Archive for the 'LOLrio Kart' Category

 

The Fall 2009 Roundup: Überclocker Updates, RazEr Redux, Analog Antics, and the End of the Tragedy of the LOLrioKart

Oct 05, 2009 in Bots, LOLrio Kart, Project Build Reports, Project RazEr, SEGFAULT, Überclocker Remix

…wins for the longest post title EVER on this site. That’s because it addresses quite a few topics. I can finally characterize the academic term so far as having entered a steady state, which just means I know which nights I can bumble away safely, so it’s time to step up work on the projects. I’ve devised a list of theoretically attainable goals for the next few months, stretching into the coming winter months.

Überclocker Remix

Let’s start with some pictures of epic motor ownage. I cracked open the toasted HTI gumball machine motors out of curiosity after removing them from the bot. What awaited me inside was a scene of utter devastation.

That doesn’t look very healthy. It appears the commutator decided to just melt off the backing material. This motor actually still ran, just throwing blazing white sparks everywhere. The discoloration of the copper next to the crater attests to the extreme heating that occured.

The brush cap from the left side, which simply failed open circuit at the event. Well, now the reason is clear why it failed open. Half of the brush conductor spring just sort of flew off and melted itself into the other side of the plastic brush holder.

The carbon brush itself was bouncing around inside the motor.

Another view. That bit of spring must have been pretty hot to instantly melt itself into the plastic.

And another view of the copper droplet that is the commutator. Oddly enough, the windings themselves seemed for the most part to be just fine.

Here’s Überclocker looking decrepit on a table. Since a robot with no motors is akin to a dog with no legs, or a fish with no fins, I began the quest to search for a… well, more legitimate motor. That’s when I remember that I found these, from Way Back.

DeWalt drills are classic musclebot motors. Sadly enough, these were of different voltages (!?), which not only surprised me as to how on earth their previous user expected their creation to move in a straight line, but saddened me because I… well, want mine to.

It was enough to perform a fit test and draw up plans to modify the gearbox to accept these motors while UPS channels their Brownian Motion to get a matched set of motors to me. They are the “new” DeWalt motors, where “new” is relative to 2003 or so. These drills have 3 speeds and are infinitely more of a bitch to mount. So I will only be using the motors in my custom frakenb0xen.

Fit test. The good news is that these motors are roughly the same length as the 700-size HTI motors, but a little fatter. No issue, considering the gearboxes have plenty of wiggle room.

The gearbox modified to accept a DeWalt motor, with its Alien Technology Motor Pinion of neither metric nor Imperial tooth pitch. Needless to say, this will be removed and the HF motor pinion crammed on in place.

So am I over-motoring the HF drill gearbox parts by putting a real motor on them? Perhaps. However, I think it’s a legitimate move in a 30 pound robot, because the laws of physics dictate that I can only put so much power to the ground. I’m mostly after the “real motor” bit, not so much increased drivetrain power, because the robot doesn’t have the traction to use it.

With motors now on the way, this conversion ought to go quickly since I’ve already drilled the new mounting holes to accommodate them. Überclocker should then be able to attend more events.

The (Possibly?) Final Chapter in the Tragedy of the LOLrioKart

So by now all ya’ll have probably heard of this.

While the details surrounding the citation were totally illegitimate and imply a degree of recklessness that was not present at all, the bottom line is that the kart is not going on any more open road adventures until it’s legit. And by legit, I mean registered and insured and fully street legal.

Whatever measure this takes, it will happen. It will simultaneously the most confusing and most glorious thing on the planet.

But the good news is that through two weeks of intense demos and driving during Orientation, the kart didn’t explode. The motor controller, version 6, is more or less stable. That’s huge. That’s like, me doing something right in electronics for once.

Of course, if I actually run the numbers on the electrical characteristics of the power converter, it would probably make real EEs run away to vomit. But the kart has survived more than twenty power cycles without misbehaving, save for the flakey DC-DC converter that caused the initial failure of version 6. A replacement module with better-designed (read: existent) filtering solved the problem.

So I’m satisfied. There will be little active work on LOLrioKart this term, with most of the fleeting effort concentrating on the battery system. After said weeks of operation, two cells in the battery pack are now just resistors. I regularly saw the voltage dipping under 45 volts on acceleration, which is concerning to say the least. Battery management solutions are condensing around me, so I may make the jump to lithium iron phosphate cells.

Now let’s move onto the new shiat.

This is a Xootr Street push scooter.

Gee, that looks kind of like every other push scooter on the planet. You know, like a Razor scooter. I thought you already had one of those? With like… a motor on it, right? That you built? I heard you built a motor. Can you show me how that works? Can you build me one?

… </average_miters_visitor>

Oh, that’s the difference.

As much as I love RazEr when it works, it’s time for me to realize that it’s too freakin’ small. I’ve managed to hit the tiny-but-functional goal, and at the same time the maximum recommended rider weight a few times. With some more scrupulous design, I could probably fit more batteries in there, but otherwise all the useful space is essentially occupied. And while 5 inch wheels are great for shoving your average copier motor core into, they are not great for shoving into your average pothole.

I need something bigger. More legit™. So thanks to MITERS for coming up with an engineering sample of the Xootr Street. I won’t actually be making any mods to this one, since it’s … not mine, and stuff.

This thing measures a bit over 3 feet long when fully deployed. The wheels are 7 inches in diameter and cast aluminum. It’s the smoothest thing ever on the ground because of the large wheel-to-bearing diameter, which minimized rolling friction. And the deck is absolutely enormous….

… and HOLY MAGNESIUM JESUS ON A STICK. It is in fact CNC machined from billet aluminum. These guys are just like me, except with infinitely more style. A scooter? Made from real metal?

And the 10 center-side pockets are just big enough to comfortable seat two A123 26650 cells apiece! How about that. 20 cells yields almost 150 watthours of battery pack energy.

Ground clearance check. The deck height, oddly enough, is almost the same height of the Razor A3 frame. The wheel line is just an inch and a half or so higher to fit the 7″ wheels. Overall, as can be seen, there is about 1.25″ of “fiddle space” from the bottom of the deck (not including the pockets) to the top of the 1.5″ parallel.

This is good, because hiding all the goodies under the vehicle frame contributes to vehicle aesthetics and the illusion that something which is not supposed to be motorized is moving under the directive of an unknown force.

There are no motor drawings or plans for this yet, but the profile of the wheels and their spacious internal diameter make them amenable to stuffing axial flux coreless motors inside, maybe even one per wheel. I’ve been itching to build a real surface-wound (no iron core) pancake motor for a while, but have been put off by their complexity in manufacturing.

As more details condense from the bot-aether, I’ll give this project its own page, category, and possibly a snappy and witty name. This is not a high priority project, as I don’t even have the vehicle yet, and it might spill over into Spring term.

Spring is a better time to blaze around anyway.

Now Announcing Project SEGFAULT

Segways.

A bad pun on the word segue. A fundamentally unstable faceplant-waiting-to-happen of an inverted pendulum. A cool exercise and great demonstration of basic control theory.

DIY balancing personal transporters have been attempted and perfected many times before. It’s almost passè. There’s even instructions on how to do it and code for your choice of microprocessor. All you need is two fat motors, a rate gyroscope, an accelerometer, and determination.

The whole thing about “microprocessors” is what has been putting me off. I like to think I’m familiar with mechanical engineering principles. I’m shake on electronics and EE. But I’m the last person you want to ask about anything software related. I hate software. With a passion. Even though I use it ALL day, I shudder to see what goes on under the glitzy Web 2.0 interface, or under the ultrasonically-welded sealed cap of an Atmel chip.

…so that’s why I want to do it all in ANALOG ELECTRONICS.

That’s correct. Op amps, comparators, linear components, passives… it’s a 6.002 (or 6.101) paradise. I stochastically arrived upon this idea near the beginning of the term, but it took a few weeks before I took it upon myself to do some research on gyros and accelerometers, and sketch out a rudimentary control network composed primarily of rail-to-rail op amps.

Then I remembered that Dale had built an analog balancing robot, so naturally I read the site and discovered I was doing it totally wrong.

I have a sneaking suspicion that a relatively non-chaotic differential equation like the one that governs inverted pendulums can be pretty easily translated to a continuous time control system (analog, as opposed to a discrete time digital control system). The idea as a whole is to have a purely analog, continuous-time front end controlling a Class D amplifier, also known as a switching amplifier or if the output is bidirectional a locked antiphase amplifier. Basically this just means your transducer wiggles back and forth really quickly… but some times more in one direction than another, so the summation of the movements is a velocity.

But Charles, isn’t a switching amplifier a digital thing?!

Yeah, if I implemented a real linear motor driver, I would have a battery life of 30 seconds and require heat sinks the size of Hannah Montana. Sssshh…. don’t tell anybody.

With the plan now more grounded (HURRRRRRRRRR PUN) than before, I’m moving forward with the mechanical details, as I always tend to do first. Once I have a rolling frame, I could conceivably roll analog or digital, or mixed-signal. As always, this entails a trip to MITERS and a few hours of mining for parts.

Yeah, so it’s nothing much yet. I grunged these 9″ pneumatic tires for the project as they were the only two matching wheels in MITERS that weren’t already on something.

9 inches? Isn’t that a bit small (&thats_what_she_said;) ? It is, but there’s nothing fundamentally wrong with having smaller wheels on such a machine. It just makes obstacle negoatiation tougher. If anything, I can get away with having less torquey motors because of the increased mechanical advantage.

The design work continues! After I get my control theory a bit more in line, I’ll sketch up a schematic of what I think should work. There are endless supplies of linear circuit components at MITERS and kicking around the EE labs for experimentation. I have accelerometers and gyros on the way from Sparkfun for experimentation.

…Oh, that’s the other cheat here. Real, modern MEMS sensors. I’m going for the analogginess here, not period-realism.

SEGFAULT will get its own page and category as it develops. This is my number one goal for the end of the term, and I’m actually going to try to get the controller graded. Here goes… something!

The Eternal Tragedy of the LOLrioKart

Aug 17, 2009 in LOLrio Kart, Project Build Reports, Reference Posts

The saga continues.

There are three reasons why I work on the kart more than any sane person world. The first is if I’m not doing anything else at the moment and need a distraction from the tribulations of life. The second is if I’m preparing for an event or situation where it would be publicly seen… after all, a working model is better than a nonfunctional sculpture.

And the third is if I have a neat idea or cool part and it HAS to be implemented NAO.

Like some instrumentation. Because operation of the kart is always a game of power electronic dice, I decided that some kind of readout of system conditions was necessary. It just so happened that MITERS had some old skool panel meters hidden deep within its bowels.  There were a few interesting options, such as a leak rate meter… what on earth does that measure?

I decided to start with a simple battery voltage monitor, since I had no convenient Hall Effect sensor,  shunt, or other low-value resistor (besides the SwapFETs’ incredibly low 2 milliohms) or a real constant current supply to calibrate a current meter.

A semi-known fact is that most ammeters are in fact sensitive voltmeters. While it’s easy to make a loop of wire and a magnet respond to 10,000 volts, it’s not nearly as easy to do with 10,000 amps. So a resistor game is played to turn the 10,000 amps into a very small voltage, like 100 millivolts or something. Enough to tick a needle on a voltmeter that has “10,000 amps” written on it.

You can easily convert an “ammeter” to a voltmeter if the “full scale deflection” voltage and current draw are known.

I settled for this meter for the voltage monitor, since the other one actually says amps on it. This one measures “Current-volts-microns”.

I have no clue what kind of SI unit that is, but it was the winner because of its simple 1-millivolt-per-tick scale.

So let’s convert this 100-mV meter into a 100 volt meter.  To not explode the meter, it should span a voltage of no more than 100 millivolts (0.1V). In a 100 volt system, that means 99.9 volts must be dropped across a resistor in series with it before it’s connected to the circuit under scrutiny.

The meter drew approximately .5 milliamps (0.0005 amps) at full scale deflection. So the resistor in question must drop 99.9 volts while passing 0.0005 amps. Now just pimpslap Georg Ohm and you have the resistance value needed – (99.9 / 0.0005) = about 200,000 ohms. Actally 199800, but I didn’t have one of those, and the kart isn’t going into space or something.

…yet.

Zip tied to the kart.

Through this meter, I found out that the batteries drooped in voltage under a good hard launch from 61 volts (freshly charged) to about 56. So they’re not too dead.

Or they are, but even being completely fucked are still awesome just by virtue of being cacknormous.

In a continuation of Reason #3, I found a road blinkie. You know, those things on top of orange construction barrels. It contains a few amber LEDs, runs off D-cells, and automatically switches on and off via photocell.

Well that was easy enough. A half inch bolt threaded through a spacer and into the mounting point of the light and I had improved the road safety of the kart hundredfold.

Let’s move onto more imporant things. For the past while, the kart has been randomly cutting out. The 12 volt DC/DC converter has been resetting for apparently little reason – not just under acceleration, but even sitting still. I wasn’t sure what was causing it, but suspected some sort of transient effect scaring the DC/DC unit.

In tearing down the electrical system, I decided that it was a good time to build a more legitimate motor driver.

It was time to get away from the cobbled-together hardware PWM generator. Producing signals in software makes for a much more versatile controller that can be reconfigured easily. I happened to have some Arduini kicking around, and a Protoshield kit leftover from last year’s Überclocker build.

Rounding out the components is an IXYS 6 amp dual gate driver with isolated high side. Using a halfbridge driver like this lets the controller perform regenerative braking. The high side required an isolated power supply, so I yanked out this 12v-12v DC/DC converter-converter from another motor driver board. I wanted some more electrical isolation between the fragile microcontroller and the harsh environment of my non-EE projects, so I salvaged some optocouplers from some weird board that had to have been made in the 80s.

Finished a few hours later.

I was able to use the Arduino language’s built-in PWM command, so the software was extremely simple. Normally it operates at 500Hz – far too slow. But changing the timer/counter initial counts causes the PWMs to run substantially quicker. I ended up going with the 4kHz option.

The two gate outputs are on the bottom side of the board. The left is the high side, and the right is the low side. For now, to keep backwards compatibility, I left the high side unconnected in the kart.

Scoping the gate driver outputs. This was using some test code where I had independent control over each channel. The waveforms look good, except for a bit of twanging in the high side, which I suspect is just a ghetto scope probe.

Making the driver board fully modular meant that the system wiring could be cleaned up substantially. Before, I had a mess of signal wiring and power wiring all meeting at the terminal strip. However, I could now devote the entire terminal strip to power connections. The system DC/DC converter (a 12 volt, 3 amp unit) fans out into 5 outputs now, so I don’t have to try putting two wires into one terminal. Overall, everything became more organized.

So did it work?

No, of course it all blew up. The problem obviously does not lie within the gate driver system, because everything worked fine for about 20 minutes. Then the aforementioned DC/DC converter began repetitively cutting out.When it dies, the entire kart shuts off because the contactor opens up.

I had gotten into the bad habit of curing these brownouts by hard-cycling the battery switch to reset the converter. It worked a few times.

Then when I hit the switch again, the drive FET made a muffled popping noise and the kart jumped for a split second. Then all was quiet.

Okay, so this explosion wasn’t as spectacularly fire-filled as the other 5 or 6, but I still have to remove the whole electrical system to replace the brick. Amazingly enough, the gate driver assembly survived the whole ordeal.

Explanations that my EE friends (who still refuse to just build me a working controller, eh guys?) offered up include transients on the 12v rail resulting from inductive spikes coming from the contactor, or the lack of a local bypass capacitor  on the input side of the converter causing very short voltage dips to shut the converter off.

Either way, the DC/DC unit is now the problem child. The ghetto moves to another part of the city.

At least I got this cool Volvo dashboard gauge cluster  for free at Swapfest. Sort of defeats the purpose of me adding my own voltmeter.

The Ongoing Tragedy of the LOLrioKart

Jul 20, 2009 in LOLrio Kart, Project Build Reports, Stuff

The next “broke” cycle has arrived. Once again, it’s (you guessed it) the motor controller, under mysterious and  nonintuitive circumstances.

But first, I am proud to announce that the kart is now able to stop.

That is, in under half a block’s distance.

Here’s the reason why. I bought a set of 140mm disc brakes and cable-actuated brake calipers from electricscooterparts.com, which incidentally sells all kinds of electric scooter parts. Now that I know that things like this exist, I wonder why the hell I didn’t spec them out for the kart originally.

Oh, right, because I didn’t know they existed. The quality of components seems to be about par for Orient-imported small vehicle parts; by which I mean the brake disc vent holes had burrs around the edges, the bolt circles were not quite concentric, and the left and right brake calipers were, while sharing the same mounting dimensions, different parts physically beyond being simple mirror images.

So it was out with the old and in with the new. I dismantled the front wheel assembly on each side and cleaned everything off.

The inside of the wheel rims were thoroughly caked in small brake band particles. The fact that there was little in terms of brake left over on the bands themselves probably contributed to the kart’s dismal stopping ability (read: none).

So extremely bald front tires.

The tread was not exactly deep on them to begin with, but all the rough handling, skidding, and serendipitous toe angle of the kart has essentially vaporized the tread off the tires. The rubber thickness is still adequate, but I just shouldn’t be driving in the rain.

Then again, there are bigger problems to expect if I try to drive in the rain.

Integrated wheel-o-brake hub, to be made from hugeluminum round stock. It carries the bolt pattern for the cheap wagon wheels on one side and the brake disc on the other, and is bored for a .5″ bore R8 type ball bearing. I tried my best to perform an interpolation of the intended bolt circle diameter using the three bolt holes on the brake disc.

Here’s the hugeluminum billet in question, set up in a position ripe for disaster. Real machinists and South Bend lathe lovers avert thine eyes.

I needed to turn this billet into two smaller billets, but our horizontal bandsaw was broken, the N51 auto shop’s was optimized for steel cutting, and I was not going to wrestle this through a conventional bandsaw. The last option was chucking it in the lathe and parting down the middle, which filled my imagination with vivid images of tooling setup explosions and broken back gear teeth.

However, with judicious use of centers and power crossfeed, disaster was averted, and I had two equally sized not-hugeluminum billets.

A little while later, a hub emerges. The bolt circle was drilled using my handy dandy indexing fixture.

Test mounting everything. Surprisingly, taking the average of the three bolt radii resulted in a disc that was centered with minimal wobble. It almost makes me think they did it on purpose or something…

Nah.

It’s time for Pretend-O-Brake. Here is a setup testing prospective brake caliper mount positions. The brake caliper was designed by real engineers, so there’s not a single straight line on it to reference dimensions from. Mounting it would be a nontrivial matter, so I decided to resort to some cheating in the form of the abrasive waterjet.

I designed a caliper mount based off existing part dimensions and alot of caliper-balling (eyeballing the dimension measured from an imaginary line projected off the end of your caliper tips, directed towards the feature in question).

Here’s the designed part. Just for kicks, I threw it into Inventor’s built-in ANSYS stress analysis add-on to see theoretically what might happen if I brake too hard. The verdict is that I could make this part out of jello and still have it be able to lock up the front wheels and skid.

Alright, so not jello, but at least birch plywood.

The mounting points for the calipers are slotted such that I have an ability to adjust them a small amount if I found that caliper-balling wasn’t enough.

A few hours later, parts cut out of some leftover half-inch aluminum. Abrasive waterjets are beautiful things.

You know that extra hole next to one of the caliper mounting slots? That was originally for a design-on-the-fly widget to connect the caliper mount to the steering pivot block. However, when I performed a test fit, I realized that I could just cut out a step in the caliper mount and have it slide over the block in question. Square objects cannot rotate over eachother by nature, and the Nut of Wheel-Retaining will hold everything in place.

Well then. Cutting down a portion of thickness is certainly easier than making two more whole parts.

The end result is a quasi-floating brake caliper. Better than a fixed one, IMO, in taking up for the lack of alignment inherent in stuff I build.

All mounted up. The spacer length between the wheel-o-brake and the steering pivot block required a bit of trial and error to get right, but once everything was cranked down, the assembly was solid.

Another view of the assembly, all cabled up.

And now duplicate for the other side, accounting for chirality.

It turns out that real brakes stop moving objects substantially better. I was able to lock up the front wheels and skid during runs in the hallway – sort of the opposite extreme of not being to stop at all, but at least I have the choice of locking up or not. The tires have substantially more traction outside on concrete, and I was not able to lock up (without stomping excessively hard), but that’s a good thing. Stopping distance from top speed was reduced to “under the length of the N52 parking lot”, scientific tests be damned.

Overall, I consider adding brakes to the kart a great success.

Guess what? It’s SWAPFEST time! LOLrioKart has been the unofficial promotional vehicle for Swapfest since May. This time, I could show up and have a fighting chance at not extensively damaging property or causing wanton personal injury.

Then I

Well, I sure as hell didn’t, but something did. I put the kart in a Prominent Advertising Position™, then went around to gather cruft. When I returned to start putzing it around, this happened.

As soon as the battery switch was engaged, the precharge resistor set on fire. This tells me that the ESC is stuck wide open, and so the Etek tries to drink all few hundred amps of its stall current through a 50 ohm, 1 watt straw. It, in turn, does not last long.

Because the ESC was damaged in the ON position, I elected to not hit the contactor button. At that exact moment, it would have taken off and landed in a pile of server parts. Servers are fundamentally more expensive than anything on this vehicle.

And thus I kept the kart off until I grabbed a friend and rolled it back into MITERS. I have not yet opened up the electrics to see what went wrong (besides it existing in the first place), but my suspicion is on the gate driver again.

Anyone have a real, 60 volt commercial DC motor controller of over 300 amps capacity they want to donate to the cause?

Swapfest finds

Swapfest is always an interesting adventure because of the variety of people it brings. By variety, I mean old ham radio enthusiasts. However, the distribution of cruft and oddities is quite Gaussian in nature. There’s tons of the usual – electronics supplies, small discrete components, computer parts. A steady amount of the esoteric but not out of the ordinary, such as vacuum tubes, antique radio equipment, and random shit from someone’s attic/basement/garage/hole-in-the-ground. But every once in a while, you stumble upon something that is so weird or awesome that “Holy Iridium Jesus” is the only proper response.

This is one of those finds. I was told that it is a military aircraft radio component of some sort, an early form of spread spectrum radio called a data translator. I prefer to call it AWESOMSESAUCE.

I didn’t have a real camera available, so the multi-kilopixel cell phone camera has to do. But I think the astonishing engineering detail is visible even from here. The thing is packed solid with conductors, tubes, motorized digital-to-analog converters, and crazy components that I don’t even know the function of. Seriously. A motorized DAC. It even has NUVISTORS. I don’t even know what the hell NUVISTOR is, but it sounds badass.

This is from an era when mechanical engineering and electrical engineering were truly intertwined and engineers had to have a deep understanding of eachothers’ practice. This is not like “mechanical engineers design a structure and the electrical guys slide a board in”. This is “your product is so incredibly part-dense that your fucking components are structural members.

I stand by my position that old people, no matter how weird they smell, are more hardcore than my current generation will ever be.

The only specs that my 3G-enabled friend could dig up was this milspec, which doesn’t really say anything besides “register for our website”. Anyone know what on earth it is?

At the $60 quote price, I was tempted to buy it just so I could put it in a display case. But a display case hardcore enough for this thing would have to be made from cast magnesium with solid hand-refined fused quartz windows and lit by radioactive phosphorescent compounds.

Anyway, to return to Earth, I got a few things that I could, you know, actually use. Past the supply refills for MITERS, I got this box of giant transistors.

A scan of the datasheet when I returned ousted them not as FETs, but IGBTs. Because the ginormoFETs that I bought at Swapfest the last few times were dubbed Swapfets, these are now Swapbutts, because IGBT is only properly pronounced “igbutt”.

The total count is

3x 1000v, 200A

1x 1200V, 150A

and a single 2000 volt, 300 amp unit. H00t.

I also got a Hot Wheels RADAR gun. This is a real RADAR gun, but with reduced power and sensitivity so small children can bite it.

Maybe now I can actually find out how fast I go? It’s also fairly hackable.

The Neverending Tragedy of the LOLrioKart

Jun 28, 2009 in LOLrio Kart, Project Build Reports

It has been an eventful few weeks.

I started at iRobot as a summer engineering intern, tasked with building Terminators.  I was invited along, and subsequently went to, the Buckminster Fuller Challenge award ceremony in Chicago with Smart Cities.

And I finished, broke, finished, then broke, then finished LOLrioKart. I’m waiting on the next “broke” cycle.

Let’s start with a batterygasm.

From the deepest dredges of “Well, they technically never asked for it back”, here is a pile of A123 lithium nanophosphate cells. These are the most ballin’ shit in terms of batteries available today.

The backstory is that A123Systems, through its ancient ties with MIT, donated Over 9000™ cells which failed quality control to the Electric Vehicle Team. The Media Lab also received some for sampling, and being Smart Cities, we quickly snapped them up because… well.

Anyway, I was tasked with the fantastic task of determining what “failed quality control” means. For the most part, it means “smudge” or “wrinkle in the cardboard”, but a few cells were genuinely low voltage or had high internal impedance. Through a series of trials and strictly controlled processes involving a giant power resistor, car battery, and multimeter, I determined that essentially 95% of the cells in each case of 100 were most likely good for our purposes.

Great news for us, better news for me, because A123 probably has more.

Anyway, to equal the 54 volt, 30AH nickel batteries I already have (nominally – these cells are totally fucked and probably return less than 20AH as a pack), I would need about 225 cells – 15 cells in series for a nominal 48 volts, and 15 cells in parallel for about 33AH. The reason I calculated the numbers for 48 volts is because I do have access to 15S chargers for the chemistry, from the car. That’s something like $3500 in batteries if I were to drop some cake for it.

Or two boxes of cells. Come on EVT, you know you want to donate some to The Cause.

In order to resolve the “dude, what the hell is 42 volts doing on my frame?” issue, I stripped the entire electrical system down and pretty much rebuilt it. At the same time, I took apart the back end for cleaning. If you’ve never seen the kart’s running gear, here it is.

While rebuilding the electronics, I decided to try to minimize the footprint of the ginormoFET controller. Here’s the dismantling in progress.

And here’s the completion.  By stacking the busbars, I gained a few square inches more… board space? Deck space? Scrap-of-plywood space? Additionally, it was easier to arrange the wiring to suit the rest of the electricals.

I decided to forego fan attachment until heat was determined to be a major problem.

Contactors donated to The Cause by another MITERer. They are rated to switch 100 amps. In theory, they should never be switching current in my electrical system, merely passing it after closing. Switches tend to conduct far more current in a circuit than they can reliably close or open, so I’m not concerned about melting the contactor.

Also included in the deal is a Hugeasspacitor™. 33,000 microfarads of love at 75 volts.

Most everything in place. I mounted all components with short wood screws this time, which saved alot of drilling and… yes, threading of wood. That was such a dumb idea that I only could have done it at 4am.

The DC key switch is a battery cutoff switch, and isn’t intended to actually turn the kart on and off.

The power system has two stages. First is the closing of the battery switch with the contactor still open. A resistor bypasses this contactor and goes straight to the controller, which allows the Hugeasspacitor™ to charge at a reasonable rate.

The reason for this precharge resistor is, without diving too much into Course 6 theory, that capacitors appear as an instantenous zero-resistance  to a sudden step in voltage. You know, like closing a switch really fast. What that means is if I just threw the capacitor onto the battery, there would be a Big Spark as infinity amps tries to flow into the cap at once. The problem is that if the cap is now charged, there is still infinity amps trying to cram into it. Not good for the capacitor, and especially not good for whatever poor switch gets caught in the middle. It’s easy to weld contactors like this.

So the second stage of the power electronics is powering the contactor, which opens a very low resistance path. I can now drive off into the nearest oncoming semi.

A 12 volt DC-DC converter provides the contactor current. This is placed before the resistor but after the switch so I can run accessories without the main controller being powered.

Alright, a furious night of building and debugging without pictures later, and here’s the system ready for a test run. The night was mostly consumed with debugging my dumb hardware PWM generator that I pledged never to make. Because it’s on a breadboard, there were Over 9000™ things that could have been wrong with it.

It ended up that my comparator was dead. After tearing the whole thing apart to discover that, I threw on a new comparator, coated the board in hot glue, threw it on the kart, and called it a night.

The safest way to perform a test run is of course to strap a 36 volt 10AH lithium polymer pack right under your ass.

A beauty shot, if you stretch the definition of “beauty”. Notice the emergency stop button. This is the contactor controller.

Yeah, yeah, testing… It was late and nobody wanted to grab the camera. So LOLrioKart sails down the hallway successfully. In this configuration, I drove it to Swapfest the next day for some lulzy in-field testing.

So I couldn’t resist. I had to put the voltage-leaking Nicads pack on the kart, because there wasn’t another way to get greater than 36 volts. My DC-DC converter, rated for 48 volts, shuts off exactly at 36. What’s the nominal voltage of the lithium test pack? 36. If I floored the throttle, the kart would turn off.

Not exciting.

Before throwing the packs back in, I thoroughly coated the bottom of each pack in rubber sheeting, just in case I missed a spot and metal touched metal while in the basket.

Despite my efforts, there was STILL live voltage present at the frame. How’s about them electrical gremlins?

However, it was a high impedance leak, so I wasn’t worried about shorting something through the frame. I decided to go ahead with this installation.

Scoping out a(nother) PWM generator problem. I went through FET driver chips like crazy, for reasons totally unexplainable; not even the resident EEs could figure out what I was doing wrong.

The voltage leak was ruled out as a cause because the DC-DC converter provides voltage isolation and no component is frame-grounded. That I know of, anyway.

Out-of-range operation was also ruled out, since I’m running the chips at less than half their maximum voltages. The FET gate had a bleed resistor and the throttle input has an RC filter inline.

Transients were the main suspect, so I arranged some more low-value caps around the important parts.

It seemed to be stable. Time to figure out which way the motor is supposed to be hooked up!

This is what we call “Nope, it hooks up the other way”. I like where this is going.

Alright, so maybe not this picture, because “where this is going” was straight backwards into a shelf.

Giving the nicads a wakeup charge. By virtue of sitting for two weeks, some of the cells have fallen back to zero volts.

That’s how totally fucked they are.

Using the HOLYCRAPWHATISTHAT, I dumped 25 amps into the cells, which is pulling something like 1600 watts.    After an hour and so, they were nice and warm.

Totally the most legitimate throttle pedal ever. That’s a spare bettery switch key zip-tied to a bike hand throttle zip-tied to the frame.

Video time! I decided this was legit enough to take on the streets and have some fun, so I drove to campus and found some testing grounds. It had been raining for two weeks at this point, and I couldn’t really hold it in any more.

Afterwards, I decided this pedal was just not legit enough to keep, and that my scooter needed the throttle back really badly, so I fabbed up a pseudopedal. It’s not really any more legitimate.

I had a “resistive throttle box” already, so I just scrounged some parts from it and assembled them onto a mount I cut out long ago. While it’s functional, the positioning is the least ergonomic thing in existence. I kind of have to side-roll my right foot onto it.

Alright, so it’s good for now. Time to start working on the priorities, like…

…instead of, you know, functioning brakes.

Seriously, the little band brakes have deteriorated to the point that stopping doesn’t really take less distance if I completely step on the brake pedal. They really were not made for the task of stopping a 350+ pound vehicle at n miles per hour, where n is between 20 and 30.

And so this is how the kart was set up for its first ever road trip, from MITERS to the extreme western tip of campus, a distance of roughly one mile each way. No video is available due to it being completely spontaneous

I’m clearly still alive. More work to come, like BRAKES.

The Summer Build Season 2009

Jun 03, 2009 in LOLrio Kart, Nuclear Kitten 5, Pop Quiz 2, Project Build Reports, Project RazEr, Stuff, Überclocker Remix

It has begun.

While I seem to be in “build season” mode year-round, it is during long breaks with little in the way of academic or life obligations that I get the most done. Last summer, I began work on LOLrioKart and built Überclocker, Pop Quiz 2, and Nuclear Kitten for Dragon*Con.

… which sort of sucked horribly for everything. Except NK, but only by about *this* much.

So what’s coming down the projectubes this summer?

Mostly the same thing. D*C is my biggest bot-celebration of the year, so once again the combat robot fleet takes high priority. Since there’s really just one robot that needs rebuilding, I also have the usual pile of small electric vehicle projects, of which only one is actually urgent.

Übercløcker RЭmiχ

I started redesigning Uberclocker some time in the fall of last year, hoping to get it done by Motorama 2009. Of course, due to scheduling concerns and logistics, this didn’t happen. But what that presented me with was the chance to put it away and not look at it for several months.

This is pivotal. The basic design has already been hashed out, but now I get to return to it after not thinking about it for a while. I am now in the process of analyzing the 3d model for any “impossible objects” that I might have included, or Really Bad Ideas. Such design flaws plagued the real life Uberclocker 1.0 at D*C last year.

Planned upgrades from 1.0? Well, besides EVERYTHING, the primary focus is on drivetrain reliability, center of gravity, and the upper clamp arm.

As a member of the pushybot school of combat robotic thought, I value maneuverability and driving above jawesometacular weaponry. Uberclocker 1.0 had a strange serpentine timing belt setup that seemed like a really awesome idea at 5 in the morning, but… wasn’t.

The robot also suffered from “centrally located center of gravity” syndrome at the event. While a CoG near the geometric centroid of the robot is good in practically every other case, the fact that the bot’s sole purpose was to grab another opponent and lift it off the ground meant that it just sort of faceplanted every time I attempted a lift. Not a very impressive show. The redesign lengthened the wheelbase of the bot, and selective weight reduction moved the CoG back about 4 inches, without additional ballast.

Oh, that’s right, Uberclocker 1.0 weighed in at an incredible 22.5 pounds out of 30 at the event. I’ll fix that too.

What I didn’t really get to (properly, anyway) in the redesign was the upper clamp arm. The previous arm was both weak and structurally unsound. While I think I took care of the “unsound”, I still have my doubts as to the clamp mechanism’s effectiveness.  In the past, clampbots have used pneumatics to actuate the upper half of the clamp. This is advantageous because a pneumatic actuator requires no “holding power”, unlike an electric motor, which has to be continually powered to produce torque. Pneumatics also have a certain amount of spring-back ability that a solidly coupled electric actuator doesn’t.

But robot-heaven forbid that I make Überclocker even more complicated by incorporating a pneumatics system for the one actuator that might need it. Thus, I’m still partial to a (spring-coupled) leadscrew-type mechanism, over the current design candidate’s motor-on-a-weird-gear. Except this time it won’t be driven by a beetleweight motor.

I intend to keep the “Chinese puzzle” frame, and will be refining it for ease of assembly. I devoted a few weeks to just fabricating the frame parts last time – no, never again. That’s what computer-controlled machine tools are for.

Pop Quiz 2√2

Incidentally, 2√2 is about 3. Not quite there, which also describes this planned rebuild of Pop Quiz 2. It’s not quite a complete conceptual revision, but there will be significant upgrades all around.

PQ2 is one of the (if not the) flattest 1lb class robots around that has an active weapon. It hits lower than some undercutters. The problem is that going the extra 1/8″ down in this current design meant that I had to ditch practically all the well-known, battle-proven parts – Sanyo gearmotors, SPEKTRUM 2.4ghz receivers, etc.

It was a fun thought experiment come to life, but the robot had a horrific reliability record, almost no reception due to the FM ground-band receiver, and a 5 minute chopped hack of a master power switch that ended up disintegrating after exactly 1 hit at D*C 2008. Pop Quiz had about 15 seconds in the arena.

Not cool. For ’09, I am INCREASING the height of the bot. Me, making a robot taller. How many times does THAT happen?

The robot height will be increased to about .400″, enough to cram in a set of real Sanyo micro gearmotors. The rest of the robot’s electrical system is sound, and so is the weapon motor. I’ll most likely end up reusing the electronics anyway, minus the cheesy little FM park flyer receiver. Instead, it will be swapped out with the latest Spektrum DSM offering, and I will run one transmitter between all the robots.

There’s no current virtual model for PQ2.8284171, but just imagine the current bot 0.025″ thicker.

Nuclear Kitten 5.1 Digital Surround Sound Edition

I’m actually satisfied with the performance of one of my combat ‘bots for once. NK needs very minor rework to take another run at D*C. The weapon motor needs some magnet reglued, and the weapon pod pivot axle is slightly bent and needs to be made better anyway. Past that, I have a spare blade to replace the faceplant-into-steel-bumper bent blade.

The only point of concern with NK is the drivetrain. Despite having a mechanically isolated weapon, I’m still blowing drive gearboxes, just because the bot is that much more powerful. I might switch to something like the 50:1 Copal motors || redesign the motor mount || use softer wheels.

No frame changes are necessary, since the bot escaped D*C rather unscathed.

LOLrioKart

Since I discovered that the main battery pack was leaking voltage all over the place (somehow, through an eighth inch of rubber?), I stripped down the entire electrical system and tested all the batteries. It turns out that the steel casings of the cells are live, something which I’m fairly certain should never be the case. While it’s fairly common for the battery negative terminal to also be the casing, the errant voltages are always somewhere between 0 and 1 volts.

This case voltage doesn’t seem to have negatively affected the cells, but I’m fairly certain it’s the culprit behind stray frame voltages. Somehow.

The focus for LOLrioKart work will be the electrical system. I intend to complete and test the ginormoFET controller and possibly implement dynamic (or regenerative!) braking using the upper leg of the half-bridge. Mechanically, the kart is fine.

Well, except for the brakes, but they’ve always been undersized and insufficient.

Ultimately the goal is to run it for longer than 1 minute on all 54 volts, or the full pack voltage of whatever eventual power system I might come into. I’m heavily considering crating up LOLrioKart and shipping it down when Dragon*Con comes around, so I can drive it in the parade. This could possibly be the worst idea I have ever thought of.

Project RazEr

It’s been hanging on a utility hook since the last controller fire. Everything works and the batteries are still charged, so all I need is a BLDC motor controller. Since everything still technically “works”, I don’t intend to touch the scooter that much, if at all. Any work on it will be replacing the shell of the wheelmotor with something more substantial (and better engineered, and more reversably built).

Time to get crackin’.