Saturday, April 10, 2010

First shipments made


We sent out our first shipments this morning! We have most of the parts produced for a couple more kits, so we expect to be able to ship new orders out quickly.

I'm working on cleaning up the Alibre assembly files and hope to have them posted today on the Wiki. I also hope to have a hardware list up today or tomorrow. Documentation is still in the works.

Tuesday, April 6, 2010

Steppers, Stops, and Skeins, oh my! (Part 1)

I recently purchased a kit for Wade's Geared Nema17 Extruder. This thing rocks! It pumps out a pretty hefty volume of material compared to the DC-motor based extruders I'm used to working with, at least on a test-bench configuration. However, trying it out on a 3D printer led to a long and continuing saga of soldering and software hacking.

Electronics Modification

This part is documented: extra wires need to be soldered onto the motherboard to connect it to the extruder controller.

This part is in the forums somewhere (I wish I saved the link): the extruder controller doesn't have a current-limiting driver, something that steppers really need to reach their full potential without burning out.

My solution (chances are others have done this also): run the extra wires from the motherboard to a stepper board instead of the extruder controller. The extruder controller now just does temperature control.

Firmware Selection

I've been using ReplicatorG and Skeinforge with the Generation 3 firmware ever since I purchased my MakerBot. Unfortunately the Gen 3 firmware doesn't currently support stepper-driven extruders. (I could have missed something; please post comments/corrections in the comments).

I decided to switch to the 5-D firmware and RepRap Host software. This sent me a long series of rabbit holes that I'm still working my way out of.

Firmware Changes

Many machine-specific parameters are compiled in the 5-D firmware. Things such as steps-per-inch, stepper polarity, and whether acceleration is needed or not are all in the header files in easy-to-change form. Everything, that is, except the stepper polarity for the extruder. This isn't a problem if your stepper is connected to your driver using screw terminals, but it is a problem if it's connected by a polarized plug. I dug deep into the sources and made the necessary change.

End Stops Part 1

The Generation 3 firmware mishandles end stops, so most people using Gen 3 don't bother putting end stops on their machines. I fell into this category. I was surprised to find out that not only does the RepRap Host software handle end stops, it requires them. I searched for a way to disable the homing sequence in the configuration window, but couldn't find one. I never bothered soldering up the end stops in my electronics kit, so I thought I'd just work around it on the software side.

Falling Back to a Familiar Standby

The RepRap Host software doesn't require end stops if it's used with externally-generated g-code. No problem! Replicator G only works with externally-generated g-code. Re-enter Skeinforge.

Skeinforge Upgrade

Skeinforge is a rapidly-moving target. Gen 3 users, including my myself, normally use an older version of Skeinforge. It's what most Gen 3 users are used to, it's what they document, and it's what they point new users to. Unfortunately this older version doesn't support the 5-D firmware, which requires a very different way of controlling the extruder.

Skeinforge Changes

Skeinforge is a rapidly-moving target; it's hard to know which version is new enough to have the features you need, but not so new that it breaks them. I went with the latest; it broke the features I need. Either that or I got confused by its large number of parameters.

Problem 1: E-axis handling. It was generating g-code which drove the E axis a much longer distance than the other axises (by at least an order of magnitude). I dug into the code to figure out why. I closely examined the formula it used, but was unable to make heads or tails of it. I replaced it with the following:

E distance = movement distance * flow rate / 255. Why /255? I'm used to the flow rate being a PWM setting in the range 0-255. I'd probably be better off dropping that old mentality and the /256.

Problem: Skeinforge was designed for DC motor-based extruders, which have very poor flow rate control. Skeinforge adjusts filament width for different portions of the print by varying the X-Y motor speed, which causes the filament to stretch out. My formula cancels this effect. I suspect the original formula was designed to preserve it. I should probably go back to reread it with this in mind. If I understand it, I should be able to adjust the parameters to make it come out well.

Problem 2: fast Z. Skeinforge has a Maximum Z Feed Rate setting. It pretty much ignores it. The resulting g-code was driving Z at a speed that was well beyond the set limit and what the printer could do. This effectively turns the Z motor into a speaker that makes nice sounds but doesn't turn. I did some surgery on (the code that regulates speed). No effect. I selectively disabled Skeinforge features until the problem lessened; was a culprit. It completely clobbered speeds on rapid moves. Fixed that. Tried again. Still too fast. Tracked it down again. Lots of filters modify paths but either preserve the feed rate as-is (not usable with the 5D firmware) or completely replace it with one of the fixed settings (again, not usable with the 5D firmware). At this point I gave up.

Note: this isn't a problem with Skeinforge; it just expects either the firmware or the host software to limit Z (Gen 3 / ReplicatorG does this). It also isn't a problem with the 5D firmware / RepRap Host Software; they just expect externally-generated g-code to completely control speed. It's an integration problem.

End Stops Part 2

To be continued...

Thick Sheets

Since we've modified the y-chassis a bit to better suit our design changes we wanted to make sure at least that item was included with our kits. We thought we could just use our CNC router to cut the thick-sheets but we just didn't have the right bits.

Up-spiral bits work well for thicker materials but quickly de-laminates the plywood along the cut edge. We tried sanding them but just wasn't a worthy finish.

So today started with a short road trip to visit a man with a laser. After several hours of fiddling with getting my 3D cad to produce DXF files with 'hairline' lines we finally got some pieces cut that look as good as we wanted. Its costing us more than using our own machines but I feel it worth it.

The rest of the afternoon was spent cutting blanks of parts. We've got it laid out in such a way that we produce enough of 1-2 parts at a time for 5 kits. So today I cut the z-rod-clamps and the y-motor and y-idler parts. It took a few hours but only because I didn't trust my blank layout enough to leave the machine unattended. It also didn't help that the vibration caused one of the limit switches wires to break at the solder joint. Always wire your switches to break contact, that way if a wire breaks your machine will stop like mine did; always better to know before you need it!!!

The parts still need a little more hand sanding but have turned out wonderfully.

Saturday, April 3, 2010

Batch #1

We are ready to build and ship batch #1. We are going to start with a limited run of 5 units to test the waters. NOTE: We now support shipping internationally, if you have a problem ordering from our website please contact us and we will get it fixed ASAP.