Dragon*Con 2010: My Robots Are All Totally Skullfucked Edition

chorl

It’s August! That means the end of the summer build season, MIT’s Freshman Orientation, and most importantly, Dragon*Con, are all coming up soon.

In other words,

AAAAAAAAAAAAHHHHHHHHHHHHHHHH

D*C’s Robot Battles has been my annual robot party since 2002 when I first began spectating (and 2003 when I began competing). I’ve tried to go every year possible – 2007 was the big exception because my very own freshman orientation trapped me on campus then. I’ve always enjoyed the atmosphere of the event moreso than most other competitions just because it’s so not serious business. It’s a primarily sumo and show-off event because of the limited audience protection, at least for the 12 and 30lb class events – even more tame than the NERC Sportsman class I entered Überclocker and Cold Arbor in for Motorama. The event is seriously almost as old as I am, and it’s always been like that.

So now… speaking of Clocker and Arbor, how are they doing?

Yeah… about them robots

That doesn’t look too good. The bots have all been sitting, piled on top of my cart of miscellany, since February. They’re relatively undamaged as far as active combat robots go, but Moto took its toll on the drivetrains. I went through 4 and a half gearboxes at Moto, running through all of my spare 24:1 drill gears. After Arbor was eliminated from the competition, I harvested its gearbox parts to keep Überclocker running…but not for too much longer.

Long story short, Arbor has 1 semi-working drive side and Clocker has zero.

cold arbor

Here’s Arbor after retrieval from the cart skydeck. Past the drivetrain (or lack thereof), it’s also been the subject of parts harvesting. I think I’ve stolen the two Dimension controllers (which were briefly used to run Segfault), the Spektrum receiver, and the 5 volt BEC out of the electronics bay – those are all scattered about MITERS and so need to be retrieved or replaced.

One of the issues I intend to address is the front frame assembly. First off, it’s physically bent about a degree and a half. Not much, but several of the braze joints in the bend region have failed and some of the sheet metal has become twisted. This was probably just a result of battle, but either way it’s unsatisfactory.

Much of this front assembly was designed using 5AM Joltgineering™, therefore structurally unsound. I want to do a better job making it stiffer, so the plates may be recut and rebrazed.

Gearbox issues aside, I’m otherwise satisfied with the drivetrain. The oversquare wheelbase and central mass location means that Arbor actually handles very well. The drive is fast, but the super-soft McMasterBots wheels were grippy enough to avoid uncontrollable sliding. I’m also satisfied with how the Delrin hubs have endured in the front half of the drive.

Comparatively, ‘clocker handles like a total brick since all of its mass is in the rear 33% of the robot.

But I’m extremly dissatisfied with how the whole swinging saw assembly is mounted. If you call, several months ago in the last Arbor update before the Motorama update I never wrote, I said:

However, this was the first time that I discovered that Arbor would never work as I anticipated in its currrent configuration.

I was referring to this. In what must be yet another symptom of 5AM Joltgineering™, I somehow made the entire 14 pound swinging saw pivot off the front sheet metal assembly. As in, everything. All moment loads, all bending, and all shocks were transmitted through the beefy 3/8″ aluminum saw pivot mount…. right into the 1/8″ aluminum plate in the front. The above picture shows the “load triangle” pretty well.  One point of the triangle is located at the left side by the actuator trunion screw, and the other two are effectively shared by the two cap screws from the right side (front) and the screws on the top and bottom, which… happen to be missing, and probably were all through Moto.

From a Course II standpoint, this assembly is one giant piece of unwanted flex. It became very clear during Moto (and during testing) that the entire saw was prone to pulling itself into the material (or opponent) and becoming stuck hard simply because the whole frame twisted several degrees due to the torque of the worm gear drive.

My plan for redressing this problem is to make the saw’s structural loop much larger. Effectively this means swapping actuator positions – placing the saw actuator at the back end of the robot and the claw actuator where the current saw actuator is.

The light red, green, and blue lines indicate where the current structural loop of the saw lies, and the dark shades show where it should lie after modifications. The bigger the loop, the more the structure can resist torque about the orthogonal axis (in this case, the direction of saw rotation). But because I’m keeping the green line a constant length, I should have the same “swing” of the saw available.


As long as I’m wailing on the saw assembly, I might as well talk about Deathrunner. It’s been shiny, menacing, powerful, and reliable, but Deathrunner is going to be replaced with something else for D*C.

But why? Well, Deathrunner weighs 4 and a half pounds, was wound somewhat hackishly (the number of turns and wire fill percentage is a total waste of the stator), and hangs awkwardly off the saw arm. Even worse, it’s sensorless. Now, I could very well add sensors, but then I run into the problem again of not having a sensored controller powerful enough to feed it – no amount of DEC modules will drive this thing. I noticed that the sensorless controller had problems keeping up with sudden changes in the motor speed, such as those caused by the saw biting something.

Overall, the weight could be better used by a short Magmotor (!) or something similar. It’s much easier for me to control a DC motor, and I don’t have to worry about its transient response.

For now, the candidate motor is a big DC brush motor about the size of the classic Mini-EV. It otherwise seem to share all the MEV’s charactistics, such as being fast and obnoxious. Since it IS a fast motor, I might put one stage of “pre-gearing” on it by harvesting parts from one of several junked industrial planetary drives I have in the cruft pile.

überclocker remix

Poor Überclocker.

Being 1 event older than Arbor, it’s more beat up. A few things are bent, screws are missing, and there are little saw nicks all over the place from Freakin’ Enforcer, but fortuntely the major structural components are still sound.

Again, the number 1 issue is the drivetrain. More precisely, it’s the lack of one. A combination of “DeWalt motor into Harbor Freight drill gearbox” and battle impacts destroyed both gearboxes. At the event, I pulled parts from Arbor to keep them running, but ultimately Clocker lost out of the tournament by virtue of not being mobile enough to attack anything.

Besides the gearbox, the external portions of the drive have been flawless.

Well, most of it. This right side has apparently been gimpy since fight #2 at Moto because the internal binding screw backed out, so the standoff went all over the place. In the grand scheme of things, an easy fix.

I have about this much space if I want to switch to a stock solution like the Magnum 775 motors (which actually seem to be a bit too long). If I want to keep the current drill gears arrangement, I’d have to return to 550 motors because I’m out of 15-tooth pinions for 24:1 drill gearboxen. That would be a pretty stiff power and thermal mass sacrifice that I don’t feel like making.

Or I could keep fucking around with drill parts. A while ago, I posted some information about the 3 speed DeWalt (read: legit) drill gearboxes to Delphi Robotland, including a gear ratio count and pictures of all the stages.

With some crafty adaptation of the 2nd stage gear carrier’s sun gear, I could use the first two stages as a 17:1 planetary gearbox that has bigger and meatier and more gears than the comparable import-class drill. I started thinking about it, and hopped into Inventor to model some of the major components.

Here’s a preliminary layout showing some of the changes to be made to the parts. The sun gear will be turned down to a 14mm stub shaft, which will ride in a 14x20x12mm needle roller bearing. Its center is bored out to 12mm.

The first stage ring gear with the weird wavy flange remains as the first stage ring, but I intend to machine off the weird wavy flange to save on diameter. The second stage ring gear (the one with the dog clutch teeth that are unmodeled above) will remain the same.

All the ring gears will be heat-shrink-fitted into a custom aluminum casing…

…which looks the same as the current Clockerbox, and is made from the same 2″ square aluminum.The difference is that now the motor mounting plate is actually a plate instead of, say, the entire back half of the gearbox. It makes things a bit easier to manufacture.

The output gear will be the same one on the robot now, and will ride on a short chunk of 12mm drill rod shoved into the bore of the former sun gear, and with a Double-D profile machined into one end to simulate the old Clockerbox output shaft.

Dropped in place…

This new assembly is about 0.1″ longer than the current motors, which is an acceptable change.

I might switch Clocker over to the same kind of McMasterBots wheels that Arbor currently uses. It doesn’t hurt to have more traction on the D*C stage, especially since going from 24:1 to 17:1 is going to boost the robot’s top speed even more.

Here’s where I get to find out if my robot driving skills have faded any from the 2003 Test Bot 2.0 days.

While I have the gearboxes designed, I’m debating whether or not it’s worth just going with the 775 gearboxes because they are a stock solution – that is, I don’t have to build them. It’s mostly a matter of cost versus time spent – I could buy the 4 gearboxes (assuming Arbor also needs a pair) for $400 or so, or build two FrankenWalts for virtually free, and if necessary, two more for about $100.

It comes down to do I think I can get them done in under approximately 32 hours because my time is apparently worth about that much this summer.

RazErBlades: Completion and Deploy

chorl2 Comments

I am satisfied.

To me, there’s no more magic in ultra-small mobility devices. Building the Death/RazEr/murderblades has shown that a handful of brushless DC motors and a lithium polymer battery is fully capable of pushing a passenger around at 10-12mph, which is a reasonable sidewalk speed. Extreme stealth is also possible –  RazEr was a miracle of packaging, but the skates beat it out by far in terms of volumetric component density. Additionally, I’m very satisfied with the way that the Skatroller turned out in terms of user interface – so much, in fact, that I might start making more vehicle throttles wireless.

Now that Otakon is over with, I’m going to start collecting more test data and video with other people who can actually wield the ‘blades and not look like dumbasses, unlike me. Anyways, here are the events of the last week or so.

After I left the remaining skatemotors on a shelf to set, I began completing the left motor driver board. It was fundamentally “done” weeks ago, but I never added motor connectors because of the lack of motors. On this board, I elected to discontinue using side-bullets and on-board mounted sensor connector. It was too difficult to maneuver the cabling in the tight space, and the large power wiring directly pulling on the board traces worried me. So this board uses sensor and power pigtails that extend outside the aluminum frame.

I put together the sensor pigtails using the same headers and 5 (originally 6) pin cable. A few globs of Goop sealed the electrical connection.

I had to flip the direction control pin on the left board also, since the motors were mounted oppositely to the right side and therefore wanted to run the left skate backwards. Unfortunately, there wasn’t an easy was to do this since the DIR pins were connected to logic ground through a circuitous (hurrr) trace that also hit several other pins.

Solution? Cut off the mating contacts of the signal header. I then hardwired the DIR pin to the DECs’ onboard 5 volt rail using 30 gauge wrapping wire.

After the board was assembled and installed, I gave both skate units a full charge. It was the first time the left skate had been charged period, since it was never used before this.

skatroller revisited

It was time to get started on updating Skatroller. For this version, I wanted to have control over the DECs’ output enable lines. The output causes the motor to brake if the commanded speed is less than the current motor speed. Now, the DECs aren’t actually regenerative controllers  or anything, but enabling the outputs while commanding zero speed acts as a dynamic brake. It’s just another added convenience if I want to limit speed, as this kind of braking will never actually bring the motors to a full stop.

I decided to use another sensor input instead of trying to calculate or design ranges of inputs for one FSR. Above is my spare FSR mounted in the original “wrist forward” position. The whole thing now acts sort of like a large rocker switch.

Additionally, I’ve elected to pitch an Arduino Nano on the board just out of convenience. It’s easier to read in two sensors and do whatever I want with the data using a microcontroller and some software (as much as I hate to admit it).

…but first I had to pre-cut all the fusible links in the Lilypad breadboard because they are the most annoying things ever.

I scolton briefly thought about connecting all the circular perimeter holes to alternating terminals of a METALPAKKK such that the sheer short circuit current would blow all the inter-pad links, but the setup for that would have taken longer than just going through them with a knife.

To facilitate alignment, I used a machine parallel as a straightedge to guide the +1 Exacto Knife of Trace Gouging.

I got a Lipower board from Sparkfun as a more efficient means of powering the Arduino and XBee stack. The Lipower takes the 3 to 4 volts of a single lithium polymer cell and outputs 5 volts. The Arduino uses the 5 volts directly and the XBee board internally down-coverts it back to 3.3 volts.

For simplicity, the Lipower board was double-sided-taped to the 900mAh lipoly cell through a layer of heavy heatshrink. On the other side of the battery, I stuck a piece of Velcro. The battery never sees any loads on its pouch surface, which is what I want.

I found these board standoff headers to connect the XBee board with the Arduino & glue circuitry below.

The arduino board  houses connectors for the 2 FSRs and the battery. It also has a small input RC filter for each FSR and another RC filter on a PWM pin of the Arduino to bring the square wave PWM back to an analog voltage. This is all shoved between the two header rows that the Arduino sits on.

Here’s the back of the signal processing board, showing my usual tactic of point-to-pointing with 30 gauge wrapping wire.

After verifying that the circuit worked, I coated the whole bottom side in a healthy layer of hot glue. After the glue set, the self-leveled surface got a chunk of Velcro attached to it so I can mount it to the wristpad.

And now here’s the whole rig mounted to the wristpad once more! No obnoxious LEDs this time around – the only indicator of power is the three little red LEDs, one on the Lipower board, the Xbee board, and the Arduino. The assembly is almost excessively stealthy, especially when hidden under the cavernous sleeve of my modified fuzz jacket.

The carrying case for the ‘blades was a recommissioned Facebook swag bag obtained at a career fair many moons ago. The skates sort of fit in perfectly side-to-side, and the wristpads filled the rest of the space. So here’s the final shot of them ready to travel.

I ended up not having time to replace the wheels with the harder compound K2 wheels, but that will happen later.

deploy

The Otakon deploy wasn’t particularly exciting since the convention center specifically banned wheeled vehicles inside and there was no planned photo shoot for the Air Gear series anyway. There wasn’t a good reason for me to just stay outside the convention center and orbit around on the streets more than once – which is what I ended up doing. So, the ‘blades were under power for maybe 10 or 15 minutes, then stored  back inside the rest of the time. They’re certainly stealthy enough such that I didn’t rouse too much attention. A few people “got it” because they were familiar with Air Gear (though not hardcore fans). Overall, in terms of outward appearance, the ‘blades aren’t very impressive. The engineering is mostly hidden inside.

Pics or it didn’t happen? I’m sure someone had pictures, but I kept my camera with me at all times, so I don’t have any voluntary pics of the whole setup. Overall, what the con showed me is that I’m too lazy to actually cosplay and too focused on building props and gadgetry that nobody at a pop culture convention or without at least some familiarity with engineering would care about.

But, as I said originally, now that the RazErBlades are fully functional, reliable, and require no particular explanation of quirks to operate, I’m going to lend them out to friends and peers who have a better handle on inline skating and possibly put up a few more demo videos later on. For now, however, I’m going to call this version finished. It’s always open to improvements in packaging, power, and usability, but it’s August already and Dragon*Con and my annual robot party are fast approaching.

Soo… what did I end up inventing? Air Gear or Jet Set Radio?