Greetings from The Blessed Realm, little bits of which are seen in every place people drive by (or luckier people live in) and label God’s Country!
Today we’re going to go into rather exhausting detail regarding an infrequently done but sometimes very necessary chore if CAD/CAM is a part of your jewelry or crafting repetoire.
CNC milling machines are wonderful tools but they are subject not only to mechanical breakdown but also electronic breakdown. 1 thousand million clock cycle per second computer systems are practically throw-away these days, and stepper motors are not too hard to replace, so keeping spares of these in stock is always a good and inexpensive idea.
But sometimes the motor driver board either loses a single motor driver channel overnight due to burn out, or even completely goes bye-bye.
Some times one commits a No Shit Sherlock and can as a result easily deduce the immediate cause of driver board failure such as a short in the motor wires, or excessive heat buildup due to an untenable usage of motor torque while jogging or running an NC script. Either of these causes are very well known for releasing the magic smoke so necessary inside advanced semiconductor integrated circuits present on the driver board for properly functioning.
Other times the board can have a service reduced life for any mysterious reason; such as static electricity discharge, dirty power, insufficient air cooling, or even excessive running speeds over several years’ use. However it happens, the board simply decides to head West Over Sea any time it darn well feels like it, usually that time which happens to be least convenient to you.
This can put you into a truly difficult pickled cucumber, especially if you are in the middle of a project. It can even be worse… the board can be out of warrantee by years, especially if part of a CAD/CAM system you purchased used from someone else!
Which was exactly my situation.
Back when I was laid off in 2005, I purchased a 3 axis Taig 2019 ER/CR milling machine with 4 axis Xylotex control box from a jeweler who was using it to make wax models. The original owner used TurboCNC software to drive the control box. I quickly learned to use Ubuntu/EMC2 instead.
Over the intervening time I had learned quite much about using this milling machine for making molds, lettering, fixtures, and machine parts.
But recently some of my aluminum swarf drifted into the control box and shorted out the X axis channel. Leastaways that was my hypothesis for the cause, especially since I blew out bits of swarf when I took the control box apart.
Fortunately I had made very seldom use of my A axis, so I modified my .ini file for EMC2 to use the parallel port lines for A axis as my X axis.
However, this severely limited my options for future art. I therefore resolved to replace the board as soon as practical. However, I soon discovered that simply swapping out a Xylotex X3J board was not practical. I had no original invoice. The company would sell me a new board, but would not replace the X axis driver IC for any amount of money.
This left me so incensed (tell me, who would want to go out of thier way to be so stubbornly arrogant to a customer?) that I decided to go with a different manufacturer.
To that end, I found what turned out to be a solution functionally equivalent to the Xylotex X3J 4-axis stepper motor driver board, and that was the Mechatronics 4-axis board from Easy-CNC. The price was excellent, and the board was designed with all ICs socketed, for making it easier to keep spare parts on hand to maintaining the board rather than replacing it.
You have to order online, but rather than selecting the presented delivery options, simply mention in the comments box to request delivery by US Postal Service from their California office (thier plant is in Mexico), and you will get free shipping. Typical delivery time is 2 weeks, although some people have complained about much longer shipping times. I was just lucky, I guess (shrug).
The Xylotex maintains that socketing the driver motor parts is a bad idea since the heat dissipation transfer becomes vastly inferior. Maybe so… but I’d still rather replace a part than a board, thank you very much. Further, the Mechatronics application notes allow you to derate the maximum power consumption for each channel by adjusting a potentiometer, reducing the need for forced air cooling. I provide fan cooling anyway, but derating is a much better safer than sorrier thing to be done as a general principle.
For all who are interested, here was my journey through the replacement process:
Step 0: Unplug the control box, leaving all other connections intact. Turn on the control box even when no power is attached. This will discharge the power supply capacitor using the driver board as the load.
Attempting a repair without having first performed the discharge of the accumulated charge from the control box’s power supply can lead to serious injury or even death!
Step 1: Disconnect the control box from power, motors, and computers. Note and record all wire connections, especially from power supply and motor windings. Consult the Xylotex 4-axis control box user notes as needed. Windings are marked on the user notes as A, A#, B, B#
for each of the stepper motors X, Y, Z, and A.
Step 2: Note and record jumper settings for stepper motor microstepping. Consult Xylotex application notes for details.
Step 3: Get a better enclosure for the control box, one which allows plenty of air flow but can completely convert the driver board and shield it from conductive swarf. It should also be metal!
(I saved up an obsolete CD-rom juke box I bought 6 years ago because I had wanted it for a vacuum tube amplifier chassis. I decided now was the time to use it!)
Step 4: Remove all unnecessary parts and equipment from your selected chassis.
Step 5: Locate a convenient part of the chassis as a new ground plane for the contents of the old driver box.
Step 6: Inspect the wiring of the original driver box. Just what is wrong with this picture? I’ll tell you: floating ground! Very unsafe! We’ll fix it later by replacing the 2 conductor power cord with a 3 conductor power cord.
Step 7: Locate a metal box of sufficient size to mount on the ground plane of your chassis.
(I saved up this one from 25 years ago from a store going out of business. A fine vintage of metal box. Time for it to do its duty!)
Step 8: Drill holes in new box. Drill some on the bottom of box, but close to the edge for connecting the box to chassis. Then drill others on bottom for mounting the parts of the power supply. Measure hole distances for Mechatronics board through wrapper (touching through wrapper is relatively safe to the electronics), and drill corresponding holes for spaces in top of new box. Drill another hole through top of box to admit power supply leads.
Note: I leave the actual drilling, measuring, placement, transferring, and remounting of the power supply components (without disturbing any connections) as an exercise for my student.
Step 9: Begin replacing the power cord. After having purchased a 3 conductor replacement power cord from a hardware store, use pliers to crimp a solderless lug onto the ground (GREEN colored insulator) wire of the cord.
Step 10: This is how the power cord looks after crimping a lug to ground is done correctly.
Step 11: The 2 conductor power cord is connected at two respective points to the power supply. Very carefully for both caps: unscrew an insulating cap, untwist the old power cord conductor from the other conductors that were under that cap, twist a non-ground conductor of the new power cord with the other conductors (which is why I had you put a grounding lug onto the GREEN wire, so you couldn’t twist that one on by mistake) , then rescrew on the insulating cap.
Step 12: Final step of replacing power cord: Screw ground lug of new power cord securely to new box.
Step 13: Even though the control box has its own on-off switch, I prefer to test unknown circuits with a surge-protected power strip incorporating its own circuit-breaker. This squid is one such example, and can be found at most hardware stores. Be certain the power strip is inactive before plugging in the supply, but that the power supply’s on-off switch is set to the ON state.
That way, if you have happened to shorted your power supply wiring during the components transfer, you can by remotely controlling the power, be obeying the command of this Vala: never to touch any live circuit under test!
Step 14: Connect leads from power supply that had been formerly connected to the Xylotex board, to a digital multimeter reading direct current electrical potential (translation: DC volts).
Now, activate the power strip.
The supply should read at least 30 Volts but not any bit greater than 35 Volts. 35 Volts which is the absolute maximum supply current tolerated by either the Xylotex or Mechatronics boards.
Step 15: If you have reached this point, congratulations! Your power supply is functioning in its new home. But your celebration will be short-lived (and also yourself) unless you first take some precautions prior to connecting the supply to a new driver control board!
Deactivate the power strip first. Then unplug the power strip from the power supply.
Step 16: Using extreme care, discharge the power supply’s output filter capacitor by holding the power supply output leads by thier insulation and touching them together extremely briefly. Normally the driver board functions like a bleeder resistor but since one is not presently connected, you do not have that option.
(I should have been more cautious and worn gloves. Some heat and sparks were liberated when I discharged the capacitor. I used two hands when doing this, one hand would be unsafe, but I needed the other hand to take a picture of the output leads.)
Step 17: Having no drill available to drill a hole in the new power supply box for exit of the new power cord, I instead bent a corner in the box to accomplish the same purpose.
Step 18: The power supply being finished and tested and determined safe for use, mount the new box to the chassis using screws.
Step 19: It would be such a shame to render a new Mechatronics stepper motor driver board completely useless due to discharging static electricity through the board in the process of replacing the old board with it, and seeing as how most people generally do not have ESD (electro-static-discharge) safety equipment in their laboratory.
The next easiest way to set your body to ground potential in the absence of ESD equipment, is to maintain frequent contact with already grounded metal. Practically any metal will serve, such as the metal components from this fan.
The only metal you should not touch is the chassis of your new power supply, because you should not trust its ground at this time.
Step 20: Locate 4 metal spacers compatible with the mounting corners of your old Xylotex board. The spacers that the Xylotex board were mounted on were plastic, and had mounted the board to a plastic case. We want to make certain the general ground for the Xylotex board is securely connected to a grounded chassis, so we will use metal spacers and metal screws.
The corners of the Xylotex board are smaller than those of the Mechatronics board, so you know that if your spacers will not touch circuit board traces on the Xylotex, you should also be safe with the Mechatronics board, and all without opening the wrapper just to check if the spacers will fit!
Step 21: With yourself touching grounded metal periodically to maintain a reasonably low potential of static electricity, carefully open the static protective bag to the Mechatronics board.
Step 22: Using metal screws and metal spacers, mount the Mechatronics board to the new box. Thread power supply leads from filter capacitor through provided hole in top of box. Do not let leads touch each other or any other conductors!. Close top half of box onto bottom of box using screws provided with box.
Step 23: Observing correct polarity, connect the power supply output leads to the Mechatronics board. Activate the device under test through the power strip, as before. Four light emitting diodes should light up on the board, corresponding to hopefully safe and sane functionality of the driver circuits intended for each of the four respective stepper motors.
Step 24: Adjust the maximum current which each of the stepper motor drivers may draw. This is done while no motors are attached.
According to the Mechatronic application notes, the maximum current is 2.5 Amperes (translating units for direct current electrical current). Also according to notes derate this by 70% for safe use with poor or nonexistent forced air cooling. Then multiply by 2 to get desired potential between power supply ground and a test point for the X axis motor driver circuit, which is labeled on the board Test Point One, or TP1. The desired reading should be 3.5 Volts. Adjust corresponding potentiometer as mentioned by application notes as needed. Repeat for Y, Z, and A axes.
Step 25: Deactivate power strip. Wait for light emitting diode indicators to extinguish completely before concluding that the power supply is discharged safely. Using your notes, connect stepper motor cables where indicated by Mechatronics application notes, to the Mechatronics board. The labelling is different: A# on Xylotex corresponds to A- on Mechatronics. Note that conductor positions will be different, so observe connection labelling extremely carefully.
Step 26: While device is inactive, connect a stepper motor to the X axis cable. My rotary table is relatively portable, making it easy to use as a test device.
Note: I like to use 4 conductor telephone connectors and wires for hooking up stepper motors to control boxes. They carry sufficient current for many small CNC systems such as Taig and Sherline, and it makes for very quick snap-in-place installation of stepper motors. I find it superior to 4 wire computer power supply cables and connectors for that reason.
Step 27: Activate power strip. The motor should be held in a very strong grip by the electrical power, unable to be turned by casual manual forces. Adjust electrical potential between power supply ground and Test Point Two, or TP2, as shown in Mechatronic application notes for X stepper motor driver circuit, to 2.5 Volts. Deactivate power strip. Wait for light emitting diode lights to fade completely prior to detaching stepper motor.
Repeat steps 26 and 27 for Y, Z, and A stepper motor driver circuits.
Step 28: The device under test now is now verified as functioning. Check board switch settings for microstepping for each driver motor channel board, to make certain they correspond to the microstepping settings recorded on the Xylotex board from Step 2. This will help make certain that the software will behave correctly.
Then, load the ground plane into the chassis box.
Step 29: Lock the ground plane into the chassis box with screws. Thread all cables out through available holes in your chassis box, hopefully in a direction away from where swarf will fall. While doing this, attach parallel port cable to Mechatronics board.
Step 30: The Xylotex board had provision to power a fan, but the Mechatronics board does not have that feature. I have a spare fan and the chassis box is large enough, so I provide a fan to provide a reasonable imitation of forced air cooling.
Step 31: It helps to secure the fan so that it will not easily move when the chassis does. A wire twist tie serves well here.
Step 32: The board replacement for the control box (and also by the way, the control box replacement in passing, and a grounded power cord for the ungrounded one good measure) is now complete.
All motors cables should be connected at the same time from the motors to the control box, and the parallel port should also be connected to the computer at this time.
Never connect or disconnect stepper motors or the parallel port cable while the control box is live.
Always activate the control box first, prior to starting up the computer.
Final notes:
I install onto the hard drive, the live CD from the Linux CNC website, Ubuntu Version 10 (Lucid Lynx) Real-Time with EMC Version 2.3. Very painless, except for a network file-sharing setup problem that is not relevant on single systems without benefit of network. It turns out that the Mechatronics 4-axis board behaves functionally identical as the Xylotex X3J 4-axis board, so simply use the EMC2 software settings for the latter model board.
Mil gracias to the owners of Easy CNC! All praise to their wine and ale!
Again,
Aulë
{ 1 comment… read it below or add one }
Man, you weren’t lying when you said this was exhaustive detail! But I love it because I’m the type of person that needs STEP-BY-STEP instructions! Thanks for this! It’s definitely helped me!