Archive for March, 2014

 

All-around Updates: The Anime Boston Recap, 2.00Gokart Round 3, & Chibi-Mikuvan

Mar 28, 2014 in Chibi-mikuvan, Electric Vehicle Design, MIT, Bostoncaster, Cambridgeshire

I have resurfaced.

Like last year and the year before, major gaps occur in my webospheric presence because I’m busy with corralling a group of undergraduate students before one of them sails right off the 3rd floor of the building on a silly go-kart – 2.00gokart is running again this spring, with only minor changes to last year’s edition. In the mean time, Chibi-Mikuvan has been progressing slowly.

Because this post is going to have some obvious… length issue, here are jumps to the directly relevant sections:

  1. The Anime Boston recap (a.k.a “My Fangirls Rejoice”)
  2. 2.00Gokart’s current state
  3. The work on Chibi-Mikuvan since a few weeks ago

amine boson

One of the quirks of running a shop is you actually never have time to use your own shop; go figure, because you’re either fixing something or helping someone else with tools or their own projects. And many projects there were in the past few weeks: the IDC has been the ad-hoc command headquarters of the MIT Anime Boston brigade, probably because I know everyone and am there all the time anyhow. I even joined in this time! Historically I’ve been an incredibly lazy cosplayer and have just done whatever involved a lab coat or sunglasses.


Except that one time at Dragon*Con, with the 6-foot steel venier caliper, but I digress…

I think the only other time I went above and beyond for a character was the RazErBlades, which were more independent project than not, and I threw together an easy version of the character for Otakon 2010.  My interest in this domain is primarily that of impractically large transforming mechanical weapons, but I have  never taken it seriously enough to work on one as a project in its own right.

But that doesn’t mean I won’t facilititate or encourage people doing so. Check out Jamison’s Impractically Large Transforming Hammer-Cannon (from League of Legends) That He Finally Blogged About, for example.

And the one I am partial to, Cynthia’s Impractically Large Transforming RWBY Scythe.

I’m a fairly close follower of the RWBY series because of its proportion of fancy transforming mechanical weapons, all of which I say “Monty Oum, you son of a bitch.” to because I’m almost certain there are some volume discrepancies going on, such that if you actually built the weapons and had them function visually in real life, there would be no place to put the actual weapon part. But Monty designs are hardly the worst perpetrators of this in all of impractical transforming weapon history. In fact, I think a lot of thought was put into their actuation and mechanical design for the most part, especially for Ruby up there. Things at least don’t magically appear and disappear.

Anyways, I strongly recommend reading through Cynthia’s design and build process because it covers all the bases of design to iteration to implementation, all in a first large mechanical build. My own first mechanical projects were way more, umm, ad hoc organized. I saw a ton of the prep work that went into it, and my involvement was limited to some backend hardware support only (e.g. “make 23 of these e-clip things” “ok”) during the final days of the build. So yeah, here’s the link again to Cynthia’s Impractically Large Transforming RWBY Scythe (which I am told will become slightly more practical but no less large soon)

I elected to make myself some accessories and attend the convention as the fan-made “Rule 63″ of this character:


Image links to creator’s DA page

Okay, you can’t give a character that weapon, call him Garnet (I must use literally a ton of this stuff a year), and expect me not to bite.

Luckily, it still ranked on the favorable end of “easy” to “You have to be cosplaying for as long as I’ve been building robots to do it right”. I even made up a “make versus buy” chart for it:

 

One of the end goals of all the “Makes” was to use some of the rapid prototyping tools I had in the IDC which could be reasonably accessible to anyone – the Replicator 3D printer (which has sort of become our “student beater” machine), and a laser cutter. Harking back to my Maker Resources 2013 presentation at Dragon*Con, this year our group of maker-oriented con-goers (not to be confused with conga’ers) decided to host a panel with much the same topics, geared specifically towards costuming:

 

Unfortunately, I don’t actually have many pictures of my build, largely because it took place during the last two days before the convention where I was mostly aiding the completion of other props and handling 2.00gokart. But stuff did pan out. For instance, here’s a rose sigil thing that I made from the scrap outline of Cynthia’s rose cutouts. The bracket on the back was designed to snap-fit into the buckle of a large tool belt I bought and chopped up for this purpose.

The material is “silver” PLA, which I bought from Amazon (and which Zenn Toolworks hasn’t stopped calling me about to review… yeah guys, it’s filament! It’s all melty and stuff! Yay!)

It’s not silver in the traditional sense, but more like a gray PLA with some metallic sheen in it, which I suppose gets the job done.

A ton of other parts were also made in this same PLA – the large ammo boxes, for instance, which I drew up to hold two side by side .50 BMG rounds up to 6 high, because I don’t know if that was the idea or not, but had the dimensions of the .50 BMG in front of me. Plus, the scythe is allegedly also a .50 caliber sniper rifle. The ammo boxes had removable lids and actually served very practical purposes during the con. Besides those, the decorative crosses were also made in the same material.

I also used it to print the decorative bullets for the belts. Unfortunately, due to time, I didn’t make anything else to hold them to the belts, so we went without them – that will come later. I had a few feet of black cargo webbing and decorative rivets ready for the task.


Termed by my compatriots as “nerd-cute” or “nerdorable”

I think I shot pretty close in the end, eh? This was on Sunday, after Cynthia had broken her scythe demoing it so many times, so she designed and made a comically small stand-in from leftover MDF.

I ended up not being able to attend the panel, unfortunately, since Friday night / Saturday morning I was plowed over pretty hard by a (what I assume was) exhaustion-driven opportunistic flu/cold. It was bad – as in, I could barely stand up and walk straight bad. I ended up sleeping most of Saturday off in the IDC, and felt better enough on Sunday to tag along to the convention, since I paid $60 for that entry pass, dammit.

Which I lost, by the way, some time in the chaos of the week and had to borrow Nancy’s. Also, I never thought I would ever buy suspenders for any reason in life, but this was it. (They’re black, so not really visible in the picture).

While I have no plans for Dragon*Con but to bring back this character in more detail, Cynthia plans on a full rebuild of the scythe, so I’d pay attention to her site in the mean time.

2.00gokart: Year of the Weird Angular-Framed Karts

It’s back!

This year’s 2.00gokart session saw record application and enrollment. I had 64 students, mostly mechanical engineering sophomores but there were some serious left-fielders like Architecture/Visual Arts (course 4) seniors apply, but could only take 20. Man, my acceptance rate is getting to be almost as bad as MIT itself.

I expanded the field to 20 students (i.e. 10 vehicles) this year because of the experience over the summer with dealing with 27. It’s incrementally not much worse, especially now that I’ve produced more reference and lecture material which has cut down greatly on the time-consuming basic questions. The operations are now much more streamlined now that I have experience myself.

The rule changes this year are very slight, but are again designed to put a little bit of a twist in:

  • Your vehicle now has to fit through a standard U.S. doorway, basically 33″ wide. Sorry Nelson. And like half of everyone from last year…
  • You now have the option of getting once nice wheel…. or two Harbor Freight pink wheels. Cue evil laughter here.

Besides that and some minor clarifications, it’s the same thing as last year.

As usual, the class started with a “demo night” where everyone got to see examples from last year, and past students dropped by to visit. Here’s dgonz giving a short informative talk about the dangers of “dgonzing” in your chassis design.

A few weeks in, and people have their first orders.

This year, I got sheets of hardboard (Masonite) from a local wood distributor for super cheap, so everyone got to prototype their heads off on the laser cutter again…

…before I committed it to metal.

There are a lot more teams daring to wander outside the safety of 90 degree angles this year, including Triforce-kart up there. Which I’m sure is not the actual name, but I’m naming it just like I’ve named other things “5-degree-kart” (for having a frame that is a 95 degree trapezoid) and “bus-ass kart” which… you’ll see later.

The hardware in general is more robust this year, I think in part due to the added lecture / reference content and the availability of more examples from past years. Remember – these don’t come from kits, each piece is cut or machined from the students’ own designs.

In general, the design diversity is up from last year, which is what I want to see. Here’s one of the three teams that have elected to do live-axle, but they’ve also went and bought a differential (and named it Humphrey…). All this equipment came from Surplus Center.

Electrical system-wise, Kelly + SK3 still rules, but there are more dual-motor drive setups as well as one team going super experimental and taking a shot at using the Trackstar 200 – the big one. I eagerly await the results of this test since I’m using one on Chibi-Mikuvan.

Speaking of which…

Chibi-Mikuvan

Ah, now the section that will take the longest since it’s about me!

In the past few weeks, I’ve completely welded and assembled (and painted!) the frame, plus gained much more experience using the Shopbot CNC router to make the foam cores for the body. I also tried making the battery pack housings, but there’s either some quirk of the machine I’m missing or my parts are all scaled around 95% in the Y direction. The frame is almost mechanically done, upon which I’ll focus on getting the electrical system installed.

In the last episode, I cut all the tubing parts to size but had not yet put anything together. I had one giant weekend of welding some time ago in which I assembled the entire frame. The first things to come together were the steering knuckles, which also mount the brakes.

After dialing in my practice again with those, I decided to work on the motor mount. Recall that I’m using an angle grinder gearbox to “preduce” the motor speed before it goes into a chain drive. What better way to mount an angle grinder gearbox than with the disc guard ring it comes with? I cut the ring off using the other large angle grinder, then wire brushed the paint off in the critical areas.

Here’s the motor mount welded up, along with some of the outer frame parts. I wanted to put together as much independently as I could before joining the long frame rails, just so there was less fixturing shenanigans.

In the welding room…

I made tack welds to the frame with a TIG welder, but then came back with the MIG welder to finish the beads. This strikes many people as weird – and it kind of is, since typically you do it the other way around. My rationale is, the TIG allows me to exert no force at all to make the tack, whereas the MIG will always have a little wire poking your part and could therefore move the fixturing.

Well why not fixture better? I think the reason I fixture tenuously – generally with only those red magnets – is the same reason why I can’t finish the weld with the TIG welder. Time and patience. I’m insufficiently patient to do a nice TIG joint, when patience is the key virtue in getting a good one.

Spray and pray!

You know what they say, though. A grinder and paint…

…makes up for a welder who ain’t.

To be fair, there’s no shitty welding on the frame, but I also don’t take myself seriously enough as a welder to say anything more insightful.

The frame was thoroughly cleaned with acetone first, then I put down a few coats of self-etching primer followed by black engine enamel paint.

Overall, after a day of drying, it came out very nicely.

I test fitted some hardware to gain more insight on the lengths of spacer needed for the front wheels. Now that they’re mounted, the front disc brakes look even more ridiculous. Seriously, I think I could stop 3 other sketchily-braked entries in the next PRS race.

Rear axle in bearing blocks installed.

A closeup of the front axle kingpin and spindle assembly.

It’s up on four wheels! No steering parts yet….

The steering column supports are a fairly classic tactic around here of drilling some holes in Delrin (acetal) blocks. Acetal is a bearing plastic, so it’s super slippery while being pretty rigid. Two pin-jointed blocks constraint a steering column at any angle you please, then two shaft collars (one on the bottom, one up top) constrain it axially.

The driving link at the bottom is welded onto the column – instead of bolting into a face-drilled shaft collar like on Chibikart. This is just for expediency.

This forms the extent of the mechanical work as of yesterday. Likely right after I hit “post” here, I’ll go hook up the steering linkage and use a vise grip as a steering wheel and get pushed around the hallways.

Here’s some Shopbot work making the battery pack sides and the bodywork!

The battery pack sides capture the Fusion Sticks into groups of 5 so I can parallel the cells. They’re 3D milled parts by design; I guess I could split them into 2D layers, but I wanted to learn the 3 axis milling mode of the Shopbot. The material of choice is a 2×10 chunk of sanded fir I bought from Home Depot. To stay within the PRS budget, I need to make this from something reasonably strong but cheap, and wood actually qualifies well there.

After roughing and finishing, the end result looks pretty good!

I made two versions. The one on top is both roughed and finished, and is the best quality. The bottom one was one of my attempts to shortcut the process by only roughing. The Partworks software that came with the Shopbot is sort of limited in the things it can do – it’s for beginners and general non-engineers, after all, so isn’t full featured like MasterCAM or HSMWorks. It won’t cut the part out in “roughing” mode, only finishing, so I tried to trick it into thinking the part was thicker than it actually is such that it would “cut out” in the roughing cycle by virtue of stopping too far down. This did work, but the internal features were then too far down also!

Seems like the only way to really make this work is to make sure the stock is thinner than you tell it, which couldn’t work in this case because the parts are 1.5″ thick and so is a “2 unit” dimensional lumber.

I’ll just put up with the extra 30 minutes of finishing. What’s weirder is that these parts are seemingly compressed in the Y direction by about .05 inches consistently, almost like someone put in a “scale 95%” in the program that I haven’t found. I’m going to try running another version sideways (long direction oriented in Y) to see if it is signficantly shorter, which would tell me “someone set a fixed scale percentage”, or still 0.05-0.1″ shorter, which would indicate to me an offset problem.

With some lessons learned making the battery sides, I started routing out the foam cores which will eventually be between the fiberglassy bread in the composite sandwich shell.

I bonded the foam together with slow-curing epoxy that was filled with “milled fiber” until it was pasty. Which is really overkill since it seems like 77 spray adhesive worked just as well, but let’s keep it legit since this thing is totally going into space after all. I made several bricks that were to contain the four sides of the body.

Foam is messy. You can’t use the dust collecting nozzle because it would hit the part, so the foam flies everywhere and generally covers everything. And it’s ultra static-y when you try to vacuum it up.

Doing a finishing pass after the initial rouging!

Foam machines like a dense air, so I set the machine to run as fast as it could. All of these parts finished in around 1.5 hours.

One  of the sides right after cleanup.

The foam was held to the MDF disposable surface by…. hot glue. That’s it. I drooled hot glue in a vaguely grid pattern, about 2 lines per foot, in roughly the shape of the part, then slammed the foam brick down before it cooled off. It worked great!

To dislodge the part, I used a giant dustpan to split the hot glue under the edges, then slowly pulled up with it.

IT’S ALMOST A THING

Too bad that I welded the front wheels 1 inch too far forward – mistaking the end positioning of a dimension while jigging it up.

This means two things: One, that the frame needs to be cut in 2 places, and 1 inch subtracted from one side and added to the other, or two, the body has to get split and a 1″ foam extension added.

I went for the second, since it would also make the gluing easier to manage (I didn’t have any 48″+ clamps). So I split the body in half on my hot wire cutter. A 1″ cross section will be made and bonded to the body, bridging the two halves, and the whole thing rejoined with carbon fiber rods running lengthwise to give the bridge some structure.

Bonding the rear panel to the two sides was easy, since it was nice and arch shaped. I just piled heavy things on top to keep everything down, and used 1 clamp in spreader mode to set the angular displacement (It wanted to lean to one side). For added legitimacy, I used the fiber-filled epoxy here, as Burt Rutan would.

The front half was also easy, just another mess of clamps.

I received an order of 2 gallons of Nice Epoxy yesterday, and otherwise have all the supplies needed to do the fiber layup on-hand. I’m hoping to get to it this weekend, but it miiiiiiight involve a little more psyching myself out beforehand.

For now, I’ll work on getting the frame to mechanical completion because then I can wave it in my own students’ faces to encourage them to finish!

 

 

The Legendary Saga of Chibi-Mikuvan Engineering, from October Until Now

Mar 07, 2014 in Chibi-mikuvan

Welcome to another edition of Big Chuck’s Automotive Blog!

Well, I guess this time it’s Big Chuck’s Miniature Automotive Blog. I actually have not had a full engineering post on Chibi-Mikuvan, which has been in on and off development since late September. I’ve talked about it in bits and pieces, and did some parts investigation type posts:

It’s also gotten some random cameos and teasers in other posts. I feel bad, though, when I do too much work and then don’t say anything about it. So here it is – the start to finish of Chibi-Mikuvan so far, ending last night. This warrants another “get a drink” warning.

We begin with the first picture seen in the introductory post. I found a drawing from carblueprints that showed the Mitsubishi L300, the equivalent in non-US and Japanese markets, into a 2D sketch and began tracing it.

I imported the picture at an indeterminate size, but kept shrinking it until the nominal dimensions matched up with Inventor grid lines.

The “ground point” of this design was wheel size. I was planning on using the dreaded Harbor Freight 8″ pink wheels, which are actually 8.5″ OD. This was scaled to fit the standard 205/75-14 tires of the L300 / Delica, at 26.1″ nominal OD.

Coincidentally, everything lengthwise ended up almost exactly something nice: 28 inch wheelbase, 53.5″ length overall. I picked a neat-looking number for the height at 23.5″.

Here’s the more finished sketch. I simplified the geometry some (how can you get simpler than this?!) like using pure circles for the wheel cutouts and arc segments for body lines. The US version which real-Mikuvan is one of has a longer snout – it’s actually even longer than the scale model shown here, but the proportions were off in this scale model such that when I modeled it at the full length, it was just hilariously bad looking. I settled for a “looks reasonably funny” number for the length.

Width was the problem. Japanese cars are pretty narrow – at scale, the overall width of this thing would have been only 22″. That’s narrower than Chibikart, and not only would I not fit inside the body shell, it would be very tippy. I decided to start with a 26″ wide shell. Because I made all the sketches at the origin’s midplanes, I symmetrically extruded outwards in both directions.

This is the solid reference model for the body shell. At this point, I still hadn’t settled onto a construction method yet. One way was to build an internal ‘skeleton’ of sorts, around the perimeter, and cut out the sides and panels in very thin material like polyethylene plastic. Another way was Epic Thermoform, and another still was a milled foam shell.

Isn’t it wonderful to be able to model 90% of your car’s bodywork in three solid features?

Coming from the Beyond Unboxing posts, I made critical-dimension models of all the parts I wanted to use. The shell seen here is a fake hollow version to make it easier to work inside the assembly. Shown is the angle grinder box, the Pink Wheel of Maleficence, the T20 inrunner motor, and a Ford Fusion dynamite stick.

The frame layout game begins. This time, it was a bit easier because I already knew what the wheelbase and track had to be. The diagonal line shown is an approximate Ackerman linkage reference line. I also knew how big the batteries had to be, so it was a matter of designing a big ladder around that.

I went shopping for stock go-kart sprockets right away. Basically, the seller which gave me the most technical data on something won – I spec’d out a 60 tooth #35 chain sprocket from mfgsupply (not to be confused with mfg.com, which can also supply you things if you so desire), along with a matching hub for a .75″ keyed shaft.

I’m too used to building long continuous one-layer frames with 80/20 rail. Not being able to make continous frame rails was kind of bugging me, even though I knew that I could just butt up steel frame tubing and weld. I briefly toyed with this idea of milling “Lincoln Logs” (muscle memory forces me to type Lincoln Labs)  to allow me to make a continuous frame rail.

Shown in this image is one of the bearing blocks I plan to use – these come from Surplus Center.

The steering parts are now getting a bit more fleshed out. Because of the need to support the battery pack as well as to pass a solid rear axle in bearing blocks, I designed an “asymmetric Chibikart” kingpin and knuckle setup – where Chibikart captures the steering knuckle in between the pairs of ‘winglets’ on each side (these would be A-arms in a vehicle with suspension), this design keeps it entirely off to one side, entirely using the winglets as bearing blocks. In some ways, it’s like upside-down thug MacPherson struts.

The downside to this is that it needs to be built extra solid, but it keeps the design relatively simple. I won’t have to fashion some weird angled or offset member to accommodate the steering linkage.

Time to add a seat. I picked a leftover (from the summer silly go-kart camp) Razor Ground Force go-kart seat as my choice. For budgetary reasons, I couldn’t splurge on a real ‘human press-fit’ go-kart seat. I modeled this up with best visual approximations and a tape measure.

Here’s a size comparison with Chibikart. The driving posture will be nearly the same, but everything is just a little bigger. The seat is shifted forward in this picture – I wanted to get a sense of seating position, and there were several spots. This one was in fact too far forward and I wouldn’t really be able to get in and out.

If I said I didn’t want to make weird angled brackets, well, that clearly all went out the window the moment I had to reconcile the height of the body with the height of everything else. This was my first brute force stab at the problem, and it became the solution for a while. Because the frame is ‘underslung’ – axles, bearings, batteries all on top of it, I had to either bend something up or angle it to interface with the bodywork.

With the frame more settled, I turned back to making the steering linkage. The only way the steering could work for this design, because of the battery taking up the entire middle, was “linkage forward”. This is the reverse of traditional go-kart steering setups, for good reason: to get an approximation of the Ackerman geometry, it’s way easier to design with the linkages behind the lateral axis joining the two kingpins. Because otherwise, hokeyness has to happen:

Yes, those are crossed linkages: left wheel on the right side of the “Pitman arm” steering link, and vise versa. Everyone who’s tried a linkage-forward design in 2.00Gokart has gotten it wrong, chiefly because I had not forced them to simulate their linkges in CAD before making them (That’s changed this year, so none of y’all get to fuck up). If you keep the linkages left to left and right to right like in the linkage-behind design, you get reverse Ackerman geometry for most of your steering travel.

At the generally low speeds these things run at, it causes excessive wheel scrub and unpredictable changing between understeer and too-much-steer: Oversteer isn’t the right word here since it’s the outside wheel suddenly getting traction and whipping you into the turn, not the rear end flying out sideways.

Moving to the back, I cooked up this motor mounting solution which actually involves reusing the clamping ring from the disc guard of the 9″ angle grinder. The guard is made from some hefty, basically 12-13 gauge steel, and the clamp already fits on the nose of the gearbox, so why not use it? The plan is to cut it off and reweld it to a bent bracket to adapt it to the frame.

To stuff the inrunner into the gearbox, I plan on machining a custom shaft that is 12mm in diameter, steps down to 10mm (with a keyway to be cut into both pinion gear and shaft), and has an 8mm hole with a split-clamp on the other end to fit on the motor shaft. It will be tightened down with an extra heavy shaft collar acting on the clamping region.

Short of machining my own tapered locking bushing into this area, I decided this was about the most secure way to interface to the motor’s otherwise nearly smooth shaft. It has a D-flat in it, but hell if you’re getting me to trust a set screw mount at nearly 30,000 RPMs.

I spent some time putting some thought into how I’m going to mount the batteries. I was going to arrange them in ways the manufacturer never intended. I did plan on reusing the tabs they came with – why not do so? The cell module shells snap into each other, so it was going to be easy keeping them in place. I’d just need to figure out the cell orientation and make a thing to mold around them.

I went through a few iterations of cell layout before settling on this one. Basically, the cell ‘sticks’ can be turned around inside the shells, so I could make several modules that had the same polarity (there were two different mirror-symmetric shell designs) and then bus them all together in parallel. Then, those meta-modules would be bussed together in series. That’s how this big bracket was developed.

It carries 15 modules, each with two cell sticks in them. Five cell sticks in the same row get paralleled together, then those series-feed into the next five cell sticks, and so on. At the end, the connection switches rows (which I ‘ll need to design a custom bus-plate for) and winds back on itself. It’s basically a more epic 6-cell “3×2 brick” battery of the olden Nicad days.

These 15 modules will end up providing 28.8v at 40Ah, or a cool 1.1kkWh, the biggest battery I’ve put on anything so far that could still perform to nameplate ratings, conceivably. LOLrioKart used to run 48v 25Ah nominal Nicads, but the cells were so trashed there was no hope of them ever being 25Ah.

Getting close to something that looks like a silly go-kart. I salvaged a road bike handlebar and quill, which has been crudely modeled here, but might not keep it – it’s positively enormous in real life. I might trim it to a more useful length.

 

Here’s how the frame looks inside the bodywork. This was the frame design as it stood for about 2 months. I didn’t like it even before finishing it. It was too squiggly – too many angled cuts and welds to get right, and a lot of extraneous material. The battery pack was going to weigh 60 pounds and the frame another 60 – plus a conservative estimate of 10 pounds of bodywork, and I was looking at a 130+lb empty vehicle. Yeowch – optimizing in the wrong direction is coming back from grocery shopping for a whole fuckton of humble pie.

Steel. It’s a terrible thing.

Some time last month, while the 2.00gokart students were still in the early design stages, I sat down and completely refactored the frame into something which made a little more sense. This time, the frame is inverted relative to the axle and battery pack. The battery is now the lowest point on the vehicle, and it most likely will still not clear the damned Maker Faire cable raceways.

Inverting the layout in the vertical direction relieved the complexity of mating to the bodywork greatly, allowing the frame to be made totally straight and therefore easy.

I re-imported many of the parts from the first design to use in the second. Things which remained intact include the steering parts and all the rear axle components, as well as the seat mounting tube.

Around this time, I also firmly decided to make the bodywork from a foam-fiberglass composite sandwich. I’m basically going to turn into the Burt Rutan of silly go-karts for this. After all, I didn’t buy a copy of this for nothing. I decided that a thin sheet-over-skeleton body was going to be too fragile.

To this end, I used the solid model as a reference and made ‘thickened’ sidewalls which can all be machined from a single slab of foam on the Shopbot. The intention is to do this, then bond the foam together, then apply 2 layers of fiberglass cloth – enough to give it structure, then polish it off like the real thing. It would be painted plain white and then the artwork will come after that.

If someone can find me a thermoformer large enough, Epic Thermoform is still on the table.

With the mechanical parts largely being copy-paste, I moved onto modeling moer electrical system parts. This is the contactor deck from the original Ford battery – it’s missing one contactor that controlled the battery negative, which I took out because in my system I’ll only be switching positive. I’m going to try and use it otherwise stock, just to get more usage from the pack. All hybrid batteries will come with a contactor pack like this or similar, so it can be a valuable resource in its own right.

To make the shape, I again imported a picture of it and began scaling until the size made sense. The 6″ caliper acted as the scale item in this case – between its arms is 6″ +/- about 0.01.

I’ve added more detail to the frame now, including the new front and rear bodywork mounting points, which double as bumpers. The extra front biased volume is going to give me much more legroom. The little holes in the bumpers are so I can attach the bodywork with quick-release pins.

The frame next to the bodywork model. The folded sheet metal brackets will be bonded to the body and travel with it – they’re only shown in place here for visibility purposes.

I mulled over this design for a few days to make sure I still liked it. It was time to start cutting steel.

I got a great deal on eBay for mild steel tubing – nine 4 footer sticks of 1″, .065 wall for only $35 total (shipping that much steel was a whole ‘nother tax break expiration). That’s not far above scrap pricing. Someone’s obviously trying to get rid of a lot of this stuff, and it might have been actually surplus or scrap – it was the dirtiest, most greasy steel I’ve ever had the joy to touch. An entire can of brake cleaner went into cleaning just the five rails I cut up.

Here is one, mounted on the coldsaw, about to be sectioned into frame pieces.

The resultant frame cuts! Not only did I process all the square tube, but the round stuff and hub parts too.

Here’s a dummy frame mocked up. The whole thing is 47″ from front to back – the bodywork brings it closer to 5 feet.

I had the joining plates waterjet-cut from 1/8″ steel. These include seat mounting flanges and reinforcement plates for the front steering knuckle area, as well as the flat plate profile for the motor mount. Overall, this vehicle features very little waterjetting, and it could all be bypassed if I were working to stricter budgeting requirements, but that would be taking Powerwheels racing too seriously.

The small tube chunks are all parts of my BurnoutChibi-derived hub solutions. In fact, BurnoutChibi was a prototype for this design, especially the fronts.

I decided to fabricate instead of buy drive hubs because 1. nobody made drive hubs for shitty Harbor Freight Pink Wheels, and 2. commercial cheap go-kart hubs are just slabs of steel welded to tube anyway. The bore of the tube is almost exactly .75″ – it even fits over the driveshaft I bought. It will straight up be broached for a 3/16″ standard keyway.

My first instinct is to all-aluminum-billet this, like old LOLrioKart hubs, but it’s being kept cheap and steel to more closely follow the spirit of the event.

The front hubs are an exact dimension change of BurnoutChibi hubs. I bought the steel tube such that its inner diameter was almost exactly 1 3/8″, necessitating minimal reboring work to stuff bearings into.

And check out these custom, almost 7″ disc brakes! Is this serious braking overkill or what? I think my actual van brakes are not much bigger.

I can make up for everyone elses’ shitty dysfunctional scooter brakes at the race.

To utilize these hubs, I had to carve off the existing bearing hubs from the Harbor Freight wheels. I chucked this into hugelathe and ran a standard boring bar into it, boring away at the face of the wheel until it flew off.

Using hugelathe, I also finish machined the hubs after welding them together. BurnoutChibi’s hubs did wobble a small amount due to welding warpage. These hub plates were all bigger, so the warp was amplified. Post-machining was also needed to make the boss that the rim halves sit on, and to clean up the interior of the tubing for bearings.

The internal bearing spacer dropped into place. I whipped up a “spacing donut” for the Makerbot to chew on while I did the welding and machining. This spacing donut is 95% air and only serves to keep that spacer aligned roughly with the bearing bore so I don’t have to play “chase the spacer” every time I have to pull a wheel.

Here’s a finished set of front wheels. I’m waiting for an order containing broaches to finish the rear drive hubs.

Meanwhile, I’ve been drilling the necessary holes into the frame tubing. I hope to be able to weld most of it together this weekend, as well as test-make a body panel on the Shopbot.

Big Chuck’s Automotive Blog: The Past Month and Some’s Van Adventures

Mar 02, 2014 in mikuvan

Welcome to another edition of Big Chuck’s Automotive Blog! This post, being a little long in anticipation, will also be extremely long and full of content. I intend to cover the chronology of a handful of van adventures stretching back to around New Years, after the Great Oil Pan Debacle, and ending most recently with fighting some alternator troubles. Guess what? There’s more bodywork!

Operation: RUSTY MEMORY Part II

Originally, I posted a picture of the boarding step hole, and was intending to work on that. However, the very weird concave geometry in that area scared me away for the time being. I decided instead to focus on another problem spot – one that, oddly enough, I don’t have a good picture of. The best picture might actually be this, from when I got a new set of winter tires:

It’s the spot by the rear of the wheelwell, which is also visible in one of the first images.

At first, this spot seemed to be better suited for practicing, since it was primarily convex or flat. I knew that I would be chipping off someone else’s hack to add my own, because the area was clearly made of flaking Bondo and not metal, but I figured it couldn’t be too bad.

Famous last van words.

This spot was different than the hatch and underside which I’ve done in prior posts. First, this is a prominently visible part of the vehicle. Second, through the first two jobs, I’ve become more confident in my “body man” skills. I planned this job to take more time and detail than the previous ones. Hell, I even asked the Solar Car and FSAE teams if I could hog the garage for the whole weekend plus some, instead of just pulling in, beasting it, and slinking away.

So here I am in the auto shop one weekend with an air saw and Dremel with a carbide burr, shaving a yak.

Step one was, as usual, discovery and exploration. I started by knocking that corner in and breaking it up into dust; the old adage “by the time you see rust, it’s too late” holds. Next, I carved away most of the steel around where rust gave way to ductile metal out to about half an inch away.

Notice the green coating inside – that’s a dose of “rust encapsulation” compound that I bought on recommendation. About a week before I broke into this region, I gave a thorough covering through the holes in the bottom. Hey, at least they were good for something. I was told that this would aid in holding off worse corrosion and give me some more months to get to repairs.

Only the outside skin has been carved in this picture – the inside wheelwell area is still in the process of discovery. Check out that thin sliver remaining of the outer skin – that was kept so I had an idea of the lines to follow.

Taking sweeping cuts with the Dremel on the inside now.

The whole area cleaned up, corners filleted, and more paint sanded off in preparation for fiber layup.

The final pile of excised cancer, plus a mass grave of deceased Dremel wheels.

My usual tactic is three layers of fiberglass cloth on the outside only, but that would have caused too much protrusion here. Instead, I only did two on the outside…

…and two from the inside, reaching through the wheelwell hole. I then closed the area off with two layers in the wheelwell area.

The large brown patch in both preceding images is a berm made of fiberglass-filled Bondo I picked up because I was advised it has much higher strength than the regular pasty stuff. I then mixed in some short-strand glass filler from the Solar Car team (basically, the whole thing will eventually turn into a solar car).

The finished region is probably the strongest point on the whole body. I’ve heard of people mixing their own glass filler with normal pasty Bondo before, but who’s gone even harder and done glass-filled-glass-filled-filler?

Night #1 was spent letting the whole goopy pile cure under the influence of a work lamp.

The next day was devoted to finishing and sanding. First, some of the excess glass and filler had to be removed from the wheelwell area behind the folded flange, but I couldn’t get in there with anything facing the right way. Solution?

Face it the wrong way. This upside down flap disc was a shoot-around-the-corner method that I made accidentally at first but realized the brilliance. With light pressure, this was actually working beautifully.

After initial sanding and cleaning, this is Bondo layer 1. I continued using the fibery stuff, but without additional fiber. I do like this substance a lot, but it IS substantially more difficult to mix and apply because of its tendency to behave like trying to fork spaghetti out of a serving dish – some of it wants to come along, some of it doesn’t, and you end up making a drooly mess. It was easier to mix small wads, grab the whole wad, and smear it all over the place (rubber gloves are basically mandatory here).

In the middle of hand and power sanding the mountaintops down. At this point, I was still going for rough fit.

Hmm, not quite there yet. I promised myself I would take time and put energy into making this corner look nice, so…

Layer two time! One thing I learned about body filling is that slathering is essential, compared to being conservative. You slather and then shape & sand away, and so the method leaves you the maximum possible error budget to make adjustments. I’ve been too stingy before, which pains me greatly to admit.

This time, in order to have more control of the shape, I only used a power palm sander briefly to knock down the peaks, then used a flexible body file to d….

Wait, no, I didn’t have a body file. I used a short rough D-profile wood file here. This stuff sculpts easily, and the process did not take as long as I imagined.

The other side, which doesn’t have damage in this region, was used for reference. This is also another reason why I shyed away from the step holes for now: No reference, because both sides have holes.

Looking way better now – this was near the end of the rough shaping process.

I moved onto fine finishing with manual sanding. This time, I had 80, 240, and 360 grit sandpapers (guess who I stole it from….) and went progressively finer as I converged on the shape. Serious body guys would go even finer.

After I was satisfied with the outline, I used “spot putty” compound to cover minor divots. There were multiple passes of this stuff too – apply and smooth, come back in half an hour to sand gently, repeat. It seems to be nail polish filled with the same mineral fillers that make up Bondo.

In fact, that must be how it was invented.

After that ordeal, it was time to start painting. First, I rough-sanded and cleaned an area substantially outside the boundaries of the repair for the new primer to stick to. I used auto store spraypaint primer – nothing special. It was applied in several light coats – I’m getting way better at making spraypaint not run.

The next day, it was time for several body color and clear coats. After the first white coat, I took away most of the masking plastic and let it “blend” the surrounding area, which got a quick hit with left over 360 grit beforehand. No actual mechanical polishing blending was done, it was all just technically overspray. Luckily, white is a hard color to fuck up. You can discern the color difference if you’re looking for it, but I’m again counting on the fact that 99.7% of everyone will not know I am a fake body guy.

The interior of the wheelwell got the Slather Policy. I cleaned and painted this area in the same passes as the exterior, but did not care where it ended up. In fact, the more overlap, the better!

It was finished off with a few coats of spray-on underbody paint.

So there we go. This took from Friday evening until Monday afternoon – the first night was dedicated to glass curing, the second to let the filler layers cure, and the third was in the middle between primer and top coats.

With this experimental application of glass-filled-glass-filled Bondo being successful, I think I’ve formulated a plot for the wheelwell area. Cut away what I can, make a ‘backing’ glass layer in the wheelwell itself (which nobody will look at), then fill the whole area with this concoction and sculpt to shape, following with a top glass layer. I’m interested in reading up on how to deal with concave areas, since you can’t really reach a file or similar into a corner.

Operation: ALTERNATIVE SOLUTION

As mentioned during the Week of Motorama Hell, on the Monday of the competition week, the (probably original) alternator stopped alternating at some point. In this nondescript picture of the front of the engine, it’s the blob of grunge with a pulley on it to the lower left.

In fact, it probably gave out over the weekend, but I only noticed on Monday night when hey, all my lights are really dim and stuff and it’s kind of running like shit since reserve charge on the battery is enough to scoot around town getting parts for a few hours. I’m amazed at just how many parts on this thing were within 10,000 miles of peacing out. Like small prey rodents, reliability engineered machines tend to hide illnesses until there is no other choice.

Well, there was not much I could do but buy a replacement and get it shipped fast. I went the Rock Auto route, because all of the area auto stores had to special order this part anyway.  Since the vehicle hasn’t exhibited any electrical trouble up until that point, I figured the alternator just finally ran out of brushes. Having taken apart a few in the recent past to investigate using them as wound-field AC motors, I know they have brushes, and I also know that brushes like to wear out over time, so….

Anyways, the alternator wasn’t hard to get to. What I’ve learned is that there are often two ways of removing a part – following the carefully laid out instructions in the service manual and disassembling the entire vehicle, or just forcefully shoving my arm into a nether region with a mini-ratchet and accepting that I’m going to leave some blood and skin on something. I actually prefer the latter  because I can see the screw from right here, dammit!.

(Note: the previous sentence was a dramatization; only small scrapes were suffered from being shoulder deep in the cooling fan, power steering pump, and radiator)

So I’ve gotten the tensioner loosened and the pivot bolt thing out and now it’s time to unbolt the B+ terminal and…

…it shears right off. Great. At least I can solder.

Getting this thing out was a careful multi-point reorientation job while slowly pulling up. The gap next to the exhaust manifold cover and the lower wiring harness seen was its escape path – it just barely fit.  One… alternative… path is to take off the oil filter and drop it out underneath. The official by-the-book replacement is 75% of the way to a new timing belt.

This thing is looking pretty ragged. Because it was Motorama Thursday at this point, and my package was nailbightingly undelivered, I decided to try rebuilding it with scooter motor brushes. I hold to my statement that Mikuvan will soon become 1. a solar car, or alternatively, 2. a small, cheap Chinese electric scooter.

I rebuilt the air conditioner blower motor with harvested scooter motor brushes. It’s still working.

So, how do I take the alternator apart? Why, the old “Pry with screwdriver”. In the electrical service manual, it literally tells me to stick a plain screwdriver between the bracket and stator and pry. There’s even little slots in the laminations to jam said screwdriver into.

Haven’t I learned anything from the last time something told me to “Pry with screwdriver“? It must be the Harbor Freight screwdriver.

Alright, now that I’ve successfully torn the diodes off, time to sit and wait for Fedex. At the very least, I confirmed that it did run out of brushes – they barely moved when the rotor was taken out, having reached the end of their spring travel.

(I now know that I was supposed to pry the front bracket off, which would have caused the [pulley, front bracket, rotor] assembly to come apart from the [stator, rectifier, brush holder, rear bracket] assembly cleanly. But there were no screwdriver slots there!)

Fortunately, Fedex delivered at 7:30pm on Thursday. In the days prior, we were hit with a few more inches of snow, so everything was backlogged a little. I was fresh off destroying the old alternator, and so was getting ready to call the car rental place by this point.

Hey, you guys sure you want the core?!

Once again, I found myself outside, at night, in Massachusetts, in the middle of winter, trying to solder.

I had to replace the B+ terminals that got ripped off, so I crimped then soldered some 1/4″-stud ring terminals on.

Here it is. At around midnight Friday, everything was back up and running. To reinstall the alternator, I carefully dropped it through the same hole the old one was fished out from, then some more deep-arming with a ratchet on the front side and everything was tight again.

There was only one problem. Either the new pulley is a tad smaller, or the alternator belt that was installed was of the wrong length, because I bottomed the tensioner out and still had enough slack to cause squealing problems at low engine speeds. This translated into neutral-coasting towards red lights while keeping the engine RPMs above 2000, where it could finally catch on. Consider it practice for a manual transmission, but this was how the entire Motorama trip went down (highway cruising wasn’t a problem, luckily).

Afterwards, I decided to try an experiment as long as new belts were within reasonable reach at local parts stores.

The Brief Tragedy of Slinkybelt

I’ve always wondered if adjustable-length V-belts were a legitimate replacement for a conventional endless V-belt. They come in a few flavors, such as PowerTwist or Acculink. The story is the same – interlocking drink can tab shaped beltlets that twist-lock into place and allow you to formulate a custom length belt, as well as install them like you would chain drives -no disassembling machinery. That last part I really liked the sound of.

The alternator belt is the last thing to come off before I start removing timing belt covers – it’s the last accessory belt in the disassembly path. I didn’t want to spent 6 hours doing all that again, so I took an interest in the adjustable length belts for this reason. I ended up discovering that I could violate general topology by threading the belts slowly over the 7 blades of the cooling fan, but this did not end my curiosity.

I bought a few feet of the Powertwist type off eBay last week. When I got it, I took the cheap shot route and cut the old belt off. Here’s a picture of Slinkybelt installed:

My initial assessment was that it seemed to work, but definitely “grew” more than a standard belt. This seemed to be indicated in the instruction sheet, so I was just happily adjusting the tension out to an absurd amount to compensate. It was also making rather unhappy slappy sounds, where it was advertised to be quieter….

Unfortunately, it blew up on the next drive. I noticed the unhappy sound growing louder, then suddenly it all went quiet and all the dashboard warning lights lit up. Awesome!

And that was all Slinkybelt wrote. The rest of it fell off on a side street somewhere around here.

A few robot builders on Facebook who had used this type of belting in large robot weapons noticed that I had installed the belt backwards. Wait, belts have a direction?! These do, apparently – whether the twist tabs travel  “leading” or “trailing” matters in how the pulley transmits forces to the beltlet bodies. Trailing is the correct direction; I had them leading. It seemed more intuitive, but it was wrong. There were arrows printed on every tenth link that I didn’t notice. On closer inspection, yes, there were, but they were heavily smudged or almost illegible.

Using my remaining stock, I fashioned a new one out of obstinacy and wanting to see if the claims made by its sellers were legitimate; user error doesn’t discount a product’s efficacy, in my opinion. After driving around a few days with the belt correctly installed, I’ve come to the following conclusions:

  • The urethane material they’re made from seems to have less traction against the drive pulleys than rubber. This results in slippage even if the belt tension is tight – it seems to count on a large wrap angle, such as those present in two-pulley industrial fan drives or something, where my alternator has maybe 110 degrees of wrap at most. I noticed substantial slippage at low engine speeds when the alternator’s field has to be more strongly energized.
  • The slippage failure mode makes very little noise, unlike the screeching of a rubber belt, so it was hard to just discern by sound. I was actually watching how bright or dim the dashboard lights became as a function of engine speed.
  • I did have to adjust the tension multiple times as the beltlets “bit” into eachother at first. This is probably more trouble than anyone would actually go to in practice.

Overall, I see the appeal for near constant speed and load industrial drives (like fans and pumps) which they are sold for. For automotive applications, I’m not sure if they’re worthwhile for the above reasons – wildly varying speeds and loads, plus a different general belt path topology that tends to give less wrap per pulley, meaning that the individual beltlets have even less surface area to grip with. The alternator has to deal with speeds between 1000 and 10,000 RPM (if I really hammer it from a light or tollbooth), and wattage loads of between maybe <100 to nearly 1000 watts if all the accessories are going full power.

Yesterday, I decided to end the experiment and spend half an hour violating said topology to install a standard drive belt. Slinkybelt will live under one of the seats to be used for emergencies, or maybe in a future robot.

That’s all for now! Next up, time to return to working on the tiny version of Mikuvan. If I’m not working on one van, clearly because I’m working on another…