Click here to view the embedded video.

The video on the left implements this technique. You can see how it works, by skipping the stops at the stations in the video. The video on the right is original source video, sped up to match the duration of the video on the left. You can see that it does not skip the stops at the station.

I implemented this in Max/MSP/Jitter. The basic algorithm keeps track of the last frame written, and constantly compares the incoming video feed with that frame, calculating a constant difference score that tracks not only the number of differing pixels, but also the amount of difference. When this difference exceeds a defined threshold, then it captures that frame.

Comparing against the last frame captured, instead of simply the previous frame, ensures that even gradual changes will be recorded.

1. On long trips, driving at around 55 mph will get you to your destination faster and more relaxed than by speeding – fewer fuel stops outweigh the greater speed
2. Before asking questions, ask yourself if you really want to know the answer, or if you’re just showing off
3. Get duplicates of any key toiletries (toothbrush, deodorant) and travel accessories (phone chargers, plug adapters) and keep them packed, next to your suitcase. This way you can pack for trips the night before and still brush your teeth before going to the airport.
4. Telling someone to “just be yourself” is rarely good advice. However, telling them to pretend to be someone else opens up the door to learning and transformation.
5. Never buy just one tube of toothpaste. Get two or three at a time, you’ll run out less frequently. Same goes for toilet paper, buy the jumbo pack.
6. Change only one variable at a time
7. Whenever you’re trying to get something done with a group of people, communicate constantly. Communicate more than you might think is necessary.
8. You can’t make anything from a good mango that is better than that. Just eat it raw.
9. Once you get started on a difficult task, it will seem a lot easier.
10. Memories are startlingly inaccurate. Keep records. Revisit them and be surprised.

The first problem was solved easily: ordering a roll of 4″ wide thin Kapton tape from here. It just about matches the width of the build platform, adheres easily, and most importantly, hot ABS sticks to it like there’s no tomorrow, with no need to sand it or otherwise prepare it.

For the second issue, I turned to the increasingly vibrant 3rd party Makerbot parts market, and ordered a Makergear plastruder. This is a replacement for the Makerbot nozzle, which makes a number of important changes to the design, including a stronger PEEK insulator instead of the existing teflon, a ceramic heating element instead of wrapped nichrome, and a much heavier nozzle head.

New Kapton and Makergear nozzle

The Makergear nozzle comes with a clever mounting bracket, but unfortunately it doesn’t fit my Paxtruder, so I salvaged the big retainer washer from another nozzle, and mounted it the 0ld-school way. Nice how you can get two upgrades from completely different sources to work together.

These two elements have led to really reliable printing – don’t need a raft, and no filament jams. I printed one half of the Blender monkey, and was pleased with the results. I had been printing slightly hotter than necessary to try to prevent jams, and now I think I can dial the temperature down a bit.

Suzanne the Blender Monkey

I’ll print the other half of the monkey later. I accept it will come out better, less floppy ears…

Fortunately, there is a lot of great innovation on this front: a fellow called Charles Pax has created the Paxtruder, which uses a Delrin piston and a screw mechanism for the filament drive. Another member of the Thingiverse community, inspired by this, has created a version of the Paxtruder that is a drop-in replacement for the original extruder body, and uses many of the same parts.

A friend of mine very kindly offered to laser-cut the acrylic parts, and I machined a scrap of Delrin to make the pusher, and now I have my very own Paxtruder:

Drop-in Paxtruder in place

It looks great, and works great. It is trivial to get the filament driver pressure exactly right. In addition, the design of the Paxtruder makes it super easy to remove the motor (to clean the gear), and to remove the nozzle assembly. I highly recommend it as an upgrade to the Makerbot.

Assembled Paxtruder

This whole process reflects the power of Open Source hardware: many of the enhancements I’ve made to the Makerbot come from the community, which is empowered to innovate and share. Some of the enhancements can even be made using the Makerbot itself, in a virtuous cycle of machine evolution. Eventually these improvements get rolled into the current production model of the Makerbot. I suspect something like the Paxtruder will be the basis of the upcoming Mk. 5 extruder.

1. When someone asks if you know something, a simple “yes” is rarely the best answer. Stating what you know and confirming it is better.
2. Constraints increase creativity
3. Doing things, however imperfectly, has an effect. Just thinking about things does not.
4. Dessert recipes in English almost always benefit from halving the amount of sugar in them. (This is not always true for recipes in other languages.)
5. You are not aware of the effect alcohol has on your mind, body and personality until you give it up for a month – and it’s greater than you think.
6. Travelling to do something or meet someone is more memorable than travelling to see something
7. When working with someone skilled in another domain, try to learn enough of what they do to be able to have an informed conversation.
8. Children are not little adults, their lives have an internal logic of their own which should be acknowledged.
9. Fatigue is often a symptom of dehydration – drinking water is sometimes more effective than coffee, or a nap.
10. Paying attention to a safety briefing is always a good idea: the downside might be a few minutes wasted, the upside might be saving your life.

Heated build platform in action, printing an Escher cookie cutter

I’d been put off by the large number of surface mount components involved, but it turned out to be much easier than expected. The 20+ resistors and LEDs are cosmetic, they light up with a red glow when the platform is heated, but I figured I might as well assemble them too. I was able to put the whole thing together in less than an hour, with no special surface mount materials or techniques. Just put solder on a row of pads, pushed the pieces in to place, melted the solder, then went back and soldered the other side of the piece with a tiny drop.

I ended up making a few mods to the platform (this seems to be a recurring theme…)

• First, I inserted a six-pin Molex type connector to make it easy to unplug and remove the platform.
• Second, I encountered the common issue where the MOSFET on the extruder controller shuts down due to excess current, so I set it up such that the heated platform is controlled via a 12V relay (only $7 from Radio Shack). Took about 10 minutes to do, and now the thing works very reliably. The instructions for doing this are on the Makerbot wiki (look for “alternate wiring – relay”) – highly recommended.
• Finally, I used a countersink bit and some M3 countersunk screws to make the surface of the build platform completely level. Gives a bit more usable print area, and avoids problems with the nozzle hitting the bolts.

1. People who know how to ask for help are more popular and successful than those who offer unsolicited help
2. When someone is snoring, gently stroking their neck along the line of the carotid artery will silence them
3. In an organization, misbehavior by members low in the hierarchy is usually an institutional problem, misbehavior by leaders is usually an individual problem
4. Adding a teaspoon of vinegar to the water is crucial to successfully poaching eggs
5. When solving a technical problem, knowing what tool to use is most of the solution
6. Limiting options increases productivity
7. Being able to create positive emotional states in others is key to success in life
8. The best work often comes from the people who produce the most work
9. If a shoe is not comfortable when you first try it on, it will never become comfortable
10. The meaning of a message is determined by the receiver, not the sender

First, a terminal block mounted on the extruder body. This allows individually disconnecting the motor and the heater barrel from the extruder, and using shorter wires.

Terminal block on extruder head

Unfortunately, the spacing on the bolt holes in the terminal block does not match the spacing of the bolts on the extruder, so I made a simple adapter with a piece of scrap plastic. I also reversed two of the M3 50 bolts, so that the terminal block mounts on the back of the extruder. This improves visibility of the filament guide, and makes running the wires from the motor easier. It also makes it possible to remove the extruder motor (ie. for cleaning the drive gear) without taking the extruder out of the Makerbot.

Second, I added a 6-pin molex connector into the bundle of cables that runs between the extruder and the controller board, in order to allow for easy disconnection of the entire extruder as a unit. I figure I’ll do the same when the Mk. 5 extruder becomes available.

Molex connector for extruder cables

And finally, some spiral cable wrap to keep everything tidy. It turns out it really helps to keep the cables out of harm way as the Z stage goes up and down.

Ta-da!

Now time to settle down for some serious printing…

I really wanted to print a piece called a “Z-Axis Wobble Arrester”, an upgrade that improves output from the Makerbot. I was to discover that this is actually a very difficult piece to print, due to the narrow walls and fine tolerances of the “springs”.

Here is a picture of various “drafts” of the piece:

Five attempts to print a part

The earliest attempts are on the left, getting steadily better until I got to the part on the right, which is actually functional. Keep reading for a summary of the process I went through to get to a finished part…

The first part used the Makerbot default settings, the ones that will be in use if you install skeinforge 0007 and select the “Makerbot ABS” profile. Layer height is .35mm, feed rate is 25mm/s and extrusion width over thickness is something like 1.8. While the the geometry is perfect, and the layers are laid down perfectly, parts that should be solid are hollow! The good news, even with this first print, is that the Makerbot hardware was working perfectly – very precise layers, excellent adhesion, very little warping. This reassured me that the issue was in the skeinforge configuration, not in the hardware.

I figured that the skeinforge was thinking that the extrusion was thicker than it actually was, and so I should tinker with the extrusion width over thickness setting. So I changed that 1.6, thinking that now skeinforge would think there was room for more plastic. This led to the second part. As you can see, the solids are still hollow. For this part I also set the raft interface layers to 0, which made it much easier to detach. At this point I also realized that the skeinforge preview gives you a very accurate sense of what the print will look like, and whether or not the solid areas will actually be filled. This significantly sped up the configuration process, since I didn’t actually have to print to make settings changes.

For the third part, the biggest change, based on suggestions from the Google Group, was to reduce the layer height to 0.28mm and increase the feed rate. This has the effect of making the filament smaller. I may also have tinkered with the “extra shells on sparse layers” setting. The third print was an improvement – the “springs” are clearly separate, whereas in the first and second prints they were solid and didn’t really flex.

For the fourth part, I increased the feed rate even more aggressively: layer height of .28mm, feed rate of 40mm/s and width over thickness of 1.3 or so. This finally started to fill in the solid parts of the sides, though the area around the screw holes is still hollow. This was shown clearly on the skeinforge preview, I should have believed it. I also switched to the modified wobble arrester model with thicker sides, thinking that this would help.

Finally, for the final piece, the critical change was a parameter in the Inset module, for overlap removal. Apparently this will prune extrusions that are too close to previous ones – however, it was actually removing extrusion paths that were necessary. I changed this parameter to 0.1, to disable it, and changed the extrusion width over thickness to 1.4. Extra shells on base layers and sparse layers went back to 3. This print was very successful. The walls are filled in with concentric shells, not the fill pattern, so it is very solid. The springs flex well.

However, there is a price:

Effect of feed rate on layer regularity

The earlier prints are on the top, and the later prints are on the bottom. As you can see, the prints with a layer height of .35mm and a feed rate of 25mm/s are much more regular. I suspect that forcing the Makerbot to work faster makes it sloppier. I will be working on trying to achieve a happy medium: solid walls, with the kind of Z-axis quality you see in the earlier prints.

You can also see warping in the pieces, they are curved at the ends where they pulled away from the build platform. This is partly due to my impatience, since I peeled them off the platform while they were still warm, but is generally a known issue. I think this will be solved by installing  a heated build platform.

The process was quite straightforward, but I made a number of modifications that seem to make it more reliable and easy to use.

Here it is, in all its glory:

Makerbot 1479

Note the elegant paintjob, white interior and two coats of matte urethane on the exterior. The quality of the plywood on recent kits is really nice, and I wanted to show it off.

Assembly was pretty straightforward, and the Makerbot kit is very cleverly designed. However, it pays to read the comments on the Wiki at each stage: there are changes and suggestions that are not in the main instruction text.

After a lot of tuning, I now have some good configuration settings, and have had some good results printing complex parts. This one is an upgrade for the Makerbot itself:

Z-Stage Wobble Arrester

I made a number of modifications along the way, keep reading after the break to hear about them.

The first two modifications are to the extruder assembly. I replaced the standard pinch wheel with the new Mk. 5 wheel, which is better designed and grips the plastic filament much more effectively. I also used the spare idler wheel to make a double-width idler, which works very well with the Mk. 5 wheel. When making the double-width idler, make sure to enlarge the opening, otherwise putting the bearing in place will crack the acrylic.

Extruder assembly, showing double idler

You can also see another major modification, I moved the extruder controller board to the side of the Makerbot. This allows ready access to the idler wheel nut and bolt, for adjusting tension and releasing the plastic feedstock when it gets stuck.

Side-mounted extruder controller

The slightly awkward placement is to allow easy access to the SD Card. I’ll tidy up the wires too.

Finally, I used a length of copper pipe to protect the insulator barrel. If left uncovered, the PTFE plastic insulator will soften, and will be deformed by the high pressure plastic feedstock going through. Some people have used small hose clamps to bind the insulator to the heater barrel, but this 1/2 inch copper pipe fits exactly, and does the same job. (Looks nicer too!)

I plan to install the Wobble Arrester kit, which uses self-printed parts, a modification that dramatically improves the quality of the prints.

I also have the parts for a heated build platform, which keeps parts warm during printing and keeps them from warping as they cool.