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# Roller Coaster Gantries
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 - kinematic mounts are three button head cap screws on 20mm grid w/ reciprocal / wherever-u-like mount ins 
 - all axis have scroll-along top plate w/ connection to motor plate, final scroll kinematic triangle 
 - all axis have scroll-along bottom beam plate w/ 20mm grid w/ last scroll kinematic triangles 

## BOM

### Hardware 

Type | Size | QTY | Where Used | McMaster PN
--- | --- | --- | --- | --- 
SHCS | M3 | 2.5mm Hex | 91292A110 
SHCS | M4 | 3mm Hex | 91292A116 
SHCS | M5 | 4mm Hex | 91292A124 

Type | Meaning
--- | --- 
SHCS | Socket Head Cap Screw: machine screws with hex heads in a 'socket' - i.e. the head is the socket, not the driver. 
FHCS | Flat Head Cap Screw: similar to SHCS but have triangular heads, used when making fastener surfaces flush.
BHCS | Button Head Cap Screw: rounded head socket heads !
PLSTCF | Plastic Thread-Forming Screws: have triangular lobed threads and torx drive caps, wonderful in plastics as the beefy threads mean no inserts required. 


``` OLD DOC: move this to /kunits/README.md and /kunits/images ```

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Scratch / Landing page for the roller-bearings and 2d-sheet-stock axis system.
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With RCT, we break axis into individual kinematic elements - and roll those elements into machine designs. 
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![gantries](/images/one-two-three.gif)
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A reasonable system for beginners, and easy to manufacture (with another CNC mill). Particularely, this system begets the [Madison Park Vocational Machine](https://gitlab.cba.mit.edu/jakeread/mpvm)
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![mill](/images/mpvm-v03.jpg)
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## Building Axis and Machines from 'Kinematic Elements'
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Machines are made of degrees of freedom, and those degrees can be assembled from 'Kinematic Elements' i.e. here I have one Motor / Pulley Unit, as well as Lateral (into the gantry) and Cross (across the gantry) supports. I'm doing a mediocre job of explaining this, but here are some images:
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To scratch a machine together, I pull elements into Rhino as .step files, and lay them out into axis - here's one linear degree of freedom:
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![basically](/images/kunits-basic.png)
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Then I assemble those axis together, keeping track of where I'll be adding plates of material:
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![units xz](/images/kunits-before-form.png)
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Then I go about filling in detail design, adding tabs etc to bring beams and chassis together.
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![one](/images/kunits-one.png)
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![two](/images/kunits-two.png)
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![three](/images/kunits-three.png)
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![four](/images/kunits-four.png)
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## Fabricating Axis 
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I then mill these axis on our shopbot, or any CNC mill you like - the N17 size elements can likely be laser-cut with acrylic or similar (delrin would be nice, but is expensive and a bit toxic to cut, so goes the lore). 
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![cam](images/mpvm-rhino-cam.png)
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I do CAM in Fusion with a .step I export (after flat-packing) from Rhino.
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![mill](/images/mill.jpg)
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## Assembling Axis
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I typically assemble machines one axis at a time. That's not saying much, but here's an image to get a sense of how the hardware goes together:
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![one](images/rct-one-rob.jpg)
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The 'adjustable' elements use a captured nut to pre-load bearings against gantries. TODO is better documentation of this, but here's an image of the flexure in simulation to get a sense for what I mean:
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![sim](images/preload-sim.png)
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# CAD for You
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### RCT Elements NEMA17 Size 
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CAD For these elements is available in the repo [cad/elements/rctElementsN17](cad/elements/rctElementsN17)
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This set assumes you're building with 1/4" HDPE or similar, Nema 17 Motors with GT2 Pulleys of 6mm width, and have access to a set of M3 Socket Head Hardware and 'MR115' or '5116' trade names or similar, 5x11x4mm. Lots of those.
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### RCT Elements for NEMA23 Size
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CAD For these elements is available in the repo [cad/elements/rctElementsN23](cad/elements/rctElementsN23)
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This set assumes you're building with 3/8" HDPE or similar, Nema 23 Motors with GT2 Pulleys of 9mm width, and have access to a set of M5 Socket Head Hardware and 'skate bearings' - 608ZZ or similar, 8x22x7mm. Lots of those.
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## Hardware Notes

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! to add here
 - hardware stackups, BOM, tuning note 
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## Notes for Jake

 - RCT Mod
  - tabs on rail supports still no bueno 
  - std. order side-wall taps / wall-to-surface -
  - of course the belt tensioning needs help ... fold-over or something ? glue it down? single track? 
  - belt tender assy - 3dp walls, bearings to hold-down, m4 screws on to carriage at edges ?  
  - motor rotational tensioning: pin one 

  - and make tools for drill, tap 3dp 
   - also drill / tap m6 / m4 verticals 
   - m4.3 or similar nice for m4 thru on motor 


  - order up tiny clampz 

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## BOM
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 - [N17 Bearings](https://www.amazon.com/5x11x4mm-Replacement-Precision-Bearings-MR115-2RSBU/dp/B00Y5W3JYS/)
 - [N17 Pulleys and Belts](https://www.amazon.com/DerBlue-Meters-Aluminum-printer-Rostock/dp/B0714R39BC/)
 - [N23 Bearings](https://www.amazon.com/608-2RS-Skateboard-Bearing-Rolling-bearings/dp/B073ST742Z/)
 - [N23 Pulleys and Belts](https://www.amazon.com/2GT-Timing-Belt-10Meters-Pulley/dp/B01COEMZC0/)
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# Machines using RCT Gantries
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![mill](/images/mpvm-v03.jpg)
[Madison Park Vocational Machine](https://gitlab.cba.mit.edu/jakeread/mpvmachine)
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![smallgantry](images/smallgantries-fab.jpg)
[Small Gantries Workshop Machine](https://gitlab.cba.mit.edu/jakeread/smallgantries)