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.

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

Machine Design / Robotics can be basically broken up into three fields: Hardware, Electronics (also 'hardware' to some people) and Control.

In the CBA Spirit, we figure everything should be modular, recomposable and parametric.

Hardware - RCT Gantries

As in 'roller coaster tycoon' - we use roller bearings as guide elements.

These are parametric linear axis that you can use to fabricate your own linear machines. The repo linked above has hardware documentation, parametric CAD models, and more explanation.

Electronics - ATK - AutomataKit

This is a collection of 'endpoints' for the network that makes up our machine controllers. I.E. each motor, sensor, what-have-you on the machine is given one tiny controller. That controller is responsible for doing very simple things: turning motors about, running low-level feedback control, reporting sensor data, etc. Machine Controller themselves (see next link) are assemblies of these tiny controllers, which we coordinate over a network.

That network protocol / etc is described in the link above, along with links to the currently-available hardware endpoints (and their repositories).

For machine week, you'll have four ATKStepper23's, two ATKBreadBoardBoards and one ATKRouter to hook it all up.

• ATKRouter
• ATKStepper17
• ATKStepper23
• ATKBreadBoardBoard
• ATKBLDCDriver

Control - RNDMC - Reconfigurable Numeric Dataflow Controller

'RUN-DMC' - get it?

This is a piece of software that is designed to help you assemble higher level controllers from the modular pieces of networked hardware mentioned above. It serves a graphical programming interface, or can be used to write a regular old program (in javascript, as a kind of library).

Also This - Open Assemblies

This is just a place where I put links to everything else, including this. If you're ever trying to find something, go here first.

Going About Designing a Machine

Any kind of design process is nonlinear / contradictory. To that end, this guide takes the form of an unordered 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.

Another important note: the process posted here is proscriptive, but it isn't meant to be restrictive. I.E. we only have parametric designs for linear axis here, but there are lots of ways to make rotation happen, and the motors provided are torque-y. There are no rules, this is just an attempt at helping you do the thing!

2) CAD Wrangling

Configure Parametric Axis in Fusion 360

Really, this happens once you know how long / wide you'd like each axis to be.

To start, head to the RCT Gantries Repository and read it and then 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.

WARN making beautifully parametric CAD designs is hard work. Some things might break - especially if you make drastic changes to parameters.

File >> Export

Make sure to change 'type' to .step, and check the 'save to my computer' box.

Set Relations Between Axis in Rhino

Rhino is a great swiss-army knife tool for CAD wrangling. The linear axis we have here can kind of bolt-to-anything, but it will be useful to figure out / plan what / where / how we're going to bolt them together.

.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.

If you're more comfortable in Fusion, you can save configured axis as new files, and include them in an assembly, mating them together there.

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 - although at the time of writing there is only one available for 0.25" thick aluminium, it wouldn't take much to write a new model for 3/8" thick HDPE, or come up with your own mounting blocks.

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. Have I made this point already?

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.

The thing about parametric hardware is that it's kind of going to be like the vise-grips of robotics. Great for most stuff, not perfect for anything. Generality = mediocrity (if all we are interested in is performance). All this to say, trying to stay in the rigid bounds of a parametric system all the way through is often more effort than it's worth: at some point it becomes productive to abandon parametricism and just draw things.

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.

Again, I do this in Rhino because I like to be able to push things around and nest curves by hand. You can also export faces directly from Fusion by:

1. right clicking on a face
2. creating a sketch on that face
3. rick-clicking on that sketch in the feature menu (left)
4. selecting 'save as dxf'

First, pick out the 3D Printed Parts and slice them up. Each axis has these 3D Printed Bits:

• Belt Holders (both sides)
• Belt 'Tenders' (for the motor-adjacent rollers) - 4x

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

For assembly, it's best to follow along the documentation on the RCT Gantries page.

Filippos has put some documentation together from his experience doing all of this.

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

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. Mostly, there is a 1/8" 'O-Cutter' that machines HDPE like a dream, I recommend having two or three of those on hand... Also some taps.

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	or below	Power !	Amazon
Power Supply	24v 500W Letour	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

1. Parametric CAD Software from Autodesk, available free for students and educators. ↩

2. Non-Parametric CAD software available from McNeel, loved by generalists and computational geometry-ists. Educational licenses available. ↩