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# Roller Coaster Gantries
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These are machine design elements that we use at the CBA when we're spinning up custom machines: they're parametric, aim to be reconfigurable, and we can make them in the lab with a minimum set of stock hardware.
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## Machines Using RCT Gantries

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[Little Rascal](https://gitlab.cba.mit.edu/jakeread/littlerascal)
[Mother Mother, a generalist](https://gitlab.cba.mit.edu/jakeread/mothermother)
[Claystack, a ceramics 3d printer](https://gitlab.cba.mit.edu/jakeread/claystack)
[the Madison Park Vocational Machine, for high schools](https://gitlab.cba.mit.edu/jakeread/mpvmachine)
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# Usage
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This repository should help you figure out how to build your own axis: it contains some explanatory drawings, videos, as well as CAD files and Bills of Materials for various design elements.
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A typical machine-level workflow is described [for machineweek, at this link](https://gitlab.cba.mit.edu/jakeread/machineweek-2018).
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![](video/SEQ-fusion-parametric-enc.mp4)

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First, find the model you'd like to start with on this page and download it, or clone the whole repo. The ```.f3d``` files are parametric Fusion 360 files. Files here are tuned for material thickness choices - but the exact thickness of your material can be tuned in the model: i.e. the 0.375" HDPE model will also work for ~ 8 - 11mm HDPE if you're working with sensible units in another country.
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In Fusion, you can open this file up and use (from the top menu)
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``` Modify >> Change Paremeters ```

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Each of these models should have some parameters starred, these are what you'll want to configure. Go ahead and set axis lengths and material thicknesses according to what you're doing.
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There are also two sets of hole patterns in the last two 'groups' of features on the feature history bar. One puts a 20mm square grid on top of the axis, the other on the bottom. You can leave these in, or customize them, or add whatever mounting-to-the-next-bit design you'd like.

When you're satisfied, you can export the model as a .step file, using the file menu, to prep it for fabrication.
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``` File >> Export ```
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Make sure to change 'type' to .step, and check the 'save to my computer' box. Now you're ready to import it into another assembly.

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**Alternately,** you can save the changes to a new file and import that model into another Fusion 360 Assembly.

# Material Choice

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I've made a little table of different materials we can use. Typically, I stick with Aluminium (on a waterjet) or Acrylic (on a laser). Alternately, Delrin or HDPE can be machined, Delrin is medium-ok to lasercut, and I haven't tried (but am curious about) composites like FR4 and FR1. Probably more towards FR1: glass is a PITA to machine.
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In the fullness of time, and with infinite fab, I figure gantry components (especially elements which see bearing contact) should be made from steels, water or laser-cut.

| Material | Young's Modulus (GPA) | Specific Young's | Cost for 6mm x 24x24" | Machinability |
| --- | ---: | ---: | --- |
| ABS | 2 | ? | 52 | Not Dimensionally Stable, but OK to Machine |
| Nylon 6 | 3 | 2.5 | 130 | Painful |
| HDPE | 1 | ? | 23 | Easy |
| Acetal (Delrin) | 2.8 | ? | 89 | Breezy, also lasers, and non-cracking |
| Cast Acrylic | 3.3 | 2.8 | 46 | Breezy, esp. w/ Lasers |
| 6061 ALU | 69 | 22 | 87 | Breezy with WJ, Painful on Shopbot |
| FR1/CE (Canvas / Phenolic) | 6 | ? | 81 | TBD, probably WJ Pain and Ease on SB |
| FR4/G10 (Fiberglass) | 22 | ? | 98 | Painful on a WJ, Slightly Easier on a Shopbot |
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## The Blocks
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### [N17 Linear and Pinion-Type Belt](gantries/n17_linearPinion/)
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![n17lp](gantries/n17_linearPinion/n17-assem.jpg)
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### [N17 Linear and Pinion-Type Belt, Reduced](gantries/n17_heavyPinion/)
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![n17lp](gantries/n17_heavyPinion/n17-hp-01.jpg)
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### [N17 Linear and Pulley-Type Belt](gantries/n17_linearPulley/)
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![n17pp](gantries/n17_linearPulley/n17pulley.jpg)
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### [N23 Linear and Pinion-Type Belt](gantries/n23_linearPinion/)
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![n23lp](gantries/n23_linearPinion/RCTN23-alu-img.jpg)
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## The Beams

### [Torsion Ain't Easy](beams/)

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## Bonus Kit

### [E Chain with Tape Measure Backbone](tapeChains/)

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![tc](tapeChains/tapeChains-2.jpg)