Issues with Gen7 Electronics

So in a previous post I showed a picture of the completed Gen7 board. You may have noticed that one of the Pololu Stepper controllers was missing. Specifically the Extruder one. This is because it blew up. Well flamed out is more like it. As I was testing the Gen7 board I was trying to hook up a stepper motor to each axis and see if they would move using the RepRap host software. For some reason when I tried to test the Extruder it burned out my stepper controller. Not sure why. I have posted my situation to the RepRap forum at the link below:

Forum Post

One word of caution. If you do use the Pololu stepper controllers. MAKE SURE YOU SET THE TRIM POT FOR CORRECT CURRENT LIMITING!!

This is detailed on the product page itself:

Product Link

I didn't realize this was needed and when I was running my motor for the first time it got too hot to touch! Once I had the Trim Pot set correctly the motor ran find and cool as ice, though I fear I may have damaged it as I was originally running the full 12V and virtually unlimited current through my 4V, 1200 mAh rated stepper motor.

Z-Axis Issues

So while I was building the Mendel, I had a number of issues with the Z-Axis. The first issue I had was that the threaded rod I got to drive the Z-Axis was not straight. I didn't realize this until I had it assembled. The Z-Axis kept binding when I tried to turn it by hand. After pulling it apart again I realized that the rods were not straight. I ordered some new higher grade stainless steel threaded rod from McMaster Carr. Once I got this cut and assembled it worked better.

However I feel that the entire design for the Z-Axis is a bit fiddly and I'm still having problems with it. It really depends on absolutely perfectly printed parts that are 100% flat. Mine aren't. There are a lot of parts to it and a build defect in any one of them can cause issues. Anytime either end of the axis mount is twisted the slightest bit, the nuts bind on the threaded rod and the Z-Axis becomes impossible to move. If you look in the picture below you will see the non-motor end of the Z-Axis. Notice the space between the bearing and the smooth rod for the Z-Axis. If I try to tighten this bearing up to close the gap it twists the axis and binds it. Still not quite sure how I'm going to overcome this.

If I am able to get the Mendel printing with a fair degree of accuracy. I may look into printing a set of Prusa Z-Axis mounts as they seem much simpler and potentially more reliable.

Oh and by the way...

I've been building my Mendel too! Here is a pic of it almost complete:

PCB Complete

As promised I am posting a picture of the Gen7 board completely soldered. It was quite a bit of fun and I have proceeded with some testing of the board. That will be detailed in another post.

PCB Drilling

Well I got all of the drilling done on the PCB for the Gen 7 Electronics. I used the following equipment for the drilling:

http://www.sears.com/shc/s/p_10153_12605_00953169000P?prdNo=1&blockNo=1&blockType=G1

http://www.sears.com/shc/s/p_10153_12605_00961121000P?

I originally had the Craftsman Variable Speed rotary tool, but when I went to use it I could see the drill bit visually wiggling as it turned. Not good for PCB work. Strangely enough the single speed one seems to be more accurately built. Still some wiggle but not near as much.

I originally purchased all of the recommended drill bit sizes based what came out of the gEDA pcb files. But I only ended up using three sizes as follows (wire sizes shown):

#68 - For the ATX connectors
#60 - For the stepper motor connectors
#58 - For everything else

The #58 seems to be pretty much the all purpose bit. All of the regular through hole components worked fine with this size. The smaller three pin connectors did too as long as I passed the bit through the hole one more time. There is probably a better drill size for this kind of connector (they were originally listed as needing a #60) but there is so much play in the rotary tool that I was afraid of completely blasting away the pads on my PCB if I went bigger.

So much less of an exact science than I thought, mostly due to the tools.

I purchased all of my bits from this guy. Prices seem reasonable and he threw in a bunch of extra bits too!

http://stores.ebay.com/carbideplus

I started soldering in components before posting this so I will post a picture once all of the soldering is complete.

PCB Etching fun

I spent some time over the weekend getting a PCB created for the Gen 7 Electronics.

This was my first time etching a PCB and it was definitely a learning experience. I pretty much followed this guide to the letter:

How to make PCBs at home

Here are the results:

This was actually my third attempt. The first two did not come out well. When I removed the magazine paper on this final attempt there were some issues with the toner pulling off as well. However, I was able to go over all of the places where the toner pulled up with a fine point Sharpie and that worked as a great etch resist.

I had to modify the PCB layout a bit as my power supply is ATX 24 pin and the original board is only setup for ATX 20 pin. These were minor changes.

One other interesting thing I learned is that this stuff works incredibly well for removing the toner after the etching is complete:

I bought this a while ago from my local Auto Parts chain.

The toner literally will just wipe right off (or if enough is used, be blasted right off) after spraying with this stuff.

Be warned though, this stuff is pretty volatile. I did the spraying outside just to be safe.

So there it is. I have my PCB drill bits on the way and will be having a blast drilling the 300+ holes in this board :P

Best Laid Plans

Well I had great plans for this evening. I was going to get down in the shop to cut and drill the thick sheet pieces for the Mendel. But alas, I was trapped working until 10:00 pm.

Sooo... I pulled up a table in the livingroom and did some soldering while watching TV.

I soldered up my six Opto Endstops as per the instructions below:

OptoEndstop 2.1

I also soldered the header pins onto my Stepper Controllers

BEHOLD MY AWESOME CREATIONS! (snicker)

A Mendel in my Mind

After much perusing of the RepRap site and negotiating with my wife about "yet another hobby", I have been able to start procuring all of the bits needed for a RepRap Mendel.  Here is a rundown of how and where I have gone about procuring parts:

Component	Quantity	Vendor (component link)	Notes
Printed Parts	x1	Eckertech Inc.	I was impressed with the photos of the build quality on this site. A little pricey, but I figured it was better to start with quality printed parts.
Vitamins	x1	Thingfarm	All of the hardware and belts to put it together
Thick Sheet	x1	Home Depot	1/4" MDF
Main Electronics	x1	Digikey	I am going to use the Gen 7 Electronics with an etched PCB. I will post a link to a Digikey BOM as soon as I have finalized it.
Power Supply	x1	RadioShack	Bought in Store
Opto Endstops	x6	Makerbot
USB to TTL Cable	x1	Makerbot
Stepper Motors	x4	Pololu
Stepper Controllers	x4	Pololu
Hot End & Adapter	x1	MakerGear	SuperPack (.40 mm Hybrid) Wooden Mounting Pieces - Wade
PLA	x1	MakerGear	3mm PLA 4043D / Blue (was actually a nice translucent ice blue)

Some notes on why I chose the vendors I did:

I am in the U.S. and wanted to try and avoid too much international ordering/shipping. With the vendors above I at least stayed on the same continent.

While I would have loved to purchase a ready built Gen 6 electronics kit from mendel-parts.com I was already over budget. So I opted to go with the Gen 7 electronics and etch my own PCB. We'll see how it goes.

As of right now, everything but the Printed Parts and the Vitamins have arrived.