Archive for the 'Überclocker' Category

 

Summer 2008 Build Season Wrap: Dragon*Con 2008

Oct 14, 2008 in Bots, 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…

Ãœberclocker Update 18: I think I’ve fooled the Robot Gods… for now Edition

Aug 23, 2008 in Bots, Nuclear Kitten 5, Pop Quiz 2, Überclocker

Alright, so I’m in Atlanta.

Sunday and Monday evening were mostly spent tuning the signal module. I found out that the Victors do indeed have optocouplers larger than the asses of most Hollywood women, and not even the Atmel chips could drive them. In the end, I still have to splice some small signal transistors (ran open-emitter style for non-inverting buffering goodness) into the PWM cables so the Victors would notice my desperate attempts to communicate.

The signal module is an Arduino embedded Atmel controller, and the code was all written by me. It’s my most complicated recent microcontroller adventure. I excavated a little of what I learned about discrete-time control systems from 6.01 to implement the control loop. Essentially, the AVR waits for an incoming R/C signal and reads each pulse width to determine my throttle stick position (and thus the fork position). It then has 18 milliseconds to determine what to do with it. 18 millseconds at 16MHZ is alot of time.

The AVR chips have a 10-bit analog-to-digital converter, so it reads the arm potentiometer and returns a value between 0 and 1023. Conveniently, R/C PWM signals have pulses between 1000uS and 2000uS, which is close enough to 1024 and 2048, 2^n values. So it was rather easy to make a proportional-only controller by scaling the armpot values. I added an integral term to the output equation also to get rid of the steady-state positioning error that resulted from the Victor controller’s deadband around 1500uS. This got the arm responsive enough for me to call it a night and tune it later.

Then stuff broke.

Of COURSE I had to go back and make a few solder joints more permanent, and otherwise touch up the PCB I mounted everything to. I didn’t notice that I had made a very tiny solder bridge between +22 volts (the robot’s main battery) and the output side of the 5v regulator chip.

When I plugged it back in, the AVR controller quite literally exploded in my face. It’s in several pieces.

So then I really did have to call it a night…and started packing the bot up. I ordered a new Arduino board (since the roasted one is very securely soldered to the PCB and not worth the effort to extract) and should have it next week. For anyone interested in learning from my adventures in making a giant servo, I’ll post my code when it’s cleaned up and tuned.

Uberclocker

I stuffed two suitcases full of robot equipment with clothing and personal supplies interspersed between the goods. Here’s Uberclocker locked into its handy bot carriage, with spare parts and hardware. As there was plenty of space in the suitcase, I zip tied NK and Pop Quiz in, to keep the bots in one place. The other suitcase contained the charger, transmitters, and tools.

Somehow this all got past Homeland Hilarity, but the botcase suffered a bent caster wheel. In order to make the thing self-supporting, I borrowed a hammer from one of the baggage offices to beat it back into shape. Wait, I just got handed a massive claw hammer by an airport desk clerk? Huh?

Anyways, in Atlanta, I got to work on the new clamp arm actuator. Here’s a rendering of the new design.

The gist of it: Solid aluminum structure, indirect gear drive. The leadscrew is fixed to the fr0k and does not rotate – instead, this whole assembly climbs up and down it. This takes all the loads off the motor shaft and instead transfers it to some big chunks of metal. The only way to destroy the clamp arm now is to rip the leadscrew clean out, or applying so much force that the nut strips out.

I’m not saying this can’t happen, but it’s unlikely to happen at D*C.

Here it is implemented. Yes, I’ve been COMPLETELY spoiled by easy access to machine tools – while this would have taken me a few minutes walking to get done at MITERS, I had to drive no less than 50 miles round-trip to make this sucker, and of course make Dale put up with my really bad habits that I’ve accumulated from working without supervision.

Suburban Atlanta needs a few you-build-it freelance engineering places, so I think I’ll make it a mission later in life to start them. Although I suspect the culture to support it is missing…

This actuator is a throwback to something I made in late 2005 for Science Olympiad. My robot entry for that year had a linear actuator attached to a movable jaw that could clamp down on objects. I custom-made the actuator using some gears hacked out of an R/C car, a block of UHMW, and patience on the drill press. The output gear is threaded on the inside to ride up and down a piece of threaded rod.

Pop Quiz 2

In the same machining session, I made a new blade collar for Pop Quiz. This retains the blade on its drive motor, so it’s a pretty critical part. Stock steel shaft collars didn’t come in the width I needed, and would have been a tad too heavy. So I made a quick aluminum clamp-style shaft collar, 1/4″ wide, 1.25″ OD.

I’m still facing severe failsafing issues with Pop Quiz. It’s been a reported problem with the tiny GWS receivers, and there seem to be no workarounds besides the usual anti-RF stuff, but the thing is still pretty jittery. It goes nuts if I turn the radio off when anything is moving.

Pretty bad for something that can remove outlying body parts with ease. I might switch back to the other micro-style receiver and mod it for height.

Here’s Pop Quiz in its final state.

In other bot news, Nuclear Kitten’s replacement battery pack arrived and will be swapped in shortly.

Dragon Con is A WEEK AWAY!

Ãœberclocker Update 17: This is not funny Edition

Aug 16, 2008 in Bots, Project Build Reports, Überclocker

Actually it is. From the past several builds, I have come to a conclusion that beginning exactly one week before I am to leave for an event, things will go horribly wrong that will leave whatever I am building crippled and disabled and unable to function up to its full potential. We saw this with TB4.5MCE for Battlebots IQ, where I lost an arm ESC and couldn’t obtain a main battery worth its weight in beans. TB4.5SP1 for Motorama had a whole third of the bot go out two days before I left, and only some last minute hacks allowed it to run at all.

There are plenty of rational explanations, of course, since I usually get to rigorously testing my engineered systems only in that last week or so, and untested systems like to break if they’re not properly designed and built. But the fun explanation is that the robot gods are just out to get me.

Oddly enough, nothing wrong wrong with NK except losing a LiPo cell, which is not a terminal disaster.

Over the past few days, I have been slowly wiring up Uberclocker. Working in an environment where everyone else is also working on something interesting means I get distracted far too easily, so it’s really taken _that long_ to wire the bot up.

Here’s most of the wiring. For a bot with 5 motors, 4 controllers, and 2 batteries, the wire layout is surprisngly clean. In this picture, the master power switch had not been mounted and no cell balancer wiring is installed.

This was the condition of the wiring for the bot’s first remote-controlled powerlift – the previous one was by touching wires to battery leads, which isn’t exactly a legit in-arena tactic. So what weighs more than or equal to a 30lber?

Well, at MITERS, plenty of things, but the only thing compact enough was this…

…45 pound rackmount uninterruptible power supply battery pack.

I approve of this bot. It can raise the 45 pounds pretty briskly and can suspend it in the air with no motor power applied (with the controller in Brake mode), and can bob it up and down. I don’t have an amperage number yet.

As expected, the back end of the bot lurched upwards on beginning the lift, but fell back down due to the support from the rollers in the front. I didn’t practice balancing the bot with a load on the rollers, but that should probably happen some time.

Then stuff broke.

First, while running the clamp arm with no load, the Banebots 12-45 controller popped its reverse direction. It was a very audible (and frightening) pop that made me think one of the FETs on the Victor 883 controlling the fork motors fried.This was strange, since I was using a motor far, far smaller than what the BB controller should be capable of handling, and it was not clamping down on something or hitting a travel limit. Just small reverse throttle.

So I have started the replacement-under-warranty process with Banebots. We’ll see how THAT one goes – chances are they’ll be considerate and ship me a new one in Atlanta.

After the mild scare, I decided to continue testing by dropping in the ANT150 controller from Nuclear Kitten. But again, that didn’t last long, because…

… the actuator motor shaft snapped. The B62 has a reported history of fracturing output shafts, and it looks like the bug hit me. However, it looks like the shaft actually broke in flexure, which tells me that the radial support at the base of the leadscrew is poor.

I’m not surprised. When the clamp arm hits something on its way down, the load on the actuator is essentially pure compression. Any buckling of the part connections at all could lead to catastrophic failure, which seems like what happend in this case.

This is bad. Very, very bad. Considering the whole leadscrew assembly was green Loctite’d together, it’s going to be nearly impossible to extract the broken shaft stub. A replacement motor is a hefty $30, and I’d have to buy and machine a new section of leadscrew.

Bad indeed. Without the upper clamp arm, Uberclocker is a giant spatula of questionable sexiness.

I’m now in the process of specing out parts and designing a new leadscrew machanism. This will be an indirect drive type device that will take the stress off the motor shaft itself. The motor, furthermore, will be mobile along with the upper clamp instead of being pivoted in a fixed location on the forks. Instead, the leadscrew will be fixed with a pin type joint at the base.

Using an indirect drive leadscrew mechanism, similar to the “beak” of my 2005 Science Olympiad robot, should make the whole thing more reliable anyway.

This will have to be fabbed in Atlanta, since I won’t get any parts I order now by Monday and actually get anything done. So with the clamp out of commission, I tied it to the fr0k to secure it and continued finishing and finalizing the wiring. I installed the battery balancer plug, another Convenient DB9 Connector of LiPo Balancingâ„¢ , physically mounted the power switch, and cut holes in the top plate to accomodate them.

Besides the DB9 connector, I also put in a direct connection to the battery using a Deans female side connector mounted to the left Ebay. For this bot, the charging current needed will exceed the limitations of the 24-22 gauge wire that fits in the DB9 connector, so I will use that only for the charger’s balancing function, and the big connector for actual charging current.

After tidying up the interior some, it was time for a beauty shot. Cheesy cell phone camera style.

The bot’s now only missing stickers and blinkenlichten.

And also the signal module. The signal module is my name for the receiver + fork controller combo that will occupy the left side Ebay. The fork controller will take input from the Spektrum Rx and do two things – one is buffer the signals for the Victors, and two is correlate my transmitter’s Throttle stick position with the position of the fork. It will take input from the potentiometer mounted to the fork and drive the ESC accordingly.

I decided to let it process al l the receiver signals (and passing drivetrain commands straight through) instead of making a separate buffer board for the drive only – it keeps the wiring cleaner and allows for future expansion of more advanced control schemes.

There is minimal hardware left to implement, since the microcontroller already comes with its neato support board.

There are exactly three days left. Can I get everything working?!?

Ãœberclocker Update 16, Nuclear Kitten update 3: A picture is worth 9000 words Edition

Aug 10, 2008 in Bots, Nuclear Kitten 5, Pop Quiz 2, Project Build Reports, Überclocker

So I can’t find the sub-micron sized grain of dust or metal shaving that is caught in the lens actuator of my camera. Unfortunately, this means that I will have to start haunting Ebay and local consumer electronics outlets. Until then, I suppose everyone who reads this site (all -0.000001259 of you) will be in suspense, save the occasional grainy cell phone camera picture.

The basic rundown is that Ãœberclocker is ready to be wired and NK is also approaching mechanical completion.

Ãœberclocker

I drew up the “EBay” assemblies and prepared flat patterns to make them out of sheet metal. Unlike TB4.5SP1 which had all its electronics in a bunch, Ãœberclocker features “distributed electronics”. There’s not really an advantage to either method, just that I couldn’t find space in this bot to slam all the electronics in one place.

Each is a work of 1/16″ aluminum origami (read: smashing in a vise and banging on it while wielding a torch) that bolts to a close frame member. There is nothing secured to the baseplate, unlike TB (and all my previous bots). Furthermore, all of the Ebays are dismountable from the outside.

This is the left side Ebay, which houses the main switch and Convenient DB9 Connector of LiPo Balancingâ„¢. The big switch came off a 1980s era PC power supply which, despite being a 7 inch cube, could manage maybe 200 watts. It is mounted such that the top bezel is flush with the top cover plate of the bot. A little rectangle will be cut out of the top plate to pass it.

Since Ãœberclocker isn’t a severe duty bot, I decided to forego making a normally closed switch like I did for TB. The detent is strong enough for me to not worry about it randomly clicking off.

The rear Ebay clamps the batteries between itself and the rear of the bot. It also carries the Victor 883 controllers for the drive motors. The right side Ebay houses a third Victor and a small Banebots ESC to control the clamp motor.

fr0kp0t mounted. This was an afterthought, and I really didn’t want to take the entire thing apart again, so it was just clamped and hand drilled. The potentiometer is rather exposed for something which will be telling the fr0k everything about where it is in life, so it might get a larger metal cage. The pot is coupled to the fr0k through the shaft set screw.

There is currently no bottom hard mechanical stop for the fr0k, and so it can swing all the way around the bottom of the bot (no doubt ripping off the entire bottom plate in the process). To prevent this, I’ll add some things that stick out of the fr0k towers. While I could easily limit the travel in software, a hardware backup is good for preventing self-eating disasters.

So Ãœberclocker is ready to be wired up and programmed. The fr0k, with the chain tightened (by removing one pitch with an offset link), successfully powerlifted 30 pounds, so I know torque isn’t a problem. Maybe there will be a drive test soon…

Nuclear Kitten 5

NK went from 0 to about 50% done in a day due to the “snap-together” chassis. The only thing I needed to build for that were some nutstrips ( 1/4″ aluminum squares with regularly spaced tapped holes), which was tedious but trivial. Past that, I had to machine up the weapon motor and drive wheels.

I specifically bought a 4-40 spiral-tipped tap so I could powertap all the holes, 7 each in 12 nutstrips. Sadly enough, I’m short about 4 inches worth of 1/4″ square aluminum stock to make the last of the nutstrips. This is within range of just biting the proverbial bullet and machining down some bigger stock.

Blurry ass-picture showing some frame bits and the nutstrips. Ignore the obvious non-trusses that populate the inner rails. My excuse is that it was 5AM Joltgineering – I’m not sure why I didn’t just link the corners with triangles instead of making an ugly V shape.

I like this “Chinese Puzzle” frame – I think I’ll keep the tricks in mind for future projects.

While the waterjet pump was still primed, I tossed on a plate of 1/4″ 4140 and cut out the blades.

Because the blades are now steel, they are thinner in profile. This should be more than enough for 3lber duty, especially after heat-treating (famous last words).

After discovering that the grungy MITERS horizontal bandsaw cut much faster when I dropped a weight on the end of it, I started on the disc motor. The motor itself is almost identical in structure to my wheelmotor and much simpler in construction. I also didn’t have a stiff and consistent tool holding device when I built the wheelmotor. Overall, this resulted in a very fast build of the disc motor structure.

I made two side plates out of 3″ aluminum round and the center axle out of 1″. A steel pipe was turned into the magnet ring. This steel pipe appeared fine on inspection, but upon contact with a cutting tool, turned to powder on the inside. Fortunately, the rust wasn’t deep enough to affect the final ring dimensions.

I also made all four drive wheels. Each wheel consists of a stock SDP (redundancy?) pulley, an aluminum “rim”, and an O-ring “tire. The process was fast, since each rim only had radial features that could all be made by selective parting tool use. The drive motors themselves are in transit and should arrive Monday. Previously, I ordered a few Speed 300 size RC motors off Ebay to retain the absurd speed and maneuverability of NK4, which featured those motors spliced into the aforementioned gearboxen.

Upgrading the wheel size the morning before I ordered all my parts (more 5AM  Joltgineering), I failed to account for the fact that one of the frame connector pieces now interfered with the front wheels. Something will probably be sanded down.

After taking a Taco Bell break, I put the disc motor together for a test fit. This motor has a very tight airgap to maximize torque, and I was worried about the tolerances adding up and causing the stator to grind against the magnets. To my surprise, it ran concentric and true – with no rubbing. Cheers for the robot gods. I then went back and preliminarily installed all 28 magnets (in groups of 2) with ultra-thin CA glue. The empty spaces will be filled in with epoxy.

So, here’s a picture of NK in that “well, it LOOKS done” pose.

Old NK is undergoing the scrapping process to extract the goodies (there’s not much left).

Only a few spacers here and there remain to be done on NK.

So the summary of things to do is:

Ãœberclocker

  1. Wire up!
  2. ???
  3. Profit!
    1. Make bot carrier

NK5

  1. Weapon pivot axle and spacers
  2. Wind motor
  3. Tune drivetrain for belt tension
  4. Wire up

PQ2

  1. Wait for giant plate of titanium (est. Tuesday)
  2. Cut blades out of Ti
  3. Machine a blade retaining collar
  4. Integrate receiver and mixer into a single module
  5. Think of how to get reception

A week remains…

Team Test Bot Pre-Dragon*Con 2008 Botgasm, Part 1

Aug 06, 2008 in Bots, Nuclear Kitten 5, Pop Quiz 2, Project Build Reports, Überclocker

It’s official – I have gone insane. Two weeks before my departure to Atlanta for a “vacation vacation” and Dragon*Con & Robot Battles, I have started on a new bot.

Yes, it’s Nuclear Kitten 5.0. Slightly revised again from the previous design as my experimentation with a new building paradigm.

The story goes like this. Big Blue Saw is running a free parts giveaway to raise awareness of its business. The parts are limited to a 9″ x 9″ square of either 1/8″ aluminum or acrylic. In a moment of engineering epiphany (or perhaps madness), I realized that NK5 could potentially be made from assembled 2D shapes cut on the waterjet. I learned this technique of building from working with the Media Lab guys, who regularly make large 3D assemblies using 2D cutouts. I got some practice this summer by building my awesome disc things, which are concept models for the Citycar test platform.

So I designed a “Chinese Puzzle” style chassis for NK5 over the course of a night. Here’s a 2D experimental layout of the first revision of this chassis, using slightly different corner attachments. Sadly enough, the sheer number and complexity of the pieces put me way over the “free part quote limit” – by about 300%.

However, the lure was just too great. I refined the design to reduce the number of parts and increase the stiffness of the whole thing, as well as make sure each connection has a physical interlock and isn’t dependent on just slip fits and screws. I also spent more time going over the entire thing to make sure there were no “impossible objects” – like tabs wider than their slots or impossible assembly procedures.

One fine afternoon (i.e. “yesterday”), I scrounged a piece of 1/8″ aluminum from MITERS and headed over to the  Media Lab.

But first, a prototype. After the last epic partfail, I have learned that it is wise to wreck inexpensive material first  than to just stab your stock with whatever the machine does. This was slightly different – I wanted to see how the frame would go together.

Using the GIANT LAZER and some 1/8″ model plywood, WoodeNK was born. I am very tempted to actually make the bot from wood. The good news is that everything goes together as planned.

…and so the design was transferred to aluminum on the waterjet. Careful file inspection and a bit of manual pathmaking made sure that the very complicated combined profile was cut correctly.

Unfortunately, in a strange turn of events, my camera decided to kick the bucket last night, so this is the last “good” picture of the frame.  Initial inspection of the interior and listening to noises tells me that the lens mechanism is jammed. Since I’m rather harsh on my equipment, I suspect a good dose of pocket swarf or some industrial grunge from MITERS might have found its way into the mechanism (which is surprisingly exposed for being behind a shell).

A year and two months. Hmm, my last camera died during the TB4.5MCE build… I might take a stab at repairing this one, but as with all modern miniaturized electronics, it might not be worth the effort.

Some progress has been made on Pop Quiz and Ãœberclocker also.

Pop Quiz

For the past few weeks, PQ has been sitting on my desk within arm’s reach, but I haven’t worked on it at all. In fact, I had to constantly shuffle things around to actually do other things on my desk. But with Ãœberclocker awaiting some 1/16″ aluminum, I got back on it.

The first order of business was to rig up a master power switch of some sort. This was actually quite difficult due to the bot’s height. Currently, Pop Quiz uses a separable link as a switch – essentially just the main battery pack connector, accessed through the holes in the top plate. Not a very secure design, since the connector can – and has – fallen out of the hole and into the path of the blade while spinning.

Electrical self-eating is a shitty way to lose a match. I settled on a hybrid pushbutton switch setup using some right-angle panel mount switches. I have a whole bag of these things from an AHRC meeting from two years ago, and they have been begging for a use. While the switches themselves say “0.4VA MAX”, the contacts are all solid brass and quite substantial for a switch this size. I figure this can’t be as bad as thin aluminum tabs on the Lipo cells.

Here’s the switch mounted in the sidewall of the bot. The panel thread was either #10-uber-fine or 5mm, but it force-threaded into a #10-32 tap hole.

A nut and a dot of CA glue secures the switch axially.

Next, I threaded in a set screw from the other side.

Result? Hex wrench-actuated main switch. When the screw is tightened, its tip pushes the momentary button switch down and the bot activates. Turning the screw counterclockwise allows the button to spring back up and the bot turns off. This should never trip by itself in battle, because that would involve somehow ripping the screw out of the bot, which means I probably have bigger problems.

I dubbed this the “Why-not-chi” switch after a commercially available switch for larger bots.

The balancer connector for the Lipo pack is thus the only thing that should be accssible immediately from the outside of the bot. It will get its own slot in the top plate.

The above picture is actually the last one I managed to get off the camera before it refused to power on again. So, no pictures of the actual wiring rig that I hooked up, which probably qualifies as the worst rat’s nest job I have ever put together. In something this tiny, it’s hard to keep the wires straight, especially 22 gauge with thick insulation.

The only thing I have not fully installed in the bot is the receiver and tiny mixer. The receiver will need some modification to fit under the cover plates, and both parts will have their servo connector pins removed and the channels hardwired to eachother, effectively becoming one package. There’s only space to accomodate this and some wiring.

I also have to solve the problem of “how do you get reception in a bot with 4 open-frame motors, a huge ring of spinning magnets, high-speed switching controllers, and two massive conductive ground planes (the carbon fiber panels)?”. Custom base-loaded antenna is one option, or take advantage of the fact that CF is conductive and make some sort of slot antenna. Or both.

Or neither, and just amp up the power of my transmitter to overpower everything else in sight, as well as control every 75Mhz R/C model within a mile.

Pop Quiz is only missing a blade at this point, and I have a sheet of titanium on the way for that.

Ãœberclocker

Ãœberclocker doesn’t look much different than before, since there hasn’t been much done in the past few days. However, I did take myself up on my own word, and have swapped the Mabuchi 550 frame drive motors for the beefier 775 motors.

The drill motor shells already had the 700 mounting pattern molded into them, but no holes, so  I had to drill out the appropriate holes. I decided to just swap the entire drill housing since the black nylon ones appeared more durable than the ones already in the bot – which already showed some crazing and characteristic discoloring from being under strain.

A #9 drill bit opened up the drill pinions to an elegant Loctite-assist press fit for the larger motor shaft

I also made these “inter-side rail stiffener blocks”, which give the front half of the drive pods something else to keep them steady. They were a bit flexible due to the single-point attachment in the front.

Unfortunately, adding the larger motors meant that the Victors are now a bit cramped. There’s no problem with wire access, just that everything is a bit closer together than I would like.

Ãœberclocker only has electrical work left, including making the servomechanism setup for the fr0ks. Some “EBay” plates will be cut out of 1/16″ aluminum and folded to shape to carry the electronics, including the battery.

So, how on earth do you get a 30 pound robot with an almost a 4 square foot top-down profile from one city to another? One method is to build a crate and ship it. Unfortunately, arranging shipping logistics both ways and building a crate is going to cost a good chunk of money.

30 pounds is just under the margin of how big a robot you can bring on a plane. So that is what I intend to do – just fly the bot as checked luggage. Many people have done this before. I do have a suitcase that is large enough to hold the bot – the one I brought all my shit up here to MIT with. However, you can’t just throw a robot in a suitcase, especially not one that’s this pointy. The suitcase is not hard shelled, so having something big and metal inside is probably bad news waiting to happen.

To overcome this, I decided to design an internal skeleton for the suitcase that will securely retain the bot in transit, as well as snap out of the case to use as a “bot dock”.

This is the “bot dock” portion of the design. It suspends the wheels of the robot off the ground, a critical disaster-prevention step checked for at many events. It’s just a few slats of wood selectively cut to let the bot slip into its center.

More importantly, it secures the clamp arm and the fr0k from moving when the bot is in the pits. This is also a safety procedure – the fr0k has easily enough torque to shear body parts off, and the front of the bot is a pretty big pinch point. The clamp arm, although less dangerous, is better off secured. This botdock
makes sure both parts are immobilized.

Next, there is a similar structure in the suitcase that holds this bot+dock combination.

Yes, I actually measured out the internal dimensions of the thing. Two side plates and 3 crossing slats, which will all be secured to the suitcase by wood screws, allow for the bot+dock to be fixed in place with the pictured wooden latches. It also acts as an internal hard skeleton for the whole case. There is enough space around all this to shove in my pit equipment (or the insectweights!)

All this is made from 1/2″ plywood, and a quick run on the waterjet or CNC router will take care of it. Assembly will be by wood glue and wood screws. I think it’s a necessary step to prevent disasters if I’m not shipping the robot and equipment down separately.

Exactly two weeks from today! Onwards!