Convention food: Homemade snack bars

Gencon - the wonderful gaming convention my wife and I attend every year - is less than two weeks away.   As usual, all thoughts of moderation fled when I downloaded the event schedule, and I have signed up for at least 8 hours of events every day of the convention.  On top of that, there's a motorcycle rally in the city the same weekend, plus a concert or two and some other events going on.  Between all that and the 40,000+ gamers at the convention, I expect it to be nearly impossible to get into any of the city restaurants for food without a multi-hour wait - which I won't have the time for.

Sure, there's always the Indy Convention Center food court, but the food from there is terrible, overpriced, and rumor has it there was some nasty food poisoning going around last year.

My wife taught me the habit of preparing non-perishable food before conventions and long trips.  She's been making jerky and fruit leather for some years.  I've learned to make a sort of homemade snack bar, useful for those marathon gaming sessions when I won't be able to get out for real food.

This year, I've made three batches of snack bars:  a coconut-pineapple batch, an experimental chocolate-chip batch, and a kiwi-strawberry batch.  The recipe starts out essentially the same for all three.

The Recipe

The recipe is made up of three main parts.  First is an oat-based dry mixture that's toasted in the oven before mixing with the other parts.  The second part is a wet sugar and honey based glue material that needs to be heated and melted before mixing.  The third part is dried fruit or similar non-cooked material added into the mix at the last step.  The exact recipe of each part can be varied to taste, so long as the overall ratios are kept about the same.

Timing is important, as you want to mix the three parts and press them into the final form while the dry mixture and the glue are both still hot, as they will solidify and become unworkable as they cool.  You will want to have all your ingredients measured out and ready before starting to mix anything.

Part 1:  The dry mixture.

We start by preparing the dry mixture.  I use a large glass casserole dish to mix the dry ingredients.

First, two cups of Old Fashioned Quaker Oats, to make up the bulk of the bars.

Add three-quarters of a cup of ground flax seed or wheat germ.  I'm using flax seed here.

Then add three-quarters of a cup of shelled, unsalted sunflower seeds.

Now we need about a cup of finely chopped nuts.  You can buy chopped nuts, or you can get whole shelled nuts and crush them yourself.  For the first batch of bars (coconut-pineapple) I used a package of macadamia nuts, which are soft and quite easy to smash, along with some walnuts since I didn't quite have a cup of macadamias.

To crush them, put the nuts in a plastic ziplock bag, then carefully whack them repeatedly with a measuring cup or other heavy blunt object.  You can also use a fancy nut chopper or wooden mallet to do this.

Finally, for the first batch of bars (pineapple-coconut), I added three-quarters of a cup of dry shredded coconut to the mix.  The other two batches didn't get anything else added at this step.

 

Now stir the ingredients in the casserole dish, mixing them evenly.  Heat your oven to 400 degrees and put the casserole dish in the oven.  Set a timer for 12 minutes, and then while the dry mixture is roasting you can prepare the second part of the recipe.

Part 2:  The glue mixture.

 Put a medium-sized saucepan on the stove over medium heat.

Melt 4 ounces - half a stick - of unsalted butter (or you can use salted, but then reduce the amount of salt added later) in the saucepan.  Be careful not to burn the butter, you want to just melt it gently.

For the basic recipe, measure out two-thirds of a cup of brown sugar, and two-thirds of a cup of honey.  You can optionally replace some of the honey with any similar sweet syrupy material.  Maple syrup works well.  You can use molasses, but it has a strong flavor so use sparingly.  Chocolate syrup can also be used, as can peanut butter, if you want to add those flavors to the bars.

Add the sugar and honey to the melted butter, and stir well.  While stirring add half a teaspoon of salt and two teaspoons of vanilla extract.

While the glue material is simmering, you should periodically open the oven and stir the roasting dry mixture with a heat-resistant spatula to make sure it cooks evenly and doesn't burn.

Part 3:  Dried fruit or similar flavoring ingredients

While the dry mixture is roasting and the glue is simmering (don't forget to stir both periodically!) prepare your dried fruit.  This part is where you can experiment the most with varying the recipe in order to give each batch a different flavor.

For the first batch, I bought a package of dried pineapple.  Dried pineapple comes in two different basic types - there's the heavily sugared stuff that looks like chunks of golden jelly, and the natural stuff that's flat and stringy.  So far I've only used the first type for making these bars, although it should work just as well with either.

To mix evenly with the other ingredients, you want the dried fruit to be finely chopped.

My trusty ulu works great for this.


Nearly any kind of dried fruit should be usable in this step.  In theory, you could also use chocolate chips or small candies if you're making a dessert bar.

Part 4: Mixing it all together.

Once the dry mixture has been toasting for 12 minutes, the glue is melted and ready, and the fruit is chopped, it's time to mix everything.  You'll want to do this quickly, getting the materials mixed while hot before they start to set up.

Take the dry mixture out of the oven, and transfer to a large mixing bowl.  Do this carefully, as the material will still be quite hot.  Then pour the heated glue into the bowl, and start stirring.  Add in the dried fruit or other ingredients.  Mix well, making sure to get all the oats and such fully wetted with the glue.

You can turn the oven off at this stage, you won't need it anymore.

Once the mixture is fully blended, turn back to the still-hot casserole pan you roasted the dry mix in.  Clean out any remaining bits of oats or whatever, and then line the pan with wax paper.  Transfer the still-hot mixture from the mixing bowl into the casserole pan, and spread it evenly.  Then take a second piece of wax paper, and spread it over the top of the mixture.  Press down on the wax paper.  You want to compress the mixture into an even layer and press out any air remaining between the grains.

Let the snack bar mix in the casserole pan cool to room temperature.  Then transfer it to the refrigerator to let it cool and harden further.  You could theoretically put it straight into the refrigerator after pressing it into the pan, but I worry about thermal shock cracking the glass, so I let it cool in stages.

After the snack bar mixture has cooled and hardened, remove it from fridge.  Flip the pan upside-down over a cutting board, and pull down on the wax paper until the mass comes loose.  Peel off the upper wax paper sheet.

Now, with a sharp knife, cut the snack bar mix into 16 (or however many you desire) bars.

You can wrap or bag these individually and store them in the fridge or freezer.  They should keep for quite some time.  I like to vacuum-bag them and put them in the freezer, thawing them out only right before the convention.

The Black & Decker food saver took some time to learn how to use reliably, and doesn't work well for all types of foods.  I have managed to get it to bag and seal these bars consistently now.


The coconut-pineapple bars were a recipe I'd made before, and one I knew would work well.  For the second batch, I decided to try a more dessert-type recipe.  I substituted a bit of chocolate syrup and molasses for some of the honey, and used chocolate chips instead of dried fruit.  I also used chopped hazelnuts and pecans in the dried mix instead of macadamias.

The chocolate chips melted the instant they hit the other still-hot ingredients, so rather than the effect of having chocolate chips embedded in the oat mixture I ended up with a homogenous chocolate-flavored bar.  It still seems to have come out reasonably well.


For the third batch, I decided to make my own dried fruit, using our dehydrator.  Ideally, this would have started with a trip to one of the local pick-your-own farms to gather ingredients by hand.  Sadly, the heat and drought we've been having this year mean none of the local places had a decent crop.  I had a hard enough time even finding a decent selection at the supermarkets.

After throwing out the spoiled ones, I have enough strawberries for a third batch of bars.

The tops are cut off, and the rest are sliced into pieces about an eighth to a quarter inch thick.  These go into my wife's food dehydrator, set to low and left to run overnight.  You want to make sure they get fully dry to the point of being crispy - any moisture will make them spoil faster.

I combined the crispy dried strawberry flakes with some dried kiwi fruit I bought at a store.  I had originally bought the dried kiwis for snacking, but didn't like them much after trying them.  I figured to try them in this recipe.  Note that like the pineapple chunks, they need to be chopped further to mix evenly.

For the dry mix, I omit the dried shredded coconut, and used chopped walnuts for the nut ingredient.  In the glue, I substituted a little Grade B maple syrup (darker, with a stronger flavor) for some of the honey.

This batch came out beautifully.  Very sweet, with strong kiwi-strawberry flavors, and visually is very distinct with the red and green of the dried fruit visible in each bar.  I'm calling this a success.

With these - and the jerky and fruit leathers my wife will be making next week - I should be set for the convention even if I never manage to get out for a real sit-down meal for the entire weekend.

Gencon Schedule Solver

Gencon has an absurd number of events taking place over the course of 5 days.  Many of these events are things I'd like to attend, with varying degrees of liking.  Many of the events are run at different times through the weekend, giving me multiple opportunities to attend them.  Some events - such as the True Dungeon events - have over 100 timeslots, others have only a few.  The number of possible schedule combinations are huge.

I could simply pull out the calendar and go over it manually, working out the optimum schedule on my own, but I'm lazy, and when presented with that kind of challenge I prefer to automate it.  So I created a Python script.

This script was in part an excuse to learn how to use some of the url library functions in Python, as it connects on its own to the Gencon community file directory and downloads the latest event calendar automatically.  On extracting the event file it then processes it and attempts to find all events which are the same event run in multiple slots, and combines them into single entry.

There's a fairly simple command-line interface I wrote to search the event list to find the events I wanted, and then assign a priority to each one.  The script then works through all the possible permutations of events, assigns a rating to each one, and then either presents the best possible schedule, or walks the user through the registration process and adjusts the schedule as required to account for events filling up.

It's still crude and buggy, but works for its intended purpose - optimizing your event schedule.

I made the mistake of mentioning this on the Gencon community forums, and immediately received requests for the script.

I have put the script on a pastebin page here:

http://pastebin.com/Rmuf0iJS

Or you can download it as a file from here:

http://www.2shared.com/file/QSKfjxeY/Gencon_schedule_solver_2012.html

To use this, you will need to first install Python 2.7.  Then, either download and extract the zipped file, or create a new file in the Idle python text editor and copy-and-paste the text from pastebin.

Run the script.  The first time it is run, it will create a directory for event calendars.  It will ask you if you want to download the latest schedule.  Obviously, you need to say yes on the first time or it won't have anything to work with.  You can then search for events, create wishlists, and then have it solve for optimal schedules.  Command help is imbedded in the script, just type 'help' at the command line.

Replacing a broken leg

The final sections of the legs on my walking robots are made from a piece of waterjet cut steel, which the servo attaches to, welded to a short steel tube, containing the homebrew shock absorbers on the feet.  The weld between the servo mount piece and the tube is the weak point in the design.  One of these welds cracked after GenCon 2011.  I never got around to fixing it, instead using some Shapelock plastic to shore up the joint as a temporary patch that held well enough to become permanent.

At Wicked Faire 2012, another leg failed at the same spot, this one cracking badly enough for the shock tube to come completely loose.  I wasn't going to be able to patch this one back together short of re-welding it.

Since I now have access to a 3D printer, I decided to try and see if I could print out a replacement part  instead.  I wanted to keep the existing shock absorber tube, so after a few trial designs I made a two-part plastic assembly that clamps together around the tube and attaches it to the mounting tabs on the servo case.

The mounting frame is still using the same screws to mount to the servo tabs, as I'm still using the rubber mounting blocks to try and spare the servo gears the worst of the impact shocks from walking.

It seems to work, but I'll have to walk it around for a bit to make sure it's as durable as the old steel frames were.  Once I'm confident in the design I'll be printing out parts to rebuild all four legs this way.

This part is close to the maximum size the machine can print - I had to rotate it 45 degrees to fit it on the print bed.  This brings up another problem I've been having with the Makerbot recently.  Large prints, especially parts like this which stretch diagonally across the bed, tend to warp and shrink as they're being printed.  This can result in the part breaking free from the bed mid-print, or merely coming out curled and distorted.  Repeatedly cleaning and resurfacing the print bed, and even using a raft on some parts, didn't seem to help.

After reading some tips on the Makerbot forums, I started to suspect the ambient temperature and drafts.

It probably doesn't help that the printer has been moved to a back closet, next to a large window.  The window is kept closed - actually, it seems to be impossible to open - but it's still somehow cold and drafty in there.  Cold air blowing through the open printer frame can make the part cool prematurely and warp as it's being printed.

The preferred solution to this seems to be to cover the gaping open holes in the Makerbot frame with custom-cut acrylic sheets.  I didn't have those handy, so I've gone for the cheap but immediately available solution of taping paper over the openings instead.

Seems to be working so far.  No warping on this part, although I do have a fairly aggressive raft in place as well.

Makerbot Upgrades Part 4

The office Makerbot has been printing nearly constantly for nearly a month now.  It's already more than paid for itself with parts we'd otherwise have to send out for manufacture.  The modifications I've described so far have made it run reliably enough that I can leave it printing unattended in a back room for hours.

I have noticed that the printer is getting noticeably noisier over time.  There's a creaking in certain spots of the X stage travel, a horrible screech when the Y axis moves quickly, and the whole machine shudders and rattles when the Z axis moves downwards at the start of a print.  I've also noticed that it takes a lot of force to manually move the X and Y stages, even when the stepper motors are completely unpowered.  I've decided that my next modification will be to redesign the X and Y stage slides, replacing the oil-impregnated bronze bushings with roller bearings.

First to be rebuilt is the X stage. As shipped the X stage rides on two 9.5mm precision steel rods, each passing through two bronze bushings pressed into ribs in the X stage structure.  This design is over constrained.  The print bed heats the entire X stage, which attempts to expand and pushes sideways on the two steel rods, anchored at their ends in the Y stage.  That's probably the cause of the creaking sound and some of the resistance in the X stage movement.

I ordered a few dozen miniature ball bearings, and then designed printable parts to hold them.  I designed two arrangements of three bearings each, to replace the two bushings on one of the rods.  On the other rod I placed only two bearings, so that the stage is physically located by only one of the rods, with the second only providing vertical support, so that the X stage could expand without pressing sideways on the rods.  The support structures for the bearings now took up most of the space under the X stage, so I joined them together, replacing two of the wooden ribs under the stage.

As I did I also replaced the clamping mechanism that clamped the belt to the stage.  On the version of the X stage I built the belt is clamped by two little wooden sticks that are only secured with one bolt each, and easily work loose over time.  I replaced them with a single large piece of plastic, held in place with two screws, to spread the clamping force out and not as easily vibrate loose.

There's really not much room to work with under the X stage.  To get the bearings to fit I had to cut several holes in the X stage mounting plate, and carve a long groove in the Y stage structure to clear the lowermost bearing.  I did manage to get everything to fit, and when I finally reassembled everything and ran the machine there was no creaking as the X stage moved.

The Y stage had been making a terrible screeching sound when moving quickly, so I set about replacing the brass bushings on that next.  Unlike the X stage, the stock ThingOMatic Y stage isn't over constrained.  On one steel rod the Y stage slides on two brass bushings, but on the other it already rides on ball bearings, so the Y stage can float and expand or contract independently.  There's also a lot more space under the Y stage to work with, so I had an easier time designing the bearings in.

I still had to cut holes on the Y stage bottom plate to fit these in.  Here I replaced each of the brass bushings with a single piece of plastic holding three bearings.  Three screws into the face of each anchor them to the Y stage structure.  It's not quite obvious from looking at it from the outside, but I'm also using the bearing blocks to clamp the belt to the Y stage, replacing the two original little wooden clamps.

After I reassembled the machine and ran it, I found that the noise from the Y stage was completely unchanged!  Moving the Y stage rapidly still resulted in terrible screeching sounds.  On closer inspection I traced the sound to the Y stage belt idler pulley.  Both the Y and X belts in the ThingOMatic have idler pulleys on 4mm bolts, without even a brass bushing let alone bearings.  Over time the bare plastic-on-metal contact gets noisy.

I had previously installed Thingiverse item 12528 on the Y stage idler, so the pulley wouldn't be hanging supported only on one side by the plastic baseplate.  Based on that design, I made a new part to support the pulley with ball bearings on each side.

I'm using the same 4mm bolt as an axle, but not instead of the plastic pulley turning on a stationary bolt, the pulley and bolt now spin on two bearings, that are then supported by the plastic bit anchored to the printer structure.  This completely eliminated the Y stage noise.  The Y stage now moves so easily, I have to hold it in place with one hand while trying to remove printed parts from the bed to keep it from sliding around.

For completeness, I've also upgraded the X stage pulley with bearing supports.  This was a much trickier job, again due to the limited space available.  There's barely room in the ends of the Y stage for the pulley as it is.  To get the bearings in there I had to replace the entire upper wooden structural cap on that side with a printed plastic part, and cut a hole in the lower wooden part to fit the support for the lower bearing.

The poor Y stage on this machine has quite a few new holes cut in it now, but both stages are really, really smooth.  The only noise as the machine prints is the singing of the stepper drivers.  It's almost like some kind of music, especially when it prints circles.

The default printing speed set in the ReplicatorG software is 30mm/second.  I had trouble getting the machine to print complex shapes accurately early on, so I dropped the speed to 20mm/second for a while.  Since upgrading the X and Y stages with bearings I've increased the speed back to 30mm/second without noticing any drop in quality.  I even printed a few parts experimentally at 50mm/second.  Some of the surfaces were a little wavy and there were a few small gaps, so I don't think I'll be printing many parts at that speed, but it's nice to see the machine still works fairly well even at that speed.

The next step would be to replace the Z stage bearings, but as the Z stage moves slowly and infrequently, I'm not sure it's worth replacing the bushings there with bearings.

Recipe: Mini-Shepherd's Pie-Muffins

Apologies in advance as this post has nothing to do with robots or Makerbot upgrades.  Rather, this is something I've made for a few parties and had enough people request the recipe that I've put together these visual instructions to share.

Drew's Mini Shepherd's Pie-Muffins

Ingredients

3 pounds of Yukon Gold or similar yellow potatoes

1 cup lamb stock or beef broth

1 stick unsalted butter

1 egg

About half a cup of parsley

1 cup shredded cheddar cheese

A few cloves of garlic

1 medium-sized white onion

1 stick of celery

2 carrots

(Substitutions can be made to the vegetables, see below)

2 pounds ground lamb or beef

A bit of all-purpose flour - about a quarter cup as needed

2 teaspoons Worcestershire sauce

3 cans of Pillsbury Grands biscuits (the kind that are eight to a can, so you have 24 biscuits total)

Some olive oil

Cooking spray

Salt, Pepper, Nutmeg, and Paprika as needed

This recipe began as a Shepherd's Pie recipe I've been making for years at home, as a good, filling, yet reasonably inexpensive way to make dinners and lunches for several days fairly inexpensively.  Recently I was invited to a potluck event, where the requested theme was for Irish food.  Shepherd's Pie was a reasonable fit, but I wanted to make something that could be hand-held and eaten without needing a bowl or utensils.  My wife suggested making individual hand-held pie-muffins, and so this recipe was born.

This recipe takes about 3 hours to do and makes 24 pies.

Step 1:  Mashed Potato topping

Wash the potatoes.  Peel them and chop them into chunks.  I prefer to use Yukon Gold potatoes for this, but any large yellow potato will work.  Make sure you peel the potatoes completely, any remaining peel in the topping will have an unpleasant texture.  I once experimented with multicolor fingerling potatoes, which gave the pie an interesting blend of colors but were very difficult to peel properly.

Put the chopped potatoes in a sufficiently large pot.  Pour in the beef or lamb broth.  I used to use  Scotch Broth soup for this, as it contained lamb broth plus various chopped vegetables all in one, but the brand of soup I used has since been discontinued.  For this batch I'm using the last of a batch of lamb stock that my wife prepared some months ago from some lamb shanks, but canned broth will work just as well.  The one difference is that canned broth has a lot of salt added for some reason, so keep in mind that home-made stock may require salt added to match the same taste.

After adding the broth, add enough water to cover the potatoes.  Add salt if needed, and add pepper to taste.

Cover the pot.  Simmer over medium heat 15 minutes or until potatoes are soft.

Remove from heat.  Drain the liquid through a strainer.  Save about half a cup of the liquid for later.

Melt one stick of butter.  Wash and chop the parsley.  Add the butter, the parsley, one egg, a pinch of nutmeg, and half a cup of the shredded cheddar cheese to the potatoes.

Now mash the potatoes and other ingredients well until you have a smooth mixture.

This will make up the topping layer on the mini-muffins.  Set this aside for the assembly step later.

Step 2:  Meat and Vegetable Filling

We start with the vegetables.  In addition to the potato topping, a shepherd's pie should contain a mixture of various cheap vegetables - onions, garlic, celery, carrots, parsnips, or whatever else you have spare.  As this is a recipe meant for using up leftovers and scraps, the exact mixture of vegetables can very depending on what you have on hand.

Unfortunately, the only appropriate vegetables I had on hand when making this recipe was some garlic.  My wife and I don't normally eat much of this kind of vegetable - we're more into dark green leafy vegetables these days.  I could have bought them all separately, but it seemed a bit silly to me to buy an entire pack of carrots for just one, or an entire bundle of celery for only one or two stalks.  So I cheated.

There we go.  Carrots, Celery, Onion, Parsnips, Turnips, Leeks, Parsley and Dill.  All the required vegetables in a single package, in just about the right quantities.  Feel free to call me a heathen and prepare your pies from fresh vegetables instead.

 I just needed to chop them further and add the garlic.  You don't really want large chunks of vegetable in the filling for this recipe.

You should have about 2 cups of chopped vegetables when done.

Add some olive oil to a large saucepan over medium heat. Add the vegetables and cook until soft.

Remove the vegetables from the pan and set aside.

Add a bit more olive oil to the pan, then add the ground meat.  Traditionally, a Shepherd's pie should be made with ground lamb.  I couldn't find any ground lamb locally when I made this recipe.  As the idea of this kind of recipe is to stretch cheap meat with potatoes and other vegetables, I decided it was perfectly in the spirit of the recipe to use cheap fatty ground beef instead.  Technically that makes this a Cottage Pie instead.

To the beef add the Worcestershire sauce and about half a cup of the liquid from cooking the potatoes.  Traditional recipes usually call for sage or rosemary at this point, but my wife is deathly allergic to those spices so I don't use them.  Feel free to add them if you like.  Brown the meat, mixing it to ensure even cooking.

Add flour as you cook to thicken the mixture.  You want to end up with a semi-solid paste-like texture, as these pies need to hold together once cooked.  When the meat is just about cooked return the cooked vegetables to the pan and mix well.

This will make up the filling of the mini-pies.  Remove from heat and set aside.

Step 3:  Pie Crusts

Preheat the oven to 425 degrees F.

Spray your mini muffin trays with cooking spray.  I use four disposable aluminum trays that hold six muffins each when I make this, but there's no reason you can't use non-disposable muffin trays instead.  Open a container of biscuit dough.  Remove the biscuits one at a time, and with your finger spread each one out into a disc of about twice their original diameter.  Press the dough disks into the muffin tins to make dough-cups.

Once all the biscuits are in the tins, place them all in the oven.  Cook them for 6-8 minutes, then remove from the oven.  You do NOT want them to be fully cooked at this point, they should be just starting to turn brown on the outsides but still raw in the middle.  Keep the oven hot, you'll be needing it again soon.

While cooking, the centers of the pies will have swelled up.  With a spoon (or your fingers, once the pies have cooled enough) press the centers back down to make them into cups.

Step 4:  Assembly and final baking

Fill each pie-crust just full to the edge of the crust with the meat and vegetable filling.  You should have just enough filling to fill all 24 pies.

Next, scoop enough potato topping mixture onto each pie to cover the meat.  Again, you should have just enough to evenly cover all 24 pies.

Onto the pies sprinkle a bit of paprika, and then the rest of the shredded cheese.

Now return the pies to the oven, and bake for 12 to 15 minutes, or until the cheese is melted and the dough is browned.  Remove from the oven and let cool slightly before removing them from the baking trays.

Makes 24 muffins.

These can be eaten immediately while hot, reheated at a party, or stuck in the fridge for a week and eaten cold for lunch.  So far this recipe has been a huge hit at every potluck I've brought it to, but it also works well as a way of making a week's worth of dinners and lunches in one evening.

Makerbot Upgrades Part 3

When building our Makerbot ThingOMatic, I was surprised by how little thought was given to cable management.  After carefully detailing the mechanical assembly, the instructions for wiring the machine are little more than a hookup diagram and some vague advice on taping the wires together to keep them neat.  There seems to have been little to no thought given to how to run the wires to the moving parts of the machine.  Most of the wires can be run along the inside corners of the machine and merely given enough slack to let the moving parts move freely.  The real problem is the build platform cable.

The build platform moves along two different axis, and is in near-constant motion when the machine is printing.  The connector on the front of the platform is completely unsupported, and the cable tends to drape down onto the rails and belt and get pinched against the frame when the platform is near the front of the machine.

It's unsurprising that the HBP connector is one of the most common parts to fail on these machines, and the Thingiverse has countless files for strain reliefs and cable clips and management systems.

My first attempt to keep this cable out of trouble was to simply zip-tie it to the mounting for the Y axis endstop switch, and then try to encourage it to coil in loops off to the side of the platform, as shown above.  This really wasn't satisfactory, the cable was still scraping on the Y axis belt, and tended to get caught when the platform was all the way at the front of its travel.  Getting pinched didn't just risk damaging the cable, it interfered with the movement of the platform, which was a problem as some of the parts I needed to print nearly filled the entire print volume.

A cable guide downloaded from the Thingiverse helped to some degree.

While not a complete solution, this at least kept some strain off the HBP connector.  I also began experimenting with designing a piece to anchor the build platform cable to the side of the Y axis.  My first few attempts didn't work very well - while they were keeping the cable bundle mostly out of the way, I was still losing some travel on the build surface due to the cable getting in the way of the platform's movement near the edges of the print envelope.  This solution worked well enough for printing small parts, but I needed to come up with something better to get the full use out of the machine.

We use industrial pick and place machines for circuit board assembly at the office.  While helping to maintain them, I had noticed that they used a cable chain system to manage the wire bundles to the moving gantries.  I decided to try and build something similar, as much to see if the ThingOMatic could print well enough to make that kind of complex moving part as to try and fix the HBP cable issues.

The result is this.

Admittedly, it's a bit of overkill for what it needs to do.  It's also not at all how cable chain is normally used - the chain should really be lying flat in a channel and bending with a constant radius when the gantry moves across it, not hanging free in space like this.  This works well enough for what I needed here anyway.  The chain constrains the cable to a single plane of movement, keeping the cable in front of the build platform from rubbing against the stationary parts below, and keeping the cable off to the side from getting pinched between the corner of the build platform and the frame of the machine.

Since I installed this modification (and those mentioned in the previous posts) the machine is working well enough to sit in a back room printing objects unattended for hours.  The cable chain has held up remarkably well, considering that the moving parts are just irregular plastic surfaces rubbing against each other.  I have yet to see any sign of the HBP connector failing, but I expect it will eventually, as even with the strain relief the connector is being operated beyond its rated maximum current and temperature.

Makerbot Upgrades Part 2

As I mentioned in my previous post, one early print on the machine was ruined when I touched the Z-motor while it was running, giving the machine a static zap that locked up the Z motor control board.  No permanent damage was done to the machine, but the part being printed was ruined.  The Makerbot ThingOMatic does not incorporate any static protection in its design.  It is made from a mix of wood, plastic, and metal, with several large metal pieces (including the motor housings) that are ungrounded and electrically floating.  As I found out, it can be easily crashed by static electricity.  In theory, it may even be generating its own static, as there are a lot of places in the machine where conductive and non-conductive materials are rubbing against each other.

This page has a guide to installing static drain lines.  The instructions are meant for the MK5 extruder, rather than the MK7 we are using, but what needs to be done is essentially the same.

There are five points that really need to be grounded on the printer.  The three motors, the extruder, and the print bed.  I started by preparing five lengths of wire with crimped ring terminals on the ends.  Green with yellow stripe is traditional for grounding wires, and we had plenty of it on hand anyway.  First was the Z axis motor, which I had already learned the hard way needed a static drain line.

The Y axis motor doesn't really need grounding as badly, since it's buried down in the base of the machine, but for completeness I connected it while connecting the others.

The X axis motor is tricky, since there's very little space where the wire can be attached and run without interfering with the X axis travel. I think I've managed to install it without reducing the X axis travel, but to be really sure I may go back and drill a hole to pass the wire through.

Grounding the print head is easy, as there are multiple unused holes on the mounting plate and no clearance issues with the wires.  There is some controversy as to whether this part should be grounded.  Some people have had their extruder temperature readings go off when they connected this wire, possibly as a result of shorts between the nozzle thermocouple and the frame.  I was careful to make sure that the thermocouple was electrically well-insulated from the nozzle when I built the printer, and I haven't seen any problems with the temperature reading after installing this ground lead.

The last grounding wire connects to the heated build platform.  We have installed the aluminum heat spreader, which makes connecting a ground wire easier as I don't have to figure out how to connect a wire to metal foil.  I have rearranged these wires a few times since this photo, as part of the ongoing challenge of dealing with the HBP cable.  I'll get into that more in the next post.

The five grounding wires are run down to the power supply in the base of the printer, connecting individually to mounting holes on the metal frame.  These are static drain lines, not power grounds, so even though they are theoretically electrically connected to the ground lines in the power connectors they need to be run separate from the power ground lines and from each other back to the chassis ground.

With these in place, the sensitive control electronics should be protected from static zaps to the motors, extruder, or heated bed.  I haven't had any prints fail due to static lockup since making this modification.  I have found a persistent issue where the Z axis sometimes randomly reverses direction while homing after a print, but I suspect that's a software rather than hardware issue.

While I was making this modification, I also made the modification described here to all four stepper motor controllers.  The power supply provides 12V and 5V on each connector.  The stepped drivers only use the 12V, generating 5V locally through a linear regulator.  I cut the regulator off each board, and then added a jumper to draw local 5V from the power connector instead.  In theory this should make the stepper controllers more reliable.  I haven't noticed any obvious difference, but it seemed like a good precaution to take.