Adding Images, Text to follow...
Here's a breakdown of the parts and shots of the project so far. Epoxy putty has been used to reinforce the mounting of the motors as well as several other points where mechanical stress seems to be more likely to be a problem for liquid-type epoxies.
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Boarduino and 2x ULN2003A A Boarduino is simply an Arduino variant that is designed to be used with breadboards. I am a huge fan of the BoArduino, as it can be plugged directly into standard perfboards for semi-dedicated prototypes without the cost or pin alignment issues of the standard Arduino form factor. Other than the form factor, it is functionally identical to a Serial Arduino, as to save cost and space, the USB-to-TTL serial interface is done off-board. ULN2003A are NPN Darlington Arrays which lend themselves to TTL-driven switching applications. Each chip has seven Darlington pairs as well as a supression diode built in, to handle inductive loads like solenoids and motors. I use ULN2003A heavily, as they are very inexpensive (fifty cents or less each) and reduce component count drastically. ULN2003A is ideal for Unipolar stepper motors like the ones I am using, as well as other switching applications that require less than 30v and a total of less than 500ma load on the chip. Another benefit of ULN2003A (or any of it's relatives that are configured for TTL logic levels) is that the Darlington pairs come premade with built-in base resistors. A lower component count always makes a project more likely to succeed.. so the fact that they are designed to take their switching signals straight off the Arduino's logic pins saves a little money and complexity. |
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Two Gear Reduced 5v Stepper Motors Movement is driven by these stepper motors, which can be bought for around two dollars each online. They are mass-produced for applications like operating valves and air vanes in air conditioners. They are very slow, but due to the 1/64 gear reduction, they have tremendous torque,especially considering their tiny current draw. I expect that the speed of the motors may make me replace them with something more robust at some point. The table movement can be done in tiny increments too small to actually move the table beyond the play in gear train, but at top speed it travels so slowly it takes five minutes to move the work surface through it's roughly 12" travel range. |
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Ball Bearing Rails, Base, and Work Platform Two sets of ball bearing drawer slides carry the work platform, which is moved in the x and y axises by a bracket connected to the drive screws (which in turn are connected to the steppers, one per axis) allowing for reasonably accurate movement. These were gotten from a home supply store as "14 Inch Side Mount Ball Bearing Drawer Slides", two per package for about twelve dollars. We need two sets. In use, a third axis, consisting of the router (a Dremel type tool) on it's own drive screw will provide the routing depth, the z axis. Other than depth, the router remains stationary and the work platform along with the routed material is moved relative to the cutting head of the routing tool. The material I have used is 3/8" standard plywood, purchased from a cull bin. If you don't have enough, buy a half sheet and keep the scraps for other projects. If you look closely, you will see that the plywood cuts are sloppy and not even particularly straight. It's the rails which make them move properly, not being perfectly square in shape! |
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2x limit switches These are some I got off ebay, I think they cost around fifty cents each. All that is really needed is a switch that will be pressed by the platform when it reaches the "Home" position. Without some way to detect Home position, the system can't be sure where the platform is exactly. Starting from a known home position allows for repeatable and accurate movement, at least as much as we are looking for. At this point, I see no need for rotary encoders or more complexity than a home position switch. Since we can control the stepping motion relative to that point, our stepper motors provide much more accuracy in terms of measurement than a position encoder.. which would also add cost and complexity. |
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| 1/4" 20 TPI threaded rod and Hardware |  |
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A Buttload of Epoxy and Screws A good amount of this project utilizes fudge factors and making parts in questionable ways. Necessary for this effort is several types of epoxy (shown here are a two-part liquid epoxy, as well as stick-type putty epoxy) as well as screws and random bits of metal as needed. Truly, if you don't consider duct tape a legitimate construction material, read no further. There's also wire, tape, oddball brackets, and many screws ranging from wood screws to panhead machine screws, nuts and washers and the like. It's key that the rails be connected to each other securely, and to the platform and base as well. As long as you aren't restricting the rail movement, adding more screws (within reason) and epoxy isn't a bad idea. If using epoxy, be sure of that you are doing what you want, it's very hard to undo epoxy because you forgot to put a screw in the rail. Typically, firmer connections will help minimize play in the work suface motion. |
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