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    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.

    Just kidding, it's our best practices for how we believe automation equipment should be done.

    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:

    spindle

    Hopefully to come:

    • rotary tool w/ inserts a-la Zund
    • Piezo Touch Probe

    Reference

    BOM

    Hardware ! per Axis ! For 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 M3x40 2 Used only when pre-loading bearing rollers 91292A024
    SHCS M3x30 2 Used only when pre-loading bearing rollers 91292A022
    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 14 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

    End Effector: Spindle

    What Spec QTY Where Used Link
    ESC 40A 6S 1 Driving Motor Hobbyking
    Motor 35-36 1800kV 1 Motor Hobbyking
    Collet Set ER16 1 Tool Holding Amazon
    Collet Holder ER16x100L 1 Bedrock Amazon or Ebay
    Spindle Pulley GT2 40T 12mm Bore 1 Transmission Amazon
    Motor Pulley GT2 20T 5mm Bore 1 Transmission Amazon
    Timing Belt GT2 10mm Wide 75T / 100mm Loop 1 Transmission Amazon or Robotdigg
    6001 Bearings 12x28x8mm 2RS or ZZ 2 Spinning VXB
    Belleville Disc Springs 12.3x21.8x0.75 2-4 Preload McMaster

    Tools

    What Where Used Link or McMaster
    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

    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. ↩