The Makings of the Make-A-Bot’s Mak… Damn it all.

chorl5 Comments

You might notice that I’ve been missing for about a week after having produced nothing of substance for even longer.

I’ll be honest. I’ve been spending the time staring emptily at Make-A-Bot while it cyclically exudes a little molten filament of plastic and waves it around. Watching this thing work is disturbingly addictive, and I wouldn’t be surprised if I’ve already been hypnotized and brainwashed into building clones and replicators. That, and the end-of-year institute shutdowns coupled with the recent eastern seaboard blizzard meant that I didn’t have much else to do, or new parts for Manbeargryllspigtankmelonsharkweek to ogle over.

Maybe I should just get it over with and print myself a chin rest.

Anyways, the past while has been filled with more experimentation and silly prints. I’ve also started down the neverending path of making upgrades to your 3d printer by 3d printing them. Here’s a selection of some things made on Make-A-Bot recently.

MaB has been having issues holding Z-axis tolerances for whatever reason. All my parts would seem to come out a millimeter or two taller than they should be. I couldn’t tell if it was ratiometric (which would entail fiddling with the steps-per-mm parameter in the machine definition file) or just random. One attempt to find out was making this 50mm tall (by design) piece. It was also a good test of the thin wall ability of the machine.

It ended up around 52 millimeters tall, which told me that somewhere along the line an extra millimeter or so is getting added. I’ve had 20mm prints come out around 21, and 10mm prints come out around 11. It’s definitely not ratiometric.

So what the hell is it!?

Oh well.

One of the cool things about 3d printing is the ability to make silly sculptures at will. Here’s a hamster. This was done using 0.25mm layers at 60mm/s speed. I was surprised the thing could move that fast.

There was plenty of overhanging areas for the line to sag, but it seemed to handle those well. The ears, however, were a bit troublesome because I didn’t have a Minimum Time per Layer parameter set. They couldn’t cool fast enough before another layer was paved over, so the ears ended up a bit droopy. Setting a MTPL would make the nozzle hover around the part for a while before continuing.

Between the ears is more Undamped Drooling, something that I hope to fix soon.

And here’s a.

No, I can’t see how everything can go horribly wrong at all.

This print was a “high aspect ratio” piece done at 55mm/s and 0.3 mm per layer, and it came out great. I was afraid that the shaking of the platform when printing small profiles at the top would cause bad surface finish – and it does show a little. Otherwise, same problem as the ears of the hamster – small profiles didn’t get the chance to cool off.

The model is called the Pink Panther Woman.

Something which aided first-layer sticking performance some was parking a space heater right next to the machine. It kind of simulates a closed-cabinet heating system by keeping the build surface and atmosphere immediately around it nice and toasty. This was just a random hack to help some of the larger prints stick, such as…

This stepper motor mount for the extruder. I’ve been aiming to switch to a stepper-based extruder for better control of the flow rate. Stepper extruders are also one of the best solutions to Undamped Drooling since they can predictably and quickly cycle back after an extrusion run in order to “depressurize” the filament.

The part itself is a quick rework of this thing, with the “control tower” elongated to fit my bigger steppers. Unfortunately, as I discovered, the extruder control driver chips are not current limited. That means they can realistically use a stepper with 10-20 ohms resistance…. not my crazy 0.8 and 1.4 ohm ones. The driver chips entered over-temperature shutdown about as fast as I could turn my attention from the control software. I’ll need to locate 10-20 ohm steppers before continuing.

Print parameters for the part was the old-but-good 40mm per second at 0.4mm per layer. This one seems to give the best and most consistent surface finish at the end – the faster 0.3mm setting I settle on only seems to give good finish on smaller parts, whereas larger parts would see some filament not quite being packed down on the layer below.

After getting tired of looking at flat black things, I decided to pull out the roll of PLA I also bought. PLA is a clear (when injection molded or properly extruded) material that makes LED-worthy prints. As I found out, it’s also tenacious on plain acrylic (do not use a raft… it does not end well) and also exhibits great extrusion characteristics. It sticks well to itself, and when extruded very near its melting point, it cools almost immediately upon exiting the nozzle and so parts with overhang seem to build better. Oh, yeah, it actually does melt instead of turn goopy like ABS.

The down side of legitimately melting is that it does store more heat for longer than the ABS. This was noticed later on parts which had small, quickly-printed profiles which began sagging. The solution ended up being just activating the minimum time per layer option.

But for now, I used the stock included PLA settings on another version of the hamster. It turned out pretty well, but not what I’d call transparent. Or even really translucent.

I decided to use shot glasses as calibration objects this time. I figure they are more usable than small cubes of varying sizes…

The “Cool” tab in Skeinforge (where the minimum time per layer option is found) also lets  you add a ventilation fan to the extruder. I found a 120mm case fan and tossed it on the extruder controller’s spare output. The “Cool” options then turns on and off the fan during the time the nozzle spends hanging out waiting for the minimum time to pass. On the rims of the shot glasses, this helped immensely.

I later discovered that turning the fan around (such that it pulls air upward after it flows past the part) is a much less harsh thermal cycle and resulted in better clarity for the PLA while still letting it maintain structural integrity.

The calibration cups were used to test different temperatures and feed rates. There appears to be several schools of thought on how to extrude PLA – one of them says keep the temperature at or near the melting point (about 200 to 210 deg. C), and another says just beast it all and crank the temperature way up to 240 degrees.

Well, they all seem to work fundamentally, but one of those is definitely not waterproof. Though it’s leaking out of the seam along the side, not the base.

“C” and “No C” refer to whether or not I had the cooling cycle enabled.  Emptying the glasses (don’t worry, they were full of Mountain Dew) better shows the effects of the different settings:

What I’m observing so far is that the hotter you let PLA sit as it prints, the more optical clarity you get between layers. Make sense, since one layer mushes into the next better. However, you also lose structural integrity. The “No C” print exhibits this clearly – it’s almost transparent in some places, but very inconsistently so. The angle makes it look good, too. It actually has many deformed strands and sagging perimeter threads coming off it, and flexed during print like nobody’s business.

The very first glass is at the left. This was before I added the fan to the cooling cycle, so I indicated it with just “pause”. It demonstrates better clarity than the actively-cooled one (215/45/C) at the right, which had the fan going the whole time.

The best one, though, was the 240 degree print. The fan seemed to bring the body of the cup down to barely below its softening region before the head started on the next layer. It demonstrates a more consistent translucency than the other prints, which I find more pleasing than splotches of clear. Not as absolutely transparent as the first print, but the first print took forever since the wait cycles had to be so long.  With the fan’s help, the last print finished in a little under 40 minutes. The “M” in the logo is also less deformed.

For now, it seems I’m a member of the just beast it school of PLA extrusion philosophy.

Lastly, I tried another high-aspect-ratio print using the cooling cycle enabled process. The Undamped Drooling on this one was almost disgusting since the “tower” was so narrow that it spent more time waiting than printing. I tried taking care of it with a torch – it kind of worked, I guess.

This was done at the prescribed 240 celsius, 45mm per second setting. The layer height is set to 0.35 millimeters to compensate for the increased speed.

So that’s all for now. Eventually, some day, after I finally get my trippy heater board I’ll try printing larger things in ABS. I’m interested in the combination of heated build surface and cooling ventilation for sure.

I’m also legitimately considering renaming Make-A-Bot to something that doesn’t sound exactly like Makerbot. It was great as a project development name, but I’m starting to run into issues answering questions about it, and explaining to anyone else where to get their own. It’s just more explanation than I foresee myself doing without being snarky.

Any suggestions!?

Project LandBearShark

chorl8 Comments

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.