3D Scanner – Part 6 – Laser holders

The scanner uses line lasers directed on the object being scanned. They don’t move but they need to be positioned.

This calls for a holder that will not only attach to the frame of the scanner but will also allow some limited movement. Preferably only limited movement when manually moved.

I thought about an axle like I made for the bearings but that would only allow movement in the horizontal axis. Instead, I decided on a ball joint. The fun was actually designing and printing it. I took a number of attempts before I had it working. The 3D design software lets you take a solid and subtract that from another solid so that the two should fix perfectly. That bit wasn’t hard. The thing I forgot is that if you have a ball inside a tube (socket) and that ball is bigger than the internal diameter of the tube, there’s no way the ball is going to pop into the socket when the parts are printed separately. So, I added slits down the side of the tube to allow for the tube to open up to allow the ball to pop in.

This is the ball part. It holds the laser:

 

 

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This is the socket part. It attaches to the scanner frame:

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With the laser and threaded rod. The threaded rod is loose because the internal diameter of the socket part is just enough to form a thread when I screw the rod in but then it wobbles once in place. I’m going to clamp it with a nut on either side.

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With the ball joint together. The laser will be hanging down and the friction of the material is enough to keep it in place when positioned.

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3D Scanner – Part 5 – Driver board case

The driver board needed some kind of enclosure.

I split the case into 3 parts: bottom, middle and top. Once again, this is for print reasons. 3D printers don’t like overhangs that much so the split was necessary so that the print was easier.

Bottom:

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Middle:

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Top:

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The driver board sits in the bottom part:

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The middle provides the top part of the holes for the connections:

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The top covers the board but also has posts that stop the board from rising to much:

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Each layer has a screw hole and the whole case is just tall enough that a 14mm M3-0.5 screw is sufficient to keep it all together.

 

3D Scanner – Part 4 – Turntable support

After identifying the reason for the print failure, I printed a cleaner version of the turntable support. I redesigned it to take the 4 struts. The design is modular for a couple of reasons but first and foremost it’s because, if I merge the struts with the motor support, there will be so much support material it won’t be pretty.

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I made the gap between the motor and the sides of the structure a little wider and this meant that the motor fit a lot better.

I also printed the 4 struts and popped the bearings on.

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You can see that I added a t-shaped tab to the strut design and that slots into the holders on the side of the motor support.

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With those printed, I can slot them into the motor support.

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You notice that there is a part of the tab which is not in a slot. Again, that was for printing reasons so I printed a second half of the same motor support design but without the top plate.

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That slots onto the struts and provides more stability.

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I thought about securing both halves to each other but the struts and tabs  plus the weight of the turntable ( and whatever is being scanned ) provides enough downward pressure to keep it all together.

Next step is to print a new coupler because I redesigned it to take more screws.

 

 

3D Scanner – Part 2 – Printed Parts

With the driver board working, I need to put the turntable on the motor which means I have to build a structure around it.

Some designs print the turntable as a whole. Others print quadrants and attach them together with screws. I’m having a little problem with my prints curling. I know it’s related to the temperature of the hot end but it’s a pain to tweak when all I want to do is to print a flat circle. So, I purchased some pre-cut 7″ diameter wooden circles from Amazon (http://www.amazon.com/gp/product/B00TGFWNMI) for $10. The suggestions I’ve read talk about either painting the turntable with a rubber coating or using the non-slip rubber matting that can be cut to size. I intend to use the latter.

To build the structure, I’m working in parts and will merge some of them so they can print together.

First step, is to attach the structure to the stepper motor. The motor is a NEMA-17 size which has some specific dimension. Lots of drawings can be found online. I’m new to 3D printing so there must be some rule of thumb to apply when copying dimensions verbatim.

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It’s supposed to be 42.3mm square with a 31mm gap between the screw holes. It took me several iterations to get the screw holes to line up with the holes in my design but I managed it.

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Now that I have the design for the top part, I can merge that with the other parts later.

Next step is to couple the motor shaft to the turntable. The shaft is 5 mm diameter and around 21-22mm high. My first pass at the coupling is designed so that the turntable is screwed onto the coupler ( screws descending ).

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While I didn’t allow for any slop in the coupler itself ( it’s a tight press-fit onto the shaft ), I’ve included a hole for an additional screw to clamp the coupler to the shaft. I haven’t tested this yet but I have concerns whether the coupler is too small to allow the turntable to move smoothly. I may need to extend top of the coupler in the 4 directions so that I can add more screws to attach it.

 

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The coupler on its own is not enough to support the turntable so I have to build some support struts. Other designs include a large ring bearing but my plan is for 4 struts with a skateboard bearing on each one and the turntable sits on top of those bearings.

I designed an axle for the bearing with a split down the middle to allow the bearing to pop on but not come off without additional force.

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This one took a few attempts to get right as the diameter of the axle has to wide enough to fit through the bearing hole and tight enough to allow the bearing to spin correctly. Also, the wider part seen on the left has to be bigger than the bearing hole to prevent the bearing coming off but, when both sides are squeezed together, it has to be able to fit through the bearing hole. Now you see why it took a few attempts. I’m not an engineer and I don’t play one on TV.

Anyhoo, once I had that to my liking, I designed a simple strut to attach it to.

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That was fun to do because I could use the 3D design software to take the axle I made and merge it onto a basic strut.

I took another go because I wanted to make the struts a little more aesthetically-pleasing. So, this is the final design.

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To give you an idea on how this is supposed to look, imagine 4 total struts supporting the turntable:

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3D Scanner – Part 1 – Driver Board

I’ve been looking at a Kickstarter project from the guy who is responsible for FreeLSS. This is a 3D scanner using a Raspberry Pi to control a turntable, a couple of lasers and the Raspberry Pi camera. The software takes multiple images of a 3D object as it turns on the turntable and stitches them together to make a 3D model that can be printed.

The Kickstarter project is to put together the STL files to be printed for the structure and also to provide components for the driver boards.

Unfortunately, I was too late to jump on the bandwagon but, with the designer’s intention to make the whole project open source, there’s enough detail on the website to build the driver board and make a structure to support the components.

In another “How hard can this be?” moment, I’ve decided to take up the challenge and see if I can build this.

The hardware driver board is simple. You need something to work the lasers and something to turn the turntable when signals from the Raspberry Pi are received.

The FreeLSS site has the following design:

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The A4988 chip is the driver for the stepper motor and the ULN2003A is a Darlington Array responsible for working the lasers.

I’ve made a couple of adjustments:

  1. The input voltage is 5V for everything. I understand that the designer has made a similar change but that’s only been available to Kickstarter backers. This is handy because the stepper motors I have take a 5V input. Full disclosure: I successfully blew up a couple of L9110S’ by pushing too much voltage through them. They can handle up to 12V but no more.
  2. I’m not powering the Raspberry Pi from this board. I’m happy with powering it from its own power supply. Eventually I can build something that will power both the driver board and the Pi.
  3. I’ve replaced the A4988 with 2 L9110S H-bridge chips. This was because I had the chips available and I didn’t see a need to buy another driver board for this. This will require me to make modifications to the turntable software so that it will work with my driver board. That’s the beauty of open source 🙂

With those changes, I put together the schematic:

DriverBoardSchematic

and, after a couple of attempts at getting the board together, I have something that will drive both the lasers and the stepper motor and not get hot because of short circuits. Here’s a video of my working board.