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Ideas Going Into the Visible Robot

The idea:
The basic idea behind the “Visible Robot” is to create a simple extensible 3-axis robot that a parent and child can build together to learn about the fascinating world of robotics.

The idea comes from the days following one Christmas when my father watched me assemble a model Ford V8 called the “Visible V8,” answering my questions along the way. From this experience, as a pre-teen, I learned how an internal combustion engine worked.

For the more advanced, this 3-axis machine can be built upon and extended into a light-duty desktop manufacturing workstation. The Visible 3Bot and the Finix Auto Tool-Changer—ATC  (a beta product) gives peeks into what might be done in terms of extending the Visible Robot’s ecosystem.

             “The 21 st century belongs to the skilled and the creative.”

Some will find this design wanting in one way or another and will design and build improvements to it. I encourage them to do this, using the same or similar licensing terms. I sincerely hope they’ll become the giants who provide their shoulders for others to stand on.

Ideas going into the design:

Open Source: The machine is intended as a base device that can be hacked, extended and improved. By its licensing (http://finixsystems.com/licensing), extensions can be made and given (or even sold) back to the community.

Open: True to the model of the “Visible-V8” of my childhood, the Visible Robot’s workings are clearly visible via its open-box mechanical architecture and glass bed. The viewer can see all the components and how they work together.

A Workcell vs. a Robot: Beyond simple visibility, the openness of the design allows various other devices to be placed alongside and within its perimeters. These auxiliary devices will complement the machine in giving it increased capabilities. Examples: a conveyor bringing parts to the machine, a carousel offering other tools to use, etc.

Scalable: The simple cartesian (box-like) design allows for sizing the device to accommodate the needs of the working space available and the workpieces to be manufactured. Changes to the lengths of the frame members (and possibly their diameters) and the angles of the stiffening supports are all that’s required.

Extendable: The design was intended from the outset to be a basis for a tabletop “workcell”—a small manufacturing center with associated programmable tools, sensors and feeders. The form-factor chosen is that of a gantry-style cartesian-coordinate structure. The open-sided design is intended to allow for enrichment of its ecosystem. It allows for extending the system to include new functionalities, such as tool-presentation devices, cutting bit exchange, vision inspection, new gripper types, and 4th and 5th degree-of-freedom joints.

Multiple gantries can be driven along the same common axis to give additional productivity and capability. Think of the robot as a “one-armed paper-hanger” and how this might be helped with a second or third ‘arm.’ (See http://finixsystems.com/product/visible-3bot/).

Easy to Print: A simple, small-footprint 3D printer is all that’s needed to print the parts of this design. All the 3D printed parts can be printed in non-toxic, non-fuming PLA. The parts to the working prototypes were all printed in my small home office/computer room which has no outside ventilation. No support material is required for any of the parts.

Easy to Assemble: The base and gantry are fastened with standard 5/16” and 3/8” nuts. M3 (3mm) screws are used throughout for non-structural component fastening. The printed components themselves contain holes serving as lock-nuts for fastening. (For those in metric environments, 8mm and 10mm can be substituted easily for the 5/16” and 3/8” parts).

Easy to Align: With all corners of an axis fixed, a precision machine can be difficult to align due to very slight differences in shaft parallelism. Allowing a small amount of ‘slop’ in just one corner retains the precision of the device—the ‘reference datum’ is on the opposing shaft to the ‘sloppy’ one—yet allows much easier alignment.

Easy to Wire: Easily obtained ribbon cable, with attached Dupont connectors can be used for the wiring. These are made to be easily pulled apart to give as many wires as needed for connection to the motors, micro-switches, etc.

Designed to be Built Anywhere: The base design includes precision parts such as linear bearings, leadscrews and anti- backlash nuts, which give the machine its resolution. Coupling and framing those precision parts is a combination of 3D-printed plastic parts and  inexpensive threaded rod and nuts and bolts that can be bought at any hardware store.

Conceptually, aside from the necessary precision components, the intent was that the machine could be built in the developing world as easily as in the developed.

Value-oriented: The combination of precision parts where necessary, but otherwise inexpensive components leads to the ideal of a “value-oriented” system. The Visible Robot is not targeted at the “low end.” Instead, it is targeted as a foundation for a useful light-duty desktop machine tool, capable of performing tasks—albeit at lower precision, lower speed and smaller tool and part size—that one would see done in a machine shop.

Minimal Tools Required: To accommodate building the machine in the home, whether the home is a sprawling home in the suburbs or a hut in the jungle, it is designed to be assembled by hand, with minimal tools. Fastening is by nuts and bolts rather than by weldments. A tiny home or neighborhood-based 3D printer can print the needed connecting parts. The parts printed for the machine were all done on a Printrbot Jr., with a workspace of 5” x 4.5” x 4” (130mm x 115mm x 100mm).

Nuts are typically a part of the printed component, achieving a locking of the screw similar to a lock-nut, thereby avoiding the need for extra fasteners—nuts and lock washers.

Stiffness: Mechanically, a measure of stiffness is achieved using inexpensive threaded-rod (T-rod) set at angles bracing the ‘X’ and ‘Y’ axes.

To avoid reliance on an inherently imprecise plastic extrusion process, metal-to-metal contact is used where it can be. The ‘X’ and ‘Y’ shafts, gantry shafts and ends of the threaded-rod frame all contact one another.

The ‘Z’ axis has three shafts to help resist moments (side forces).

Cable-routing: Care has been taken with the design of cabling routing, such that it is not free to interfere with the travel of any axis or the workpiece.

Easy Workbed Leveling: The bed can be leveled using the four thumbwheel leveling dials—one at each corner. A hex-head (Allen) bolt and spring mechanism is used to set the “Home” position of the Z-axis (typically, on a 3D-printer, the nozzle position just above the workbed).

Open Source: Source code for the parts is available as well as the compiled “.STL” files, such as one would find on Thingiverse, Pinshape, Shapeways, or in other parts repositories, some of which are listed here: www.reprap.org/wiki/Printable_part_sources. Nearly three years of work—trial and error—has gone into the design, therefore, the code is being provided “Free as in speech,” rather than as “Free as in beer,” for what I consider a fair and relatively nominal charge.

Acknowledgements: This design would not have been possible without others who have gone before and provided the Arduino platform, robot-control ‘shields’ for it, design software, robot control software, slicing software, etc. In this design and its implementation I’ve used the Arduino, Printrboard, RAMPS, Megatronics, OpenSCAD, Repetier Firmware, Repetier Host, Curaengine and Slic3r, and the vision of RepRap—the self-replicating robot. I thank and am indebted to the developers and maintainers of these stalwarts of the Free and Open Source Software and Hardware world.

For hacking the design of the plastic parts, a free and open-source program (OpenSCAD) available at www.openscad.org is used. (BTW: a nice first-entry into the world of programming languages in that one can visualize the outcome of the program as a shape that one’s just created)!

RepetierFirmware (not included) is suggested as the firmware base for the ArduinoMega/RAMPS control board.

RepetierHost (not included) is suggested as the robot controller.

RepetierFirmware and RepetierHost are both available for free download at www.repetier.com.

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