Saturday, December 31, 2011


Well its now 55 minutes into the new year. 55 minutes past my CNC dead line. Sadly I didn't make that dead line but I am close.
What do I have? I have a CNC table with working X and Y axis. The Z axis wouldn't run due to the less than capable stepper motors. the final thing I have moving forward us a clear path and end goal.
That path is to buy a gecko 540 drive and stepper motors. This will run over $500 but its going to be controlling a $1500 table so that price is on par. I've been hired on at ORNL so I will be able to generate the capital required to finish this project up. So here's the big question. When? That's the hard line. This next semester is going to be jam packed. Senior design. The ORNL internship. Searching for a post graduation job. The list goes on.  My initial though was to push the deadline out till the end of February but to be safe I'm going to say March 15th. This gives me time to gather the funds, wait for it to be shipped, have some unknown delay, get it together, and crank out a piece.
There it is. I'm happy. Big things are happening this year. I graduate. I get a real time job. I finish the CNC.
Thanks for reading

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

Saturday, December 3, 2011

Making the stable connection

 Its like one of those movies that starts with the ending scene. I put together a "Shield" for the Boarduaino to connect the motor drivers. Now its one step further away from looking so ghetto. Unfortunately one of the shafts of the steppers is slightly bent. Its not something I've noticed before so I'm pretty bummed. Never the less I'm hoping that its not enough to matter with helical cut motor couplers. 

I'm weird about symmetry so three motor connectors just wouldn't work. Which is cool because I have four stepper drivers to. Maybe one day Ill incorporate a fourth axis. For now its just a spare connector on the proto board since there's no designated pin for a fourth axis in the GRBL config file.

 There are 4 pins required to run each of the stepper drivers. 2 ground pins, a STEP pin, and a DIR pin. Its complicated to route the wiring on the bottom of the proto board without making it look like a rats nest. A finger nail clipper makes a great wire cutter. Its easy to handle and if you have a hang nail its good for that too. :-)

Here's a picture of the final wiring on the underside of the proto board. It's all pretty close but there's no shorts. The wiring will be hidden in the end when the whole thing is mounted in the computer case.

Hopefully Ill get a chance to connect this all back to the table later this week. Ive got some finals and a proposal to give to the Biosystems Engineering Department. Here's a couple pictures for you interwebians.

Trying to revive the dead.

As an engineer and resident nerd, when a piece of electronics breaks the first thing that comes to mind is can I fix it? I've managed to bring a sound system back to life with a single capacitor. Actually I met a guy while working at Radio Shack that was buying LCDs on Craigslist and fixing them by replacing capacitors on the main board.

So when my router stopped working I decided to crack it open. Netgears routers are simple to take apart if you have a set of torrix bits. There are four screws under the feet. Typically these feet are glued in place but it seems that Netgear may reuse these shells or repair them often because the feet are hinged rather than stuck in place with an adhesive.

 Looking at the internals, its pretty easy to look around. There's no metal covers hiding anything. Everything is open for the pokin'....Sorry. Ill never say that again. Anyway upon inspection I saw that it indeed had a blown capacitor. The green one on the left had a bulge in the top of the canister.

This gave me an opportunity to play with the macro setting on my Nikon D3000.  Enjoy the eye candy. It hard to tell its blown without comparing it to the brown cap beside it so I took a picture with both of them in the frame.

 You can see how flat the one on the right is. Its almost convex compared the blown capacitor.
Radio Shack is way overpriced on parts but the convenience of being able to go down the road and pick it up the same day makes paying 1.49 for a single capacitor ok. Its slightly larger than the original cap due to the fact that it has a higher voltage. When dealing with capacitors you can substitute one with a higher voltage but its important to keep the farads the equivalent. They balance the impedance of the circuit as well as other fun stuff.

So after all this did it work? Sadly it did not this time but it did give me a good reason to upgrade to a N router. It also may provide some useful spare parts in the future. There's several SMD LEDs, resistors, and other junk that could be salvaged with the aid of my high tech solder reflow system (an electric skillet). For now I'm going to keep it intact just in case I come up with another idea to fix it. Drop me a line if you have any clues.