2.JPG [ 63.94 KiB | Viewed 1662 times ]
Capture.JPG
Capture.JPG [ 58.61 KiB | Viewed 1662 times ]

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PostPosted: December 19, 2016, 2:30 pm 
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123d catch is really bad, not surprising it gave bad results (I haven't ever had good results with it). I use reality capture, it's fast and the quality is awesome.

The final quality is largely dependent on the surface treatment of the object (matte surfaces with patterns and textures are best) and the quality of the photos. You need sharp images with as close to everything in focus as possible. Also camera sensor noise screws things up. For that spindle and LBJ I shot 270 photos on a tripod with a cable release at Iso 100, f11, 1/10 of a second exposure. Generally for the best results start by doing 3 loops at different heights. Each photo on the loop should be about 6" of movement. After the intial pass around the object I move in close and shoot multiple positions of each detail. Also try and keep in mind what might not have been in focus your first pass and make sure to get the back sides of things that might not have been captured well the first time.

Also, before processing, I drop the contrast in the raw files and adjust the exposure. You want to open up the shadows as much as possible without losing any detail in the highlights. The images look super flat but that gives the software the most data to pull coordinates from.

For that block you could dust it with developer spray to make a bunch of white flecks on the surface. If you want to send over those photos I can run them through my software and post the result.


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PostPosted: December 19, 2016, 8:56 pm 
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Holy snot, that's actually quite good if it's down to a 3 thou error. :shock:
My Microscribe 3DX arm only has a resolution of 5 thou with an accuracy of 9 thou, so this is on par, if not better.

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PostPosted: December 20, 2016, 9:52 am 
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asmasm wrote:
123d catch is really bad, not surprising it gave bad results (I haven't ever had good results with it). I use reality capture, it's fast and the quality is awesome.

The final quality is largely dependent on the surface treatment of the object (matte surfaces with patterns and textures are best) and the quality of the photos. You need sharp images with as close to everything in focus as possible. Also camera sensor noise screws things up. For that spindle and LBJ I shot 270 photos on a tripod with a cable release at Iso 100, f11, 1/10 of a second exposure. Generally for the best results start by doing 3 loops at different heights. Each photo on the loop should be about 6" of movement. After the intial pass around the object I move in close and shoot multiple positions of each detail. Also try and keep in mind what might not have been in focus your first pass and make sure to get the back sides of things that might not have been captured well the first time.

Also, before processing, I drop the contrast in the raw files and adjust the exposure. You want to open up the shadows as much as possible without losing any detail in the highlights. The images look super flat but that gives the software the most data to pull coordinates from.

For that block you could dust it with developer spray to make a bunch of white flecks on the surface. If you want to send over those photos I can run them through my software and post the result.


sent you a pm!

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PostPosted: December 20, 2016, 11:58 am 
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asmasm wrote:
I did some testing for how accurate I can get the dimensions. Neither my method for measuring off of the 3d model or my cheap HF calipers are very precise. The scale factor looks to be somewhere in the range of 0.1% to 0.06%. I'm getting a block that threw a rod from a friend. I'll paint that one and upload the result.

. . . images removed . . .


Actually, I'd consider those dimensions to be very good. I'd be very interested in knowing more about the nuts and bolts of your photography process. I have a fiberglass Haynes Roadster nose from Jack at Kinetic. I'll be using it on my build initially. In the long term, I want to replace it with a custom nose build by me from aluminum or steel using metal shaping techniques. I'd love to have a scan of the fiberglass Haynes to use as a basis for that future custom shape done in MOI, Rhino or Fusion 360.

Cheers,

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PostPosted: December 20, 2016, 12:08 pm 
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Here is the result out of realitycapture with your photos:
Image


A few observations with your photos. It looks like you moved the block around to get different sides. Generally you want to make sure nothing anywhere in your photos as been disturbed. When you move objects around you get conflicting alignment information between the background and the scan subject. Also when the block moves the lighting on the surfaces changes which results in mismatched pixel colors and difficulty making an alignment.

The main things to improve for better results would be a better camera system. The images are a little soft and the sensor noise is approaching the same level of contrast as the details in some areas- that makes it hard to find matching points.


Lonnie-S wrote:
asmasm wrote:
I did some testing for how accurate I can get the dimensions. Neither my method for measuring off of the 3d model or my cheap HF calipers are very precise. The scale factor looks to be somewhere in the range of 0.1% to 0.06%. I'm getting a block that threw a rod from a friend. I'll paint that one and upload the result.

. . . images removed . . .


Actually, I'd consider those dimensions to be very good. I'd be very interested in knowing more about the nuts and bolts of your photography process. I have a fiberglass Haynes Roadster nose from Jack at Kinetic. I'll be using it on my build initially. In the long term, I want to replace it with a custom nose build by me from aluminum or steel using metal shaping techniques. I'd love to have a scan of the fiberglass Haynes to use as a basis for that future custom shape done in MOI, Rhino or Fusion 360.

Cheers,


The camera is a nikon d800E with a sigma 50mm 1.4 being shot a f/11 on a tripod with a cable release. Scanning a fiberglass nose would be pretty straightforward but you would need to treat the surface so it wasn't glossy and had some details for the scan to pick up.

As far as shooting goes you want to take a lot of images in circles starting with the whole object in frame, then moving in closer.


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PostPosted: December 20, 2016, 4:02 pm 
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asmasm wrote:
Here is the result out of realitycapture with your photos:

A few observations with your photos. It looks like you moved the block around to get different sides. Generally you want to make sure nothing anywhere in your photos as been disturbed. When you move objects around you get conflicting alignment information between the background and the scan subject. Also when the block moves the lighting on the surfaces changes which results in mismatched pixel colors and difficulty making an alignment.

The main things to improve for better results would be a better camera system. The images are a little soft and the sensor noise is approaching the same level of contrast as the details in some areas- that makes it hard to find matching points.


That's better than mine! Did you do any pic processing before putting it into the software? Also the block stayed still, i think i mixed up two different shoots in that photo batch and those pics were from my camera phone so I will try to track down something better. Have you figured out a way to bring the file size down to be useful in other softwares without killing the shapes???

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PostPosted: December 20, 2016, 11:13 pm 
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Plastidip?


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PostPosted: December 20, 2016, 11:55 pm 
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Nope. Really careful photogrammetry:


I note strategic use of a short person to manipulate the tripod without getting in the camera's way. Kudos! :rofl:

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