Archive for the 'Cold Arbor' Category

 

All Good (And Poorly-Maintained) Things Must Come To An End: The Great Project Purge of 2012

Jun 26, 2012 in Chuckranoplan, Cold Arbor, Nuclear Kitten 5, Project Build Reports, RazEr rEVolution, Test Bot 4.5 SP1

i swear to god i will fix this later

At some point, I need to stop telling myself that. It’s well known that my stuff isn’t exactly world-class in terms of reliability and Six Sigma class in quality, but even I can get sick enough of it to declare it a loss and start over. Over the past few months (and years) of neglect, quite a few of the robots and silly vehicles have become damaged and non-operational. I kept Swearing That I’ll Fix It Soon, Guys, but my shelf of stuff is long past overflowing with parts and project detritus and some of them contain good parts that I don’t want to keep buying. With my general shift of operations towards the newly opened IDC space just up the Z-axis from MITERS, tearing down some of the old derelicts and returning their parts to the Earth (/my storage bins) became more appealing – especially as I started collecting more stuff, most of it landing on my fresh new corner desk.

So it is with great sadness (and hidden catharsis) that I must announce the decomissioning of…

Cold Arbor

Cold Arbor never really worked – the frame was too flexible to accommodate the huge teeth of the saw. After Motorama 2010 and Dragon*Con’s Robot Battles ’10, CA pretty much only ventured off my shelf for the occasional demo – it illustrated, visually, what a “combat robot” was very well. Pretty much everyone’s first reaction at the word “Battlebot” is “You should put a saw on it to cut through the other robot!”, and CA is…. well, pretty much a saw. It never really stopped driving, but then the saw actuator broke so it couldn’t do the extending thing any more. Arbor, being the biggest lead weight I had on my shelf, was therefore the first to go.

But before I tore it totally down, I decided to use it still-functional and very smooth drive base as a test dummy.

Last year in the Austrailian robot fighting circle (did you know that Australia has a very active robot combat scene too?), one of the builders began to modify Hobbyking brushless controllers to act as H-bridges for DC drive motors, utilizing 2 of the 3 half-bridges available on the average BLDC controller. I’ve been advocating something like this for a while – use the cheap hardware base that is Chinese brushless motor controllers instead of custom-developing an expensive niche robot controller solution. The choices in robot controllers these days are either said niche and expensive but generally reliable controllers, or these one-tiny-FET-per-leg overfeatured doodads that I’ve literally had zero success rate with. Or you straight build your own and have them work, but I’ve also not successfully managed that yet. There’s nothing on the market right now which is just a bucket of large FETs like the old Victor 883s (which you can still buy, but they’re now a design so old it can almost drive).

That aside, I have also never bothered to schematic-trace the brushless ESC boards or learn & put up with enough raw Atmel C to reflash the microcontrollers (though I suppose I could have flashed Arduino onto them…). So, a ton of hot air rage on my end, but lots of action in the 40+page thread over on the Robowars forum, which has seen all of the cheap common ESCs reverse engineered and firmware implemented for – up to and including its own confusing beepy configuration menu.

They’ve now started selling them (when I say ‘they’, I really mean like one dude), and I took the chance to get some modified “85A” units based off this Hobbyking ESC.

First, I had to remove most of Arbor’s existing electronics. Okay, so my success rate with the Sabertooth controllers isn’t zero – Arbor runs two of the closely related SyRen controllers, but $75 for 25 amps is stupid these days, and I’m also royally undersizing their loads – one is running a little Speed 400 class motor and the other is running a drill type 550 motor which sees about a 10% duty cycle on raising and lowering the saw.

Way cleaner wiring and layout with the ESCheap85 in – I could easily see a robot with a whole rack of these next to eachother. The massive spam of SMT FETs technique used to great success by cheap Chinese controllers is an acceptable compromise, in  my opinion, between one-tiny-SMT-FET per leg used by the Sabertooth and Roboclaw and other most-likely-designed-by-newly-graduated-college-students controllers, and the one-huge-nice-FET approach I usually take. It keeps the board size down, too.

After hooking this up, Arbor was taken on several somewhat strenuous (and absurd) test drives.

None of it was very scientific, nor was there really enough space to seriously stress the bot out. I’m going to have to use these in battle myself before I’m fully sold on the idea, but based on the reports of the substantial number of Australian users, they’re pretty bulletproof, and a few American users have already run 18v DeWalt drills in drivetrains using them (the same motors that Clocker uses). The 85A type has been praised as a “Victor replacement”, but its more limited voltage range (30V fets and 35v capacitors) doesn’t quite convince me it can be swapped directly into a native 24v (up to 28v fully charged and more during dynamic braking) system. I fully agree with the concept, though, and for about $1 per amp I don’t have any complaints past my own reservations.

That doesn’t mean I’m no longer going to attempt my own controllers – I have yet to successfully execute a small current-controlled vehicle H-bridge, of which robot controller is a simpler subset. But that’s for another post.

At the end of it all, here’s Arbor mid-scrapping:

Scrapping is such a negative word. It took me a while to crack open that weapon drive gearbox, since I sealed it up so well at the start – and some of the bolts were bent.

Here’s everything I ended up keeping from Arbor. All of the motors, pretty much all of the drive mechanics (especially those delicious custom gearboxes, which were one of my first good ones), and of course the saw and worm drive in case I rebuild it all. The VictorHVs and Sabertooth controllers were also kept and filed in my robot controllers bin.

prospect for rebuilding: slim

Arbor was a very complicated robot with lots of moving parts – it’s something which is more difficult to get right, and it’s usually more disappointing (to watch as well as to operate) when it doesn’t work. Arbor’s build was rather rushed and many details weren’t completely thought out. I’m more likely to build a 30lb bot that is either more plainly functional or spend alot more time to build a complex but well-designed and tested robot before trying to compete with it.

Going down the line, next I pulled out…

nuclear kitten 5

NK5 was heavily damaged last Robot Battles, and ever since then has been sitting on the shelf. However, the disc motor still works great – and I can make spare discs, so that’s definitely being reused on something. The controllers and motors were also potential salvage items.

NK5 was the last robot I built before I converted fully over to “T-nut” style construction, visible in pretty much all my stuff from 2009 onwards. The design actually dates from late 2008 – my first major t-nutted endeavor was the ill-fated 2.007 robot. The frame has these wonderful corner bars that I machined for this application, but it seems like now you can buy everywhere. I really liked these, so I went ahead and saved them. Tapping into real metal is way better than t-nuts at any rate.

Here’s NK’s remnants pile. The frame materials were just not worth keeping, but I kept the motors – the gearboxes are not stripped, but one of the pinions fell off (but is intact). They might become donor parts for future gearboxes. I am a fan of these little 25mm metal gearboxen: while they are not planetary, they’re big and chunky inside to make up for it, and fairly cheap at $10-15 each.

prospect for rebuilding: hell yeah

I can’t guarantee when, but D*C 2012 is likely because I pretty much have everything-minus-frame. The disc is up for some revision, though. Big tall vertical disc spinners are no longer in vogue, being replaced by small, low bricky drum things with built-in motors (of which there are now like 50).

Next up is my pride and joy,

test bot 4.5 MCE

Really? The bot that made it to real-deal-Battlebots-IQ, then Motorama 2008 and back? The first thing I ever worked on at MITERS? Yep, since its default parking spot since Moto 2008 has been in Clocker’s lifter when it’s not doing other things.

TB certainly has the most grime of any of the bots, and the lifter was pretty much utterly trashed – it took a direct from the vertical disc bot Igoo at Motorama 2008 (that video is slightly painful to watch).

This is one of my first drill motor hacks. I did a few in 2006 for the original TB version 4, but they were either terrible or dismantled very quickly. This thing predates my entire website, pretty much. The extension shaft with the pinion was added when I redesigned the lifter for Moto 2008. It had an additional outboard support, but since it was made of UHMW, the whole gearbox still flexed too much to keep the gears in mesh, and so the pinion stripped very quickly in battle.

After I took the damaged arm parts off, I realized that TB’s drive base was actually in very good mechanical shape. I still love those gearboxes, too: they are super special 12:1 drill box hacks that I made with mating the salvaged 18 tooth planet gear and 9 tooth pinion gear of the first stage of a drill motor with an intact output stage. Coupled with the extremely overvolted 9.6v drill motors, this made the bot have a rather zippy top speed of 14mph. The first version of this gearbox predates the website (again) – this version at least had the luck of being milled, so things actually lined up!

I briefly entertained throwing the BotBitz ESCs in the frame just to drive it around again, but decided against it for the time being. It’s sure been a long time since I’ve had a 4WD drill-powered box.

So I closed it right back up again. Only the damaged arm and wedge parts were scrapped – otherwise, I think I can put something interesting in this bot again, or at least give it a better sendoff at a serious combat event later on, as the most honorable fate for a combat bot is still, in my opinion, being thoroughly vaporized into a cloud of small particles.

prospect for rebuilding: not for Robot Battles

TB4′s design was optimized for “arena” combat which has more guaranteed smooth floors and a more pressing need for huge, thick angled armor. The RB stage is purposefully left fallow to discourage pure wedges – a passive aggressive attempt at encouraging more robot creativity, which I contend has been successful in the past few years even though it kind of locks me out from competing in 12lbers again there with this design. Maybe Motorama 2013….

Finally, a project that I hate to see get tossed so early, but…

razer revolution

It’s lived a decadent life of being a demo attention whore as well as occasionally coming in handy when Melonscooter was on blocks, and has seen 4 different motor controllers (Double DEC’er, Melontroller, Tinytroller, and Jasontroller!), but recently RazEr Rev has become kind of a wreck.

I donated the front end to another MITERS scooter effort after the new battery got 2 dead cells after only a few weeks – definitely a case of bad initial conditions. Since then, it’s been sort of chilling in a corner, slowly being eroded away by the tides of cruft and dead power supplies that ebbs and floes around the shop.

The Jasontroller works great, the battery can be surgically corrected (I’m literally going to scalpel/X-acto knife the dead cells out and make it into a 10S pack), and the Dual Non-Interleaved Razermotor is a little rattly in the bearings but otherwise functional.

So that’s pretty much all I kept. Oh, and the extra heavy duty generation 2 Razor handlebar, after they moved away from welded-to-frame folding joint but before cost cutting made the joint like 24 gauge steel. This front hinge is massive – the steel is something like 0.13″ thick.

The reason I decided to scrap RREV now is because I’ve become dissatisfied with the frame design. It uses a design which I now consider inferior to other similar scooters in the way it’s put together. Starting over with the frame will be a great way to optimize the design towards less material use (like giant plates of 1/4″ aluminum) and make it simpler to assemble in addition to making dedicated space for the battery and Jasontroller, both of which were “aftermarket” additions. It should end up lighter for the same performance, but I don’t see it getting any smaller. Sorry Jamo, but Razor Wind is a little on the small side for my tastes now.

All this talk of what I’m gonna do means the

prospect for rebuilding: immediate

I already ordered some more giant aluminum plates (…sigh) and will probably be redesigning the frame this week. I’ve already got the changes planned out – they’ll just need execution. Like NK5, it will just be a matter of moving old parts over to a new chassis – there’s otherwise not much about RREV that I’m unhappy about. It’s definitely going to get a stock fender.

other stuff

I didn’t take any pictures, but all the Chuckranoplans have been parted out and recycled too. I’m probably not going to be touching this for a while until I stop being afraid of foam so I can build meaningful scale models. 3D printer models were fun for design practice, but are too heavy to work.

Alright, now that I’ve eaten half my offspring, I can start considering rebirthing them again!

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.

Segfault

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.

Land-bear-shark

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.

 

Dragon*Con 2010: The Real Wrapup…Finally.

Oct 08, 2010 in Bots, Cold Arbor, Events, Nuclear Kitten 5, Project Build Reports, Überclocker Remix

hey charles, don’t you owe all of us a dragon*con 2010 event report or something?

Yeah, yeah. The beginning of term, lack of motivation, and the lackluster (but entertaining) run of the robots at Robot Battles meant that I just Haven’t Gotten Around to writing up D*C2010. But I seem to be on a streak of making up for missed writing assignments this week with all the site updates, so… here we go.

Welcome to Dragon*Con. If you missed my description of it last year, don’t worry. It hasn’t changed a bit. The atmosphere is still as eclectic as ever, and the crowds just as dense. Actually, they were probably denser. D*C is one of the biggest conventions in the continental United States.

But I’m not a fan enough of anything to really enjoy the con for most of its con…tent. So let’s move onto the robots.

Also, I like girls with big guns.

Right. Anyways, robots.

Like last year (and years past), Southern Polytechnic rolled out their VEX robotics kits and sponsored an open build-off on Saturday. The participation was pretty intense, with young children showing up strongly. At the end, there was a ball-gathering competition.

sunday sunday sunday

Time to stop diddling. The “Microbattles” event is held on Sunday, before the big competition. NK hasn’t been here since 2008… in fact, when this version was first built.  So NK is running 2 years behind the development curve. How have its opponents evolved since then?

Oh…

The robot caliber this year is seriously advanced compared to years past – alot of it, in my opinion, due to the fact that the other Southeastern builders that I used to smash robots with have also now advanced to college machine shops and have become spoiled like me.

I mean, except Thomas up there, who’s just magic.

Cake, from the Georgia Tech crew – another one of the high-caliber machined and fabricated bots.

On the other end of the spectrum are things like this, which are built by people who are just out to have some fun and entertain the crowd.

Speaking of the crowd…

The Robot Battles events seem to always have outstanding attendance no matter what. The International ballroom has a seating capacity of several hundred (the exact number escapes me). At several points during the event, it was standing room only in the back of the room. And at least once, who I can only presume was the Hyatt Regency’s fire code liaison came booming over the room intercom instructing everyone who was standing to leave.

Disappointing, but oh well.

NK made a run through the tournament bracket before being Caked in the winner’s bracket finals. Cake, being a lower hitter, won every collision. I originally was going to forfeit any matches involving the high-energy weapon bots since I was more interested in maintaining NK’s operational status, but hell, it was the finals.

So I went for it. Overall, NK came out pretty undamaged for the amount of ass-kicking Cake dished out throughout the tournament.  No prizes this year, but the finals match was stunning.

Here’s NK’s highlights for the Microbattles tournament.

clocker and arbor

The day after was the big robot tournament.

Dragon Con is my annual robot party, since it’s precisely at the end of summer and represents the last bit of fun I’m allowed to have before flying back for the academic term. So I spend all summer building or upgrading the robots, among other activities, and bash it all up at the end.

This year, I brought both Arbor and Clocker. It’s been a while since I’ve run a 2-robot tournament, but with Robot Battle’s more laid back atmosphere, it wasn’t nearly as stressful as Motorama. In fact, I rather liked it.

Most of the usual suspects were back, with hacks, mods, and upgrades aplenty. Here’s (Big Blue Saw Presents) Jaws. Also back in the mix was Dale, Evil Robotics, MH, Found Objects, and others.

But this year also saw quite a few newcomers. The Armed Robotic Critters, for one, came with a whole fleet of critter-themed 12lb and 30lbers. Overall, attendance this year was back above pre-2009 levels. 2009 was sort of a bad year for the competition due to several builders having to skip the competition.

Then you have Sporkinok.

Really it’s not even an antweight, but Seth brought it (and a 12lber) anyway. Just for Grins and Chuckles™.

Only at Robot Battles…

….does this kind of stuff happen. You know what’s really hard to catch when you’re a 12 pound robot? A 1 pound robot.

I really can’t say enough about the level of audience energy at Robot Battles. The Regency 6 and 7 ballrooms combined sat over 1000 people….and again, during the event, was reduced to standing room only. The event also encourages the audienec to participate by helping start, end, and occasionally judge matches.

Yeah – you don’t come here for SRS BIDNESS TERNAMINT. You come here to put on a show.

Clocker did great for a while, but then immediately suffered another left-side drive failure. What the hell?

A quick examination revealed that the left gearbox output shaft was poorly assembled (read: did not press hard enough) and slipped its interference fit. Now, what was really weird was that shifting the whole shaft axially some times caused it to re-engage just enough to give the robot differential traction. So Clocker ran sporadically, but was crippled at other times. When the drive disengaged, I just threw on a Zip Tie Ratchet.

Here’s Clocker’s highlights video from the competition. I managed to execute another Robocopter spin with Jaws around a minute and some in.

That’s the move I designed Clocker to perform, and it did so admirably. Unfortunately, the clamp motor was unresponsive, so I couldn’t throw Jaws off the stage. As close as it turned out to the camera guys, this was probably for the better.

Oh, Cold Arbor.

As nice as the upgrades I made were, it still didn’t stop the saw from just catching and binding. I pretty much expected that to happen again, since this milling blade was made for multi-ton machines – not a 30 pound robot. Arbor was visually very impressive and garnered alot of audience applause, but ultimately it suffered two losses because it just couldn’t do anything.

If Arbor is to be actually competitive, I’d have to rethink the whole concept of the robot. Right now, it comes down to an issue of severe uncurable positive feedback – the forces of cutting are squarely directed into jamming the saw further into anything it contacts.

If you observe a regular cold saw or even power miter saw in action, you’d notice the saw’s swing is more vertical than horizontal. In other words, the tangential force of cutting is directed perpendicular (or nearly so) to the direction of saw motion.

Arbor’s movement is very horizontal – made even worse by pivoting the saw at the base of the robot. Therefore, the force of cutting is directed downwards and back into the robot, which is the same force vector I’d generate by cranking downwards on the saw with a pry bar. The net result is that any impact of the blade has to be compensated with massive torque inputs – realistically, more than the worm gear output can probably handle or anything short of an Etek can generate.

overall

Neither a win, nor a fail. I went to the event to put on a show (since there’s really nothing to win), and I think the bots did that just fine. I’m still keen on the concept of an actual working saw bot, however, so don’t expect Arbor to just disappear into MITERS. It will be rethought (possibly while I make sure Clocker’s gearboxes don’t let loose ever again, EVER).

Dragon*Con 2010: It’s a wrap

Aug 30, 2010 in Bots, Cold Arbor, Events, Nuclear Kitten 5, Project Build Reports, Überclocker Remix

cold arbor

First, I would like to say that I finished Ninjabridge.

It looks like this:

Yup. Back to a relay.

Ninjabridge worked briefly after extensive noise-reduction and ground loop prevention surgery. Sadly enough, it suffered a gate drive failure and subsequent Epic Shoot-Through at almost full saw speed. Nothing was particularly happy.

And so with the sun rising yet again, I pitched together this 12v SPDT relay assembly. It’s triggered by the previously mentioned R/C switch.

At least the saw works. Some more drive testing confirmed that my fears about the saw’s startup and running current pulling down the entire system were unfounded. Here’s a video of Arbor nibbling on some wood.

And a “pre-event” picture (not that D*C is a destructive enough event to warrant it, but hey.)

Überclocker

After putting all the screws on Arbor, I turned my attention back to Clocker to address one last detail that hasn’t proven fatal, but isn’t very healthy to ignore.

The bot’s drive chains have been getting increasingly looser as matches passed. The left side, in fact, has become so loose that the chain hits the ground on the bottom side of the frame. This is just begging to get snagged on something, or to make the chain walk right off the sprocket.

I’ve been meaning to put a chain tensioner on the drive since I built the bot, but never got around to it until now. The tensioner is just some simple bits of milled Delrin that has holes for perpendicularly tapped screws. I freehanded the vertical holes with a cordless drill, which brought back memories of before I was saved from a life of meager tools and hand fabrication. It was a heartwarming moment.

With the tensioners, the drive is substantially quieter. I would also venture as far as to say the bot is a little more responsive, too, since before the tensioners, the front wheels could spin 30 or more degrees before engaging.

If the chains ever get looser (Robot Jesus forbid) the Delrin sections can be milled more to compensate.

So now it’s time for a Clocker photo – I cheated a bit here, and actually took the picture before adding the tensioners.

And an everyone shot:

boxxy

No, not that boxxy.

This year, I’m going to be shipping down the bots ahead of time – which really explains why I’m working on them now and not, say, next weekend. Last year, taking Überclocker and support equipment as baggage cost me a cool $90 or so for overweight, oversize, over-the-top baggage fees. For essentially the same price, courier services will ground-ship an excessively large “package” from here to Atlanta in about 3 to 4 days.

Now, I’m defining “package” as “giant 2-foot wooden cube weighing 135 pounds and loaded with two (and a tenth) deathbots”, which might be stretching the definition some. But here’s the wooden box.

It’s made of some cheap Home Depot plywood (the same plywood, in fact, that Arbor was nibbling on. That panel became the bottom.

This time, I have enough overhead such that I’m actually bringing SPARE PARTS.

The bots go out in several hours and will hopefully arrive Thursday…

Dragon*Con 2010: Cold Arbor Impending Shenanigans

Aug 27, 2010 in Bots, Cold Arbor, Project Build Reports

Cold Arbor is now at a stage of completion where if necessary I can rig everything else together in 30 minutes. By this, I mean that the only thing missing from the bot is a means to control the DC saw motor. Interestingly enough, I’m well-stocked when it comes to brushless DC controllers, but now I want a single-direction 24 volt brushed ESC and that’s apparently asking a little too much.

The past few days have been filled with intensive Arbor work. After recutting and remaking the front sheet metal assembly, the rest of the robot came together quickly; as did the wiring. I’ve driven the sawless base around using the Hobbyking radios, and have pretty much confirmed their legitimacy for myself. It’s also just as fast and squirrelly as I remember it being.

The updated sheet metal work strengthens the area around the Slot of Saw Clearing (+1). The drop down flange extends farther in both directions from the slot, and more importantly, envelops the tabbing on the top and bottom flanges. I’ve also gotten rid of the ridiculous holes in the mounting ears that stick out backwards.

The whole show was, again, assembled using the weird aluminum-zinc solder-braze-weld alloy, then cleaned up on the belt sander.

The casualty rate for this piece was unusually high since I brushed the alloy in with far more pressure than I usually do. I’m hoping this will make for better adhesion.

After everything cooled down from the operations, I began remounting the saw. Arbor is assembled in a very linear, single-track fashion. In order to get the front off, all the sides had to come off first.

Also, in order to replace a motor, I have to use 3 different sizes of hex wrench on 4 sides of the robot at once. Once the saw arm assembly was refixed, I went ahead with steps to mount the Preduction.

Everything would have gone smoothly if I had remembered that there was actually no way of inserting the shaft collar into the assembly unless it was a two-piece split one. I didn’t, so I bought a bunch of normal 1/2″ collars.

Sadly enough, a 1.125″ diameter collar will not fit down a 7/8″ wide gap.

Solution: Just turn the thing into your own 2 piece collar. Step one is to mill a counterbore for the screw on the non-split side. Then drill a tap hole, tap the threads, and drill a clearance hole a little bit past halfway down.

Then viciously hacksaw the thing in half. Clean up the carcass on the grinder, and mezzopiano, a two piece shaft collar.

Perfection.  Here’s a little bit of saw flexing – overall, the travel is the same as before the actuator mods.

That’s it. The bot is mechanically complete. All the actuated systems move to my satisfaction, and the drive motors both work.

I discovered that the saw drew an absurd 33 amps just cruising, no load, at the full 24 volts. The cause for this was traced to the worm gearbox input shaft bushings. When the Preduction was added to the system, its ball bearing output and the two shaft bushings formed an undesirable overconstrained shaft. Essentially, the shaft has to bend at the first input bushing because the major end constraints are the very frontmost bushing and the Preduction ball bearing.

This might have been tolerable (and therefore a hidden problem) if the worm box came with ball bearings too, but with bushings, this causes massive friction. Just removing that bushing dropped the no-load amps to 17. Still high, but the MEV-alike draws 7 amps no-load already, and the rest I can realistically say is disappearing somewhere in the geartrain.

electriclulz

It’s time for that part of a project where everything usually goes horribly wrong.

The first thing to go wrong is my discovery that the fully loaded bot weighed only 27 pounds. With the greatly increased current demands of the saw motor, I elected to balance the weight by putting in a larger battery pack.

Above is the planned 6S2P arrangement of 26650 cells. The whole thing just barely fits between the drive wheels, the motor, and the front claws.

Going down to 6S relieves the motors of alot of strain. The 700 size drive motors already get pretty toasty, and the MEV-alike is a 12 volt motor. Things were really unhappy on 24v, and the single-parallel pack was being drawn down pretty quickly at Moto. Therefore, I’m also using 2 cells in parallel, each group forming a single metacell like on the METALPAXXX.

First thing to do is to put the cells together in bricks. I went my usual route of using Automotive Goop adhesive between the cells, then binding them with electrical tape and leaving the adhesive to set. Also pictured is a spare 7S1P pack for Clocker.

The 200th Cold Arbor build pic is of the infant Arborpack. I performed my usual grounding braid assembly method here – nothing particularly special

And here is the complete pack, with balance leads and after being double bottleshrunk.

Because the new battery arrangement precludes the use of the existing 1/8″ polycarbonate armored battery box, I elected to give these cells an extra layer of protection… or two, rather. I bought (and subsequently emptied to the detriment of my health) more cheap 3-liter sodas and cut up the bottles. With some quality heat gun time, the bottles shrink around the battery pack and then harden into a thick plastic shell.

Once again, in anticipation of the potential for high pulsed current demands from the saw motor, I threw a diode-capacitor buffer in line with the receiver’s power source, a cheap Hobbyking BEC. The diode sits between the main battery and the BEC input and essentially makes sure a sudden voltage dip in the rest of the system cannot upset the BEC. The large buffer cap should carry the BEC demand through transients.

I built the “check valve” system because I was planning on using a giant relay and a receiver-controlled switch to turn on the DC motor.

Loading the electronics back into the bot!

Rewiring Arbor was simple because the controllers were not stripped of their wiring, and the motors all had pigtail leads. So this process in total took maybe two hours, with plenty of wanking time allotted.

And a quick finishing shot from the front.  By this time, I had already taken the bot on a (sawless) test drive or two. The McMasterbots wheels wear pretty quickly – I’m going to have to order spares. Not for D*C, but later on.  As of the picture time, the RCS order had not yet arrived, so the saw wasn’t up and running.

ninjabridge

A relay-controlled weapon motor. Really? A relay? Really now, I think I can do better than that. If I couldn’t buy a forward-only, 24 volt compatible, variable speed DC motor controller, can’t I just build one?

These thoughts were cycling through my head as I was assembling the most impulsive electronics project ever – Ninjabridge.

Ninjabridge is composed of a Pro Mini Arduino, an IR(S?!)21844 synchronous half-bridge gate driver hidden under the Arduino, and four IRFB3006 FETs. It is (will be, after I add wires and software) a foward-and-brake controller with inherent synchronous rectification. With two 3006s per leg, I should get at least 40 or 50 amps continuous out of this thing with no additional heat sinking. Modern silicon is niiiice.

I’ve actually been in the design stages of a full robot controller – 4 channels of H-bridge DC motor drive and one single direction half bridge for weapon work, up to 36 volt operation at 40-50 amps continuous, all featuring implicit synchrec. I originally wanted to get the boards made and the whole thing ready for Dragon Con for use in this very robot, but decided against risking everything when I had otherwise functional controllers.

But there exists a “controller gap” in the medium power (12-36v, 30 to 60 amps)  range as of right now. Above this range, you have the venerable IFI Victors, and below this are the popular small robot controllers like Scorpion XLs, and the Dimension controllers that Arbor uses on its actuators. I’m not intending on striking out in the market with anything, but I want to see what’s possible with modern semiconductor and IC technology. And to this end, I think the above features are fully reasonable to pack into a space the size of at most two Victors (which are pretty large controllers).

I’ll track down more 12 gauge noodle wire for Ninjabridge and then spend a few weeks…err… hours coding up a basic single channel R/C compatible controller. Then maybe Arbor can actually damage something.