PROJECT: Half-Life 2 AR2, Update #3 - The Waiting Game


Progress has been quite slow thanks to the hectic period we are in (I'm looking at you COVID19). You would think that working from home would give me more time to work on projects, but being stuck inside for a big portion of the day is quite mentally draining....

But getting back to progress, initial tests of the firing pin assembly were quite positive, I could get reliable cycling up to 3Hz (in the game the AR2 cycles at ~9Hz). The big limiter here is the return motion, which can be improved by using a stiffer spring. However if the spring is too stiff then the forward motion will be negatively impacted. So now I am waiting for a bunch of springs to try out

To keep myself occupied I have started working on the magazine assembly. So far I have defined the area that will house all the electronics (batteries, servo, control board...), and am now figuring out the shell movement (from magazine to barrel). Here is how the AR2 is looking so far:

Also, if you have not seen my previous post I have decided to get the multi material upgrade (MMU2S) for my 3D printer (Prusa i3 MK3S). I envision this being crazy useful as it will enable me to print soluble supports, which will make printing awkward shapes (basically everywhere on AR2) much easier


RESEARCH: SolidWorks Topology Optimization

One of the things I have come to realise with my AR2 project is that having a multi-extrusion 3D printer would be crazy useful, as all my prints to date needed support material which unfortunately is a pain to remove. However, with a multi-extrusion printer you can do fancy stuff like print all supports in PVA, which dissolves in water!

Hence, I finally bit the bullet (bad time to be spending due to COVID19...) and ordered the MMU2S upgrade for my Prusa i3 MK3S. But there is a small hurdle, the MMU2S is designed for large (and preferably flat) working areas, something I do not have. So I decided to modify my current work space with a shelf to hold the 5 rolls of filament, and to spice things up I tried using the Topology Optimization feature in SolidWorks to design the shelf brackets. Overall, this produced quite an organic shape that reduced the bracket weight and gave it the best stiffness to weight ratio

The Steps

NOTE 1: I am running SolidWorks 2018 SP5
NOTE 2: Here is an easy to follow tutorial on Topology Optimization in SolidWorks 

  1. Make a 3D model as you normally would
  2. Add a SolidWorks simulation (SOLIDWORKS Add-Ins → SOLIDWORKS Simulation)
  3. Create a new Topology Study (Simulation → New Study → Topology Study)
  4. Select body material (I went with PET as I will be printing in PETG)
  5. Define the fixtures (faces where the body will be held in place)
  6. Add a force as well as it's direction (I went with 50N as at most the shelf will hold 5 1kg rolls of filament)
  7. Add a model goal (I wanted to reduce mass by 40% while having best stiffness to weight ratio)
  8. Specify the preserved regions and depth (I selected the bracket mounting faces and went with a depth of 2.5mm)
  9. Specify De-mold direction (arrow should be pointing towards flat surface)
  10. Create a model mesh (I used a 2mm curvature-based mesh)
  11. Run the simulation
  12. Finally, adjust the target Material Mass and calculate the Smoothed Mesh

The Results

  • Original model: 
    • 74.4g
    • 210851mm³
  • Topology Optimized model: 
    • 44.5g
    • 84013mm³