Archive for January, 2011

 

Kitmotter Display Stand

Jan 29, 2011 in Kitmotter!, Project Build Reports, Reference Posts, Stuff

A wild KITMOTTER appears.

I received the metal stock, bearings, and magnets for Kitmotter a few days ago, and so have been spending time hogging the 2D fabrication equipment when I’m awake during the day before the shop closes.

I’m building something a little special for Kitmotter 0001 (to follow the 4-digit versioning scheme I’ve seen in some Processing-derived software), something which should keep people from asking the question “Hey Charles, what actually powers your scooter?”. At least, it would provide an illustration to save me 1,000 words per RPM.


oh snap, it’s a motor on a stick.

It’s cute and simple. The Kitmotter is mounted on a box that will hold a controller and a knob. The knob is turned by a curious onlooker, and the motor spins. Not very informative, but it was something I had in mind since the days of FVM when I wanted to use LEDs to indicate the state of the motor and the direction of current in each phase. Because the kitmotter has transparent sides, what operating mechanics there are in it are presented in clear view.

The materials used in the construction are some 6mm and 3mm acrylic for the endcaps and some 1/4″ steel plate scrap for the rotor segments. Oh, and a Xerox Phaser 4400 stator. The rotor plates were waterjet-cut, and the endcaps laser-cut, on-campus as per standard operating procedure (but the unspoiled can go spam Simon for the same services).

Out of the same sheet of 6mm acrylic comes the stand itself. I think I’m going to start removing the paper coating from raw plates before cutting now, because it’s such a pain to take the stuff off afterwards.

Really quickly whipping the box together.

Yeah, this is definitely something I built. You can tell because of the regularly spaced T-nuts and lack of attention such details as “How many spacers did I need again?”. The answer is 2, but I cut only one. Go figure.

The solution was to 3d-print the equivalent double spacer using MaB.

Moving onto the motor itself, the first order of business was to assemble the rotor using the gratuitously oversized magnets. They’re from Applied Magnetics, which seems to be the least expensive place for gratuitously oversized magnets there is so far; at least for common fractional inch sizes. For everything else, there’s Mastercard Supermagnet George.

I must say I’m a fan of the waterjet-cut magnet retainers, since gluing these in was SO EASY AND PAINLESS compared to the martial arts tournament that was putting the DNIR together. The presence of so many magnets in a circle keep the rings aligned with eachother, and the roughened and uneven finish on the inside also helps with magnet bonding.

Great for making sure your motor never sheds a magnet, not great when you discover you somehow managed to put a magnet in backwards. I had to chisel it out and scrape off the remains with a punch.

My usual order of fluff-filled epoxy was used to bond the magnets.

The fully assembled rotor, on a makeshift shaft for concentricity validation (result: Not Very). I guess the X-Y tolerances of the machines sort of add together on assemblies like this. It’s not bad, but there’s a perceivable wobble to the bearings if spun by hand that’s not really visually detectable. More care in assembling the bearing would also fix it, I suppose. And also not spacing your bearing bores with Kapton tape because you thought the laser kerf was slightly smaller than it actually turned out to be.

Here’s a bit of a leap of faith. I ended up deciding to make the machined-shaft version, so I carved the shaft out of 0.750″ Delrin aluminum steel because I only had the raw stock size in steel. I even cut the axial pin hole to retain the stator, but then decided to just epoxy the whole thing.

The stator was wound 26 (+/- 1 ) turns and Y-terminated. On the behest of Shane, I tried terminating the windings in a different fashion. Whereas normally I’d just twist the three wires together and solder them in a giant ball and shove the ball into one of the gaps between windings, this method just runs a loop of wire to connect the three ends together. Same effect, and I think it gives a better symmetry to the motor despite it being a bit more manual work.

The phases themselves are terminated using some 16 gauge speaker wire (because it’s clear!). Here’s a mostly assembled motor. As the design showed, there’s plenty of airgap. Way too much for my tastes, but the ginormous deth-magnets should make up for it.

Once I mashed the last endcap on and bolted the whole thing together, it was time to use the official MITERS Brushless Motor Jogging Utility melonscooter to give a quick powered spin.

Result? Ignoring the severely unbalanced rotor which needed holding down of the box in order to not hover off the table, the whole thing is very smooth and quiet. My only real complaint was the massive sealed greased ball bearings adding substantial drag to the system. The idle current draw was around 2.2 amps just because of those damn bearings – at Melonscooter’s 40 volt happy discharge plateau, that’s easily 60 watts or more being dumped into the two bearings. RazEr’s original motor only drew 1.25 amps no-load. The DNIR, which is a motor 3 times as long and with something like 60% of the internal resistance (due to its longer windings being put into parallel), still only draws a bit under 2 amps no-load.

The result was that after a few minutes of fun with the throttle, the shaft was too hot to hold on to. That probably isn’t too good for the acrylic. Maybe it will run itself in with more operation.

A check with the oscilloscope confirms the RPMs per Volt as (334 electrical Hz / (7 electrical Hz / mechanical Hz)) * 60 sec. / 40 volts = about 70 RPM/V or so. In metricland, this is 0.14 Nm/A (or V*s). Note that this is with sensorless commutation using a controller which is probably playing mind games with the timing. A more reliable measurement can be had using sensored commutation.  Still, not bad for something thrown together effectively in 4 hours or so, like 2 of which were winding.

What’s next for Kitmotter? I’d need to take it apart again to wire up the sensors, then shove the controller and it into a box and call it done. The controller will probably be the shady e-bike controller that I got in Singapore.

Oh, and for total kicks, I made a 3d printed version of the endcap:

This fits the 1″ bearing version with the 3DP two-piece shaft. Kitmotter 0002 will probably be an experiment to verify that design.

Fanvan!!!

Jan 27, 2011 in MIT, Bostoncaster, Cambridgeshire, Project Build Reports, Stuff

Kitmotter

Jan 25, 2011 in Kitmotter!, Project Build Reports, Reference Posts, Stuff

Hey Charles, where do I  buy one of those motors you use on your scooters?

Hey Charles, where can I get parts for my own hub motors?

Hey Charles, how do you build a hub motor?

Hey Charles, can you make some motors for me?

Hey Charles, have you ever watched Air Gear?

Hey Charles, what does the third wire do?

OKAY ENOUGH ALREADY

Ever since the first RazEr motor was completed and validated, I’ve been getting various permutations of those questions. The operating mechanics of a hub motor vehicle are mysterious to many people not directly familiar with brushless DC motors. What I have some times found is that people (here, anyway) are willing to learn to understand said mechanics, and possibly build their own vehicles around them. Another thing I (and certain other scooter-fancying parties) have found is that building your own little EV, or even a motor, can be a decently well-rounded engineering learning experience. After all, even a simple EV has a chassis, a motor, a drivetrain, control electronics, and some kind of user interface. It’s an all-in-one package for learning the basics of mechatronic engineering, and yields a practical and usable thing at the end.

Unfortunately, the motors I’ve built are all handcrafted pieces of metal billetwork. RazEr rEVolution’s motor is crafted from a 4 inch aluminum pipe with 1/2″ thick walls and some 3.5″ diameter aluminum solid billet.

Such processes aren’t very “democratizable”, for lack of a better term. Few people will have regular access to well-equipped machine tools that they know how to use. I could also just mail one to a shady backwater motor shop in China and potentially make negative millions of dollars, but that’s not very fun and engaging now, is it? The material costs for such a motor like the DNIR alone are pretty hefty. Certainly the first batches for the early adopters (like all 3 of them?) wouldn’t fall under $1,000 USD each. And again, a shiny aluminum cylinder is very “black box” and doesn’t tell you much about what’s inside, and if the point is to make you see what’s inside, then it’s not very… err… productive. As the “decentralization” of manufacturing continues, so the accessibility of previously proprietary and industry-specialized technologies spreads. In general, that’s good for the likes of Makerdom. It also means people can stop bugging me about how to build these damn things.

Soon, anyway.

That is why for the past short while, Shane and I have been investigating how to manufacture these motors with now ubiquitous personal fabrication methods and short-run online fabrication services. Such methods include 3d printing parts from places like Shapeways or your very own machine, laser cutting components using services like Ponoko or Pololu, and abrasive waterjet machining by places like Big Blue Saw (HI SIMON). Other typical motor components like magnets and wire can be purchased readily from mail-order dealers right now. There’s still some kinks to work out, and some machine work is sort of unavoidable for most motors, but we think the majority of a motor can now be cobbled together using nothing but the willpower of the Internet.

Without further ado, I present Project Kitmotter.

Alright, so what’s going on here?

First off, the motor architecture is similar to the motors of BWD, Pneu Scooter, and the Jedboard. Shane & Company have piloted the “stacked plates” method of motor design, where…. well, stacked plates of material are aligned by pins and secured by through-bolts. The rotor is made of several stacked rings of waterjet-cut steel that have magnet-securing indents as part of the structure. The endcaps are formed by a spacing ring and flat plate with a center bearing bore. And out of my design book, the stator is secured on a (possibly machined) center shaft with a channel cut out on one side to route wires out.

The three motors above are identical topologically, but there are minor variations resulting from playing with the design.

The first motor uses a 63mm (or 2.5 inch) stator with a can that is 82mm (or 3.25″) in diameter. This is particularly interesting because 82mm is generally the largest you can core out a 125mm scooter wheel to. The 150mm variants such as this or the first three or four on this page are also corable to the same range.

The shaft, as-designed, is a single machined piece of aluminum that is double-stepped, 1″ in the center and 3/4″ on either side, with a milled channel and two end-tapped holes.. This motor was originally designed a little while ago as a prospective machining exercise for the introductory machine tools course here, and so contains a sampling of machined features.

Motor #2 is a 68mm (2.6″) stator’d design with a 3.75″ outer diameter. This thing has massive magnets – 0.25″ thick, for maximum airgap flux density. Given that these motors are designed with very wide tolerances (airgaps on the order of a whole millimeter or more, unlike my ultra-tight 0.5 to 0.3mm airgaps!), I think the fatter magnets are beneficial as the ratio of airgap to magnet thickness becomes smaller. The center shaft on this one is much the same as the first: single piece and machined.

I don’t know of a wheel that fits around this motor at the moment, but a 68mm stator was chosen for reasons I will detail shortly.

Here’s something a little different. This motor is essentially motor #2′s design – quarter inch magnets with the same rotor plates, but 3d-printable endcaps and center shaft. The shaft has been up-armored to 1 inch diameter (with accompanying absurd bearing) for  extra strength, since it would be 3d printed from plastic.

A plastic motor shaft might seem like a horrible idea, but it’s important to remember that in these motors, the shaft is stationary. Therefore, it can actually be considered part of vehicle structure. Furthermore, the anchoring points of the shaft on the vehicle are usually close enough to the bearing that the plastic is loaded for the most part in shear, not bending, which is one type of loading where the diameter increase helps substantially.. And if all else fails, just drive a 1/4″ bolt right through that center hole there and all the problems are solved. The vehicle loads will then be transmitted and taken up by the steel hardware, and the plastic shaft around it becomes more or less just a shaft diameter spacer for the bearing.

Printing a shaft that’s 3-4″ tall and only 1″ across at the base, though, is kind of problematic. Especially with the moving-bed designs typical of smaller and DIY fab-scale 3d printers, including mine. So I dropped in a quick way to print the shaft as two seprate, shorter prints.

The two halves are joined by a dovetail interface for alignment purposes. The idea is then to finish-drill the pilot holes to 1/4″ diameter after fusing the two halves together with epoxy or CA glue, then putting a bolt all the way through. While the shaft could be used by itself without metallic reinforcement, adding a bolt in the through-hole would make the whole thing more stable. I came up with a few other dovetail joint designs, including one that doesn’t have the mating faces handling bending loads (i.e one that is like the above but turned 90 degrees), but the idea is the same.

I printed some design iterations out on MaB to test for tolerances and fits. For the truly budget- and sanity-constrained, I think the 3DP shaft is perfectly fine as a solution.

ok, so where do i get one of those stator things?

As mentioned before in my electric hub motors writeup on Instructables, the stator is the most difficult part to get for a motor, usually. That’s because it’s a component typically produced in the thousands or tens of thousands at a time by automated machinery, so you can’t get just one. The stator is always a series of stacked, very thin, silicon-alloyed iron sheets that are insulated from eachother by an oxide, phosphate, lacquer, or epoxy layer.

No, cutting up sheets of Home Depot galvanized roof patching does not work. Nor does machining it from a solid piece of steel.

Citizen-obtainable stators include the stock factory-made ones found on places like Gobrushless to custom laser-cut laminations that you can get from places like Protolam (who supplied the rotor plates for BWD and its kin). However, the latter option tends to be rather expensive. A custom stator is, therefore, the trivial solution if you have money to throw at the problem. For Kitmotter, I’m taking the approach that I have historically used: by harvesting stators from existing sources. Generally the source has been large laser printers and copiers, which tend to have outrunner-style stepper motors to crank on the paper feed path or spin the transfer drum.Copiers and printers are copious here at MIT (and I would guess the same for any large institution with a paper-pusher army). However, what I never did was think about logging the part numbers or models of machines that my stators for RazEr, the skates, and the like came from.

A while back, I sleepily ordered a pile of different copier motors from Ebay, and therefore finally had the opportunity to do some cataloging.

I’ve saved these numbers in a spreadsheet here. Yeah, I know, there’s all of 3 different motors on there right now. If you come upon a reliable model, you should help me append the list.

Bottom line is, the 3.25″ kitmotter uses a stator from the Docuprint 2125, which seems to be rather rare, even on eBay. I only got 3 of those motors, and now can’t seem to find more. The stator was chosen for its good fit to a 3.25″ motor. Further “production” of the motor, such as for the machine tools course, would probably necessitate a custom-cut stator. The 3.75″ kitmotter uses the 68mm Phaser 4400 main drive motor, Xerox part number 127K35701 (That sounds so much like a McMaster part number. I wish…)

In fact, I use three of these things back-to-back-to-back in RazEr rEVolution’s motor. The Kitmotter only uses one stator for simplicity. They appear to be fairly common on Ebay, so I’ve temporarily designated the 3.75″ kitmotter as the “safe design”. What’s even more convenient is that these 68mm stators are the same type used in the Turnigy “Melon” motors. So, conceivably, you can just get a Turnigy motor for the sole purpose of harvesting the stator out, and making an ultra-wide motor. Or splitting the stator into several smaller segments. Trust me, you cannot find a custom stator that big for only $100.

where does the wheel go?

As it stands, the kitmotter designs have no wheel mounting provisions. For instance, I have settled on a threaded locking ring design, whereas Pneu Scooter from above actually secures the motor into the wheel using machine screws. The method used on BWD, which is wrapping polyurethane strips around the tire and attaching them with high-strength urethane glue, is currently the method of choice for Kitmotter. McMaster has urethane strip in many different hardnesses and thicknesses, so it’s not too difficult to wrap a custom tire. The tire could be sanded to fit a curved profile, or like BWD, just run straight and flat.

Alternatively, one rotor plate can be expanded into a flange shape and have circumferential radial holes waterjetted into the flange so a tire of arbitrary size can be bolted on. I have yet to find a tire that is amenable to this treatment, and that is of course a branch of investigation for the project as it progresses.

tl;dr

I’ve already ordered some of the parts needed to finish one kitmotter, the “#2″ 3.75″ diameter, 0.25″ thick magnet design. The rotor plates will be cut on-site here, along with the endcaps. I’m not going to release the designs quite yet, since they’re still unproven and may need some more dimensional adjustments. I’ll also look into tire-mounting provisions.

Regardless, there’s already more than enough information lurking in this post and others for you to boot up your favorite CAD program and fire off a design to Big Blue Saw.

What is a Singapore?

Jan 23, 2011 in Events, MIT, Bostoncaster, Cambridgeshire, Stuff

It’s the slightly confused illegitimate offspring of a British noble with a Malaysian mistress, who grew up in the care of a Chinese nanny. That’s just about the quickest way to describe it. It’s an interesting mashup album of Southeast Asian culture with British heritage. The official language is English, but on the streets people usually speak either Mandarin Chinese or a hybrid of English with Malay and Chinese (which sounds weird, but I can parse it when I can phonetically understand it due to the grammatical structure being not unlike Chinese…) You also drive on the left side of the road and walk on the left side of the sidewalk, which, needless to say, caused me to almost run into people several times and the aftereffects of which are still being felt since I now have to switch back to instinctively dodging oncoming pedestrian traffic on the left hand side once more.

So what’s the actual reason I ended up halfway around the world for a week? Some time last month I was invited by the Singapore University of Technology and Design, under the auspices of the Department of Mechanical Engineering at MIT, to attend a January information & future student recruitment session promoting the new university. SUTD is partially a MIT collaboration, the goal of which is to export key features of the various design schools and courses here and create an institute centered on the “hands-on” style of teaching design – whether it be product development, engineering, architecture, or whatever else requires design, which really is everything. Several of my peers in MechE have already been working closely with the SUTD nucleus to pilot and explore potential directions for the engineering side of things.

Now, how better to promote “hands-on” than entertaining the audience with a bunch of rideables and demoables? That’s what I ended up doing, at least to the limit of what international baggage allowances deemed acceptable. I ended up physically bringing RazEr rEVolution, the “homicide-skates“, Nuclear Kitten, and a pile of 3d-printables. Everything else, I just made some informative posters for, which will be shown later.

On Saturday morning, immediately after punching out my sleep schedule and tying it to a fire hydrant, I struck out retracing the steps of the great explorers before me.

Specifically, I started scouting out places to get parts. Something you don’t see (often) in Western nations and which I’m glad has stuck around as a behavioral tic of Singapore (if we want to talk about confused offspring) is the abundance of places to get non-consumer-grade parts and components. Such a “fix-it” and “build-it” culture has, sadly, all but died out in most Western nations. During my last trip to China, unfortunately before this current iteration of the site dating back to July 2007, essentially all I did was run around Beijing checking out the hardware. And I’m content to say that my decidedly non-tourist behavior here has been just as productive.

In Sim Lim Tower (NOT SIM-LIM SQUARE ACROSS THE STREET) there are three floors worth of small shops and stalls which sell everything ranging from the very commercial, such as these prepackaged electronics kits:

… to the slightly out of the ordinary but still organized bulk parts and discrete components, such as these LEDs (and up to and including SRAM chips and entire microcontrollers). See, I almost feel like I should get a little cute baggie and a mini-shovel and just start mining in the bins.

And then you have things like this physical embodiment of what my basement will probably look like in 30 20 10 years time.

Now, since the Singapore Dollar is roughly on par with the US Dollar (exchanging at about S$1.25 to US$1 as of the now), I wasn’t able to clean this guy out. British Airways would have flipped a shit at me anyway, and I probably would have shut down all of Boston upon arrival.

It also meant that all I could do was press my nose against this guy’s display case:

If you know me, you know that as a Mechanical Engineer I have a penchant for enormous semiconductors. Sadly enough, they weren’t that much less expensive than if I bought them new and commercially. These guys fix industrial motor inverters and deal in  electric motor drives, so it’s unsurprising these modules are just chilling in a store window.

The vast majority of these small shops are a small storefront crammed with wares and having a single internal aisle about 0.8 persons wide, also stuffed to the brim with product. You generally don’t go and pick something off the shelf; rather, you ask the guy about what you want and he (somehow) finds one. It’s the same process that governs how to find parts at MITERS, except the shopmaster isn’t me. This place had a great selection of random small hand tools and some fasteners and other implements. It’s like if I distilled an American hardware store down to a fuming concentration.

The collision of Southeast and West (because let’s face it – Singapore is not really “East Asia” geographically) results in amusing regions of stability like this:

It’s some hybrid burger place that serves both conventional, American-style hamburgers to Japanese and Malaysian/Indonesian inspired burgers of various flavors and architectures. I approve wholeheartedly.

Another day, another random small business park: an electric bike dealership.

This place actually has a website, and they sell both bikes and replacement parts therefor. Those shady-looking brushess controllers you see on Ebay all the time?

Yeah, I got one. Hey, yet another reason for me to avoid building a motor controller.

okay, what did i actually come here for again?

Oh, right.

The event itself was held at a youth center closer to town. From the outside, it looks like a hybrid of the Media Lab with a YMCA, built around an enormous Luxeon Star LED.

Oh, did I mention the event was geared towards women and girls? I didn’t know that until a few days beforehand either.

Delight turned quickly into disappointment as I discovered they actually meant geared towards junior high and high school students, in an attempt to entice them towards a career in design and technology. At a university which, conveniently, is opening to students about when they graduate. Hey, I’m about to graduate too (I think), just from the next level up.

Much of the event was a presentation and talk by the SUTD nucleus. Essentially all the top-level admins were in attendance, including the SUTD President, Tom Magnanti, a former MIT Dean of Engineering.

Along the perimeter of the conference room was the poster and demo session featuring works by SUTD and MIT students and interns. The students wandered around the displays before and after the main talks.

Guess who spammed about 40% of the posters by area?

You can clearly see the goodies on display, and the Segfault video playing on both my computer and a supplied spare screen. The posters, from left to right, are about hub motors, combat robots, 3d printing, and LOLrioKart. Okay, and Segfault too – I wasn’t sure what the unifying theme of those two were besides “EXPERIMENTAL VEHICLES”. For reference, the actual full size PDFs  are linked.

Don’t nipick the details – I had to do alot of condensing and de-technification (is that even a word?) since I wasn’t sure what the audience was going to be even as I made them. Also, spot Make-A-Bot‘s new project name.

The event itself was about 3 hours in duration, but with a long taper-off at the end when students were checking out the posters. So yeah – essentially, I got flown to Singapore for a week (airport-to-airport) to attend a 3 hour event. But it was awesome. And warm – the weather hovered around 85 to 90 degrees (F) the entire time. Upon arrival in Boston, I was greeted by 34 degrees, piles of dirty and melting snow, and of course rain. Then it proceeded to all freeze solid.

Sigh.

I hate to knock pictures from Facebook, but I absolutely must share these two from the SUTD album of the event. Here’s the Provost of SUTD taking a spin on RazEr rEVolution after the event concluded:

And finally, Big Man himself, Tom Magnanti:

So my new goal is to get L. Rafael Reif and Susan Hockfield to take a ride on RazEr.

Also, flower bunny.

RazEr rEVolution: Beasting The Everything

Jan 21, 2011 in Project Build Reports, RazEr rEVolution

Alright, now that’s over and done with…

This is the part where I recap how RazEr ended up being finished and packed up the day of departure. I’m glad to say that it worked without problems, at least at demo speeds. Singapore was also a pretty unique experience, and I’ll address that in a separate post. In the mean time…

60 hours

Some time around last Saturday night the 8th of January, RazEr rEVolution looked like this.

Two of the three sensors in DNIR mysteriously stopped responding a while ago, so I had to open it up and replace them. It involved heat-decomposing the epoxy holding the sensors in with the NEW MITERS HOT-AIR SOLDERING PENCIL!!!!!! and then adding new ones. For some reason, the ATS177 sensors seem to be a little fragile – I’ve had trouble with them going out before.

Whatever, at least they’re cheap.

After putting the DNIR back together, I decided to temporarily mount a mini-Kelly on the back just to take it around the hallways a few times. The DNIR has almost gratuitous torque, even at the 30 amp software limit of the Kelly controller. The original RazEr was pretty swift for such a small vehicle, but this thing is always on the verge of launching you off – not to the degree of Melon-scooter, but spontaneous wheelies were recorded. I was prepared to take it to Singapore just like this, even though it would have been the shadiest looking thing to find in a suitcase ever.

A few of us had fun taking the thing around the hallways. Well, until…

Yeah, uh, about 3d-printed parts being structural.

In my defense, that was a full speed head-on collision with the wall. I think even the original Razor fork would have bitten it pretty hard.

Well, time to fire up Make-A-Bot and pop out another one…

36 hours

Look! It’s mini-melontroller!

First hinted at the bottom of this post regarding Melontroller, I designed Mini-Melontroller just as a way to compactify the design even further. The circuit and pins are exactly the same, but the length is about half an inch shorter, and there are routing and placement differences. Namely, I like how clean the passive components ended up on this design.

Wait, so whatever happened to Melontroller? It did work, but seemingly only at low speeds. The control was unstable at high speeds while running the MITERS Public Etek, and I suspect it to be an electrical noise issue. Either way, something happened – either the software crashed or the power supply suddenly shut down, but the Etek suddenly stopped from high speeds, probably shooting a transient stiff enough back into the controller to take out a phase and a gate drive.

I put away Melontroller for a little while, but after getting the Kelly-rig on RazEr to work, I decided to try out the new PCB just to see if it was a problem resulting from my routing and erratic component placement. It turns out the mini version would just barely fit into the place previously occupied by the RazErDEC board.

Granted it’s at an angle, but it does clear everything. The bottom of the controller is insulated by some sticky-back foam rubber, hot glue, and Kapton tape. I’ve also cleaned up some of the wiring here.

As another touch, I found some leftover 3/8″ long flat-head 4-40 screws and decided to countersink the bottom hardware. I figure it was only a matter of time before I tried curbjumping and scraped all the screw heads off…

12 hours

Bam.

It took most of Sunday and some of Monday to debug the controller. I think I spent at least 6 hours trying to debug electrical noise problems before determining that the benchtop power supply was unstable at the higher voltages needed to run the controller. When I took it off the bench supply since it kept latching and shutting down and put the controller on a battery  pack, everything worked beautifully.

The same thing may have killed Melontroller the First.

Otherwise, the rest of the debugging was macro-electrical and involved faulty connections and accidentally powering the Hall sensors backwards, fortunately without damage. It turned out my Cool Blue Switch just couldn’t handle the capacitative inrush on contact (there’s no precharge circuitry on the controller), and it stopped working after only a few power cycles. Thus, I reverted back to a Deans-based master power link like the robots.

Make-A-Bot had long finished the new front fork (beefed up to 75% fill for strength), so I spent a while just getting a feel for the control. The synchronous regenerative architecture of melontroller means I can’t really coast on the thing, nor kick scoot, and the handlebar will punch me in the stomach if I let go of the throttle from a high speed (since it brakes the motor).

This will be resolved hopefully once I add the current sensors back in and can perform current control. The throttle will then command current dirrectly, and the no-throttle endpoint is rescalable from negative current (drag braking) to no current (coast) to …. well, what, cruise control?

Well, it works enough… Time to shove it all in a suitcase.

With the front fork removed, RazEr fit beautifully across the diagonal of my suitcase. The ‘blades fill the two triangles that result, and NK & company are stuffed in the gaps.

To my utter surprise, this whole rig made it to Singapore without incident, or even with a TSA sticker. Granted, it was 3 days late, making it there only on (this past) Sunday night, because it missed my Impossible Connection over in London. I’m also proud to say that it made the trip back too.

Next: Thingapore itself.