Computer and Controls
| Getting started on a budget |
| The original computer used on
the
first trial
table was a $25 Habitat for Humanity hand-me-down that turned out
to be a Cyrix 6x86 133MHz. This was plenty fast for using TurboCNC as the controller. TurbocCNC can be operated on an ancient 486, so getting started in CNC does not mandate a new computer. |
| Mach2/3 requires Windows XP; an
entry level Compaq 3000+ AMD Sempron with 256 MB SDRAM is used
here with Mach2, and it works fine. This is mentioned because there once was concern about the processing power required, but now even new cheap computers are fast enough. The g-code files can be transferred by memory stick, CD, or floppy disk if the shop computer is not networked. Since one of this shop's computers is over a decade old, floppies are still used occasionally. .....................
|
 The electrical components of the
system were initially screwed to a piece of
scrap plywood. The power supply is a toroid from Plitron® wired with a rectifier, capacitor and bleeder resistors. The toroid is essentially two transformers in one, so its two outputs can be wired in parallel to double the amperage. The custom built toroid, including delivery was $100, and cap, resistors, and rectifier were less than $25 giving a $125 total. That is a bargain for a custom sized high current DC power supply. There is more on the Power Supply page. |
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 The
master kill switch and router-spindle power switch were
standard household light switches. An electrical box was cobbled together from old extension cord plugs and receptacles. It controlled the main115v power to the power supply and router. Simple, cheap, and effective. Also note that pieces of old 12ga. extension cord were used to supply power to each of the servos, it works. The encoder wires were run on the other side of the table to help eliminate any electrical interference. The Gecko 320 drives have to be reset after they fault. A simple N.O. (normally open) push button switch serves this function well. With the drives visible from the work-station and the switches next to them it is easy to keep an eye on their status and reset them as needed. |
 There
are also STOP
switches wired between the Gecko's err/reset terminal and the Gecko's
negative encoder terminal. When pushed, these switches connect the err/reset terminal to ground and fault/stop the drives and motors; the motors then freewheel. The axis can then be turned by hand to the desired position. I find that this is sometimes handier than using the controlling software's jog feature, but it is necessary to reset the software's position coordinates after moving the axis this way. The Geckos do not know what was done to the motor's position when they are asleep. |
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 The
Gecko 320 Servo Drives require
5vdc from the computer which was taken
directly off of one of the stray power supply leads. (Red is 5v, Yellow
is 12v, on the ones I have dealt with anyway).An in-line ½ amp fuse was soldered into the wire, and the wire was run with the printer cable to the break-out board. It then is routed to the three Geckodrives. People have mistakenly used wall wart transformers to supply this 5v for the Geckos; this is not the source Geckos require. It should come from the controlling computer. The 5vdc can also be taken from the computer's game or USB port. ..........................
The cord that attached the computer to the drives was a standard printer cable with a Centronics connector at the printer end, and a DB25 connector at the computer end. There was no point buying a special cable when spare printer cables litter my junk bin. |
 The break-out board such as it is, is simply a
Centronics receptacle from a dead printer soldered to some terminal
strips. Note the DB25 Printer Cable pin order does not correlate 1 to 1 with Centronics. Pins 1 through 14 correlate but then they diverge for some reason.  Only pins 1 through 17 are usually used so there may be no need to connect anymore than these. It seems that the other connections from 18 to 25 vary among manufacturers, so be sure to check your own cables before soldering. Reasons to use a breakout board between the computer and the drives include convenience and to protect the computer from any electrical problems that may develop with the drives and motors. The above unit of course supplies no protection. Installing a separate parallel port card in the computer can offer protection. |
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 The right image is a simple relay
circuit that
utilizes a 2N7000 FETlington. They only cost a dime and their use
greatly simplifies the wiring of the relay. A 5 volt relay can be powered from the 5v PC power supply lead. The diode in the circuit shunts out the coil's electrical "bounce" when the magnetic field collapses. This protects the other electrical components. This diode is a 1N4006 but anything in that ball park will work. The relays, diodes and FETs all came from mouser.com. They ship in small quantities. |
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 The
components eventually found their way into a pair of old panel boxes.
The router-spindle and vacuum were still manually controlled by
switches instead of
being relay
operated, but the machine works. The covers on the case shown here were cut with the CNC machine. As relays were added to the system the control box became overcrowded and had to be rebuilt; no small task.  |
 The
new box is much easier to work with; a large cabinet
should have been used in the first place.This box is made from an old computer cabinet. The box is much neater than the photos indicate. The lack of depth perception makes the wires look cramped and tangled, oh well. The red handled toggles control the Spindle and Aux power. One position is "Standby" indicated by the amber pilots and is activated by software. Other positions are "Off" and "On" with no software control. This override is handy for test runs. It is also used as a safety kill switch for bit changing. |
 There is a bank of relays on the inside of the front panel which controls spindles, panic stop, 5v power-in-feed, etc. A cooling fan directs air directly over the Geckos. With the servos used here, this has not been critical, but on the stepper machines' control boxes the forced air is mandatory. The switches on the outside back are Gecko resets. Click here for an image of the schematic for the Aux. Gecko control. Not only does it allow remote operation of the Geckos but it shuts down all servos and motors if any Gecko faults. |
 An auxiliary
set of Gecko control switches is at the keyboard and is shown with the
trackball. The controls are housed in a 4 x 4 handy box; these cost a buck more or less and are found at Lowes etc. The LEDs indicate the condition of the Geckos. The switch on the far right overrides the fault-all option so that one axis can be disabled while the others move. This is very handy for making preliminary runs while keeping the Z from inadvertently finding a tie down clamp. The circuit for the indicator LEDs is in the documentation that comes with the Geckos, but the Geckodrive docs do not make it clear that the pos. and gnd. for these LEDs are off the encoder terminals, not the power supply. |
 That tip could save a lot of head scratching ;-) The unit resting on the back of the monitor is a USB numeric keypad; it is an inexpensive pendant that controls each axis. The arrow keys, 4,8, 6, and 2 move the X and Y axes. The Page Up and Page Down keys move the Z axis in Mach. With Mach's Keygrabber the small keypad can be programed to do a couple of other functions without tying up standard keys. A wireless keypad was tried as a pendant. The range was aggravatingly short, but an extension USB cord with the antenna placed near the end of the CNC machine made it more useful. But the wired unit has tended to receive the most use since it is dependable. |