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CNC project repository

Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 32
It has been a busy couple weekends. I have been able to put together a basic form after a couple false starts. Colby had the right Idea going with wood, I have been able to do a composite. Not having the right tools makes it that much harder.
(Below, originally notching out a simple hole in a sliver of wood to fit a bearing. Later I invested in a step drill bit which is quite pricey but cut a clean hole through 22 Gauge steel.)


Below; before metal plating (the wood is too fragile for support, the metal is strong but thin, however with an even spacing and a couple bolts it is sturdy.)


My custom ball screw assembly (upside down and without holes... and yes, it needs some grinding work done to it.


Below, after some metal (it still requires tuning/alignment.)


Below, a little welding and mounting later...

Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 33
At the moment I am looking for dual H-Bridge Drivers and a chopper drive controller/constant current controller.
If anyone has some idea about these I would like to know. This was originally Bob's idea (and it was a good idea; the IC's are better,safer, and cheaper than building from scratch and is going to save some time ) There are H-Bridge drivers on digikey with a large range of amperage and voltage and protective flyback diodes. The chopper driver controller/constant current controller seems to be for optimal torque at high speeds (I noticed a very poor torque with driving some of the spare Bipolars) maybe this was it.
Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 34
And, these are a little smaller than I thought, (double checking the spec-sheet thrice.. ) yes, 2.5Amps output. These are manufactured by Allegro MicroSystems part A3977, spec sheet in docs.


Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 35
Mounted on a couple PCB's. PSpice's Allegro PCB designer is troublesome importing parts (I keep hearing good things about Eagle though.) So, instead of wasting massive amounts of time with PSpice and Allegro (since no simulation was required anyway...) decided to design these in photoshop :) maybe that was a terrible Idea but that is yet to be seen.

These are for the MCU (just for test)


For the motor controllers with chopper drive/current regulation


And finally mounted, the pads are tinned and ready for connections.

Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 36
0.45mm spacing is a bit too much for the paper and iron transfer process. I have been getting what appear to be conductive fiber filaments shorting the power supply. However, I was able to find pcb blanks (similar to the one above for less than cost, coming from china.) Maybe leave the <0.5mm PCB fab for another project. :)
Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 37
Over the last couple of weeks I have made and potentially repeated every mistake possible with motor controller drivers. I have fried a number of chips due to a little clumsiness and a little ignorance. Project still ongoing. Posts coming soon and learning the hard way. "The driver has to be capable of adequately powering the motor. As an example, driver electronics that have a maximum current rating of 1A would not be a good match with a motor that is rated at 3.2A" from http://pminmo.com/mis...­ It seems the maximum current rating isn't going to be the maximum amount of current going through the H-Bridge, which apparently is dictated by the motor (This really wasn't intuitive to me, I thought the internal H-Bridge would limit the current going to the motor) Choosing a driver with a higher amperage than the motor rating seems like the appropriate solution. Suggestions/Criticisms are welcome from anyone:)
Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 38
If your stepper motor controller IC looks like the one in this video, it is probably damaged beyond repair (so, yes, just throw it in the garbage)!

http://www.youtube.co...­





Here are a few mistakes that make this inevitable:
1. Forget using flyback diodes if the chip does not have internal flyback diodes
2. Use a maximum Amperage chip rated lower than the current the motor will draw (Consider the current it will draw as the voltage across the power supply divided by the resistance of the coil.)
3. Use incorrect Rsense resistance values
4. Damage the logic power supply of the IC by connecting it to Vcc inadvertently
5. Leave the Rsense leads open, send a voltage signal to an output, or otherwise do what the datasheet says NOT to do.

Now, getting it right...
Latest progress.

http://www.youtube.co...­



The breadboarded circuit is being driven by an Arudino. I have built this device on a through hole proto board but it is clumsy and susceptible to an accidental jumper. At the moment I am working on integrating a small MCU (ATTiny24A) to manage the driving and a few safety features, this will eventually be put on a PCB.
Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 41
I never managed to solve the problem with the dual H-Bridge constant current IC's. I suspect it could be a bad power supply, bad breadboard, or a sometimes-bad stepper motor. 4 motor controller prototypes were constructed on protoboard (after a successful breadboard prototype) and each of those eventually failed. Spending so much time constructing a prototype and then having it work perfectly fine..then not so much..and finally not work at all is discouraging. The idea was to PCB it, however the confidence factor here was quite low and it didn't make too much sense PCB'ing (And possibly the revisions that followed) without identifying the problem.

The project continues. A new framework has been built from scratch, I have been busy with a few projects from work however I have managed to become familiar with I2C and UART protocol and a few MCU's (Atmel and Microchip.) The motor controllers themselves will be based on a PIC18F14K22. The motor driver is an HY-DIV268N-5A. These motor drivers are current adjustable (up to 5Amps.) Pictures to be posted this weekend.
Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 42
It has a while to go however the basics are there. The x and y axis are not connected yet because the end sensors aren't in place.


Robert H.
user 69712172
Group Organizer
La Canada Flintridge, CA
Post #: 43
A little bit has been added including end sensors and kill switches.


I don't know if anyone is still interested in this. Anyway, the project continues. I have to refine the C# GUI and the microchip master/slave communication, then add a laser. After that will be experimentation with SLS materials, material spreader, and finally a drop box and motor for the z axis (and possibly a fume hood and screen to dampen any laser reflections.)
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