Archive for May, 2008

 

Game over.

May 23, 2008 in MIT, Bostoncaster, Cambridgeshire, Stuff

Round 1 of 4 complete.

Insert 168673 quarters to continue.

That’s alot of quarters. Today was my last final exam, and with that out of the way, the summer season begins.

Quite alot has happened in the past year, and I think this site suffices in documenting all of it. I can’t say that I’m particularly reflective about it at the moment. Alkali metals, running up stairwells for shits and giggles, weird bikes, random explosions, a helpful alarm clock every morning from the construction outside my window

So what’s the plan for summer? Now that I’m IRL, it’s time to stop blowing off summers and actually do things. I’m going to continue my research & development position with the Media Lab, and hopefully by the end of summer we will have the Citycar prototype running. Other than that, building random things will continue as normal. Once I get the ESC replaced on Snuffles Reloaded, then I’ll continue my own R&D work on that. I’m seriously contemplating the creation of a conversion kit if the idea is viable. Other things might come as the sumemr rolls on. Whatever the case, I should be plenty busy.

The summer bot fleet will be Ãœberclocker and Pop Quiz 2, both for local events and Dragon Con 2008 & Robot Battles. Going to DC08 raised a bit of controversy within my circle of peers because the same week is freshman rush and orientation week, which is a big thing to get involved in here. But hey, maybe next time.

Bot-mode on.

Death Metal?

May 22, 2008 in MIT, Bostoncaster, Cambridgeshire, Stuff

Even more steel falls into my collection today as the end of term hits many people, especially seniors, who are ditching stuff to move house. I predict alot more fun stuff to come, so stay tuned.

First up in today’s lineup is this grand collection of enormous über-steel death-mills.

Now the little lonesome shell mill at MITERS has a bunch of buddies. Unfortunately, we have no tool holders for the Bridgeport that can even begin to swing one of these things. The shanks are all 1.25 to 1.5″ in diameter. Each mill is HSS according to their stamped labels. Some are chipped and require resharpening. Some are just weird – like that little stubby thing under the massive mill at the top. A few have six flutes.

These are all capable of serious damage if wielded properly (or improperly). I like this.

This set will go to MITERS, in the event we figure out something to do with them.

Next is…

I don’t get it. Regardless, I liked the 2 foot long slab of solid 1″ thick aluminum that formed the deck, along with the identical 2 foot long slab of 1″ thick aluminum next to it. These will be for the bots… whichever bot I will build that requires a solid slab of 1″ thick aluminum or two?

Stay tuned for the next episode!

Nü metal

May 20, 2008 in MIT, Bostoncaster, Cambridgeshire, Stuff

Over the weekend at Swapfest, some MITERS guys sequestered a large drill press to replace the one currently in the shop. I left before the festivities, but somehow they managed to lug it back to the shop.

I suppose it’s a misnomer to call it “new” metal.

And here it is. According to the dude who was selling, it dates to the 1950s, which I’m pretty sure is one World War after the MITERS lathe. All solid metal and cast iron as everything of that time seems to be. Otherwise, the layout is the same as drill presses now.

More detail of the head. It is extraordinarily smooth, and actually has a real Jacobs chuck, which is also extraordinarily smooth. The table adjustment lever appears to be missing, as is the chuck key, but I’m told there is indeed a matching key, unlike the old drill press, which required selective use of channel-lock pliers. No racks or worm drives or fancy stuff on the column, which makes me fear that I won’t be beefy enough to change up the table height like I consistenty have trouble doing with large drill presses.

Someone also snagged this thing.

I don’t know exactly what it is, but it appears to be capable of causing massive amounts of damage if used properly. The crazy milling tip appears to be removable.

Alot of new steel for MITERS this week, which should be grea tto get the summer building season starting.

Project Ãœberclocker

May 18, 2008 in Bots, Project Build Reports, Stuff, Überclocker

Since 2002, Dragon*Con in Atlanta has been my principal bot-party every year. The Robot Battles competition has been held there every year since 1991. That makes it one of the oldest combat events around. My first competition year was 2003, and I also went in ’04, ’05, and ’06.

In 2007, other matters forced me to miss the event. Fortunately, in 2008, I am no longer a miserable froshling, and may come and go as I please. This is good. It allows me to return to my fan club, which no doubt has gotten a bit stale from waiting around for two years.

Hehe, fan club. Funny.

Anyways, regardless of the circumstances, I need to make an epic comeback in 2008. I need to kick ass in an epic fashion. So, I need an epic robot. Announcing what will hopefully be my first 30lber build for the Robot Battles competition as well as the NERC/RFL Sportsman’s Class:

Cheesy shoop’d logo included in price of admission. The design incorporates the Doomsday Clock as part of the text, with the minute hand cleverly reflected one minute past midnight. Symbolizing doom… or something. Anyways, onto the bot.

The most prominent feature is, of course, the giant fr0k. I have neither seen nor heard of a clampbot-type design, which a two-part lifting mechanism can entrap the opponent and lift it completely off the arena surface, used at Robot Battles. This is quite strange – the arena surface in question here is an open stage, and if you go over the edge, you lose the round. It seems control-type robots would dominate. But D*C has seen its vast majority of entries fall under the hammer, wedge, plain lifter, flipper, and ramming box-with-pointy-things categories.

Perhaps I’ll set off a bad trend, but at least it’s more interesting than the current spinner-vs-armored-box debacle in the RFL.

So, Ãœberclocker will be a clampbot, with a few kicks thrown in. The main difference I observe compared to other clampbots in various weight classes is the set of idler rollers up front. They are spring-loaded to the floor in normal operation. When the bot has an opponent in the fork and raises it off the ground, its center of gravity will shift to forward, causing the bot to balance on the idler roller arm and the front wheels (the rear wheels being raised off the ground). If I lift the opponent higher, the center of gravity will fall back over all 4 wheels, and normal operation can proceed.

This two-wheeled intermediate, semi-stable condition is what I hope to extract a little fun from. I hope to be able to whirl the bot doublet around at a high rotational speed, then release the clamping force suddenly. This should pitch the opponent a decent distance horizontally. Hopefully right off the stage.

That is not the main strategy, of course, but it’s something to include. I hope it works.

Slightly obsolete drawing, but the basics have not changed. The drive motors will be 18 volt drill units similar to the ones I used to use on Test Bot (before I started choppin’ and screwin’ them). They will indirectly drive all four wheels, since the geometry of the frame makes direct drive impossible. Heavy stuff, of course, is in the back. I might actually stay with giant nickel-chemistry cells since they are great for ballasting….and lithium batteries of this size is going to cost as much as the rest of the bot.

The lifter motor will be a fun work of engineering. I couldn’t find any single motor and gearbox on the commercial channel (within reason) that had the torque necessary to lift and hold a 30lb opponent AND fit in the bot design. The Banebots CIM gearboxen were a good choice, but were too long and wide for the design, and with the motor, would weigh in at 8 pounds. That is not acceptable in a 30 pound robot.

So then plan is, as I termed it, to “ghettofrankenb0x” two more 18 volt drill motors. This involves adding another 6:1 drill gearbox stage on top of the 36:1 stock gearbox, all in a custom housing. Each motor is then reduced 216:1. Two of these are coupled together at the output shaft and then mated to an additional 3:1 chain drive to the lifter axle.

The output speed should result in the lifter swinging (no load) at 120 degrees of rotation per second. 120 degrees is roughly the maximum swing it has, and 1 second is *PLENTY* fast for a lifter like this. This dual motor 400+:1 reduction will have enough torque to dead lift 150 pounds, but I designed it to lift and hold a 60 pound robot at the end of the arm with the motors under power to fight backdrive. So a 30lber should actually be quite trivial.

But the drill gearboxen now suffer from “Banebots Syndrome”, which is the stacking of too many reduction stages with no increase in gear size or width. Chances are, they will not stand a dead stall. However, the point is to not dead-stall them against something solid.

Here’s the gist of it.

An all-aluminum structure supports both the lifting forks and the clamping arm. The dual ghettofrankenb0x is seen here. A small gearmotor, mounted to a leadscrew assembly, will drive the clamping arm. I currently have a B62 motor that was designed in for this job, but may switch to something of a similar form factor if it proves not up to the task.

The pivot point for the clamping arm is actually mounted in a floating assembly with the leadscrew nut. A series of disc springs hold the two apart. This is a measure to save the motor against hitting a suddenly dead stop in the form of either travel limit or another robot’s top. It also adds in a bit of “preload” to the clamping arm when it bites down on an opponent. This is not designed to save the system if the opponent tries to force its way out – a real indirect drive will make no difference in that case.

Here’s the spring-loading device for the front support legs. I could have avoided this bit of complexity with a large torsion spring or two, but had trouble locating suitable springs. Torsion springs are supposed to act over a wide range of motion. I only need about 10 degrees of springiness or so, which means a torsion spring will make very little difference unless it’s been massively preloaded. Torsion springs of the size needed to balance the robot were also quite huge to begin with.

So a “shock absorber” type setup was implemented instead. This is just a die spring from McMaster riding on a shoulder screw, which is in a movable mount attached to a drive pod standoff. It should allow the legs to move over small obstacles like the “floor bar” hazards. This is also the travel limiter for the front legs (such that the robot can only tilt forward about 10 degrees) since the spring won’t compress further than its solid length.

External overhead view. The robot is 20 inches wide and 16 inches long at the end of the chassis. The support legs take it to 22 inches long, and the tip of the fork makes the whole robot 27 inches long. This is huge. The chassis size is very reasonable for a 30lber, though. The height of the frame is 2 inches, and the height at the fork is 5.5 inches.

Top estimated speed of the thing should range between 10 and 12 feet per second. This is very zippy, and I might scale back a bit. However, fast is good for chasing down and grabbing opponents by the collar, and then whirling them around.

How many robots can I throw into the crowd?*

Building this bot will be a test of my machining skills for sure. Since the frame has many 2D flat plates, most of it can actually be pre-fabbed on the waterjet machine. For instance, this is a test layout of all the 1/2″ aluminum parts on a slab of 1/2″ x 12″ x 28″ 2024 aluminum I bought a while back for TB.

Most of the manual machining will be on the UHMW frame parts (since UHMW waterjets like total shit) and the drivetrain. In other words, pretty standard stuff. All I need is, of course, the time and machinery, both of which are in plentiful supply over the summer.

I also intend to make a closed-loop control for the main lifter arm. I am not going to jiggle both transmitter sticks in perfect synchrony as to clamp, lift, and drive at once. I have yet to find a way to shoehorn in a servo feedback device onto the leadscrew assembly for the clamping arm – perhaps a linear potentiometer or something.

So this is the official unveil of the concept. Staring the week after finals (this week), I should have three months and a week to get this thing done and tested. Can I do it?

Only time money will tell.

*The answer to this is ZERO. The crowd is at least 25 feet away from the stage. Robot Battles also has a spotless safety record because it holds common sense to be the baseline rule. Let’s keep it this way, folks.

It’s legi…. wait… nevermind.

May 17, 2008 in Project Build Reports, Project RazEr

There seems to be a disturbing trend in all my recent projects of everything progressing smoothly and going right, then the whole project grinding to a halt at the last possible second before completion and being wholly unrecoverable without spending an additional hefty sum of money. Case in point: TB4.5-SP1 for Motorama had essentially half the robot become crippled the day before I had to leave for the tournament.

New case in point: Snuffles Reloaded half-existed for about 30 seconds before the motor controller failed. The failure is undiagnosed at the moment, but probably revolves around blowing a voltage regulator which then shot the controller logic with 35 volts.

Here’s some build pics from over the past few weeks, and the (95%) complete vehicle, along with the half-existance video.

As the mechanicals were nearing completion, I started playing with the electronics. The R/C airplane controller requires a 1 to 2 millisecond long pulse spaced every 20 milliseconds, which is a hobby industry standard for control signals. However, the electric bike throttle I was going to use puts out an analog voltage from 0.8 to 4.2 volts. This is, again, a different industry standard control signal.

I decided to use a microcontroller to translate between the two instead of the awesome ghettomongous discrete-part boardamathinger that I built for the first scooter. A bit of messing around with blinkenlichten on a MITERS STK500 and I was in business.

After playing with the analog-digital converter, I made the output LEDs act as a throttle display meter of sorts, for kicks. Full throttle, all LEDs lit, and they go out in sequence as I let off the throttle. I might actually implement this using a LED bargraph chip in the future.

Next up was assembling the eight giant lithium-polymer cells without killing myself or burning down buildings.

To solder epic batteries, you need an epic soldering iron. Unfortunately, I couldn’t find the epic soldering iron I used at the Media Lab to assemble A123 cells, which are even more epic than my 4AH lipos. So if you do not have an epic soldering iron, you need an epic soldering tip.

A scavenged rod of copper and some lathe time later, and I had an epic soldering tip which fit a Radioshack 40 watt soldering iron, which I do have. The whole thing is 2.5″ long and is .400″ in diameter at the larger half.

The brass one was for testing and practice, since a rod of copper is actually pretty pricey these days to just fuck around with.

The bottom battery pack completed after some careful iron maneuvering. The epic tip made the whole operation touch-and-go, exactly what you want for soldering batteries. You never want to park the iron on a battery cell for more than a second or two.

This was a bit of a risky operation since I was laying the cells face-to-face to conserve wiring volume. Normally, batteries like this are stacked and the cell tabs folded over one another. One wrong move with the massive solid copper tip and I was probably looking at replacing a cell.

After each joint was made (and its balancer lead installed), it was covered in electrical tape. When all the joints were completed, I slammed the whole thing in a tube of giant heatshrink and parked the heat gun over it.

Giant heatshrink should be a primary structural fastener. When it starts tightening down, everything inside sort of scrambles for the lowest volume configuration, and the end result is a very neat package of parts. The pack was embedded into its mount with some also primary-structural double-sided tape.

This pack constitutes cells number 5 through 8. The balancer lead is a standard 3-pin R/C servo plug, which serves the interconnects between cells 5 and 6, 6 and 7, and 7 and 8.

And the test assembly. The connectors fit into the LASER-cut acrylic endcaps as they should, and some CA glue retains them.

Building the internal electronics bay was more interesting, since I had to fit batteries, large power wiring, a controller, a switch, the charging port, and all associated connectors inside. I cut out a rectangular piece of aluminum as the substrate (way to go, conductive mounting surface?). Originally, it was going to be flanged and shaped with a sheet metal machine to accommodate the parts, but I decided to not get fancy and just mount everything with double-sided tape or epoxy.

The same procedure of soldering and wrapping was done to the 4 internal cells (#1 through #4), with the exception that their balancer leads went straight to the Convenient DB-9 Connector of Cell Balancingâ„¢. An 8 cell pack requires 9 pins to be fully tapped. Guess what has 9 pins?

Three of the DB9 pins went to the rear of this pack, where they met with an R/C servo pigtail which connected the back half of the pack to the balancing port.  Two large power wires also connected to the bottom battery pack, one of which is the 0v  (ground) line, and the other an interconnect between cell 4 and 5.

After everything was assembled, it was time for a test run. Verdict: It moves.

Some shoving and… it fits! To install the thing, I had to take off the folding hinge, cram the assembly through to the back side about halfway, insert the folding hinge nut plate, then slide it in the rest of the way. The nutplate sat snugly above the controller, but not enough as to pinch wiring. This precision engineering part of the build came out (went in?) great.

Before I fitted the internal electronics, I threw together a source of 5 volts for the motor controller. It is an opto-isolated controller, and so needs separate logic and power rails. This was a simple 7805 regulator jammed in the empty space between the controller and switch.

Here’s an assembled-on-the-table test run video (.MOV, 4.8 megs) using the creepy custom throttle interface device. The mechanical noise is from the completely unbolted and unclamped motor and chassis resonating on the table.

Unfortunately, this regulator would ultimately cost me all the work for the past few nights and a good bit of money. Protip: A linear regulator cannot drop such a huge percentage of its input voltage and output any appreciable current. I was most likely hitting the top end rating of the 7805, around 35 volts, and expecting it to output a solid 5 volts with at least 100 or more milliamps of current. Shortly after the video was taken, some things went pop.

My best guess is that the controller logic board was hit with the full 30+ volts of the battery. A switching regulator, or even two stages of linear regulators (inefficient, but hey), even mounted externally, would have prevented this disaster.

Anyways, here’s a pic of the almost-running vehicle.

The ‘empty weight’ is probably around 13 or 14 pounds. Yes, I had to remove the rear brake in order to pass the motor cables – perhaps it would have been better to route them externally. But who needs brakes anyway?!

Regardless, there’s 29.6 volts of 4AH lithium polymer cells, a (former?) 100 amp motor controller, and a very chunky brushless motor shoved into the space of a Razor scooter. I think it’s pretty damn awesome just for that.

I will need to get a new motor controller and devise a new solution to get a stable 5 volts out from the battery pack before the vehicle will run. Seeing as how this will easily cost over $100, it might have to wait a bit. Possibly a long time – we’ll have to see.

Here’s a closer shot of the undercarriage, which houses all the interesting bits.

In the mean time, finals! Bot on, folks, while I attend to these…uhh, pressing matters.