To ease fabrication, given the materials and fabrication methods available, the initial CAD model was modified as shown in Fig. 1.
Fig. 1: CAD for BottleBot
Fabrication of Links
The links, guide arm and carriage were additively manufactured (with Fused Deposition Modelling - FDM). This greatly simplified the task of fabricating the complex geometry of the guide arms in addition to reducing machining time required. PLA was the fabrication material of choice as it is less susceptible to warping compared to other materials available for fabricating with FDM (e.g. ABS - see failed build with ABS in Fig. 2). Also, it provided enough strength and smoothness for the sliding of the rollers on the guide arms. To ensure holes were dimensionally accurate and properly-aligned, they were undersized in the CAD models and then drilled to the right sizes on a milling machine after printing.
Fig. 2: Failed build of guide arm (red) caused by excessive warping of ABS
Fabrication of Gears
The driver and driven gears transmitting motion from the motor were also fabricated with FDM. The gears were designed on geargenerator.com and exported to STL format for printing. Dimensions were chosen to amplify the motor's torque output (MA=2.5).
Fabrication of Bearing Shafts
The bearings shafts were a bit long and needed to be cut down to size to allow for a closer fit of the links. We cut the shafts using the jigsaw in the machine shop and then used the lathe with a file to smooth out the rough cut edges to allow for insertion into the bearings.
Baseplate and Stand
The baseplate was laser-cut out of a sheet of acrylic using a sketch of the baseplate surface from the CAD drawing.
Fig. 3: Baseplate
The stand was originally planned to be constructed from 8020 beams but due to unexpected shipping delays, an alternative had to be found. We choose to use wood legs as an alternative due to the wood shop having an extra supply of 2x4 available for use.
We cut two 3 ft pieces out of an 8ft 2x4 and subsequently cut those to pieces in half, giving us 4 legs. Using the jointer and planar machines in the wood we cleaned up the faces of each of the fours to achieve a smooth flat surface on each of the faces of the legs. After the facing was completed we cut the legs down to 2 ft while flattening the ends of each of the legs using the table saw.
Assembly
Mounting hubs, set screws, rolling bearings, and additively-manufactured retention rings were used to achieve tight-fits between the shafts and bearings.
The final assembly is shown below:
Fig 4. Assembled BottleBot