Archive for the 'Pop Quiz 2' Category

 

Pre-Everything Updates, August 18

Aug 19, 2011 in Bots, Land-Bear-Shark, Pop Quiz 2, Project Build Reports, RazEr rEVolution

I’ve been slowly knocking down the amount of half-taken-apart projects that have been taking up table space at MITERS. The usual shipping delays and distractions means I’m a little behind where I want to be,  but it’s not yet concerning. In other words, nothing has yet gone horribly wrong.

As of today,

  • Fix Überclocker!
  • Repair RazEr battery!
  • New motor controllers for LBS!

Pop Quiz 2

I received my shipment of carbon fiber from Dragonplate and proceeded to cut the top and bottom panels out on the same day. The CF this time is 0.023 instead of 1mm, so I lose some stiffness in the frame. I’m not quite sure why I chose the thinner panel actually – the scrapped PQ2 frame had 0.039″ CF top and bottom plates.

This was certainly one of the cleanest CF cuts I’ve made to date. I took several precautions this time to minimize delamination around holes and pierces, including fully double-sided-taping the carbon fiber to a solid wooden panel. Previously, I have either just clamped the CF to wood or taped the CF to a waterjet brick. The full support of the wood layer beneath the CF helped immensely – these cuts have almost no delam areas. The other methods would either allow the CF to flap up and down or still leave high percentages unsupported on the bottom.

The upside to this method is that I get a cute MDF billet Pop Quiz out of the process at the end. This was the backing for the carbon fiber after I stripped off the wet tape.

With Pop Quiz’s frame all printed and the CF panels cut, it’s mostly a matter of sitting down and assembling the thing. I got the VEX motor controllers in and also found my spare Spektrum BR6000 from who knows how many robots ago. Because PQ will be an experiment in using the VEX controllers, I’m going to rewind the weapon motor for 7.4v (2S) operation.

RazEr rEVolution

RazEr is officially all closed up and working again – the only thing the battery needed in the end was a charge and balance. God I love A123 DeWalt drill cells. What other kind of battery doesn’t mind getting zero-volted for a month straight? I don’t doubt that I have had some lifecycle and capacity loss because of the extended flattening, but RazEr is not a very high current system anyway.

This is what the battery looks like after I ripped off the layers of soda bottles insulating the pack. There are 2 balance leads, but no actual power connections associated with them – my balance-capable chargers can’t charge through the balance connector only. So this whole pack was kind of unserviceable from the start.

It also has bare balance wires passing directly over cells, something I recently learned was a very bad idea.

The resolution for this pack was pretty simple – add those power connections. The two Deans connectors represent the upper half and lower half of the cell. This enables it to be balance-changed by 4chan every once in a while to keep the cells level.

To insulate the balance cable better, I laid a layer of rubber cement underneath them. That will at least immobilize the wires and also keeps them, for the most part, out of potential electrical contact. Due to RazEr’s limited internal width, I couldn’t reroute the cables to the paper sides of the cell, which is what I would like to have done.

The final result, after coating with Real Giant Heatshrink!!! instead of more Mountain Dew bottles. Working with this was very refreshing – this is the massive thick rubbery PVC shrink often used for enormous power cable repair and the like. It actually doesn’t look like I threw it together in 5 minutes.

The Advanced Beast-it-troller

They’ve arrived.

From last update, the independent-input H-bridge version of the Beast-it-troller is now ready for assembly. Both of my Digikey orders for required parts, most crucially the IR2183 gate drivers, arrived the same day. Will it work?!

I also ordered (and received, too) a spare CIM motor to replace the toasted one in the left side drive. With luck, Land-Bear-Shark will be running (…again) for this upcoming Swapfest.

It’s Time for Shenanigans

Aug 16, 2011 in Bots, Land-Bear-Shark, Pop Quiz 2, Project Build Reports, Überclocker Remix

Alright, now that I’m settled in 900 miles from civilization out on the west side of the MIT campus (seriously, how do people live out here?), it’s time to comprehensively update everything. Dragon*Con is now in approximately 2 and a half weeks. So, the flying objects have been temporarily suspended in favor of two more immediate goals which I mentioned briefly before.

1. Getting the robots running again, since I ain’t going to no Dragon*Con Robot Battles without no robots.

2. Repairing some of the random vehicles, since they (along with the robots) will be exhibited at the Atlanta Mini Maker Faire hosted at Georgia Tech in a few weeks.

I’m just going to start laundry-listing everything. First, the most interesting of the upcoming builds, a rework of Pop Quiz 2.

This was the state of the robot as of two weeks ago:

Yeah. It’s kind of trashed.

PQ2 hasn’t seen any action since Robot Battles 2008, and it lasted about 20 seconds in the arena then. So how on earth did it get so destroyed? Mostly because I kept pulling parts from it and then stuffing them back without closing the bot up. I’m sure it’s also been dropped a few times, and I might have also landed Clocker on it a few times too. Pretty sad overall; while the frame is perfectly workable, I don’t like the way the frankenmotors worked out (and one of them has been missing from the start). The offset wheel axles mean that I can’t just directly swap in a micro gearmotor or similar without making the wheels much larger. Oh, and all 4 lithium cells are dead. It’s a little easier to just start over.

What few people know is that PQ2 has been up for revision several times before, each time I ended up pursuing something else instead.  I designed a new version of the robot to be built for the 2009 Robot Battles, but didn’t get around to finishing it.

This version was to have a waterjet-cut aluminum frame and replace the frankenmotors with Sanyo micro gearmotors. I even got around to cutting the frame:

It was made out of 1/2″ aluminum  with the intention of machining it down to 10mm (.39″). Now that I look at it again, I wasn’t sure how this was supposed to be done.

Actually, no – I do know. I was going to actually make a fixturing block for it and then meticulously machine it in sections, taking out a subset of the fixturing screws as needed. And then I was going to turn the head of the Bridgeport mill 45 degrees to machine and drill the holes in the front. Then I was going to flip it over and carefully use a boring head to make the inset in the center for the motor mount.

I remember being hardcore like that. But now, in 2011, there’s a better option.

YES! It’s another excuse for me to abuse Make-a-Bot. For a while, I’ve thought that ABS plastic should be durable enough to withstand 1lb and 3lb arena combat. So this is a thought experiment (turned physical) that will use a fully 3DP frame, with carbon fiber top and bottom plates as before. The drive motors are still Sanyo micro gearmotors, and the wheels will be machined plastic things with silicone tubber tubing tread. \

Here’s the entire frame being fired off at once. 5 x 5 inches is still with MaB’s build envelope. However, given the geometry of the part, I didn’t expect this to turn out well – MaB has no climate control, so large parts still tend to warp. Especially a 5 inch long solid bar.

I stopped the build after noticing that two corners were coming up. Because the robot is so short, a millimeter of curl would spoil the ground clearance and wheel contact.

The solution was to just split the frame into 4 quadrants, such that the longest continuous span was 2.5″. This relieves much of the stress from the parts not being in thermal equilibrium. In the best case scenario, I’d have MaB in a closed heated cabinet at about 120 degrees Celsius or more. Then I could also make cookies in it!

With all four frame quadrants made, I’m just waiting on carbon fiber sheets and spring steel to arrive.

I might also rewind the weapon motor to run on 7.4 volts instead of 14.8. Originally, I did it to avoid running high current in the robot, instead choosing to run a higher voltage for the same power. After building vehicles, on something this small, the difference is trivial. Using the lower voltage would mean the Sanyo motors will be much happier (they’re native 5 volts!) and I’ll have a chance to try out these VEX controller units, which are the cheapest small robot control option I’ve seen, ever.

überclocker

Suffering another loss last year due to my lack of care for detail and “baaaah, it will be fine”, ‘clocker is actually functional otherwise. The left side gearbox slipped my inadequate press fit on its output shaft early in a match, leaving the bot mostly handicapped through the tournament.

I took the bot apart to extract the gearbox, but also to clean everything up and tighten screws. It was missing a receiver (which after some digging, turns out I borrowed to use on the cute little prototype Coasterbot), and one of the Victor 883s was not responding to signal. I found out why it wasn’t receiving signal very quickly after extracting it and pulling the servo cable out: the entire internal header inside the Victor came out with it.

Oops. Solution: Make a short servo cable pigtail that passes through the cable shroud so I can still connect to it. After this, it worked fine.

The gearbox fix was quick and simple: press out the spun output shaft from the planetary carrier, throw it on a lathe, and carefully knurl it. The knurling increases the outer diameter of the shaft slightly by introducing ridges and valleys. Then shove it back in with a tanker-load of 609 Loctite, some of the stiffest retaining compound there is. Knurling also helps make threadlocker and retaining compound adhesion stronger due to the same reason – it seeps into the gaps and is therefore able to coat more surface area.

I have no pictures from the knurling process since it was done at another shop (MITERS not having a knurling attachment for the Old Mercedes)

Past putting the robot back together (and driving it into everything at full speed, repeatedly), Clocker will not have any modifications made. I might turn the clamp motor around so it has more travel available, however – right now, if I don’t pay attention to where the clamping arm is, it tends to wedge itself in the highest position and the motor is then unable to free itself.

Clocker and Pop Quiz are the only robots I intend on bringing this year – NK got banged up nicely last time, and I haven’t rebuilt it yet.

RazEr rEVolution

Ahh, RazEr. This thing has just been *working*, though I’ve only really brought it out for demo events because of its concrete-hard wheels. However, Maker Faire ATL is a demo, so it’s time to turn the power on and test it for functionality…

…wait, what do you mean I left it powered on?

Yup, RazEr’s battery is now completely flat after being left on for what must have been a month or more. I need to take it apart anyway – the way the pack is set up, it’s impossible to charge using my R/C multichargers. I split the pack into 2 strings of 6 A123 cells (but run in series for 12 cells), however I neglected to break out the middle connection so I can actually like… charge it as two packs. Or balance it, or do anything really. This should be a quick operation.

Segfault

Another one of my finished things that just works, Segfault has also been a demo piece for most of this year also. The breadboarded controller is becoming incrementally more flakey, however – probably because breadboard. Sudden direction changes or even slowing down/speeding up quickly tend to cause noise which appears as a jerk in the wheels. I can anticipate and compensate, but it’s enough for me to no longer let other people ride it.  I have a desire to put the controller on an actual printed circuit board that’s fully integrated so there’s less messy wiring, but that is unlikely to happen in the next week.

However, it does need some minor mechanical attention. The steering column potentiometer is heavily biased rightwards from when I replaced it. The left side gearbox for some reason tends to slip its output shaft (What’s with me and half-assed gearboxes?) which, fortunately, is not a Charles-induced manufacturing fault this time. Segfault uses 2 Banebots P80 type gearboxes, and the last stage planetary carrier is connected to the output shaft with a double-D flatted bore, which seems to be prone to axial misalignment. Usually I can kick the left wheel back in and it reseats fine – not a critical mechanical problem, but still annoying.

land-bear-shark

You know I couldn’t leave this thing alone for long. Last time, I said I wouldn’t touch it until Winter. However, seeing as how it just rained, it’s now chilly outside, so I declare Winter.

As usual, I will preface a LBS post with a new motor controller. Another new motor controller.

What’s different this time? Well, besides it being the densest through-hole board I’ve designed to date (because why not), it uses the IR21834 gate drive chips. Watch that number there – it’s the independent input version of the 21844 I am fond of. This means the high and low sides are switched independently, but it still has built-in deadtime.

This frees me from the implicit braking of synchronous rectification if I’m too lazy to implement current control (which I am). I’m more accustomed to freely coasting vehicles, which the implicit syncrec of the 21844 does not let me do unless there is a current sensor and current control loop (such that the motor controller output voltage matches the motor’s back EMF)…but that’s more software.

With the 2183, I should be able to drive the high side switches only, while otherwise keeping the low side switch from  turning on immediately afterwards. This would let a vehicle, say RazEr, coast freely. Regenerative braking can still occur if I command it.

A vehicle like LBS doesn’t coast at all due to the high friction of the tracks, but this controller will be a chance to test the 2183 before I put one in a more serious application like RazEr. It’s already been sent out to Retarded Circuits for fab and should be here later this week.

I’ll also need to perform battery and motor surgery as outlined previously, but this should be coming down with me too.

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’.

Summer 2008 Build Season Wrap: Dragon*Con 2008

Oct 14, 2008 in Bots, Dragon Con, Events, Nuclear Kitten 5, Pop Quiz 2, Project Build Reports, Überclocker

About time, eh? This past summer, I continued my R&D position at the Media Lab while building three combat bots. Nuclear Kitten 5 and Pop Quiz 2 are updates to the insect fleet while Ãœberclocker is a completely new build, exploring new building techniques and technologies.

Sadly enough, PQ2 and Ãœberclocker fell victim to the age-old trap of trying too many new things and making too many changes at once, and not enough testing before deployment.

The final rundown after D*C 2008:

Ãœberclocker

What can I say? While Ãœberclocker looked awesome and had more pretty machined parts than I have ever put on any other bot before, performance was massively lacking. A number of factors contributed to this.

  1. Lack of design revision and validation. Combined with 5AM Joltgineering, this led to a vast number of absurdisms in the design. Unserviceable parts, spotty attachments, poor placement, the works. Had I waited a while after completing the design, then ran through the entire process again, I probably would have altered quite a few things. The bot’s assembly was very much one-way. If I wanted to change a lifter motor, half of the thing has to come apart – and most of the electronics have to be unwired. To replace a drive wheel involved 3 sizes of allen wrenches and fiddling with multiple spacers. All of this made it a nightmare to service at the event.
  2. 5am Jolt-gineeringâ„¢. It was summer. I had neither class obligations nor a very strict schedule. Much of this bot was designed in the early morning hours. Designs need a proper balance of neurotransmitters that are absent when you hard-reset your sleep cycle. This led to things which would normally be Really Bad Ideas suddenly seeming like optimal solutions.
  3. Lack of testing again plagues my builds. I thought that an entire summer would be enough to get the bot done, but it came down to the last weekend before the event anyway. The bot was never quite fully operational either, with part failures causing the ultimate scrapping of the top clamping fork. Fortunately, tuning the lifting fork servo was rather straightforward, and it performed admirably. The drivetrain, however, was never run under battle conditions. The inadequacy of my serpentine belt setup revealed itself rather painfully at the event where I lost both drive sides due to slipping belts (Which subsequently took 15 minutes to reseat.

When all was said and done, Ãœberclocker won 1 match, not by its own merits, then lost the next two matches. At the end of my final match, one of the lifter fork motors went up in smoke from me trying to use the fork as a hammer. Compounded with the rest of the failures and the dysfunctional clamping fork, I forfeited the tournament.

All of Ãœberclocker’s matches except for one (due to a corrupted file system on the camcorder’s miniDVD media) are here.

Here’s some action shots of ÃœC at the tournament.

Ãœberclocker initiates a ninja lift on Scimitar. This was one of its only good shots – where it didn’t just fall over.

In another match with Scimitar, the two bots perched precariously on the edge. At this point, I had lost the entire drivetrain, so couldn’t quite back him off.

Ãœberclocker attempts to brute-force Poulan Rouge off the stage after failing at a lift

So, what actually worked?

  • The concept is good. Ãœberclocker was one of the more popular bots at D*C this time around, mostly due to its unique design and strategy. It just needs a better execution. A more rearward center of gravity, stronger clamp fork, and more reliable drivetrain just to start.
  • Ãœberghettofrakenb0xen performed spectacularly. The robot had no trouble dead lifting 30 pound opponents at a brisk speed. Ultimately it was rapid repeated reversal of the fork drive that caused a motor meltdown due to high current. The shaft clutch worked great in preventing gear explosion.
  • Spring-loaded front legs weren’t able to perform up to their full potential because the rest of the bot sort of prevented them from actually having any effect. However, they did allow negotiation of the hazards without much issue in most cases. The front parts were too low and would some times get caught on the edges of the bars and ride on them. This can be solved by using a bigger front roller.
  • It looks badass. What, don’t think so?

Ãœberclocker is a concept which I want to continue developing to bring it to maximum effectiveness. Design revisions include trying to fix all the problems indicated and making the strong points better. However, I have no targeted event date for the redesign, and it could be as late as Dragon Con 2009.

Pop Quiz 2

It’s the flattest active-weaponed antweight ever. Again, just like Ãœberclocker, the concept was great, but my lack of attention to detail ultimately tainted the execution. This build fixed one of the major shortcomings of the original Pop Quiz – a weak, unreliable weapon. This time, the blade was frighteningly fast, to the point that I never actually full-throttled it due to a fear of the bot just taking off.

The tradeoff was the unpredictable drivetrain. To stuff everything into a 3/8″ tall space, I had to build custom gear drives and modify the motors. While a stock solution such as Sanyo Micromotors do fit in the space, they were far more expensive than what I had already. The “frankenmotors” worked great in testing, but over extended operation, they began to gunk up. The square slot car motors themselves are already rather low quality and have widely varying no-load RPMs. This translated to different load characteristics. Throw in some manufacturing tolerances on my gear drives and I had a stochastic drivetrain.

To make matters even worse, I quite literally had no control over the bot’s direction due to the total lack of radio reception. If the weapon was running, then the bot would randomly interpret its own noise as signal and randomly drive around.  The GWS park flyer receivers have almost no filtering and seem to accept used toilet paper and old batteries as valid.

At the event, PQ had all of 1 match, lasting about 10 seconds. The single hit blew apart the momentary button switch that was the bot’s master power switch. In the battle royaly, PQ was able to land a few hits before pinging itselff off a wall and out of the arena.

All 20 seconds of Pop Quiz’s matches are here.

PQ wasn’t in the arena much at all, so I only got one picture of its work.

Pop Quiz goughes in the titanium plow of Segs, a rather innovative 8WD “flexible” bot. This same impact flipped PQ over and also destroyed the power switch.

Pop Quiz was a great trial in how flat I could build something, but returning to the previous chassis outline would benefit the practicality greatly. I can use real drive motors, have more space for batteries, and use a larger weapon motor. PQ1 had a strong drivetrain but weak weapon, and PQ2 had a strong weapon with a spotty drivetrain. It would be beneficial to combine the two traits, but like Ãœberclocker, there is no scheduled rebuild for Pop Quiz at the moment.

Nuclear Kitten 5

NK5 was a two-week speedbuild that only happened because I discovered the magic of waterjet-cutting 2D parts and assembling them like 3D puzzles. We’d been doing this in the lab for a while, but I never gave it a shot myself – that is, until Big Blue Saw ran a free part sale. It all started when I tried to stuff the redesigned frame onto a 9 x 9″ square of aluminum. While the complexity of the frame put it over the “freeness threshold”, I couldn’t resist but fab it anyway. The rest of the bot followed.

The best part about this bot was the new bladehub motor. Previously, NK used a friction drive between the blade and the weapon motor. This was spottily reliable and also required constant adjustment. With my experimentation in hub motors over the past year, I decided to build a high-speed fully self-contained disc motor just for driving the weapon. Backed by the power of lithium batteries, the spinup time to “vibradrive” was under 2 seconds. I also never hit full speed with this weapon because the bot would begin to move around the floor powered by its own vibrations.

The new disc was lighter in profile but heavier overall, being made of steel instead of titanium. The tips were heat treated to avoid blunting, and this worked well. In the Battle Royale, the disc warped at the nonhardened points after the bot faceplanted into the steel arena bumper rail at full speed. Better than just shattering, I suppose. After the second match, the disc motor threw a magnet and was dragging it across the stator for the rest of the tournament. This gave it massive starting issues, but after everything got up to speed, the weapon still worked.

The combination of NK4′s fast, balanced drivetrain and this version’s weapon meant that NK was a great performer. It fought four opponents to capture the D*C 2008 Beetleweight championship. The caliber of the Atlanta bots is really rising fast… I’m sure next year will be even more action-packed. All of NK’s matches are here.

NK took moderate damage to the weapon system during the tournament and would require a rebuild of the motor. Since everything else pretty much works, I will probably run it at Motorama ’09 or a local event.

Some performance pics…

NK does a number on Drumbeat. The gouges on the back side are a bit bigger.

A long skitter mark from when NK was inverted and balanced rather interestingly on its weapon.

Final remarks

So there it is. There’s something I want to change for future events, and that is actually being prepared. It used to be that the bots were really simple and I would have finished building weeks before the event and spent the rest of the time messing around and practicing. With added time constraints and the complete destruction of any time management ability I might have had, this is becoming more difficult. I’ll have to hold myself to the rule that if the bot isn’t finished and tested, I won’t attend the event. The fuss of having to deal with broken subsystems at the event is one whose ultimate cost is the fun factor in attending. All that results is frustration.

I was so busy with Ãœberclocker at DC ’08 that I took practically no pictures or had any time to just sit and watch the event. That’s not a very good attitude to approach the events with, especially one as laid back as D*C.

Until next time…

Nuclear Kitten 5 and Pop Quiz 2: Final Update

Aug 31, 2008 in Bots, Nuclear Kitten 5, Pop Quiz 2, Project Build Reports

I got a new camera.

It won the features-and-price contest for having a full manual control mode, like a micro-DSLR, which I felt was worth the extra pile of change. However, the vast majority of the time I’ll be using it on dumb point-and-shoot mode anyway. Regardless, this means REAL PICS!

Robot Microbattles is TODAY! Nuclear Kitten and Pop Quiz are ready. They’ve been ready, but I have been making random little changes to make their operation more reliable. Since build reports stop at the competition, this will be the final report for both bots.

Nuclear Kitten 5

I’ve been hitting random objects with NK to test its durability and driveability. So far, it has passed on all accounts. NK has historically been my most successful bot, so I hope I’ve passed the reliability onto this build to let it continue.

I made a change to the drivetrain in the form of getting rid of the timing belts. While having synchronous belt drive made the bot handle that much smoother, they also transmitted shock through the drivetrain much better. On a good impact, the recoil of the weapon would throw the bot backwards. It used to be that the O-ring belt drive of NK4 would absorb this impact, but the timing belt translated this into a violent torque impulse at the drive motor.

The result was that I blew out the left side drive gearbox. After frantically ordering a replacement set and having it 3-day delivered, I decided to bring back the O-ring drive, just running on the timing pulleys instead.

These are square-profile BUNA o-rings from McMaster. I selected a loop that was a full inch shorter than the circumference of the timing belts in order to allow the O-rings to stretch – without this stretch, they will not grip the pulleys.

This works extremely well. The bot still handles like a 4WD, but no further impacts have affected the drive motors. The motors are even more isolated from shock than NK4, since the weapon pod is floating.

And so with this revision, here is the final finished pic of NK5.

Pop Quiz 2

If I learned anything from this build, it’s that the new 2.4Ghz RC systems rock. Both NK and Uberclocker run them, and I have no issues with reception, signal loss, or range, at all. Pop Quiz is the complete opposite of that.

It uses a 75mhz GWS micro-receiver, designed for use in tiny indoor and park R/C airplanes. This means it really doesn’t have much in terms of noise rejection or good filtering, nor that much gain. Throw it from the environment of a balsa wood airplane with at most a few servos and one prop motor and into a tiny confined space, antenna trimmed, surrounded by both sides by conductive ground planes, with 4 high-current open-frame DC motors and 3 high-speed switching ESCs, and there are problems.

The bot is completely undriveable with the weapon on (Oh, did I mention the ring of spinning permanent magnets and a big metal twirly thing?). I actually can’t predict which direction it will take off in when I move the stick. I only have the ability to declare that movement is needed.

So PQ is semi-autonomous in the drivetrain. Hopefully I can emulate controlled movement enough to not get counted out. The weapon works great, and should bounce it around enough to not need controlled movement.

I lost one drive motor in testing to a thrown winding (Not a gearbox failure like I suspected any failure would be). I didn’t bring spares, and these are not motors you can run into RadioShack and get. Fail.

So I had to cut it out of the bot. This front wheel will probably be taped over with cellophane tape to give it more slip. Fortunately PQ2 is 4WD and I have three more motors. It actually handled better with this motor gone.

When all was said and done, I squished everything back in and closed the top. Here’s Pop Quiz 2.0.

Yes, the blade hits at the 3/4 mark of a quarter (about 18 and a half cents). It’s actually raised about 1/16″ higher than the design by fiber clutch washers which I put in to avoid metal-on-metal grinding. I will leave it this way, since .6875 is good enough, and it gives more top clearance to prevent disaster.

I leave for Microbattles in 5 hours.