Friday, December 9, 2011


Yeah that title is cliché as all get out but deal with it. :-) Currently I'm excited that the projects not dead. That sentence needs a little back story. Last week (that time I should have been studying for finals) I got everything hooked up and ready to go with the motor drivers and Boarduino sled I constructed to hook all those motors up in a cleaner manner. I eventually got enough spare time to get it all hooked up to the CNC and with bated breath to see if it would work. Yeah I spelled that right too! I googled it. Anyway, the whole thing went to hell as soon as I gave it the command to move any of the axes. The motor were skipping steps like crazy. There just wasn't anything that was going to make it all work.

I didn't throw anything. I didn't even get super upset. This project has been going on for years. Literally. Its just another hurdle in the road I told myself. So I left the garage and started looking for the solution. The Gecko g540 is probably the most recommended motor driver  over on so thats where I started. Ahren over at CNCRP has a kit that comes with everything to fit the need I was having.

For the small price of $520 the quick and easy solution could be mine. Right? Well no. Since Ive spent the majority of my project fund on the table itself I don't have enough left over to purchase such a fine piece of equipment. More on that later though.

Back to the drawing board I went. (another cliché phrase, is this guy kidding?)  The RepRap stepper driver V2.3 that I've built and am using is built around the Allegro A3982. Not much information is out there about the max specs of the v2.3 driver boards but Allegro provides specs for their chips so I just assumed that the circuit was built to utilize its capabilities.

"The A3982 is a complete stepper motor driver with built in translator for easy operation. It is designed to operate bipolar stepper motors in full- and half-step modes, with an output drive capacity of up to 35 V and ±2 A. The A3982 includes a fixed off-time current regulator which has the ability to operate in slow or mixed decay modes."

Hey I've got four, count them four, of these little drivers and I planned on frying one in the process anyway. After frying a HobbyCNC driver back in the first days of this project Ive come to expect to break a few things from time to time. So I scrounged up the biggest laptop supply I could find, cut the end off of it, found another old ATX power supply, cut the end off that too. Then I wired it all together and gave it a go.

After all that you're wanting me to say it ran perfect and I went on to cut something out or anything spectacular. Well not exactly. It bound up but it did have moments where it ran like it should. Even after cleaning the screw, the rails, and a light WD-40ing, it still bound in places going at the G0 rapid linear motion speed. At the slower G1 speed it did much better. This signifies that the motors are at the edge of their performance curve. Fortunately, Im still only running them at a fraction of what their capable of. Currently Ive got a 20v 6A power supply. Meaning that if I can get a hold of one closer to 35V it should make enough difference to get back on track to hit that dead line.


For now, enjoy this video of my latest Rube Godlberg project that knocks over a can of WD-40

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