Content

Background

Teams were tasked with the design and construction of a 2.5 DOF system that performed a task of their choice.

The device comprised the structure and motion elements (stepper and servo motors, pulleys, linear guides and belts).

Constraints:

• Minimum work volume: 2.5" x 2.5" x 2.5"

• System should be small and light enough to be easily carried in a backpack

  • It may be partially or completely disassembled for transport

  • If it disassembles for transport, It must be able to be assembled in under 10 minutes

The following components were provided:

• 25mm x 25 mm aluminum extrusion

• NEMA 17 stepper motors

• GT2 belt & pulleys

• MKS v1.6 board

• Access to 3D printing facilities

Design

Design Intent

Our team chose to develop a CNC pyrography machine. We settled on a CoreXY motion system, and developed a tool that used a high-voltage arc and compressed air to burn a substrate (similar to a plasma torch).

The main benefit of a CoreXY system is that it reduces the inertia of a mechanical system by relocating much of the moving mass of a typical serial linear motion system to static locations in the structure.

Mechanical Design

The aluminum extrusion was purchased from 8020.net, which provides CAD models of their products. These extrusion models, along with hardware and fastener models downloaded from McMaster Carr, provided the basis for a SOLIDWORKS assembly.

The design of all 3D-printed components followed a top-down design approach. After the basic geometry was established according to both the project constraints and the CoreXY technique, it was possible to create models within the context of the assembly. Doing so allowed for the parts to be defined directly by the geometry of the extrusion and hardware.

Effector Design

The basis for the effector was the article "Arc Lighter Becomes Plasma Pyrography Pen" by Dan Maloney on Hackaday. It shows that a high-voltage arc can be used to burn wood, rather than a more conventional approach that uses heat.

Control

We were provided with an MKS v1.6 control board (Based on an Arduino Mega). We chose to flash it with a modified version of Marlin, a popular 3D printing firmware. The main benefit of using this firmware was that it allows for a high degree of customization for varying machines with minimal programming knowledge. As such, we could focus on the electro-mechanical design of the system. Control of the system was accomplished via g-code.

Final Product

Thoughts

Overall, this project served as a great hands-on learning activity. We learned a lot about machining tolerances, design for additive manufacturing, troubleshooting for both mechanical and electronic compontents, and CoreXY geometric constraints.

One of the major issues we faced was frequent racking in the gantry, which was caused by the sliding mounts for the gantry become unaligned, which skews the gantry. To address this issue, we increased the length of the sliders along the y-axis, which reduced the angle by which the gantry could skew (It ends up being a trigonometry question to determine the minimum length of the slider).