Archive for September, 2011


Updating the Melon Scooter

Sep 22, 2011 in Melon-scooter, Project Build Reports

It’s been a year since I finished melonscooter. Barring the occasional controller experiment, it’s rarely been talked about or mentioned, and it doesn’t even have a vehicle page, which is something I should fix. This is mostly because it has worked reliably and has been more of a tool than a project (correctly implying that my project vehicles never really work that well). It’s well in the triple digit miles by now, and has saved me countless hours via not walking anywhere, therefore likely contributing to my early demise through obesity, heart disease, and maybe faceplanting into a bus or two. It’s also fairly well known around campus as a sign that I Was Here™, and occasionally gets me trolled by the campus police since it is actually capable of violating some internal speed limits (the top speed being roughly 25 miles per hour depending on things like headwind, tire pressure, and battery remaining, but is always above 20 or so)

The original design was put together in a weekend with very little forethought, and it definitely left alot to be desired. Namely, the entire drivetrain is open to the air above. This implies that whatever the tire picks up is going to end up in the air, and ultimately must land somewhere. When it’s been raining or otherwise wet out, the choice landing spot is straight up my legs and back. Thus, melonscooter is usually in hiding whenever the weather is anything but sunny and dry. This being New England, the chances of that happening as summer ends approaches zero. In the past, I’ve done silly things like tape together wheel covers and fenders:

I forgot what that torch was for.

They would usually work okay, but were just too hackish to keep using (and the cardboard ones would just melt after one trip anyway).

This was actually the single biggest impediment to using the thing regularly. The electronics and batteries were reasonably weatherproof (the controller having been moved inboard since the above photo was taken) so the only issue was me being unhappy with a trail of road grime extending from my back down my pants legs.

With the summer ending once again, I decided to just get it over with and do something about it. There were some other issues with melonscooter that I had complained about before, so I figured in one upgrade I’d take care of them all.

So here’s what the back of the thing looked like as of yesterday. Another problem with this is that the huge wheelie tail wasn’t actually all that stable. It was mounted directly to the wheel forks that were punched out of the soft steel frame tubing, so standing on the tail would actually force the axle mounting slots apart and leave it very floppy. It got to the point where I was vice-grip-crushing the axle mount slots back together every few weeks. Adding that secondary nut and bolt ahead of the main axle bolt helped a little, but the wheelie tail was still “soft” and a little wobbly up and down.

I also had no cargo space whatsoever. Trips to the grocery store or convenience store were made moot by the fact that I could only carry back what I could stuff in a backpack or reasonably hang off the handlebars. This was inconvenient to say the least.

The plan I cooked up was to make an integrated motor mount and “stern deck” kind of like the back of Straight RazEr which would clamp or bolt onto the frame rails and provide both wheel coverage, a place to stand, and potential for cargo space. After staring at the stripped down back end for a while and taking in-place measurements of where the wheel and motor were located, I came up with the following.

It’s a primarily 1/4″ aluminum, waterjettable upper deck. Due to the frame geometry and motor clearances,  I had to move away from a convenient clamp mount into through-drilled holes. A clamp would have required the volume occupied by the brake mount and I would have had to move the motor upwards a half inch or more so the rotor side could clear (the original mount had the can hovering less than 1/4″ above the frame rail). I didn’t mind fixturing and drilling some holes.

The solution for the cargo space issue lay in the standard 13″ milk crate. These things are common and give you a good cubic foot or more of storage space, and it’s common to see them on the back of bicycles. So I figured I’d make myself a detachable mount for a an ISO standard milk crate (does that standard exist?). The bars pass through a vertical plate with 2 holes, which is the primary support, and I’ll machine some clamps to hold them on the close end (those big hand knobs are for closing the yet-to-be-made clamps). The maximum extension is 13 inches, and I’ll fasten a crate to the bars with some crafty zip tying.

I was planning on making it foldable or telescoping, but this is not exactly a scientific exercise…

So let’s begin by milking the teets of the Institute and getting my parts waterjet-cut from 1/4″ aluminum. This was from the same stock that Straight RazEr was born of – I actually did buy something like 50 pounds of aluminum on eBay recently. I ordered some 24″ rod stock to make the rack of crate mounting from, but they had not yet arrived.

By the way – all the pictures this time will be horrible grainy 640 x 480 because I accidentally set the camera on my cell phone (which is actually pretty decent and has autofocusing) to 640 x 480 somehow, and didn’t notice until I uploaded everything. There’s at least one good picture, I promise. That thing takes pictures which otherwise are just good enough for me to not bring my big camera everywhere now.

I committed myself to a night of assembly by totally parting down melonscooter. I took the opportunity to clean up everything in the frame, which was covered in road junk and rusty in some spots.

While the batteries were out of the frame, I gave them their yearly balance charge. The cells have only drifted apart about 30 to 40mv this whole time, so this didn’t exactly take long.

This is what the “stern deck” looks like when fixtured in place. It picks up right where the folded polycarbonate deck leaves off. The standoff at the front of the new structure (not visible in this pic, but in the CAD image) was the reference surface for aligning the whole thing to be level. After that, it was a quick drilling job (disturbingly quick for something that’s supposed to be steel, mind you) to put the 8 holes into the frame.

Eight countersunk 1/4″-20 bolts later, the stern deck is mounted. It turns out that 1.25″ was the ideal length for this job, but I only had 1″ long screws in standard socket head. The only 1.25″ (or rather, over 1″) screws I had were flatheads. This was fine, since countersunk flathead cap screws always make something look more hardcore. I also test fitted the wheel and motor to make sure I didn’t get it totally wrong.

A view from the other side. Because the steel frame is just that soft, I used some Keps-type locknuts with 2 layers of washers: a small, standard 1/4″-20 washer pressing against a 1/4″-20 fender washer. The fender washer’s huge surface area allowed me to crank down on all of them without caving the thin wall tubing inwards.

All the electronics drop back in as they were before, except I took the chance to reroute some wires so they don’t…. hang down as low.

Priorities first: got to make sure the gaudy lighting is properly reinstalled. Putting in the countersunk flathead screws turned out to be a good move, since I couldn’t find another place to mount the CCFL inverter that was within reach of the new glow tube location – under the deck. I ended up Velcroing the inverted right to the side of the motor mount plate.

And here is everything wrapped back up. I’ll finish the Rails of Crate Mounting after the rail stock arrives. I’m also heavily considering making a similar attachment for the front of the frame for even more space. And balance: the added weight of  infinity Mountain Dew 2 liters is liable to making this thing wheelie like crazy.

See, I promised a good picture of it…

The First Results of NY Maker Faire

Sep 18, 2011 in Events, Land-Bear-Shark, Project Build Reports

From Make and through Jalopnik,

It was good that I gave all the technical details in the video so there was no possible way anyone could mess it up.

I actually still don’t have a good ‘press photo’ of Landbearshark… and forgot to take one at the Faire. I should do that.

The Post-Everything Update, Part II: Maker Faire(s)

Sep 15, 2011 in Cold Arbor, Events, Land-Bear-Shark, Project Build Reports, RazEr rEVolution, Überclocker Remix

I’m back in the zone.

After back-hauling 1185 miles over 2 days from Atlanta to Cambridge, Assachusetts (and discovering in the process that Budget Rent-a-Car’s computer system cannot comprehend a mileage with 4 figures, to my delight), I’m about to go back down about 20% of the way…to the NY World Maker Faire as part of the MITERS booth/table display.

Great… maybe I should have just stayed a few extra days and just went 80% of that distance instead.

The reason why I ended up bringing most of everything ever (i.e. more than just the robots for Dragon*Con)  down to Atlanta in the first place was because of Maker Faire practice.

The Atlanta Mini Maker Faire, hosted by Georgia Tech, was a week after the D*C robot event, so I elected to knock a week off the semester and show up after being invited by some of the GT Invention Studio folks.

The event was held in a not-too-large parking lot, and about 60 individual exhibitors were there. The above picture is of the crowd and a pretty nice electric Chevy S-10 pickup truck conversion.

With rideable objects now making up a majority of my project fleet, the event was a great chance to make sure all of them had some testing time without me in the loop. You are generally always careful and mindful of a vehicle’s limitations if you’re the builder, but no such luxuries are afforded when your vehicle is being tested by strangers who had about 30 seconds of instruction beforehand. I suppose a hallmark of a well-engineered vehicle is if anyone can operate it with 30 seconds of instruction and not have it explode.

Sadly, only about half of my “travel fleet” made it through the day.

Straight RazEr

As the previous test video showed, Straight RazEr did fairly well confusing GT students on campus. After raising the front ground clearance another inch, it could finally turn and go over the average sidewalk crack and things like that. I brought it to the MMF, and it performed admirably well throwing off several random people.

The trick with sensorless brushless scooters is that you cannot just stand on it and hit the throttle. At least, don’t do it multiple times, since the motor pulling stall current across the controller will heat it up quickly. While most everyone understood the lecture and handled this part fine, I’m fairly certain the one person who didn’t caused the demise of Straight RazEr. A few seconds after I handed it off, I heard cries of “smoke!” and “fire!!” from the crowd behind me. I turned around and without much reaction, watched the massive plume of Turnigy smoke billowing out of Straight RazEr’s upper rear deck.

The short-circuit current desoldered my Deans main power connector. Some of the smoke and “Turnigy splatter” looks like it also made it out of the power access holes.

That SR ended up exploding wasn’t really surprising – the fact that sensorless vehicles need to be “push started” is really an alien concept to most people unfamiliar with them, and the majority push off too slowly or weakly anyway. The same reason is why very few people can actually ride melon-scooter, which also has a much slower “pickup speed” than Straight RazEr due to the latter’s much wider gearing.

Oh well.

Because Straight Razer was built mostly as a troll and the controller can be replaced later, I’m not going to try to bring it to NY Maker Faire. It’s considered out of commission until further notice. I might try throwing a melontroller on it some time later, but that involves adding sensors to the motor.

Speaking of melontroller…

RazEr rEVolution

I don’t have pictures of RazEr at the event (it looks the same, trust me), but I’m definitely amazed at how well it has stood up. Not only was it extensively used to the point of battery depletion at the end, but both the motor and Melontroller 2.0 have survived what amounts to a continuous +/- 50g minimum shock test. Because of the very hard wheels I chose by mistake and ended up designing around (90D and 90A hardness for the rear and front!), every little sidewalk or road feature was transmitted without damping into the drivetrain. After the day of demos, I rode it twice around GT’s Yellow Jacket Park square essentially full throttle the whole time. Overall, RazEr’s design has proven itself to be very robust. I’m particularly relieved that Melontroller 2.0 is a stable version from which I can improve (you know, adding things like a real logic power regulator), so this is one goal for this fall and winter.

With Jamison’s new hub motor scooter sporting 60A Colson wheels, I’m also going to remake the front and rear wheels to use them. Maybe RazEr can actually be a useful vehicle after that.

However, for the time being, RazEr will be at NY Maker Faire, completely unchanged except for a full charge.


The biggest and most awkwardly shaped member of the travel fleet, Segfault was already flaky before I left, and it only got worse at the event. Not only is the controller, originally designed to last maybe a week, now entering its 10th month of use, but the drive motors are slowly giving out too. The left Banebots P80 gearmox lost an internal shaft retaining ring some time ago, which means occasionally the left wheel just completely disengages and spins freely. I’d keep the thing running by literally just kicking or hammering the wheel back in. But finally, at the MMF, this happened.

Alright, I’m finished. Before this, the controller had pretty much been totally reduced to a ball of twitching and noise. The breadboards are slowly falling apart (their contacts falling out the bottom side after the glued-on paper backing expired) and most likely the contacts are also oxidizing and being sporadic. With all of this, Segfault is officially decommissioned and the current version will not be repaired or upgraded. I will probably part it back out and repair the left P80 motor for future projects. The vehicle is too big and unwieldy, and has more than served its purpose of control theory demos, so if I end up building another Segway-vehicle (ahem) it will be much smaller and lighter.

In the mean time, anyone want a full aluminum Segway-like vehicle frame? Just add your own P80 motors and Arduinos.

Because of the state of utter wreckage it’s in, Segfault is of course not coming to NYMF.


This thing was a huge hit, and I’m proud to say that it also survived the day unscathed (though with quite a few more stickers). It looks very squat and unimposing, but few people could actually stay on and ride it because of how high off the ground the rider stands and the short “wheelbase”. The Beast-it-trollers handled the whole day’s operation in 90-95 degree weather with no problems after I upgraded the drive FETs to IRFB3207 4 milliohm parts, instead of the old IRF1407s which flamed out two Swapfests ago.

While the Advanced Beast-it-Troller has been assembled and bench-tested, I have not installed them or written the software for them… nor do I intend to for this weekend. LBS will be traveling to NYMF too, and I’ll probably be tooling around on it all day since it has about 25 amp-hours of battery onboard, and NYMF is half parking lot and half rolling grassy fields and gravel lots. Hell yes.

Other things that are also coming

I’m going to bring Überclocker and Cold Arbor along as display sculptures. Clocker is functional (not very battleworthy, but things do move) so it may participate in some demos.

The Kitmotor Demo Stand will probably be spinning on the table all day so more of you people will go and build scooters.

Finally, I’ll also truck along the erstwhile Make-a-Bot, which has been making parts for all the other projects almost trouble-free since last December. It’s now a generation and some behind the kit 3d printer features curve, and I intend to rebuild it in the near future. Maybe I’ll park it in the 3d printer nest, next to all the Makerbots to troll Bre Pettis. After all, it’s about 75% faster than a stock Thing-o-matic and 1000% more \m/etal.


The Post-Everything Updates, Part I: Robot Battles

Sep 12, 2011 in Bots, Pop Quiz 2, Überclocker Remix

That’s it! The event is over once again. If by my lack-of-enthusiasm-induced time delay is any indication, I didn’t win anything. The robots performed about as much as I would have expected given the effort that I put into them this time around (read: like none). In the antweights, Unmodeled Dynamics…no, that’s not the name of a robot, though it could be… ended up causing Pop Quiz an early loss after winning one match. And in the 30lbers, Überclocker proved to be a little behind the times now in terms of speed, ground clearance, and maneuverability, winning only one match.

I didn’t even get to twirl anyone this time around. That is how bad it was. No con pictures this time either, since I really only stopped in for some of the Robotics and Science talks and otherwise didn’t have a good enough camera to feel like taking pictures of people. Also, without a consistent videographer this time, I don’t have complete video of both robots’ matches. So, no highlights video just yet.

The events, though, were phenomenal. The insect-class event ended up attracting 36 entries – 19 beetleweights and 17 antweights. This makes it the largest insect-class event on the east coast so far, and many of the robots were from new builders. Because of the number of entries, though, the tournament had to be converted to single-elimination (historically has been double-elim) to fit in the given convention time slot.

Pop Quiz

As the testing session video reveals, Pop Quiz has a slight “sudden unintended takeoff” problem stemming from the frame’s flexibility and the low blade height. I’m interested in seeing this under some serious high speed video equipment because the development takes milliseconds. I’m guessing the combination of robot movement, slight nonplanar mounting of the blade axis (due to floor bumps or varying wheel instantaneous heights) causes gyroscopic forces to flex the motor mounting area, which because of the very low blade clearance causes it to strike the robot corners. The blade then quickly destabilizes and hits the ground due to the bot’s very low height.

Either way, sort of annoying. There’s nothing wrong with Pop Quiz right now. It in fact works just fine, so I’ll probably retain it as a demobot. However, I’m definitely out to build a better antweight – of what style I am unsure of at the moment (but I really, really do want to name it Unmodeled Dynamics)

I have one complete video of Pop Quiz’s second match, which ended in a PopQuizCopter-induced loss.

Überclocker Remix

Oh dear. Where do I even start with this one? Clocker’s now 3-year and 4-tournament record is starting to show – the design flaws of late 2008 are slowly getting worse with time, compounded by my apathy. This year, the stage has pretty much become so damaged (purposefully, since it was historically a good wedge inhibitor) that Clocker was being hung up everywhere. The 2.5″ colsons have worn down alot, so much that I had lots of trouble maneuvering. Additionally, the lack of (functional) chain tensioners resulted in the chain being caught and damaged by the stage surface for the first time. To mend this, I made some quick zip tie tensioners (continuing the tradition of fixing Clocker at an event with zip ties):

The zip tie wrapped around both sides of the chain and prevented it from sagging and touching the ground. This worked – right up until it caught on the master link retaining clips and ripped them right off. The result was a broken chain in the bot’s third match. By that point, I really had stopped caring and just wanted to continue the show, so I elected to run one-sided (and without the infamous Zip Tie Ratchet even!)

Past that, the robot’s lack of actual forward-pointing sharp things (The ends of the fork are actually fairly blunt) meant that I was easy to get under from the front. Finally, opponents were finally able to take advantage of the bot’s 23 inch long flat broadside.

At least the motors worked this time!

Clocker version 2 (“Remix”) is now retired. I’m going to be rebuilding the bot from the ground up to emphasize manueverability and terrain handling – terrain referring to bumps and inconsistencies in the arena surface of up to 3/4 inch. Yes, this thing is going to have a boatload of ground clearance, will be much faster, and also with more “grabber clearance” so I can latch onto the more irregularly shaped robots. In order to fix the huge broadside problem, the sides of the bot will be rounded like Cold Arbor (it has prove hard to attack from the sides due to its tendency to “roll” into or away from the pushing force).

I haven’t designed out everything yet, but have been making a few “concept sketches”. One of which is below (though it’s unlikely to be used)

Pop Quiz Pre-Event Smackdown

Sep 04, 2011 in Bots, Pop Quiz 2

After obtaining 4 set screws, I put PQ2r2 together for the final shakedown test.

Okay, so it turned out to be more of a shakedown than I thought. The blade is just off balance and possibly just tilted in-robot enough to cause the sudden instability and “popping” in the video. To mitigate this, I’d have to spin up just before approaching an opponent.

Because of the missing battery half, the robot only weighs 13 ounces. It’s fairly maneuverable with the four Sanyo style gearmotors and soft wheels, so I hope if it’s too light to be an effective spinner it can still get under people and shove them around.

Microbattles event in about 10 hours!