Archive for December, 2010

 

Project LandBearShark

Dec 27, 2010 in Land-Bear-Shark, Project Build Reports

This is what Boston looks like 6 months out of the year.


Seriously! I swear! We don’t even get those cool growth lights like Norwegians do!

A climate like this is one in which none of my less-than-noble steeds – RazEr, melon-scooter, or even the venerable LOLrioKart, can operate. Trust me on this – I tried getting to MITERS with melon-scooter a few times when the snow wasn’t ridiculous and it always ended with me having to push the thing after a few hundred feet because the rear tire turns into a solid cylinder of snow. And diving through the salty slush-covered roads is just asking for it.

I’ve been spoiled by having a fleet of small, overpowered personal electric vehicles for a long time now. I’ve become so reliant on their convenience that convincing me to walk some place is often an exercise that takes more time than if I had just gotten off my ass and walked. So having my entire collection be… hallwayed (since grounded doesn’t really apply here) because of such an obstacle as snow is just plain unacceptable. After all, other people seem to deal with it day-to-day just fine. But since I’m both conceited and spoiled at the same time (right?), it’s an excuse to open yet another project build; what, after Segfault and Make-a-Bot being fired off in rapid succession from their idle states for the past few months, I either have to go back to working on RazEr rEVolution (eww, another scooter), or finish Melontroller (AAAHHH SOFTWARE). At least this would give me something mechanical to crank on, and might actually prove useful in the end.

So it’s now time for me to explain this picture. If you pay close attention to my site, you might have noticed it at the end of the last Melontroller post. If not, go back and look. It’s definitely there – it’s kind of like the guy in a monkey suit running into your lecture while you take a surprise mini-quiz.


The bogie frame looks kind of like a banana, I guess.

So… I’m building a tracked vehicle, right? Nothing that exciting. Knowing me, it’ll probably be powered by an Etek and be based off some large, borderline absurd vehicle frame. It’ll probably have garish lighting and a 4 channel sound system. Hey, why not just put LOLrioKart on tracks? At least make it a half-track, at which point it should power through the snow just fine. I could probably rent it out to MIT to clear the inner roads around here too.

The tracks are from a junked Craftsman industrial snowblower, but similar ones seem to be found on all sorts of large snowblowers. These are the ones generally sold to people with long driveways or large yards, not the kind you attach to a front-end loader or small Bobcat style loader. They’re far from being even snowmobile sized. So really, LOLrioKart would be too large for these tracks anyway unless I were to actually build it as a halftrack.

But that’s kind of lame. I like LOLrioKart the way it is, and this is intended to be a new build after all. Which is why I now have to explain this picture:

Alright, so there really is no explanation. I’ll be honest: this got started almost exactly like how LOLrioKart got started two years ago – by having heaps of parts close to eachother, I catalyze their reaction into vehicles which should not exist. The tracks from the parted-out snowblower were sitting on top of the MITERS Public Skateboard temporarily when I happened to look in their direction while holding a melon.

So that makes me some kind of engineering enzyme?

landbearshark

The name “LandBearShark” came about after a long period of wanking about what you could possibly name such an abomination. Many ideas were pitched, mostly bad puns stemming from the DTV Shredder. Finally, someone suggested the pithily-simple name “land shark”. Nice and functional, but a bit overused and outdated. Plus, everyone knows that the hot topic in today’s marine biology scene is bearsharks.


What a bearshark might look like

The only thing more fearsome than the combination of a landshark and a bearshark is, of course, a landbearshark. Possibly made worse if ridden by a manbearpig.

technical

LBS is designed as a stand-on vehicle, unlike the DTV, which has handlebar controls. The skateboard is essentially a regular length board – not a longboard or mountainboard, so the ground contact length is actually not that large to react against you pulling on a handlebar. The idea is for it to be more freeform and rideable more like a real powered skateboard, such as the Exkate. But unlike the Exkate, I intend to not have a discrete hand-held controller at all. Instead, expanding on technology I first explored in Skatroller, I’ll have a double-handed control built into wrist guards that enable you to use your wrist force as tank steering inputs.

That’s right – hands-free operation obtainable with application of wrist bending force in either direction. On the skates, upwards force applies forward throttle and downward applies the motor braking, with center (no pressure, free hanging hands) as just “coast”. I anticipate doing much the same for this vehicle, except downpressure would instead reverse the drive it is linked to. With both hands, I have a full tank steering control arrangement.

A short summary of specifications:

  • 30″ overall length set by the skateboard, 26″ overall width set by the skateboard + two track widths
  • 20 to 25 miles per hour top speed
  • …provided by dual Turnigy 8085 “melon” motors. Since Melonscooter runs at about 25 miles per hour with a single motor, this will be more than enough horsepower to pound through any terrain.
  • 38 volt electrical system composed of 12S lithium nanophosphate cells.
  • Controlled by dual Melontrollers. This is good pressure on me to finish it and get it reliable so I can build another one.
    • A good reason to get the current-control loop on Melontroller running so I can avoid “Melonscooter launches” where surprised novice riders are instantly ejected by Melonscooter’s difficult to control starting torque.
  • Wireless fingers-free (because it technically DOES use your hand) throttle similar to the RazErBlades.
  • Tilt-and-leanable skateboard mounting
    • This will not control the vehicle in any way, but I foresee it being a “Operator is remaining on vehicle and has not been thrown off on launch” switch to prevent runaway flying tanks.

Now, let’s move onto the pretty CAD pictures.

Here’s attempt 1 at the design. Notice that the stock steel sides are already gone – I’m going to integrate the motor mount into aluminum waterjet-cut side plates instead, which will also form part of the frame. By the way, if you’re interested in your own melon-death vehicle, I have a .STEP file of the motor.

The shocks are some cheap mountain bike shocks I found one of in the Media Lab to measure up. In all actuality they’re probably too stiff to contribute any shock travel whatsoever, but they’re nice ornaments. I might also consider replacing the springs with something less stiff. They are found on Electricscooterparts.com under part SHK-634R.

This was about as far as attempt 1 got before I realized that there would be no way to connect the tracks to the chassis unless I turned this into a scientific exercise in suspension design. At the minimum, I was going to need something resembling A-arms, which would add alot of width to the vehicle. There’s also not that much space inside the tracks proper to put a proper bogie-wheel suspension, or even enough length for it. So I settled on a quasi rocker-bogie type configuration, which led to version 2:

In this version, the sides are split into two halves pivoting around a solid center axle (which is rigidly attached to the vehicle. The shocks mount to the ends of those halves, and therefore allow for essentially up and down travel of the track sprockets.  It’s still an arc motion, but the longitudinal displacements are small, and so the travel is linear enough. I’ll see small variations in belt tension for sure, but the massive gnarly track teeth will make it inconsequential.

I’ve also made a rough sketch of the body here. It will, once again, be T-nutted aluminum plate made on the waterjet.

Come on, I designed it. Do you expect it to be something more?

I’ve added more details in the region of the skateboard mount. The rings are high-deflection rubber shock mounts from McFaster-Carr. In this case, they are used as springs to keep the skateboard centered unless you lean. It is likely that the board will still be too “soft” even with those kinds of standoffs, so I might find myself paralleling them. Conventional rubber “sandwich” shock mounts are actually too stiff and do not allow for much travel. Optimally, the board should lean almost as much as the average longboard or skateboard.


How to tell what kind of monitor Charles uses: Inspect his CAD screenshots.

More details have now been added to the frame, including most of the slotting (but no T-nuts yet). I’ve made a front bush-bar-like structure that’s mostly decorative but serves to break the monotonous square corners that the frame otherwise has.

I added internal pattern cutouts to the large drive sprocket since it has to be custom-cut anyway. I’m not really concerned about weight on this vehicle – instead, the heavier IT is, the better. Maybe it’s a pathological thing I do since my standard technique of robot building involves beautifully (haphazardly) trussed (hollowed) waterjet-cut frame members.

The overall reduction from motor to drive is 4.5:1. If I elect to use a 9 tooth instead of 10 tooth sprocket on the motor, it’s 5:1. As on Melonscooter, I’ll take care of chain tension using one of the motor mounting standoffs.

The design as it stands right now. I finally manned up and figured out the “pattern along curve” option in Inventor, so I was able to model real tread teeth. Not that they are in any way representative of the actual snowblower treads…

I’ve modeled the two Melontrollers on the “control deck” as Eagle screenshots pasted onto flat squares. That’s essentially what a PCB is, right? I’ve also added the battery. It will be two packs of 6S, 6P A123 lithium nanophosphate cells. Essentially two 150% \M/etalpaxXx in series, for a grand total of 530 watt hours. What’s not shown is the third board that will contain the XBee radio with another Arduino that will manage signals coming from the two hand controllers and drive the motors accordingly. The rear cavity is to make space for supporting electrical components – contactors, power bus distribution, main battery switch (actually sticking out the back – it’s just an el-cheapo key switch), and possibly an onboard battery management device.

Now that Make-A-Bot is active and ready, I’ll be able to make slick cases for all the electronics and possibly even a real hard case for the batteries. There’s not a soda bottle in the world big enough to contain these packs for sure. No guarantees that any of it will be waterproof, but the big box frame will at least make it easy to seal around the bottom.

timeline

ASAP.

One important things that contributes to the rushed timeline for this thing include the fact that winter doesn’t last forever and fresh snow only falls every once in a while. The massive piles of snow already built up by the roadside and around campus are nice, but they get disgusting and hard after a few days. The best time for LBS to shine is out during a blizzard, or shortly after one.

Second of all, I won’t have all January to bash around MITERS. From the 11th of January to the 20th, I’ll be in SINGAPORE!!!!! at the new Singapore University of Technology and Design, which is a MIT collaboration to build a better technology & design university. They’re so new they don’t even have a campus yet. Those things are made to order and take a while. Anyway, I’ll be manning the deck helping with a student recruitment & general interest event. Details are yet to be settled, but I’ll probably bring over RazEr (rEVolution?) and a robot or something.

I’ve already ordered just about everything this project needs. Still, with the fresh snowstorm that just pimp slapped everyone in the New England region, parts might take a few more days to get here. After that, it’s going to be waterjet hell. In the mean time, I’ll work out how the DOUBLE SKATROLLER will be implemented.

Oh, one final thing. This is totally not being built to show Shane that I have a bigger deck.

How Many Make-A-Bot Puns Could A Make-A-Bot Make If A Make-A-Bot Could Make Make-A-Bot Puns?

Dec 26, 2010 in Make-a-Bot, Project Build Reports, Reference Posts

About this many:

Above is the product of one night’s printing. Tons and tons of calibration cubes, then a few reruns of shapes I tried already to see if the quality improved on anything but a cube.

Let’s start with the first one, which I have nicknamed the Abortion Cube:

I tried the advice on the Makerbot Blog about one way to calculate a workable feed rate for the machine. From pulling a test extrusion, I found that the extruder actually worked at around 26mm/s. Unless I really missed something, that did not work out at all. It was clear from watching the epic blobular formation that the machine was in fact moving far too slowly. So I went for the logical next step: turn it up.

So here’s a test print of a 20mm cube at 40mm/s.

Muuuuch better. Now it’s on par with the stuff I see coming out of other peoples’ Makerbots. This was still on 0.4mm layers, though. I began playing with the “aspect ratio” of the filaments by adjusting the Width Over Thickness values and making more cubes. A wider thread adheres better to the one below it and can fill areas quicker, but appears to make the machine more prone to globbing.

After Cube #2, I decided that a stiffer platform was in order. Further lowering of the layer height was probably a futile effort if the platform itself has more “rock height” than the layers. With Advanced Circuits still working on my trippy heater PCB, I elected to make a stopover solution in the form of a 7 inch square chunk of 6mm acrylic. This represents the final outline of the PCB (yes, it’s massive), but the heated area is a 6×6 inch  patch in the middle.

Here’s another cube that turned out great. This represents the numbers I ended up settling on for the time being. The layer thickness is now 0.3mm, and the feed rate is 55mm per second.

I began logging all the settings used for each cube as I made them. From left to right, the lineup represents a gradual reduction in the layer height and increase in the feed rate while trying to maintain a constant thread aspect ratio.

While making the solid test cubes, I noticed the internal fill cooling unevenly with respect to the outside edge, causing “cube obesity”. To mitigate this, I adjusted the aspect ratio of the infill threads such that Skeinforge takes them to be wider (the 1.75 in “1.5 / 1.75″), and thus puts less infill paths down. This solved the bulging issue exhibited by the two middle short cubes.

The cubes were some times stopped after 20 layers or so because I figure by that time I got the point already and could move onto the next.

I sent MaB off on a mission to make another funky quarter sphere thing. The effects of the increased feed rate were primarily seen in the outside shells, where there was less “globbing” from the machine pausing briefly. I also went back to using the ‘straight criss-crossed lines’ method of infill, over squares or circles.

The first useful part MaB makes, however, is this spacing piece for a…. well, you’ll just have to wait and see. The part was designed to be 3/16″ (0.1875″) thick, and this print managed to hit 0.180″ consistently. Accounting for plastic shrinkage, that’s pretty close. The hole internal diameters came out slightly small, but there’s a setting to compensate for that in Skeinforge.

Here’s the family photo again. I remade the Companion Cube using the 0.3mm layer height, and oddly enough, it came out a little shorter than the first 0.4mm print. I also had a second go at making the funky triangular prism (for lack of more descriptive terminology…)

The finish at 0.3mm per layer on convex (external) surfaces and straight lines is pretty impressive. Concave surfaces, though, like the inside surface of the quarter spheres, are still a bit rough.

Overall, I’m content with how dialed in the machine is right now. The current setting is now my baseline for experimenting with new ones.

In the coming days, I hope to push MaB to the limits of sanity in terms of axis speed. I’m currently aiming to hit 70mm/s and 0.2mm per layer.

Enough Making of the Make-A-Bot; Let’s Make the Make-a-Bot Make Stuff.

Dec 25, 2010 in Make-a-Bot, Project Build Reports

After a few days of Just Beasting It, I’m proud to announce that the Make-A-Bot is now making stuff. It’s kind of a change for me to build something useful for once, and it’s also very amusing to watch… I’m not sure why. I’m literally watching plastic melt and set again, but I’m finding myself entranced by the cyclic movements of the build surface. And then a thing just kind of appears at the end.

Am I in the future? What, with DIY Kinect-based virtual reality already here, I might as well be.

At the point which I left it previously, I still needed to finish the Z-axis mechanics and then wire the whole thing up. So after falling over for a while, I decided to just go back to MITERS and not leave until something came out of the extruder. The Z-axis leadscrew is really the only thing I had to machine for real on this build. So far, everything else had been stock components or waterjet/laser-cut flat parts. I think that’s the best I’ve done so far – not even the 2.007 bot could come close to that.

And here it is. The screw is a 3/8″-8 double-start Acme leadscrew (McMaster PN 99030A315) with matching nut. I was going to drill and tap a radial set screw, but decided once more in favor of the Ninja Coupling – drilling the appropriately sized smaller bore, slitting the end of the leadscrew all the way across, then applying a 3/8″ shaft collar around the slit and tightening it down around the motor shaft. Besides Fankart, this has also been my choice of attack against my Die Holder of Convenience and Überclocker’s original arm drive.

I like the Ninja Coupling. Perhaps too much.

The operation was completed on the venerable MITERS Bridgeport with my standard set of tools. Unfortunately, I neglected to take a picture of the actual machining process, but it was the exact same as pictured in the other projects anyway.

Here is the Z axis installed. The leadscrew nut has a threaded portion, so securing it to the “diving board” was done with a simple nut. There’s no outboard support for the Z axis leadscrew – all of the Z axis weight rests on the stepper motor’s bearings.

Probably not very sound design for endurance and robustness, but the Z doesn’t move very much anyway.

Turning my attention to the other side of the Z axis, I went and head and installed the small snap-action switches that will be the endstops. My “adjustable endstop” is also visible here. For the Z axis, I can move the endstop locations up and down about an inch on both the upper end and lower end of travel. It’s taken care of by the cap screw and nut sandwich.

On the Y axis carriage, the same adjustment is provided by the Neat Sliding Rod Clamp… or in this case, keystock clamp. I found that square keystock stayed in place much better than round 1/8″ rod.

These endstops were made adjustable because I didn’t really have an idea of how far I wanted the axis to go in each direction when I laid down the design, so it gives me some flexibility.

I had all the limit switches mounted, but decided to save wiring them up for later. In the mean time, I began plugging everything in and creating wiring harnesses. Wiring the bot was straightfoward, save for some guesswork as to which wires on my non-stock stepper motors went to the … umm… helpfully labeled “A B C D” connections. Come on, is “A+ A- B+ B-”‘ too descriptive?!

Fortunately, I found the correct combination for the Z axis right away and just copy-pasted it to the rest. It even went in the right direction the first time!

The space behind the ATX power supply turned out to be a great “apron pocket” to slip all the excess wire length into to keep them from just slumping around everywhere.

With all the boards connected, I was able to run some axis movement tests using ReplicatorG. At this point, I hadn’t defined the machine’s characteristics in my own XML configuration file yet, so all the distances were of course completely off. At least everything moved without incident. I had to reverse the X axis motion setting because my belt attachment on the carriage is opposite that of the Makerbot machines, but that’s inconsequential.

There was, of course, one more thing to try.


OMG! DOES THIS COUNT AS PRINTING SOMETHING?!!??!

Hitting FORWARD on the extruder control menu and seeing a little noodle of ABS plastic emerge from the head was satisfying.

setting up the make-a-bot

ReplicatorG allows the definition of custom machine settings such as axis travels, motor steps per millimeter of travel, tool characteristics, etc. in an XML file. These were settings which I had to change to cater specifically to MaB over the stock XML files for Reprap and Makerbot machines.  For instance, MaB’s Z-axis speed is on par with that of the Thing-o-Matic, and my X-Y axis stepper motors have 15 tooth pulleys instead of 17.

Here’s roughly what my haphazardly copied-and-pasted XML file looks like:

The calculations are included as comments in the file. I noticed the stock numbers for the Cupcake are very slightly different from what the raw geometric calculations would indicate – I’m not sure why. Probably manual calibration by measuring  a test print, which I might end up having to do anyway.

making stuff with the make-a-bot

After completing the all-systems test, it was time to actually lay the ABS down on a surface and pile it up scientifically (as opposed to the unscientific ABS noodle piles I was getting fond of making). Using the completely bone-stock Cupcake CNC settings in the G-code processor Skeinforge, I set Make-A-Bot off on its maiden print of a little hexagonal prism.

Again, I held off on wiring the endstops because they’re not really necessary yet.

And the first blooper occurs before I was even able to start.

I pitched together a build surface reeeeally quickly out of some scrap acrylic sheet and a piece of aluminum box channel, all double-sided taped together and slammed right onto the carriage.  Immediately after that, I proceeded to plant the at-temperature Z axis right into the surface of the acrylic… which prompt melted and left a huge divot.

Oops.

Here it is, though… the inaugural print!

…eeeww. What IS that?

It’s pretty clear to me that the stock feedrate settings were pretty far off from what they need to be. I elected to hold off on fine calibration work until after I had enough fun with the thing… which was going to take a long time at the rate I was downloading models from  Thingiverse.

The second blooper of the night comes from “filament traction loss” because I didn’t crank down the feed pressure screw enough. It air-printed a layer before I corrected the error, but unfortunately it was too late for this random triangular prism thingie.

Making a piece with long straight sides seemed to mitigate the feed and flow rate issue somewhat.

I elected to make a companion cube next because it was more interesting than a calibration cube. Overall impression: not bad. A bit goopy on some edges, and there was tons of “undamped drooling” on overhangs and layers with multiple closed cross sections like the top surface. The extruder drools alot. I believe this is a problem that is in the process of being tamed by the community through the use of stepper motor head drives and timed shutdowns and startups.


8 D

Alright, that’s enough for now. Next steps: fine tuning, calibration, and testing testing testing testing. Many things have yet to be optimized or verified. Feed rates, flow rates, layer thicknesses, all those 27,000 ratios and constants in Skeinforge, and even little things such as belt tension seemed to be impacting print quality substantially. I’m going to be reading Dave Durant’s guide like a lit major.

Here’s a compilation video of the first few prints!

Adding a loft, getting a couch, filling out the garage…

Dec 23, 2010 in MIT, Bostoncaster, Cambridgeshire, Project Build Reports, Stuff

With this site now on its own independent hosting, I’ve started the process of expanding the content further to cover more things I’ve been doing, or have done. Quite a few of my random endeavours don’t have pages associated with them yet. That’s all about to change.

First up: A whole new page on the motor controllers. I’ll be adding more later on, and as I continue to build them.

I’ve also given Make-A-Bot its own page.

More Making of the Make-A-Bot

Dec 22, 2010 in Make-a-Bot, Project Build Reports

void charles_builds_stuff( ) {

melon-scooter {

razer-revolution {

make-a-bot {

2.009 {

//todo: make a page for this

segfault {

//wtf slashdot?

}

}

…?!

This semester, I seem to have fallen into a habit of neglecting projects for long periods of time in order to work on other ones, and subsequent others still. It’s like opening multiple brackets when you’re programming in Arduino. Well, hopefully now it’s time to start closing some of the brackets. For starters,  Segfault now gets to join the rank of “random cool interactive things MITERS can put on display to recruit froshlings”. With it operational, but a little short on battery life- something that I will just randomly fix one day without thinking, it’s time to take a step back and see what I’ve left behind.









Hey, what’s this aluminum sculpture sitting in the corner here?


It’s still smiling after all these months.

Oh, that’s right… I was working on a 3d printer, wasn’t I?

I’ve been working on Make-A-Bot in the background a little, including ordering some of the final parts needed to complete it. I purchased the ABS extruder head from the Makerbot Industries, along with all the control electronics and the cute little automated build platform. Stock equipment, but it’s equipment which they’ve figured out and which would take me longer and cause me more pain to re-engineer again. Past that, though, the last month and a half has seen little physical progress because of my other obligations – mind you, both my 2.009 work (to be detailed) and Segfault were actually for class for once. Imagine that.

Make-A-Bot was left at a stage typical of my projects where I have built everything I designed already. That means without further design, I just have a Fancy Aluminum Sculpture. As lovely as sculpturework is at times, I’d rather have a 3d printer.

First, I put together the Plastruder 5 head for kicks. I must say, this thing is adorable and pretty intuitive to build. It is a bit bulky, though, on the motor end of things (Dear god, why such a GIGANTIC motor?). Maybe a possible direction to explore in the future. I was also a bit dissatisfied with the mounting surface, which doesn’t seem to actually have a solid mechanical connection to the rest of the head, but it could just be a consequence of me trying to adapt it to my own custom mounting configuration. A quick nylon through-bolting solved the issue anyway.

I have yet to try actually heating it to full temperature and shoving some of the ABS filament through.

Anyways, onto the designs:


How can you tell that I got a new widescreen monitor?

I jumped back into Inventor and started designing the support equipment cabinet that will house the feedstock filament, the power supply, and properly mount all the electronics. Without something to organize those components, MaB is just a rickety imitation of a small manual milling machine. The cabinet I designed (essentially all on-the-fly with little forethought) is actually more of a pedestal for the machine proper. Designwise, it looks like the rest of the bot with all of its edge-stitching and interspersed T-nuts. I discovered that designing panel footprints in increments of 1/2 inch made the t-nutting and edge-stitching process very fast, since the layout is always symmetric about a center line. This beats my previous tactic of calculating precise widths for the slots and tabs such that they end up symmetric. Forget that – just beasting it solves the issue, as usual. I’m fine with that.

All the important electronics – three axis controllers, the motherboard, the extruder controller, and the auxilary relay board, get a home on the “backrest”. I even OCD’d enough to model (blockily, anyway) the protruding components on the boards. I lined up the important connections to face each other or be close to each other, so the wiring should end up clean.  The electronics backpack also has slots and holes to pass wire through cleanly.

Make-A-Bot looks cute sitting on its couch-like pedestal until you realize how huge the whole thing is. That base is a full 22 by 12 inches and the top of the wooden backrest thing is 14 inches tall. Add MaB’s own height to it and this whole thing is already over 2 feet tall.

Man, this whole widescreen thing really makes my CAD screenshot proportions weird. Anyway, having purchased like 10 miles of ABS filament (which came in a massive donut-shaped coil), I decided I needed a method of keeping it all in line so I don’t have to constantly feed the filament. Makerbot does sell a spindle kit for such an occasion, but this was one part I decided to just tackle myself.

Above is the filament spindle design. There’s a truss piece under the top triangle shaped plate which holds the vertical spars together. The top plate can come completely off for filament changing, but otherwise has provisions for a detent-lock effect supplied by the vertical spars and a few degrees of rotation. It will all become clear after the fabricated pieces are assembled.

People prone to vertigo should avert their eyes:


Come on into THE VOID.

What’s THAT?

Over the course of a few days of on and off thought, I decided that I’m not going to run the automatic build surface. I’ve come to dislike the bed-type design I settled on for MaB 1.0 (Yeah – I’m already thinking about what 2.0 will be like!). Such a design is great for applications where the machine is many orders of magnitude heavier than the workpiece usually is – like most milling machines. When this is not the case, a changing workpiece weight can affect the dynamics of the machine greatly. A moving work surface also puts force on the workpiece when it accelerates. The axis inertia is much greater and also mismatched because one axis must be installed on the other (i.e. in my case, the X platform is mounted on the Y carriage). Therefore, MaB 2.0 will be an overhead gantry type machine with an fixed work surface that only changes in Z height to print layers.

What on earth does that have to do with the trippy-ass PCB up there? Well, that PCB is just my take on the Makerbot Heated Build Platform. For now, I’ll just keep the surroundings of the workpiece nice and warm. I really don’t mind limiting myself to one thing at a time. It’s just a little bigger than the stock part. And by a little I mean it’s 7 inches square and designed for 50 watts of heating power. It took a while and even more OCD to get those trace lengths correct. There will be a thin aluminum plate thermal-transfer-epoxy mounted to the center heating coil section (not bolted down, but legitimately adhered with silver-bearing epoxy).

This piece is reusable in any future MaB versions since it’s already pretty substantial in terms of square inchage.

making the makings of the make-a-bot

After designing, the next step is of course for me to build have expensive computer controlled machinery build it all. Spoiled so much I am…

Here’s the spindle laser-cut from 6mm white acrylic that I had on standby, holding the Giant ABS Donut. You can see the click-lock fingers easier in this picture. To unlock, rotate a few degrees counter-clockwise and then lift up. To lock again, drop the top plate over the 3 prongs and twist clockwise. This system turned out great. I can actually add a few thousandths more “click” to the prongs, since the laser cutter kerf removed most of my designed interference.

And now, for something completely different:

Hey, what kind of wood is that?

Long story short, I thought there were large stocks of 1/4″ hardwood ply hanging out around the Media Lab – our group usually has a pile for making quick prototypes and displays – but alas, it had been run out and not yet replenished. Not knowing where we got the wood from, I just went ahead and plucked some acrylic panels from McMaster. Acrylic, wood, same thing, right?

I elected to get tinted panels this time to try out the looks, along with plain clear panels.

The next step was to pitch it all on the laser cutter wake up in time to run to the shop before it closes and laser-cut everything. This actually took a long time, as in several days of preparation and missed (and actively suppressed) alarms; as soon as term ended, I immediately restabilized to my 9-to-5 sleep schedule. Yes, my day job is sleeping. Take that, industry. It does make interacting with a shop that is open from roughly 9 to 5 difficult.

I am, however, very glad I went with acrylic:

Let the case mod begin. My favorite part of building things is always the case mod – what can I make unnecessarily shiny, backlit, glowy, and translucent?

I made the base out of clear acrylic and the sides (and everything else) from the tinted stock. It created some unexpected contrast that I enjoy alot.

The L-shaped side plates were split in two for more convenient cutting. Since the “electronics backpack” is not supposed to bear structural loads, I just joined the two legs of the L with a ninja-tail (not quite a dovetail). The “backpack” portion drops down from above after being pre-assembled and is secured by requisite t-nuts.

The completed pedestal. Hey, if nothing else, MaB can be turned into a absolutely beastly PC. There’s even a cutout for an ATX power supply already.


Oh, so that’s what the A in Course II-A stands for.

And the moment of truth – does it actually support the machine weight?! Curse me for building a contactless tool out of heavy \m/etal.

Make-a-Bot itself sits on four little rubber shock mounts. They weren’t necessary, but I figured they were worth including anyway.

I think the design looks gorgeous. The glossy tinted sides complement the raw metal components well, and should look even better once I have some internal mood lighting.

Previously unknown fact: The spindle sits on a large 9″ diameter turntable bearing. This allows the extruder head to tug on the filament at its leisure. The bottom of the turntable bearing is not fixed to the machine. It just kind of sits there – this is not exactly a heavily loaded or high speed application here.

Oh, another detail: Check out the spring-loaded front lid that drops down for easy filament removal. When the lid is opened, its own weight keeps the hinges down, but when it’s vertical, there’s enough force to keep the whole thing closed.

As many random features as I’m putting on this thing you’d think I’m intending on making a production version or something. Not really, but I hope designers of commercial kit machines find some of these aspects helpful.

srs metal

With the pedestal completed, I turned my attention to back to the machine itself. It still didn’t have the steppers installed or the axis belts mounted yet. I decided to tackle that problem first.

The pulleys came with a 5/16″ machined brass bore that by itself is an okay bearing surface for low speeds. I would have just put it on a 5/16″ smooth precision shoulder screw, but could not find one around that was long enough.

Solution? Mock one up from a 1/4″ bore, 5/16″ OD bronze oil bushing and a 1/4″-20 cap screw. The cap screw uses the bushing as a standoff of sorts and a nut keeps the whole thing rigid.

With a few drops of teflon-infused oil at the interface, the glide is almost as smooth as greased ball bearings. Being a millimeter or two longer than the pulley bore, the bronze bushing allows for smooth pulley rotation without much regard to how hard the screw is tightened.

The steppers I ordered came with 15 tooth 2mm GT pulleys already installed on their shafts. So why bother changing them out to the stock 17 tooth ones? The smaller pulley gets me more force anyway.

I should be able to adjust the machine travel-per-step in software.

Every elegant engineering solution has a complementary ugly hack. Remember my Awesome Adjustable X-Axis Endstops?

When I become ambivalent and lazy, they become Dude, You Just Bent The Existing Contact Arm On The Switch A Little X-Axis Endstops.

Hey, it works.

The ATX power supply has its own cubby at the back of the pedestal. The bright polished brass between the dark acrylic makes the whole thing look classy.

And everything as of now. I’ve attached the axes to their respective belts, and they feel alright. No obvious jamming or tight spots, though I still don’t like the X-axis ceramic-coated rods. Important mechanics left include the attachment of the other limit switches and attaching the Z-axis leadscrew to the stepper motor. After that, I should be able to run an all-axes motion test!