Archive for the 'Land-Bear-Shark' Category

 

Random Shenanigans to Break In 2014! Beyond Unboxing with Ikea Drills, LandBearShark’s Battery Surgery, More Van Nonsense

Jan 10, 2014 in Beyond Unboxing, Land-Bear-Shark, mikuvan

Happy new year and welcome to Big Chuck’s Automotive Blog! The mission of BCAB is to share and discuss all of our misadventures in being shadetree mechanics. Not only will I post all the questionably sound work on my own wreck, but every week, there will be one story submitted by you, the readers, about any aspect of your life pertaining to your own automotive project or rolling piles of garbage, whichever you would prefer.

I kid.

The way my site visits and interesting search hit terms have been slippin’ lately, though, you’d figure I’d have gone full-time car blog. Luckily, that’s only partially true. It used to be that I got plenty of weird and interesting search hits, site referrals, and the like. I feel like I’m losing my touch there – these days it’s all full of “electric bike” or “electric go-kart” or “How to avoid electric shock installing I’m a hybrid battery” (sic) and stuff. Booooooooooooring. Perhaps I should be glad that I’ve been genericized to that point, such that my content has become more generally relevant. But I do miss the days of the Arduino powered butt massager.

This IAP, I’m watching over MASLAB which is using the IDC classroom and my shop space, while also ordering things and preparing for the next round of 2.00gokart in the spring. MASLAB is historically a ‘shopless’ activity… which means that students break into or ninja the use of whatever shops they can get into in order to finish their robots. This year, they faced difficulty getting their usual space in the EECS department, and several of their core team and students being my former students, I got pummeled with appeals for space. Now, it creates way more work for me (what amounts to an actual full term class’s worth of preparation and shop orientation sessions), but what better way to spoil even more undergraduates? Furthermore, I think it’s better for them that they have official access to much more resources that can be properly used (i.e. under my titanium fist rule) than students trying to steal and beg resources from any space they have access, or “get” access to; which in my mind is patently unfair to those who are also just starting out and don’t Know Somebody – MASLAB is often one of the first “Build a robot” things a lot of freshmen do.

Anyways, I went to Ikea:

I defy anyone to challenge me for the title of “Best Ikea Space-Filling Ratio”. Flat-pack furniture works best with a vehicle which can be 90% modeled in no more than 3 solid modeling features.

Now, none of this is actually mine, since my own life is containerized into a number of typical milk crates, and I wouldn’t touch anything Ikea produces with the most bargain of Harbor Freight allen wrenches. But while on the tour in the most perfectly structured consumerism experience, I naturally gravitated to their tool section. The selection was naturally all custom-commissioned products geared towards assembling only their shit – again, part of the most perfectly structured consumerism experience this side of Buy & Large.

1. Beyond Unboxing: Ikeaworks (FIXA 7.2v drill)

(To quickly skip to the other sections, here’s…

2. Landbearshark’s new battery

3. The Weekly Van Shenanigan: Bodywork, oil pan gasket, and fixing that subyiffer

I spent a little while looking at the FIXA (I keep wanting to say Fixya) power tool series – they have things as interesting as a 14.4v hammer drill and a standard two-speed drill. Ikea being an entity that nominally prides itself on inexpensive low-key quality (as opposed to, say, Harbor Freight, which prides itself on Fuck You), I did expect that these tools would have worked just fine in their intended household lives. It’s like a domesticated goose – all you really need is a guarantee that it will poop everywhere, perhaps not with the flamboyance of a wild Canada goose.

I found their 7.2v drill/driver interesting. This is because it evoked the shape and function of the classic Handiworks mini-drill found at Walmarts back in the Early Noughties. This little thing fueled the rise of the 12lb weight class. For a while, Harbor Freight carried a 7.2v variant which made it into the 2nd and 3rd iterations of my own Test Bot. That was about 2005-2006. Those drills disappeared with an increasing RMB to USD trading ratio, as did most of the low-v0ltage (9.6v, 14.4v) drill/drivers from Harbor Freight.

An overwhelming sense of curiosity and nostalgia drove me to pick up one of these units. I’ll say right away that for $24.99, it may not be worth it in general, even if it were identical to the old Handiworks. However, the package ended up being more compact and a higher ratio – it definitely could be robot-applicable for somebody. So thus begins the Beyond Unboxing of the FIXA 7.2v drill/driver.

The casing is shed with a few Phillips-head screws from one side. No hidden screws here. The first thing I found is that it really IS lithium ion! There are two cells, 1500mAh each, size 18650, of lithium cobalt or lithium manganese chemistry (not LiFePO4). These 1500mAh cells contrast with the modern generation of laptop and other device cells which are typically 2400mAh, likely because they are “power” cells made for industrial use – wider temperature ranges and higher allowed burst currents – than “energy” cells which simply try to provide the longest runtime.

It has a cute little BMS board attached to it that handles both charging and discharge protection. The large FET at the top is connected to a current sense circuit that actually causes the drill to shut off if it’s near stall or suddenly locks up. This manifests itself as suddenly losing power, but it resets once the trigger is let go of. A nice protection to have if you sell your tools to total rubes for sure.

This current sense circuit depends on a sense resistor, which, like the Jasontrollers, can be easily chopped to a lower resistance if somehow you are compelled to do so, God help ye.

Four more screws and the gearbox comes apart. The gearbox is unlike the standard 36:1 or 24:1 drill gearbox. Rather, the gears are somewhat smaller in pitch, 0.6 module by my closest guess (about halfway between 32 and 48 pitch, which is what they look like). What was surprising is that the first stage of the geartrain is all metal. Usually, the first corner to be cut on these is to replace the first stage with nylon gears, ostensibly for noise reduction but we all know really why.

The gearbox is 3 stages of 16:14:45, resulting in a total ratio per stage of 3.8125 and a final ratio of 55.41:1. The final stage has 5mm thick gears, compared to the 4mm thick in the rest of the thing, to handle high torque demands.

The ratio is a little high for my tastes for a robot drivetrain, but for those not aiming to hit 15-20mph, perhaps just a slightly larger wheel will suffice. Remember that I’m clouded by a decade of smashing robots into each other; very few parts which are generally useful make it into the top echelons of the battle-tested.

I wasn’t quite curious enough to take off the chuck, since the left-handed locking screw was better installed than most Harbor Freight drills and I wasn’t in the shop at the time. I suspect that the traditional drill gearbox bellhousing, albeit in a smaller size, is on this one. The drill shaft is also most likely a 3/8″-24 thread like normal, but I won’t speculate more unless I have it taken apart. It has a nominal rating of 400RPM – which, through the gearbox, yields a motor speed of about 22,000 RPM, in line with the typical small drill motor. The motor in question is a 7.2v Mabuchi RS380 knockoff, unlabeled.

2. landbearderp

Remember the Landbearshark video? Well, after that and the additional snowstorm a week ago…

Whoops. I guess I went a little too hard. I noticed something was wrong after the batteries never recovered above 16 volts even after a day of sitting. Both battery packs had cell groups which were either at 0 volts completely, or at severely damaged levels like the 1.38v group above. This was the batteries which caught fire once and also survived months of tumbling in the original Landbearshark, finally having been done in because the rest of the thing worked too well.

Damn. Well, with the potential for more weather in the next few months since this winter has really been making it rain snow, I had to replace the damaged batteries before LBS could work again.

I went digging in my lithium nuclear arsenal, which I obtained after the MBARC class ended and I confiscated all the lipos (with exception of those taken by R/C airplane experienced students). Most of the packs were in the 5S and 6S range, which was good for LBS, but they did not have built-in battery management boards and I didn’t want to add a big balance harness to LBS. However, there were also these:

One of the teams went commercial/industrial and picked up these from Batteryface. These are sold with a “PCM” module built-in, so they don’t need to be externally balance changed. I’ve used these boards a handful of times before in not-my-own applications, and they do work just fine, but I find them a little too wimpy on the discharge: for most high burst current or other high power apps, I prefer running straight battery, because the management board usually introduces more resistance or has built-in current limits.

But LBS is not particularly high power. I could also fit four of them in the space left by the 6S6P A123 pack, netting me much higher energy density: 22.2v 40Ah instead of 19.2v and 26.4Ah. I’d trade the unneeded brute force for ease of use and built-in protection.

Sounds like what these were made for! So in they go.

To get four packs in the space of two, I had to put Y-harnesses on my Y-harnesses. I chopped the discharge leads off my old battery, which had a type of 6mm bullet connector I no longer had on hand, and spliced them to two Deans plugs each. The students added quick disconnect terminals to their batteries, which I cut off and replaced with Deans.

Installing the batteries was a fun game of OH GOD DON’T TOUCH THE FRAME RAIL WITH THE EXPOSED PARALLELED CONTACTS.

The batteries are mounted to the electronics box with strips of Velcro. Their height is just under that of the box itself, so they shouldn’t be going anywhere.

Suddenly, the wiring looked less nest-like than before. Not because I made it better, but now all the excess runs were the correct length to tuck next to each other! Science.

LBS has yet to make it back outside since the weather has been… “nice”? Test riding around the building showed me that it was very much more responsive. Not only because the voltage has jumped a few from the A123s, but that the batteries must have been damaged for a while and have been sagging more for the same current draw. Hopefully the next bout of winter commuting will put these to the test.

Rewinding before the new year once again, I’ve officially commenced…

Operation: RUSTY MEMORY

It could refer to several things. First, the old magnetic disc drives that used straight iron oxide (rust) to store information; the earliest kinds that went into the “refrigerator” hard drives. Next, the fact that you can’t quite remember something.  Finally, all of the really shitty bodywork I’m about to do to prevent more problems down the line.

I’ve been leery of doing bodywork for a while, despite a slow buildup of arms in the interest of doing so. The past has shown me that I have no patience for making smooth and clean lines or blending paint. However, the recent pressure of winter and its associated wet salt slush has caused me to examine some of the spots in more detail. I’ve determined that there’s some areas where I’m getting close to now-or-never, because the underside and “hidden” rust. Remember these boarding step holes? They’ve gotten bigger:

 

Soon, they will soon break the outside body lines… and hell if you’re getting me to rebuild external lines. Other trouble spots include the majority of the left underside for some reason – the right side is pretty clean, but the left is all sorts of beat up.

Before tacking the more complex curvature of the step, I decided to practice more on a less visible spot – the left rear corner. Here’s what it looked like in May:

A complex confluence of edges in the corner with quite a few holes and thin areas to patch up. The plan I formulated was to cut away as much of the bad areas near the holes as I could get, then grind or wire brush off the rest. About two weeks before starting on this, I thoroughly coated the interior of the bodywork in the area with that “rust converter” compound and let do its job for a while. Hopefully this will help prevent the interior sheet metal from being a problem in the near future.

Let’s get started. I once again dibbed the corner of the garage for a weekend, though I didn’t need the lift. What I did need was a spot that wasn’t -30 degrees out, so things could actually cure.

When I was using the lift before, I had noticed that the arms block the area I need to work on, regardless of orientation. So I had to use a whole trade of jackstands (the proper collective noun for jacks is a trade) in that area. Since I’ll be violently thrashing on this area for a while, I used not only a stand on the frame, but on the corner of the rear suspension also, kept the floorjack a little pressurized under the differential, and chocked both right wheels in both directions. A little paranoid? Perhaps, but I also prefer to have thickness.

This is what that region has devolved into since that time. The holes have grown a bit, and much of the weaker rust has fallen off. The treatment compound is seen in green.

The excise begins by gently hammering at the panels to loosen up more internal rust. This is item #2 on the list of 3 things Mikuvan does very well: dropping little flakes of rust everywhere. The other two, of course, are emitting black mucuses of various viscosities, and raining bearings.

Maybe I should have done this before spraying the converting compound…

Next up is imprecise angle grinder cutoff wheel excise. The biggest trouble spots went first.

About 1/3rd way through the process. When the angle grinder became too unwieldy to maneuver, I switched to a Dremel with a small cutoff wheel. My goal was to eliminate as much of the obviously rusted metal while retaining features that will help rebuild the area. I cut off a piece of the wheelwell (the right angle upside-down-L cut is center in the picture) to gain more maneuvering space for cleaning the area behind it. After the cutting, liberal application of wire wheels knocked out the rest of the surface rust in the surrounding area.

What I do not have is a picture of the completed surgery, since much of this process was mentally streamed. More of the steel on the inner wall to the left was removed, as was the area with the perforations in the upper left, extending about 4″ towards the front (where the wirebrushed paint starts).

I retained my tactic of using 3 layers of fiberglass cloth (I’m not sure of the weight, but it is pretty heavy) that were nipped from Solar Car.

I decided to split this work into two sessions to make sure I didn’t have to hold onto too many things at once. I patched the outside first and let the glass cure overnight.

The next day, I worked on the inside. To cut the cloth to shape, I just mashed the fabric against the repair area and used a marker to get the rough outline, then cleaned and simplified the marker scratches to a cut pattern. The pattern was used as a template to make two other pieces, each very slightly smaller. The marker dissolving into the fiberglass resin is the cause of the blue outline.

This area looks pretty gnarly because of the untrimmed glass and the fact that I didn’t try to rebuild the down-facing curvature of the original body section.

The day after was cleanup, filling, sanding, and painting. The tattered glass edges were trimmed flat with a Dremel and cutoff wheel first, then the whole area manually sanded with a sanding sponge and then some fine regular sandpaper. I used a small amount of Bondo to smooth the transition between the glass layers and the remaining bodywork, but as the masked area shows, did not attempt to resmooth the surface from where I wire brushed off the paint.

Paint was the same procedure of primer, color, and clear I used on the rear hatch. This took several hours by itself, then I let everything dry overnight once again.

Once the outside was dry enough to put some masking tape on, I sprayed a few coats of underbody coating compound on the inside repair to seal it as well.

Here’s what it looked like as of a day or two ago – it’s gotten a little dirty since:

I make no claims to ever passing auto body school.

Based on my research, a real auto body guy would have removed far, far more metal than I did, and also have remade at least some of that inside corner box section in steel, if not straight up remake the entire sheet metal of the wheelwell area. When I can afford this service, I suppose I’ll have that done…

I’ve learned since that they make this stuff called “spot putty” which helps fill in the very small resin bubbles that are visible; plus that I’m not spamming enough resin onto the top ply to start with, a phenomenon also visible in the rear hatch work. These lessons will hopefully be put to use in repairing the boarding step hole soon, since that is a more visible location (with the door open, anyway).

Subyiffer

A quick break from inhaling styrene and toluene led me to try and figure out exactly what the deal was with the “subwoofer-like device” that I touched upon previously. I thought it was barely working, but it turned out to be sympathetic vibration transmitted through the front sheet metal and dashboard components. It was in fact totally out.

I’m sure a normal person would have replaced this with a set of 12″ subs in the back, but I dunno, it’s already there and most likely working anyway. What if it was as simple as some dumb fucker not connecting one of the wires? Wouldn’t I feel foolish for not trying to make use of it at all!?

Besides, the 12″ subs come after the electric drive conversion, as do the tacky underglows and stancing.

It was 20 degrees out, in the middle of winter, in Massachusetts. And here I am, outside, with nothing but flashlights, using an oscillosope and soldering iron to probe the paths that the signals took in an attempt to debug the amplifier board. Consider the frightening possibilities if I had put this much effort into actually studying something.

I ran into a slight metaproblem – it was so cold that my small cheap soldering iron, which travels in the robot service toolbox normally for use in the field at events, froze its power cord off. Literally. It probably deplasticized in the cold and in the process of me unfurling the cord, it broke off.

I borrowed a Weller station from MITERS in the mean time, which seems to use a plasticizer that didn’t also grow up in the South like me.

So if you’re ever stuck debugging the subwoofer amplifier circuit of a generation 3 Mitsubishi Delica, here’s what it is. The whole thing is OEM’d by Matsushita (a.k.a Panasonic). There’s 7 wires leading to the board – three of them are the ground, 12v, and “power on” lines shown, the others are two channels of signals and their return lines.

What the frontend of this amplifier does is add the two stereo channels together, then severely low-pass filters it before sending it to the amplifier power IC. This is all done actively, with op-amps. In fact, the circuit is eerily reminiscent of this generic mono amplifier circuit.

The ENABLE line controls the coil of a little relay that is in between 12 volts and the amplifier chip. Guess which wire was open circuit?

Naw, couldn’t be that someone forgot to wire it up.

(Alternative explanation: The new head unit that came Free With Purchase did not have an external amplifier enable output, so this was left unwired, but that doesn’t explain why someone took the speaker totally out…)

I took the cheap and dumb way out: Jumping the enable pin directly to 12 volts. When I turned the ignition key, I heard the faintest click of a relay and a little pop from the speaker.

Scoping the speaker’s terminals shows this nice waveform coming out. The cutoff frequency does appear to be around 150Hz.

I packaged everything back up after this fairly simple hack, and immediately ran back inside to defrost. Let’s be honest here – this little thing didn’t add that much to the experience; finally some noticeable low end now, but it seems that it saturates (clips) relatively easily. Not that I blame it at all. It was another box ticked off on the checklist of completion.

Oil pan rebuild

Item #4 on the list of things Mikuvan is good at: leaving small droplets of oil wherever it goes.

It’s done that ever since the first start. I’ve always attributed it to a crank seal problem, but recently I started suspecting otherwise, because the symptoms didn’t really line up with just a crank seal issue. If I had a leaky rear crank seal like I suspected, then the oil drops would be coming from very specific, concentrated locations. Same goes for the front seals. I’d at least see a consistent, concentrated ‘shot pattern’ from the two locations in my parking spot… which I assure you is terrifyingly disgusting.

Instead, it just seems like it’s been shitting everywhere. Since I’ve been getting under it more recently, I’ve also been keeping track of the cleanliness of the underside: Every time I look under it after cleaning up all the oil and grime, there’s more of it everywhere. There was no one consistent spot at all – the whole underside near the engine would be wet all the time and spots would appear almost at random. It was less oil leak and more Self-Applying Undercoat.

As the weather got colder, it just started getting ridiculous, and once again I was faced with a now-or-never scenario. I was beginning to suspect the oil pan gasket a few weeks ago when I first began noticing that it was always wet on the outside. Hey, shouldn’t a gasket keep the leaky stuff on the inside?

During the suspension work on the lift, I gave that area a very fine look-over.

This is the forward left side of the oil pan. First, that gasket is pushed out completely and ripped. Second, it’s disgusting.

I figured, once again, that even if it was not the main problem, it could be a contributor or aggravating factor, and that I should at least inspect it. I braced myself for yet another Yak Shaving Session where I end up having to remanufacture the entire assembly. How bad could it be!?

(Always Famous Last Van Words)

I looked at the service manual for a bit and then began disassembling the oil pan screws.

First to come off is the oil level sensor. I have no idea how this is supposed to actually work – and it just barely does. Usually, if I park on a non-flat area, it’ll throw an oil level light; and not knowing how leaky the thing actually is, I check every time, only to find the majority of the time it’s totally fine.

I have no pictures of the pan removal process, since my hands were well-covered in oil, and the whole thing just sort of fell off after I undid the last screws and put a little pressure on it with a scraper. Well, that’s certainly a bad sign. From my Youtube instructional video surfing, you’re almost supposed to use said scraper to cut the whole thing off.

Oil pan removed! This is the first time I’ve ever physically seen the inside of an engine, from the bottom end. Who the fuck thought this was a better idea than a brushless motor?

The fact that oil is everywhere on the alleged gasket sealing surfaces is, again, not a good sign.

So here’s the deal with the gasket. First, on top, there’s a layer of silicone. Not, say, specially formulated gasketing compound, but I swear it was just clear RTV used for bathroom tiles.

Next, there’s a paper/felt sort of gasket, the type that you would buy specifically to fit a model of engine.

And finally, there was another layer of silicone. 

Silicone-on-paper-on-silicone didn’t exactly strike me as a professional repair. I suspect, again, that this was like 5 different dudes’ repair hacks and I am the 6th.

Unlike bodywork, I considered this a blasphemy against the  mechanical gods. I rage-cleaned and stripped the entire pan, paying special attention to the gasket seal surface. I also cleaned up the bottom of the pan some. Luckily, there were no metal particles to be found, but there was a sizeable amount of brown and black sludge; likely from before I was also meticulously keeping track of oil condition.

Here’s a shot down the line of crankpins and big ends. Once again… who thought this was a better idea than twirling a magnet (or a blob of copper and steel) on a stick?

Here’s a picture of a 3-floor building sized engine’s crankcase while we’re at it. It’s only a little bigger.

I didn’t get any pictures of the re-gasketing process, but it entailed borrowing a small amount of this RTV material designed for gaskets and laying it out in a roughly 1/8″ wide bead in the pan’s top groove, around the outside perimeter, and in a circle around the bolt holes. I then let this cure overnight under the influence of a halogen lamp, and retorqued the screws according to specification the next day.

After a week and a half of this, I’ve only seen 3 new oil drops after having placed a white spill mat on the concrete parking spot. They were concentrated around this spot:

I didn’t notice this little vent in the bottom of the transmission bell housing until I was under there looking at it. Under the cover is the torque converter and its crankshaft adapter plate. If I had a crank seal leak, I would have seen the majority of the oil drops originate near here.  It might still be leaky; I have not confirmed its health in either sense. For now, however, the oil-shitting problem seems to have been resolved in the majority.

This concludes the latest Big Chuck’s Automotive Blog entry. Make sure to check back next week as I make even more mechanics and auto body technicians cry!

 

Winter is Coming.

Dec 16, 2013 in Land-Bear-Shark, Stuff

LandBearShark 2 is finished, but it isn’t snowing anymore.

Dec 05, 2012 in Land-Bear-Shark, Project Build Reports

Well, I can’t say that I didn’t already finish LBS2 like 2 weeks ago. I did, in fact, and it’s been around the block a few times already. But sadly, since then, there’s been no snow in the weather forecast. Meaningful amounts, anyway – a few flurries fell here and there last week, but what good is that? Do I really need to take this thing to New Hampshire!?

I was counting on some snowfall to let me combine a little testing video with the rest of the build, but given that seems unlikely to happen, here’s the build in its entirety.

The first step in rebuilding is to retire the old design. Here is LBS pulled out of under-table storage. A little dusty, but it still looks kind of glorious.

The big ATV style crashbar is not returning in the new design, because really, it was just too over the top. It was funny and contributed to the very unique look of the thing, but it also weighed about 10 pounds (made of surplus 1/8″ wall steel tubing…) and the mounting design was very much optimized for the old frame and I couldn’t quite make the design work with the new aluminum one.

Otherwise, electronics aside, many component parts of LBS are being reused. I don’t think I’m quite at the level of the Ship of Theseus yet…

LBS has been reduced to components. I took the opportunity to perform a mass cleaning of all the track parts because they had been subject to substantial dirt and grime buildup. The chains, especially, took a distressing amount of soaking in brake and carb cleaner and like an entire roll of shop towels. Chains are terrible things.

Its former frame was used as a collection bin for most of my other retired aluminum-bodied projects. I was intending on pitching it in a shop’s aluminum recycling dumpster, but ended up putting it up on Reuse (the free stuff mailing list) for people’s amusement. I figured that had I been a happy froshy bunny during this time, I would be so extremely excited, jumpy, and otherwise bunny-like if somebody posted a pile of waterjet-cut aluminum parts to Reuse that I might start building project of my own spurred by the simple fact of possessing these items. That was the plan, anyway. Paying it forward for the next happy bunny that bounces into MITERS.

(Some of it was used immediately in a productive fashion).

One of the first build exercises was spacer and standoff-making. Most of these short ones shown are parts that will go into the motor mount, suspension, and new bogies.

I’ve been gradually liberalizing from my usual hardline t-nutting policies in favor of using material more effectively when the design calls for it. In fact, LBS was one of my last major giant t-nutted plate assemblies (the other being Make-a-Bot). I actually can’t think of anything I built from scratch in 2011 and 2012 which made gratuitous use of plates where they weren’t effective.

I’m thinking it’s about time to update the How to Build your Robot Really Really Fast document I wrote some time in 2010 to be a more thorough treatment of various design for assembly manufacturing methods, rather than a cursory overview of standoffs and t-nuts.

With a few of the necessary spacers done, I turned my attention to assembling my Fake Andymark Gearboxen. I’m a fan of their very inexpensive (compared to industrial suppliers, anyway) hubless spur gears because for most robotics-related purposes, hubbed spur gears add unnecessary bulk and weight if you are just making cluster gears anyway, or using another method of power transmission like splines or direct coupling to the driven member. In fact I’m such a fan that I’ll plug them some more: SPUR GEARS!

(Some mixing and matching may be involved.)

The way my intermediate gear shaft goes together is simple. Take a hex shaft chunk, stuff a bushing into it (drilled and bored on tinylathe), then start piling hex-bore spacers and hex-bore gears onto it. A hex bore custom sprocket is in the middle somewhere. On each end is a bronze thrust washer to keep everything in check axially.

The whole assembly was purposefully made a few thousandths of an inch shorter than the length of the center standoff – involving shaving a bit of material from one of the hex bore spacers – that it could spin freely once lubed up a little, and kept itself in place. Bam, fast-build gearbox without machining complex shafts and retaining features.

I’ll also admit I am a slow convert to the hazardous, addictive, and self-destructive world of hexagonal shafts. They’re just so easy.

The two Fake Andymark Gearboxen completed. These have no mounting bolt pattern – they are hung from the center Big Shaft of the vehicle, and kept from moving by chain tension on one side and the chain tensioner on the other, upon which they brace against.

Onto frame assembly. Did I say I wasn’t going to make T-nutted things any more?

Nah, no way. I’ve not become that unprincipled. There are still a few holding the frame together, but they are no longer the majority contributor to frame rigidity. In this case, it’s pretty much just for making the right angle joint that will be backed up by long threaded rod-and-spacer preloaded columns (see Carly Rae Jepsen’s build style), which can add much more rigidity than an equivalent floppy plate span.

The bogie frames this time are much lighter in section, and maybe a little too flowy looking. The reason is that these never took subtantial structural loads anyway – recall that even in LBS version 1, they were hinged in the center at the Big Shaft. The load path goes from the rider weight into the Big Shaft, where it is met by reaction force coming from the ground, going through the track sprockets and into the track axles. But that load is expressed primarily in torsion (out of plane twisting) of the bogie frame sides, because the suspension is so damn stiff that it’s basically a truss member. LBS has always ‘sagged’ a little as a result of this torsion (think overloaded car), so there was no reason to keep using the huge heavy side plates.

The much lighter cross section of the new bogies saves about 3 pounds and cuts the design down to basically the bare amount needed to connect the dots in terms of mounting points.

Now it’s starting to look like some kind of cracked out Mars rover, or a kinetic sculpture. Everything gets slid onto the Big Shaft at once, secured by shaft collars. I switched to a 3/4″ diameter axle this time – LBS1 had a 20mm one, which is a dimension I have no clue why I picked initially, but 20mm shaft collars are espensive and I needed a few more of them anyway. 3/4″ was the closest size to 20mm that still allowed me some space to clear the CIM motors, and wouldn’t be bendy under rider weight.

After a brief game of Which One-off Spacer Is This?! I began to put the track wheels back on, and also slipped the motors onto the Big Shaft.

Without the outside bogie frames keeping the axles on center, slipping on the track itself was easy – the whole assembly just kind of bent in enough. I did have to spreader-clamp the axles to make all the screws go in, though. Overall, the track tension has increased over version 1, since it was known to be somewhat loose.

After the track pods were slipped back on, the project reached criticality. At this point, with the chains not hooked up yet, I was supermanning it and coasting down the hall – not very far, of course.

Moving onto electronics, I’ve punched together the electronics box and mounted the switch and cooling fan. Little rubber grommets have been installed in the bottom where the motor wires will enter. I also drilled, tapped the eventual RageBridge mounting holes and installed standoffs.

The box mounts to the frame using these little hanger hooks which interface with bolt heads sticking out of the electronics box. The arrangement is self-securing (the force vector of the box being loaded downwards tends to pull the hooks tighter together), or at least theoretically so – if not, zip ties will rescue it. The rear hooks were swung out, the entire box slid into position and rested on the front hooks, then the rear ones tightened down again.

Much of the wiring was recovered from the old LBS, and I made the RageBridge wiring harness to match it. Here’s one of them mounted to test for fit and wire clearance.

I took some time to finally repair LBS’s somewhat decrepit batteries. These were made 2 years ago and suffered a balancer cable short & fire some time afterwards. Since then, they have been wrapped in bubble wrap and duct tape, charged and discharged without regard to inter-cell balance.

To my surprise the cell banks were at most 50 or so millivolts out from eachother. While still alot, it’s quite a testment to the durability of A123 cells. Too bad the company itself… isn’t very.

I remade the balance harness, this time carefully routing the cables out the side of the pack, then wrapped the entire thing in some foam rubber with Kapton and fiber-reinforced strapping tape. After a night of balance charging, they were all leveled out and ready again.

The two RageBridges were stacked together with some 3/4″ tall standoffs, and linked via a small custom Y-cable going to the receiver. The bottom one powers the cooling fan through the 15V rail (which, incidentally, is going to be missing from RB version 3 to be replaced by a 5v fan output).

Each RB controls only 1 motor per side – the system is set up in mechanical parallel. Hypothetically, if one controller fails, the other can still move the vehicle at 50% power, but it of course depends on the mechanism of failure. If the failed controller becomes a short, then it would be very hard to power against the shorted motor, for instance. There was no intent of providing redundancy, just a convenient means of controlling more current than one Ragebridge can effectively put out.

With no custom software needed, it was drop the batteries in and go. LBS is basically a dumb ROV at this point, no different from one of the battlebots. The RageBridges were put into “mix” mode because the simple 2 channel Hobbyking radio does’t handle any of that fancy stuff.

After putting the other battery in, things started getting…. crowded. Batteries are retained on the bottom with a healthy dose of Velcro, and the virtue of being confined keeps them from jiggling around otherwise.

The wiring harness is admittedly a rat’s nest, but hey, salvaged wiring. It’s also be a good chance to test RB’s robustness under non-ideal wiring conditions.

Closing the top up… I designed this version to be way easier to service in case something goes wrong inside because the electrical box lid is removable through the top, after the board itself is removed.

And here’s the 98% complete shot. At this point, I didn’t yet receive my threaded rod to finish the two standoffs in the front and rear. Without those, the frame bowed a little when I stood on it. But it was functional enough for some superman-style hallway blasting.

There was one problem I discovered during this testing. The motors could exert so much tension on the chain that they were physically bending the rear bogie frame inwards, collapsing the hollow cutout and making the chain jump off the sprocket.

Well, that was dumb. The placement of the chain tensioner was pretty much in the middle of a totally unsupported span. I could, in fact, unbend it with some big channel-lock pliers. I definitely hit copy and paste a few too many times…

To address this issue, the rear bogie frame side was recut to be solid and the tensioner mount itself was made a little fatter and angled.

Here’s a picture of the bottom of the beast, showing the drive chain setup and the batteries. Still, missing standoffs (which have since been added).

I don’t have any testing video yet, since there hasn’t been exciting enough weather to do so. The new arrangement, however, has demonstrably increased torque and better steering response too. The Ragebridges are synchronous rectification drivers, meaning the motors exert a torque against any external changes in speed unless commanded to that speed, so the tracks have increased dragging ability on either side. It can alsofinally turn in place, even with rider weight on it. The top speed is right around 8 or 9 miles per hour.

Once the weather gets more interesting, expect some updates with videos!

The Second Great Awakening of the LandBearShark

Nov 11, 2012 in Land-Bear-Shark, Project Build Reports

Oh, this thing.

LBS is another great example of something I built without much forethought that never quite worked, similar to a certain basket-case go-kart. It has been plagued with reliability problems for its entire life, generally stemming from my inexplicable refusal to use real motor controllers (it’s always the motor controllers) and my insistence on keeping it brushless with R/C type motors. While its initial goals were… somewhat noble, they were pretty much antithesis to what it needed to do in real life, which was to have very high low end torque and fine speed control for scrubbing the tracks during steering, and to push through dirt and snow. To no surprise, the completely open-air electronics deck was not very enthusiastic about doing either of the latter, and the fact that it had always been geared for 20-25mph meant it really didn’t have enough torque to do anything save for drive in a straight line.

Scheduled Plug! I’m still trying to unload stuff. Have a look and see if anything interests you.

The first drivetrain version used rewound C8085-class “melon” motors, hence giving its internal moniker “melon-tank”. Unfortunately as I found out later, the motors were both wound incorrectly and Hall-sensor-appended incorrectly. Hence, this version pretty much never worked at all.  In fact, the most successful rendition of LBS had been its brief DC motor form that I put together afterwards, but even that didn’t resolve the turning issue because of the lack of braking/reversing that the “Beast-it-trollers” featured. So it still couldn’t turn, and one somewhat undergeared CIM motor per side ultimately meant they just overheated and baked. When last winter rolled around, I switched LBS back to a chain-reduced brushless form using (proper) sensored motors. This version has been around the longest and has been consistently working….with the exception that it keeps eating the Hobbyking Car ESCs for reasons unknown. Given that these were never meant to drive something with so much inertia and friction, and don’t have any form of current limiting or control, I am not at all surprised. The motors are also still geared too fast – a top speed of about 18 miles per hour, and I don’t think I have ever stayed on this thing past about 10. After the very mild winter snows melted, I took some parts out of it to let other people borrow for their own projects, and LBS has been living under a table.

Now, with LBS approaching its third Brutal Arctic Winter, it’s time I do something about all of that or close this chapter of my project book forever.

And because I was told that it will actually snow this winter, and with the allure of having a functional offroad/snow vehicle still too strong, it should be clear what path I’m taking!

I’m going to rebuild LBS the way it was meant to be the first time around – bone simple, no frills. It’s going to just be about as smart as one of the Battlebots. Full R/C throttle controls and no more weird sleep-mode contactor closing and opening. One of the causes of my reliability concerns stemmed from the fact that this thing just had too many subsystems being thrown together haphazardly at once.

Here’s the summary of what’s changing:

  • Going back to DC motor drive, using now proven Ragebridges as the drivers. Hopefully, this will be the first test of the version 2 boards.
  • Two CIM motors per side, like the intermediate DC version, geared way down to max out at about 8 miles per hour with much higher torque. My rough calculations show that in perfect traction it will have about 400 pounds of ‘drawbar’ pull. This means it might actually be able to turn in place (skid turn) now!
  • No more weight shift detection, rider switch contactors, tilt steering. Or anything.
  • Actually enclosed electronics and batteries, so going outside in the snow and dirt like it was meant to do doesn’t bury my controllers in grime.
  • Significantly less weight. There was so much wasted metal on LBS that did not need to be there and didn’t contribute to any structural load bearing.

The design has been in on-and-off development for a few weeks now, so most of it’s done already, but I was waiting to make sure I actually started on it before making a vaporware post. Here’s the rundown:

This is what the design looks like as a whole. Notice the much, much lighter aluminum sections and my more extensive use of trussing and triangles instead of big square plates. The aluminum weight on this frame has gone down by about 60% – because previous, every piece was solid aluminum plates!

The new track bogies are also much lighter in weight. Fact is, these things never took any structural loading, so they were entirely for show. There’s no suspension element or frame mounting that is rigidly coupled to the bogie swingarms. As a result, they were made much thinner and simpler. The side which couples to the ‘shocks’ are thicker in section because the loads are transmitted into the shocks and into the main body.

Admittedly, the suspension does absolutely nothing. The mountain bike suspension shock absorbers I got are rated at 700 pounds per inch – in other words, there’s basically no travel or movement at all with 4 of them on there, even if I jump up and down. Hence, I really just think of them as rigid control links in the bogies and not actual suspension elements. They are there to anchor the track axles, closing the structural triangle between themselves, the bogie swingarm, and the central frame.

 

The track pods were totally designed from scratch to be lighter and more elegant, and to minimize the use of 1/4″ aluminum. There’s no more ring of 7 3/8 bolts around the outside of each axle mount, because they were completely useless.

I spent much time trying to play “arrange the motors”, since I wanted to fit 2 motors per side. The track pods were originally designed for an ‘inboard’ drive, or motors mounted away from them driving via a shaft.  Stuffing them into the center cavity between the very short wheelbase tracks along with a method of connecting them to the main body was a bit of a pain, and part of the reason I’m glad this thing doesn’t actually have suspension travel is because if it did, the motors would be bottomed out against the tracks.

I went through several configurations and motor-vs-center-shaft arrangements before setting on this one which kept both motors on one side, hanging off the center shaft in an independent gearbox. The high center shaft meant I didn’t have to use so much metal to join the shaft to the frame since the whole thing can be kept low profile. And, the one-pivot-point mounting meant that keeping tension on the chain would be much easier. The little snail cam thing is designed to keep pressure on that swinging assembly once the chain is installed.

Check out the new drive motor setup – dual CIM motors geared to a common shaft, then chain speed-reduced to the track sprockets.

This thing will need a little explanation. The featureless gray circles are spur gears – for simplicity’s sake, I usually don’t bother modeling the teeth unless I was going to cut those gears out myself. The main spur gear is a hex bore, riding on a 1/2″ hex shaft with bushings inside so it spins on a structural standoff that helps hold the gear case together. A bunch of other hex bore objects are stacked onto the same hex shaft, and the assembly doesn’t have any axial constraining features (snap rings, set screws, shaft collars) save for the 2 end plates and thrust washers. The assembly is hence pretty easy to take apart and put together, and the hex bore transmits torque without the need for a keyway or something.

The spur gears are sourced from AndyMark. In fact, this whole damn thing is pretty much an AndyMark-powered FIRST robot. As much as I some times disagree with the philosophy of providing commercial solutions for a high school competition that allegedly encourages students to engineer and design their own robots, AndyMark really does make some neat little shortcut items. AM products are also usually built for the task at hand – which is to say, not things that you need to run for 10,000 hours with absolutely reliability. Robotics competitions are generally fast and brutal, not necessitating long part life, and I do agree with saving a ton of money making gearbox cases from aluminum sheet metal stampings, for instance, over die-case/billet machined stuff.

This means stuff costs less. Seriously, AM is about the cheapest place you can possibly get steel and aluminum spur gears if you don’t mind the limited tooth options. McMaster would have charged me about $30-40 per gear for the set I’m using, and they come with things like hubs that I don’t need. I’m pirating the popular AM method of using hex shafts for everything because it really is convenient. It’s like a real spline shaft, except improv.

In this gearbox, I’m using their 12 tooth pinion for the CIMple Box and a 48 tooth output gear.

The output is a 7 tooth hex-bore sprocket which I will custom-cut from profile.

The electronics box this time is no longer an open-top bucket. Made of 1/8″ and 1/4″ polycarb, it’s fully enclosed on all 6 sides, save for ports for switches and wiring. A fan will blow straight into the two Ragebridges in the back to keep them nice and chilled. The fan will have a foam filter stage in front of it so it doesn’t try to pull in water, and the RB boards will be conformal-coated too for splash protection. The fan will also help keep the electrical box positively pressurized -exhaust vents out the front, so if there is any place gunk could get in it would be through the slits if there was no airflow.

The Big Switch makes a return in the back side, so if this thing does try to get away from me, I wouldn’t have to full-frontal tackle it. At the breakneck speed of 8mph, too, it should be easy to catch.

The main chassis this time is pretty much just a cage with mounting holes that mount the track pods and hang onto the electronics deck, which can be slid into place and locked by the side mounting screws. Exceedingly simple compared to the first time around. I’ve ditched the big crash bar because there’s no more load cells involved, and that thing alone weighs like 10 pounds. The board itself has some little side rails on the bottom so it won’t sit truly flush as shown – I’ll make a little spacing plate if it’s needed.

Overall, the thing loses about 15 pounds compared to what it has been. While I never weighed it with the crashbar assembly on, the bare vehicle weight before was 65 pounds, so it must have been up to 75. What I lost in metal weight and complexities, I gained back some in those damn CIM motors and gearboxes. Steel and DC is heavy!

I do like the new look better, though. The space frame makes it look even more monster truck-y. Here’s to hoping it can actually live up to the hype this time.

And here’s the pile of parts!

Every post about Landbearshark ends with the motor controllers exploding

Jan 22, 2012 in Land-Bear-Shark, Project Build Reports

This one is no different. In fact, it will happen twice in this one post. Isn’t that amazing? One of them is due to Sudden Hobbyking Death Syndrome, and the other was most likely caused by laziness-induced idiocy. No, I haven’t fixed Tinytroller yet.

First, I would like to announce that my meterological precognition skills are infallible. On the day after I took apart LBS to install the load cells and wire them in, it snowed!

I swear this has nothing to do with the fact that it was going to snow anyway….seriously. Granted, it was only about 2 inches, but for one reason or another it’s the first two inches of snow this Winter. No, the October one didn’t count. 2 inches is better than asphalt, so I immediately restored LBS to its Last Good Hardware Configuration and we rolled it outside for some successful parking lot rompage. However, it still had its tilty board in this state, which caused the handling to be very unstable especially after water got into the friction washer stack and unfrictioned it.

After rolling back in, I decided to lock the board and revert LBS to full R/C once again in preparation for the next round of snow; in other words, the same state as it was for Maker Faire, but slightly more brushless and less reliable. The big rubber bushing was replaced by a chunk of very conveniently sized aluminum round, standoffs from a large chem lab shaker table that was parted out and scrapped. So while the tilty-hinge still technically exists, there’s no way I will physically bend that 1.5″ diameter round.

 

There was another important reason for the reversion to hand control. I wanted to take advantage of the built-in Xbee radio interface on the Nano Carrier to log the load cell readings on my computer as I was riding LBS around. I had suspected that the load cells would pick up any force transmitted through them, including the high frequency rumble of the tracks. The choice of datalogging program was the Arduino UI’s built in Serial monitor, and the number crunching was done in Matlab. After trying a few runs, I found that the board looseness made a clean straight line run nearly impossible. I was aiming to look at only one variable at a time, and the board steering kind of ruined that.

So, back to R/C it was. I elected to try a completely unfiltered (raw readings) run, a run with a 1 second first-order low pass filter on the two load cell readings (done in software), another run with a 0.5 second filter, 0.25s filter, 0.125s filter, etc. The numbers were arbitrary to start with, but geometrically spaced to cover a wide range of values. The tests were done in a straight hallway with a smooth linoleum floor with me standing upright and minimally compensating for vehicle acceleration – i.e. not leaning hard in one direction or the other.

And now, pretty graphs.

AAAAAAAAAAAAHHHHHHHHHHHHHHH

What is that garbage?

During tracks-up testing, I noticed a strange propensity for the op-amp outputs to suddenly go to zero whenever any throttle was applied. The tracks didn’t even have to be moving – if the controllers were trying to power the motor past the stiction of the drivetrain, without actually producing movement, the op amps would rail and then jitter erratically. Keeping in mind these were instrumentation amplifiers with gains of about 300, any millivolts of induced noise could be amplified and picked up by the Arduino. I kept the sensor wiring as far from big power cables as I could, but that made little difference. I’m also fairly confident that I have no strange ungrounded components or missing connections, as the load cell readings are great as long as the motor controllers weren’t powering.

Seems like movement helps the situation a little, but there are still plenty of instances where the readings are just trash, and plenty of places where they’re just zero.  The peak to peak noise during the movement portion of the test is on the order of 25+ kilograms.

Okay, let’s try a really slow filter:

This is a 1 second time constant low pass filter on the data. Hey, that’s starting to look like something now. There’s still spikes and jitter during the movement phase, and it’s very clear that the sensors take a long time to settle. The middle portion of the graph, while a bit spiky, clearly shows me standing mostly level (the readings are similar) That huge spike at the end is me leaning back to compensate for vehicle braking, then jumping off. The fall time of the filter shows a very clear 1 second exponential decay.

Perhaps this is a little too slow to be practical. Let’s try 0.5 seconds:

Oh dear, some of the ground rail strikes and noise is coming back now. The beginning and end show clear signs of me jumping on and jumping back off, and the middle (movement) portion is probably filled with a high percentage of zeros.

And now for the 0.25 second filter:

Unfortunately, the test had to be suspended because one of the 80A HKcartrollers detonated on powerup. I am really not sure what went on here – it was working great literally 5 minutes beforehand and I made no other hardware changes to the system.

My suspicions fall on the left side motor being found to be way out of proper sensor timing range – while I’m not sure on how it happened, it was clear from test running the motor that the sensor ring shifted significantly. This would have caused very high and excessive current draw any time the left track was being run, consequently current-stressing the controller and possibly causing one phase leg to fail short. The next time the power was turned on? Instant pop. Unfortunately, it doesn’t speak very well to the reliability of the cartroller if they can be “plastically deformed” by excessive current. Then again, it’s also risky using a motor which can potentially draw over 400 amps shorted at 18 volts (Those SK motors with an internal resistance of like 30 milliohms) with a controller that has no sense of self-preservation.

Sadness.

Ultimately what I’m seeking isn’t really a clean total weight, but a reliable delta or difference between the front and rear sensors. To that end, I think the measurements are reasonably useful. What I can observe based on the unfiltered readings, though, is that a simple low pass filter is not enough to accurately obtain an estimate of where the rider center of gravity is with the amplifiers in their current noisy and rail-prone states. If I can’t get to the bottom of the amplifier issue, then I will have to implement methods of throwing out data points which are obviously bogus, like the sudden zeroes, or throwing out any data point which is out of some defined bound from the current estimate. Dear god, I might actually need a Kalman filter.

round 2

It was going to snow again yesterday, so I begged a replacement HK Cartroller from jume just to have the thing running again. This time, the goal was to get out there before they started plowing and salting. LBS was kept in load cell, full hand control mode, but I wasn’t really out to take data so much as just diddle in the snow as it was designed to do more than a year ago.

This mission was very successful, as long as I wasn’t on it.

Driving LBS in the snow like that in dumb robot mode totally made me miss building and driving…. robots. I had a small moment there.

Anyways, actual riding performance in the snow was fairly good. It was MUCH better with the board locked – while I was previously not very keen on the idea of using four corner load sensing (so the board is essentially fixed but I can still estimate which way I’m leaning), I’m starting to get the feeling that taking out one degree of freedom in the system will make it easier to ride. Unfortunately, I didn’t get to film the first outside ride run, which went without problems until the left side chain broke.

After compressed-airing off all the snow that had gotten into the frame from doing the riderless snow-donuts (OH GOD MY ARDUINOS) and repairing the left side chain, I took it out for a second run, upon which the other chain promptly jumped off the sprockets, but this time jamming between the rear drive sprocket and the frame. That locked up the motor for a brief instant, but it was enough to toast the other cartroller. Again, the symptom was instantaneous failure on next power cycle.

Very mysterious and a little irritating.

The reason for these chain hops? I neglected to install my tensioners. You know, those little 3d printed donut sprockets that I’ve had on LBS since forever, but removed for this drivetrain version because the tension was “just right”. All chains loosen slightly once they wear in the rough forged and machined surfaces on their pins and rollers, a fact that I actively neglected.  Also, my main drive sprocket is not chamfered like all normal sprockets should be. This makes them extra-vulnerable to very slightly axial movement of the chain. I don’t want to take the drivetrain apart again, so I might do an in-place chamfer grind with a Dremel or something.

I did remount the chain tensioners after bringing LBS back inside, but now i’m out of cartrollers. I am also not sure if I want to keep replacing them – like most hobby parts, they seem to work great if not run near their maximum capacity on a system which cannot damage them through current spikes… which a 63mm aircraft motor definitely will do very easily.

While I hate to think about it, going back to Kelly KBS controllers is very tempting. They have torque control, current limiting, variable braking, and reverse… and have been running Tinykart quite well once the motor sensor timing was dialed in – something the original C80/85 “short melons” were not treated with. As I discovered when trying them with Tinytroller, the sensors as-installed were practically useless.

Going back to Kellys would mean I can run at 36+ volts again, and I can rewind the SK motors to optimize their torque production for that range, and… Hey, isn’t doing that just going full circle? Maybe I should just use some short magmotors and a Vantec RDFR36E just like an old school Battlebot. Or, go back to the CIM motors and use Victors, like a FIRST robot. I should just keep this thing as a robot and pile 200 pounds of steel on top of it to give it more traction.

Oh yeah, here’s what an exploded HK cartroller board looks like:

For the record, they emit pink smoke!