No, not to someone who wants to mass produce it for the world (for better or worse), or to mass media (yet), but to brushed DC motors, just like I said I wouldn’t do last time. I should consider a career in politics or something. Anyways, out of practicality reasons and an attempt to not to try and address 5 design flaws at once, a change from my usual build tactic, I’ve elected to switch LBS to a POD (Plain Old DC) system. DC motors don’t have blank sensor states, and controlling them doesn’t involve a state machine (or nested loops with rotor position estimators and current sensors and matrix transforms). In the space available for drive motors I won’t be able to mount anything as powerful as the rewound 80/85s, but judging by how well I was able to stay on the thing during the preliminary trial, I don’t really have a problem with this. My main goal is to get the fingerless-control designed and built so I can test if it’s worthy of further investigation.

By the way, here’s an interesting build from a few years ago that accomplishes everything LBS was supposed to do, and in a better form factor. See, I should have just done this straight away.

The concept is pretty close of the Boolean union of Snow Scooter and LBS.

Oh, also, here’s a sneak peek of Chuckranoplan 0003:

No more Delta wing?! I’ve been eyeing different wing planforms since I got this book (which is awesome but clearly shows the imperfections of being a first print edition). The authors break down the cladistics of GEVs more finely than I do, separating the field into five categories based from my understanding on operating altitude and the ability to statically hover. Of particular interest to me was everything that wasn’t the Lippisch delta wing. The real reason I don’t like them as much despite their clear advantages in ground effect is that I currently have no clue how to build a tapered wing For Real. Unless, perhaps, I build a garage-sized 3D printer, which of course is not out of the question.

And they look derpy.

I’ve been looking into some of the Chinese GEV designs recently, since they have all featured square wings with small vessel-length-to-wing-chord ratios (the wings are very long compared to the vehicle length) and aspect ratios (almost square or even rectangular the wrong way). A square wing is much more in my comfort zone of things I could conceivably build without getting too deep into specialized materials, tools, and techniques. This is important, since a 20 foot Megachuckranoplan is still lurking in the back of my mind.  One example is the Tianyi 1. This vessel (and its forerunners) are the subject of some pretty intensive analysis in the book. They represent a middle ground between the more ship and hovercraft-like types which can only skim over calm water (such as the Aquaglide) and the Legit Ekranoplans of yore which could operate at higher altitudes…. and by higher I mean like 10 feet.

To prevent this from turning into a Chuckranoplan post, I’ll leave it at that. This model will still be 3D printed hollow to the best of my ability, but the square airfoils mean that I could easily make a more conventional model aircraft wing out of some laser-cut balsa wood. Weigh estimates put the above at 220 grams dead empty, and only if MaB gets it right.

oh yeah, melontank.

This thing here is going to save my day.

What IS that?

It’s a weird little integrated 4:1 planetary gearset from some kind of Currie electric bicycle. Around 2 years ago, they started showing up on the surplus channel, but it looks like they’ve been around before that, just more expensive. The construction is fairly “discount EV” standard – sintered steel gears, cast aluminum carriers, and rivets. What’s cool about them is that they have inbuilt support rollers coaxial with the planet gears that turn the whole thing into a really big and shitty roller bearing, so they can take some moment load. Presumably in the bicycle, there was no other bearing for the chain sprocket.

I have a little bit of history with these, as they were first discovered and used for the Greenwheel project. But more recently, they’ve been ingeniously used to great effect on the ExkateCD project as a “preduction” stage to replace an existing drive motor with a faster one but retaining roughly the same output speed after the belt drive.

Hey, sounds like something I need to do. The motor they used was a stock CIM motor, the same kind used on FIRST robots, but the motor I’m going to use is a…

…

… Okay, it’s a CIM motor. Whatever. Stop judging me.

Incidentally, it’s the same motor that powers Segfault. They’re made in the tens of thousands each year for FIRST robots, are rated for a solid half horsepower each (which really means you can punch 2 or 3 into them for a very short amount of time), and aren’t too obnoxiously sized. Oh, yeah, they’re cheap, about $30 new, which makes the price to performance comparison very good for a stock janky DC ferrite magnet brush motor.

So the plan for LBS is to down-convert the 5000 RPM @ 12v by 4 first, using the Shady CurrieBoxen, and then run the stock 5:1 chain drive that’s in place now. Essentially a direct swap-in of the two brushless outrunners that are in there now. The combined 20:1 reduction might actually be too much, so I also have the option of going to 4:1 chain drive with the alternate sprocket set I have. Doing this would mean that I’d have to drop the 36v power system for LBS and go to at most 24v, which will be plenty anyway.

This will be accomplished using the unique mounting configuration for the Currieboxen that ExkateCD explored. The ring gear is bolted to the motor mount, the output is taken through the carrier plate, but the output completely floats on the motor shaft. The CIM motor shaft is just the right length to stick out past the gearbox enough to put a ball bearing on. The output coupler can ride on this bearing while being attached to the carrier plate at the same time, which is firmly held in place axially by the built-in rollers. The assembly is made stiffer than the stock (very loose) output because of the addition of the coupler-side bearing. And of course the motor mount has the same bolt pattern as the 80/85 motors.

Here’s how the assembly goes together. The ring gear attaches to the motor mount through the perimeter bolt holes, which appear to clear #8 machine screws.

And the assembly from the back, showing the coupler with 8mm ball bearings.

Here’s the assembly dropped into the existing motor mount on LBS for a fit test. The new motor setup is longer, extending all the way to the other side of the track pod, but it’s smaller in diameter. Overall, it’s not a painful conversion. I just have to sit on my ass now and wait for the motors, supplementary Currieboxen, and random hardware to ship from all over the place.

In the mean time, my focus will be on implementing the fingers-free controller. The spring demo season (where I spam exhibitions, fairs, and events of all kinds with everything I’ve built ever) is under way, so I also need to get some of the other projects running again. The poor RazErBlades, for instance, are out one bettery pack (and the replacement I bought doesn’t fit because fuck you Hobbyking for changing the dimensions of products without updating the website and picture!).  Ideally, Melontank will be ready….

by Commencement.

[dun DUN DUUUUNNNNNN]

Echoing a “short and tragic” test run of another vehicle, I managed to rudimentarily finish LBS using a wired control solution for kicks. It proceeded to fulfill that immediately by kicking me in the shins and running off, and is now the target of a 50-state man(bearshark?)hunt.

Well, okay, so it wasn’t that dramatic.

But also, only one half of that sentence was a lie.

I elected to try and get LBS running in time for the third Japanese TV show in three months to visit MITERS. Yeah – for all I know, I could be a Japanese media sensation at the moment and I wouldn’t know at all. Regardless, we are seen by the media production companies in question as some sort of… I don’t know, innovation or intelligence or amusement or something. All I know is it keeps involving crazily dressed people acting as reporters or correspondents.

I elected to Just Beast It and didn’t really take many pictures of the process. Here’s the beginning of a veritable tree of Deans connectors. I kept making 3-way splitter harnesses only to remember that I needed two additional outputs, so had to keep making even more splitter harnesses. Most of the wiring gauge is small because LBS isn’t ever going to pull that much current anyway, and because I had it. The green packs were borrowed from Matthew’s Will Be Finished Some Day scooter build.

The Provisional Melontanktroller board was completed and mounted in the center between the two Kellys. I broke out the multitude of half-stripped and crimped signal wires on the Kellys to a single 10-pin IDCC header (which I don’t have an exact matching socket for, but whatever). The major analog and digital inputs, as well as the two status LEDs, have pins on the header. I decided against running controller power through the same header since that would entail someone connecting full battery voltage to the board, which I felt like would have been an impending disaster.

The controller for the time being is this totally rigged Arbotix Commander. So this thing is pretty much the most useless thing ever made, just by itself. It has no serial or FTDI breakout at all, and the only way to program it is through the 6 pin ISP header. It’s also supposed to be Arduino compatible, but without USB hardware, there’s really no way to put the compiled sketch onto it. Of course, raw Atmel assembly or C code can just be written for it, but… but but but.

So not wanting to deal with that at all, I just soldered wires to the joystick pots directly.

The backside will not be pictured since it’s too disturbing.

Okay, here it is: LandBearShark version 0.1 (beta). Happy?!

While nothing is clearly finalized, the (really) finished vehicle will not look substantially different, since the ninja-rigging was all internal.

And a low angle view. The updated 11-tooth chain tensioners can be seen here, along with Segfault.

Finally, here’s what you might have been waiting for. Don’t worry, it’s not that dramatic.

So besides all the awkward balancing, the version 0.1 design revealed alot of issues that need to be addressed.

• The drive motor’s appended sensors appear to have very minor angular spacing errors, but that means every once in a while the sensor state enters [1 1 1] or [0 0 0] and causes the controller to throw an error. Only a small movement of the treads out of this error band will cause the controller to kick in. The issue comes from in-place turning where the motors have to apply alot of torque at zero speed, and can easily enter the error band without enough inertia to leave again.
• The suspension is indeed kind of soft, and acceleration tends to rock the rider backwards. However…
• …the Arbotix joysticks were just plain too sensitive. I didn’t write in any kind of throttle filtering or ramping, and the Kellys were configured for Beast It mode (i.e. very fast throttle ramping). A more sensitive and carefully designed signal processing algorithm is necessary.
• A rider detect cutoff switch is absolutely needed. There was a brief (unfilmed) “Melontak rodeo” where I accidentally yanked the controller cable out and one side decided to start full throttling. Luckily, it was in a circle. While I could have used one of the switches on the Arbotix controller as a “dead man’s switch”, I couldn’t quite figure out how to code the state machine that would wait for one second from switch release before disabling the controllers (to act as button debouncing and to account for airtime or jumps)1, because fuck software.

I’m actually considering either switching LBS to brushed motor drive (eww) or going to a high speed but pre-geared brushless motor – possibly even stock 80/85 motors with a 4:1 planetary gearset or something. That, or find a motor with more slots and poles. Either way, the idea is to minimize the error band that is introduced by me placing a sensor in sideways or something – the gearing would ensure that the motor has more ‘wiggle space’ where it doesn’t have to apply significant torque to move the vehicle.

And a brushed motor drive (eww) would of course eliminate that completely.  But that’s the practical sissy way out.