Machine Building at the CBA
Hello! If you've landed here, it's likely that you're getting ready to design and build some equipment. This guide is part of the MIT Center for Bits and Atoms' ongoing machines-making-machines effort, wherein we seek to turn the universe into a deeply recursive heirarchy of robots building one another.
Most machines are monolithic and static: they live their lives for one process, and are hard to modify for anything else. They tend to miss a lot of learning opportunities (i.e. they feed forward what might be fed back). They each communicate to the outside world in different ways, they hide their secrets, etc, etc.
Machines described here are parametric configurations of object-oriented hardware that can be assembled into instances of equipment, whose constitutent parts are free for future addition and modification. Machine controllers are networked collections of input and output devices that contain bare minimum state - high level planning and interface takes place within virtual machine controllers that are similarly easy to assemble, configure, and tune.
How To Play
Any kind of design is nonlinear and contradictory. To that end, this guide takes the form of an ordered list.
1) Design
I leave 'design' up to you, to save myself following the rabbit hole where I end up writing about it for too long. Look at examples, do back of envelope maths (stiffnesses, forces, speeds, weights) etc, draw things with your hands, with your friends, have ideas, etc.
2) CAD Wrangling
Configure Parametric Axis in Fusion 360
To start, head to the RCT Gantries Repository and download from the CAD folder the parametric axis you'd like to configure.
In Fusion1, you can open this file up and use (from the top menu)
Modify >> Change Paremeters
Each of these models should have some parameters starred, these are what you'll want to configure. Go ahead and set axis lengths, material thicknesses according to what you're doing. When you're satisfied, you can export the model as a .step file, using the file menu, to prep it for fabrication.
File >> Export
Make sure to change 'type' to .step, and check the 'save to my computer' box.
Set Relations Between Axis in Rhino
.step files open up beautifully in Rhino2, where you can go about setting up relationships between parametric elements. I.E. here is where you 'assemble' the components you've configured.
I've also made a set of static blocks that can be configured to connect degrees of freedom to one another, most usefully at 90 degrees. Those models are also available in the RCT Gantries Repository.
I'll also leave the chassis up to you. You can design it in Fusion, or Rhino, whatever you'd like.
Of course, it's also fair game to do everything in Fusion and build a big parametric model (i.e. instances of parametric gantries could be imported to an assembly as components), if you'd like. Rhino is personal preference.
Modifications / Connections in Rhino
Rhino is pretty free-form, and presents a good opportunity to add-in whatever details you'd like - i.e. here I'm modifying the X-Gantry of this machine to lighten it up, and to mate with the Y-connectors on the same machine. I also add a cable-routing tray.
Of course, you can get away without doing very much of this at all - just make sure you have the right holes / mounts set up to secure each axis to eachother.
3) Fabrication
Lay Out Cut Files in Rhino
Once you're feeling O-K about your machine design, you should get ready to cut it out.
First, pick out the 3D Printed Parts and slice them up.
This is a lot of manual model-moving-about and 'nesting'. I recommend drawing out some rectangles of the size you'll be cutting from to make sure you can fit everything into the stock you have available. Your favourite commands will be Orient3Pt , Rotate3D , and Move.
Then, the command that you'll want to use is DupFaceBorder - this will take the faces of your parts (with the RCT Gantries, etc, everything should render well into 2D Cuts only [i.e. no pockets anywhere]), and render them as linework. Then you can export this linework (probably as a .dxf) to whatever machine tool you'd like.
While I cheat by using the CBA's Waterjet and Zund, there are a lot of ways you could go about cutting out the pieces of your machine. HDPE cuts beautifully on a shopbot using a 1/8" single-flute o-cutter, for instance.
Assembly
- fasteners, bearings, belts, oh my
4) Electronics
- circuit assembly
- wiring
5) Controllers
- atkapi hello worlding
End Effectors
I'm working on a few end effectors. You can grab some of these design files and fabricate them, or try designing your own. Here's the simple spindle:
Hopefully to come:
- rotary tool w/ inserts a-la Zund
- Piezo Touch Probe
Reference
BOM
This is a general BOM. For How to Make Almost Anything coordinators, CBA will coordinate ordering material. Section Heads should order HDPE sheets (below, in Material section) to be delivered to their labs, and if shopbots are not 4x8' size, change for 4x4' sheets. You should also make sure you have the right tools in your shops; I've included a list of useful or rare items here as well.
For Section Heads
If you think you're interested in making some aluminum machines, find 0.25" stock someplace: we use Admiral Metals most of the time, McMaster works in a pinch but prices are high. I tend to get 12" x 48" stock sheets. This is a great option if you have a waterjet (or have a friend with a waterjet, i.e. Neil) and don't mind the extra overhead of working with stiff materials: tapping things, cost, etc. But as Ben Jennet reminded me, HDPE has 'ah' GPa of Tensile Modulus (one) and 6061 is ~ 69 GPa, so, lots more stiffness. It would be cool to see labs walking away with useful machines this year. If you get aluminum, also get some HDPE - it's still useful for chassis bits.
Otherwise, McMaster will deliver 4x8' sheets of 3/8" stock HDPE (link below), one is probably enough as long as you don't want to make anything spectacularely large.
Also, make sure you have the right tools. Most of these things should already reside in your shop, I'm keeping a list here just in case.
Everything else I can give to you at the next staff meeting: probably in a big-ish box, but not monstrous. I hope that's OK.
Material
| What | QTY | Link |
|---|---|---|
| Aluminum 1/4" | ~ 4 - 5 12 x 48" Sheets | Admiral |
| HDPE 3/8" / 0.375" | 1-2 Sheets | McMaster |
| PLA for 3D Printing | < 1kg | My Favorite |
Tools
| What | Where Used | Link or McMaster |
|---|---|---|
| Onsrud 1/8" Upcut Spiral Super-O | Milling HDPE Like a Dream | Blackhawk Industrial |
| M3 Tap | Extensively for Aluminum Parts | 2673A71 |
| M5 Tap | Extensively for Aluminum Parts | 2673A74 |
| M6 Tap | Shoulder Bolts | 2673A75 |
| Countersink Bit | Flush Mounting | 27535A48 |
| Hex Driver Set Metric | Cannonical | 5709A18 |
| Torx Driver Set | Nice, Not Necessary | 6370A1 |
| Torx Drill Driver T15 | Wonderful to have for Chassis; No. 6 Button Head Screws | 7396A42 |
| Torx Drill Driver T10 | For Flat-Head No. 6 Screws | 7396A41 |
The Rest of It
Hardware for One NEMA23 Axis with 0.375" HDPE
| Type | Size | QTY | Where Used | McMaster PN |
|---|---|---|---|---|
| Button Head Thread-Forming | No. 6, 3/4" | 10 + (4 * rail tab) (lots) | Connecting Lap and Tab HDPE, Belt Blocks, Chassis | 99512A265 |
| Button Head Thread-Forming | No. 6, 1/2" | 2 | Belt Blocks | 99512A259 |
| Flat Head Thread-Forming | No. 6, 3/4" | 8 | Flush Mounting HDPE | 95893A258 |
| SHCS | M3x20 | 1 | Belt Tensioning at Motor | 91292A123 |
| SHCS | M3x30 | 2 | Used only when pre-loading bearing rollers | 91292A022 |
| SHCS | M3x40 | 2 | Used only when pre-loading bearing rollers | 91292A024 |
| Belleville Washer | 3.1mm ID | 24 | Used only when pre-loading bearing rollers | 96445K157 |
| Locknut | M3, Nylon | 6 | Used only when pre-loading bearing rollers | 90576A102 |
| SHCS | M5x10 | 1 | Connecting Nema 23 Motor | 91292A124 |
| SHCS | M5x16 | 3 | Nema 23 Motor through tensioning arcs | 91292A126 |
| Shoulder Screw | 8mm Shoulder x 8mm x M6 | 10 | Guide Roller Shaft | 92981A198 |
| Shoulder Screw | 8mm Shoulder x 16mm x M6 | 2 | Belt Guide Roller Shaft | 92981A202 |
| Bearing Shim | 8mm ID x 10mm OD x 1mm Thick | 38 | Roller Separation | 98089A381 |
Purchase Parts
| What | Spec | QTY | Where Used | Link |
|---|---|---|---|---|
| 608ZZ Bearings | 8x22x7 | 100 | Rollers | VXB 10, VXB 1000 |
| GT2 Belt | 10mm Wide, Length Dependent | 2 | Belt! | Amazon |
| GT2 Pulley | 10mm Wide, Motor Bore Diameter | 1 | Transmission! | Above, Combo |
| Power Supply | 24v 350W Mean Well | 1 | Power ! | Amazon |
| Stepper Motor | NEMA23 x52mm | 2 | Torque ! | StepperOnline |
| Stepper Motor | NEMA23 x76mm | 2 | Torque ! | StepperOnline |
Wiring
Assuming you're controlling this thing with automatakit, these are the parts you'll want when you're wiring it up.
| What | Spec | QTY | Digikey PN |
|---|---|---|---|
| Power Entry | IEC 320-C14 10A | 1 | 486-3979-ND |
| Power Entry Fuse | 10A | 1 | 486-1226-ND |
| RJ45 Plugs | RJ45 Modular 8p8c, For Flat Cable, IDC | 20 | AE10316-ND |
| RJ45 Cable | 8 Conductor 26AWG Ribbon with Jacket | 100ft | A0082R-100-ND |
| RJ45 Tool | Crimping | 1 | K582-ND |
| DC Power Terminal | M3 Stud Terminal 18-20AWG | 20 | 277-11144-ND |
| 18AWG Hook-Up GND | 18AWG Stranded with Silicone Jacket, Black | 100ft | CN101B-100-ND |
| 18AWG Hook-Up V++ | 18AWG Stranded with Silicone Jacket, Red | 100ft | CN101R-100-ND |
| Zip Ties | ~ 6" | 250 | Q731-ND |
FNs
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Parametric CAD Software from Autodesk, available free for students and educators. ↩
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Non-Parametric CAD software available from McNeel, loved by generalists and computational geometry-ists. Educational licenses available. ↩