In part 1 we looked at the start of the track system and the usage of the raw CAD provided by 'move_to' on thingiverse.

http://www.thingiverse.com/thing:70606

Wall E Tracks

As my Wall-E is 1/2 size I scaled the model by 50% and started to break it down into parts for printing. This highlighted a few issues with the model. Some parts of the model are actually inside others, however it should be noted that this might be a result of the conversion into 123D from the original CAD design and maybe even the scaling to 50% original size.

Wall E Tracks Motorclash

This image shows the motor in the design occupies the same space as the edge of the main drive wheels. As I'm not using this motor design I have no problem here since I have redesigned this end completely.

Wall E Tracks DriveWheelMount

In this image we can see the mounting plate for the main drive wheel is actually embedded inside the drive wheel itself and needs to be moved. Moving this out however means there is not actually enough space in between the two drive wheels to fit mounting plates, bearings and motor that I had intended.

With a few changes to the design I overcame these issues but also had to make significant changes due to my scaling of the design. Specifically the holes designed for screws, shafts and bearings are all now the wrong size. Each rotating part had to be redesigned to accept M6 shafts and suitable bearings. I chose the 606zz (6x17x6mm) bearing as suitable and purchased many from ebay. In the CAD design all the points for bearings where altered to match the 6x17x6mm bearings (chosen because they are close to the scaled bearing holes already)

606zz

In addition to these changes I also broke some of the parts down into pieces so that they could be printed flat on the build plate. Some of the parts are designed with decorative effects, as seen on the Wall-E CGI models, and I had to remove some of these since my 50% scaling made them extreamly small and therefore difficult to print.

Wall E Shaft between drive wheels

This image is the horizontal shaft between the two drive wheels. This is a significant redesign from the original CAD to allow for additional space for the wheel attachment plates, bearings and motor removal. Here you can also see where it was split up for printing. Normally I would have printed this in two halves but because my build plate is only 200x200mm I cant fit the whole shaft on the plate so it had to be split into 4. It was split along its length to provide it with strength once re-assembled as splitting it as the natural joins of the rods would make it weak in the wrong direction for what I need.

Wall E Original attachment plateWall E New attachment plate

In the above two images you see different versions of the attachment plate that links the drive wheels to their shafts. The left image is the original CAD design with a grub screw preventing rotation on the shaft. Since everything on mine is scaled by 50% this grub screw is extreamly small and from personal experience using the ABS plastic to accept the screw thread also provides a fairly weak thread. I therefore redesigned it into the image on the right. This replaces the grub screw through plastic attachment with a captive nut and M3 bolt running through it. With this design the bolt that locks to the shaft is using threads from a matching nut rather than threads in the plastic itself making it a stronger grip on the shaft.

As I write this the last of the parts are being printed (on the new Da Vinci) and after ~60hours of printing I can start assembly of the left side track system, but that a subject for another post. Here's a sneak preview of some parts (Idler system that support the track as it runs over the top).

Wall E IdlerWall E Idler CAD

If you look closely you can just see that the center section was printed in two halfs and solvent welded together. This allowed it to be printed flat and with the layers orientated correctly for the load it will carry.