Archive for August, 2009

 

Überclocker Remix: Round Six

Aug 24, 2009 in Bots, Project Build Reports, Überclocker Remix

What’s nice about having no job or class obligations: The ability to haul ass day and night on one thing.

What’s not nice about having no job or class obligations: The ability to haul ass day and night on one thing, because people like me don’t know when to stop.

z0MG MECHANICAL COMPLETION

I have now reached the point that the only thing stopping me is electronics. This essentially means if the competition were TOMORROW, I could duct tape together an electrical system and have the bot run plug it in backwards. But i won’t do that – instead, I can now make the electronics mounting provisions.

…okay, so I haven’t designed them yet. This will come down to another game of CAD by night, build by day. Hopefully, with less than the whole bot remaining, there should only be one session of this game.  If all goes well, I expect ‘clocker to be running – possibly not well, but running, by Thursday.

Meanwhile, pics.

It’s a half robot!

With the IDFBs, upper clamp arm, and fr0k assembled, it was a simple matter test fitting the entire assembly. All I can say is that everything actually works as expected. The weird split-clamp-shaft-collar-hub idea can be dialed pretty precisely for torque such that the main gear just spins on the axle if I attempt to power the whole assembly past the mechanical limits.

Check out a test lift of a 25 pound isolation transformer doohickey here.Note that this run was filmed with the gearboxen running on 12 volts (out of 22) and fed from a single pair of 20 gauge alligator clips. Not very exciting.

If only the bot can be clamped to the arena surface in real life. Then I wouldn’t have to worry about faceplanting.

I finally finished the drive gears, which are 1/4″ waterjet-cut steel. Note the double-D flatted bores that slide right onto the motor shaft and are retained by a non-torqued screw. The finish obviously leaves a bit to be desired, but it’s nothing that’s not fixable with some running time covered in polishing paste.

I started tearing the Pretend-O-Bot frame back down to put the drivetrain together. There were a few holes that needed countersinking because I forgot to account for the fact that…again, screws are 3-dimensional, occupy volume, and have protruding heads.

5am Joltgineeringfail.

I only needed to remove about 6 links from each 3 foot roll of chain to get a taut-but-not-binding fit between the sprockets. This should get slightly looser as the bot runs, which should actually move it into the proper operating tension zone. Right now, the chains are definitely on the stiff side.

So here’s the other side of the robot. The drivetrain is done. If I were truly desperate, Überclocker could run in this state as a pushybot.

But pushybots suck.

I went ahead and loaded up the frame with t-nuts in the hope that I would not have to take it all apart again.

Watch me be TOTALLY WRONG.

I shifted work towards the front and finished assembling the legs. By this time, I had so many shoulder screws lying around that I forgot which ones go into which part of the assembly.

No matter, I just picked ones that looked right.

Little nylon washers keep the metal from rubbing on adjacent metal.

Legs on the drive base! So with the bottom half of the robot frame assembled, and the fr0k assembly put together and tested, there was only one thing left to do.

PRETEND-O-BOT!!!!

Oh man. It’s almost there. One or two more beast nights and it will be all over.

I get to synchronously repair LOLrioKart, make the bot crate to get it to Atlanta, move back into the dorms for fall, and handle pre-term logistics.

WONDERFUL.

Here’s a head-on view.

f

Überclocker Remix, Round 5: Integrated Dual Frakenb0xen

Aug 23, 2009 in Bots, Project Build Reports, Überclocker Remix

This is the main drive gearbox for Überclocker’s giant fork, so it needs to be absurdly overbuilt to withstand other robots landing on it.

Let’s start with a picture of me being halfway done. This was a process underway during a morning hour early enough such that I was just running the  “machining drone” brainware.

A picture of a brick of aluminum isn’t exciting anyway.

Boring out the ring gear circle generated some long and interesting curls. I’m always in a contest with myself to make the most absurdly long and interesting curls.

…then hang them all up in the space. The longest on record stretches the whole12 feet from the floor to ceiling.

I’m fairly certain that one came about from a LOLrioKart part. There’s just nothing else I can think of which warranted moving that much \m/etal.

I seem to be more interested in the chips than the part. But I’ve never seen these get ejected before, so they need recording. It’s kind of like discovering a new specie of animal. Would this be some sort of tropical aluminum snail?

These were generated using the “Okay, this hole is at the right dimension, so as long as the boring tool is set correctly, let’s BEAST THE OTHER HOLE IN ONE FUCKING PASS” method, for which I am well-known.

Yeah, about that. Guess which one of the ring gear circles got the one-shot treatment.

The two small holes in the middle are for steel dowel pins that will positively locate the motor mounting plate such that nothing slides around. Even with 6 screw holes, I still wanted some sort of piloting surface that will guarantee the correct motor placement.

(Hint: It’s the one with the really shitty bottom finish.)

An eclectic pile of drill parts! So there’s (roughly) 3 cordless drills in this picture, except you can’t tell because showing you a picture of a pile of human parts and saying “There are 3 people in this picture” has about the same effect, perhaps with more retching.

So why are some of the gear parts black? Because I figured out the coolest way to degrease them ever.

Heat-treating the aluminum gear casing for more strength.

No, just kidding. I finished the Bores of Ball Bearing Holding very slightly undersize, so I figured the best way to install them without brute force was to pull the classic coefficient of thermal expansion trick. When metals are heated, everything expands – outer dimensions get larger, and inner dimensions get… larger. It took me a long time to come to terms with that.

Regardless, freeze your bearings and cook that which your bearings need to be secured in. I chucked the bearings in with the ice cream and turned the toaster oven up to Broil, and waited a few minutes.

….Yeah, it’s used for food occasionally. So?

The bearings, now slightly smaller, slide right into the bore, now slightly larger. When the temperatures equal out, everything is as secure as can be.

While the gear casing was baking to golden-brown crispiness, I worked on the motor mounting plate. This was the most straightforward thing ever – holes in a flat bar of metal. Stuff that I used to do by hand drill, then drill press, now spend 10 minutes setting up the mill.

Sigh.

The two slots are to clear the front vent holes in the motors, so they can get some air. See, that was something the hand drill COULDN’T do!

Other side, with motors mounted. I designed for Speed 700 size motors on the lifter too, but ended up using these 550-size drill motors. The reason was that I couldn’t locate more 15 tooth pinions and 24:1 gearboxes.

Überclocker did just fine with 2 550 motors at D*C ’08, so this shouldn’t be too different. In fact, the reduction is even higher this time, so current draw should be less.

Here are the beastnormous gears that the motors will eventually be driving. 12 pitch, 15 tooth, and (originally) 1 inch wide face. Quite substantial. I didn’t need all that bulk, so I cut ‘em down to 5/8″ face.

So this is how shit goes down.

Originally, the gearbox design called for a simple crosspin to secure each gear to its respective motor shaft. I decided in about 5 minutes after looking at the model again that the idea was completely not legit. First, the space constraints were such that I could only fit a 1/8″ wide pin. Second, and worse, the pin location was limited to the distal end of the drill shaft, which was hollow. Long story short, I started investigating options that didn’t involve “concentrated point stress riser under shear”.

I excavated an idea which machine tools have used for centuries and I last used on Trial Bot 1.0 in 2005 – a tapered shaft with matching tapered bore in the gear. Good god, what? Machine tapers are really cool in that they transfer tremendous torque in a small space using the full contact area of the metal in the taper. Gee, that sounds like exactly what I need.

I settled for a Morse #7 taper with the gauge width of a Morse #1. In actuality, it was just whatever I set the taper-cutting attachment on the lathe to.

Taper what? The folks over at South Bend Lathe Works, some time 50 years ago, included a taper-cutting attachment on the machine that eventually through some circuitous history of ownership made its way into our club space. This is a really nifty device that I would have trouble explaining the exact functionality, since smarter people designed it. It adjusts to let you cut a taper from 0-5 included degrees over the length of the bed.

So I set it to “3 DEGREES”, locked everything down, and hoped for the best.

It worked. In fact, so well that now I’m trying to think of ways to get the gears back off in the event of an emergency.

To make the IDFBs work, I needed 3/2 of a drill ring gear to support 3 stages. The solution was simple enough – take a spare ring gear and cut it the hell down. Sintered steel machines very strangely because of its porousity. It soaks all the oil from the gear grease, and kind of self-lubricates, but having no real grain structure, it finishes like total ass.

Carbide tooling seems to help the situation immensely.

I pulled the freez-and-burn installation technique to great success a second time. Here’s a pic of the gearbox being filled with… you know, gears.

Both ring gears installed now. Even at 216:1, the whole thing is extremely smooth when dry. Adding grease would increase the drag a billionfold I’m tempted to just use gear oil, except the other side vents to open air and it would all just flow out and make a mess.

SPIN TEST! This thing is so incredibly ridiculous. Very smooth and quiet, even at 24 volts (the motors are 18 volt units). And pretty much unstoppable.

I tested the gearbox with both pinions mated to the fr0k gear. While the mesh isn’t a problem, the differences in motor speed are enough such at over the course of 20 or 30 revolutions, the gear skips a tooth. This will be no problem once the gear is actually mounted. The current draw resulting from mechanically equalizing the two motors will be slightly higher, but it won’t cause problems.

OMG CAN TEST FR0K AND DRIVE NAO

Überclocker Remix: Round Four

Aug 23, 2009 in Bots, Project Build Reports, Überclocker Remix

how is robbot formed

how robbot get moters

Questions for which I wish I knew the answers. One full week left of Überclocker work, half of which is Orientation for the Class of 2013, which means I sort of have half a week left.

The past while has been filled with high-intensity gearbox manufacturing. I am now relieved of work obligations, so that means I can plug on the build day and night. The drive motors are done, and with another run on a waterjet, I can have the drive base structurally complete. Hopefully that will occur by the end of the weekend.

Oh, yeah, pics. Usually by the end of a build, I’ve somehow wrecked yet another camera, but fortunately my surrogate machine is too big and chunky to forget about, then drop something on. The past few posts on this site have been garnished with pictures courtesy of my Fuji S9100, which I got for the excellent price of Free a while back.

It has too many buttons for me to operate properly.

I made two more embryonic drive gearbox halves while the Bitch Chuck was still dialed in. The bearings were put in as a test fit, but then I figured that they were sealed and it was okay to proceed without removing them.  They are 6901 type 12mm bore bearings. Each pair of two will carry a modified drill gearbox shaft in the gearboxes.

All that remained to do after putting the radially symmetric features in was… put more radially symmetric features in. Here are the gearbox halves completed and ready for population with planetary gearing. The counterbored holes on the front half are for 6-32 socket head screws to bind the halves together.

Okay, it was time to start parting out the old bot. I needed the all the juicy parts out f Uberclocker 1 – motors, gearboxen, and the Victor controllers.

Oh, and the drive wheels. I had neglected to order more 2.5″ Colson wheels. The ones on the bot were in pretty good condition, so I just transferred hubs.

Überclocker got more banged up than I remembered. When I pulled the left drive motor out, a few chunks of plastic fan fell out the vent holes. Closer inspection revealed that the motor had actually thrown a rotor winding. I wonder how long the bot was running like that, or why the motor even ran at all?

The other motor also lost its internal fan, but was otherwise functional.

I elected to not reuse these. Wheels can generally be missing chunks and still work fine. Motors gnerally do not.

Okay, so what to do now? Speed 700-size motors are more difficult to come by. I started scanning the surplus channels for possible candidates.

I installed one of the drive wheels for kicks. The mount holes still need to be countersunk, so ultimately I’d have to remove it again, but hey.

The robot will have about 0.5″ ground clearance when all is said and done.

I continued down on the drive gearboxes even without a motor to attach to them, running on the confidence that mass production has made virtually all Mabuchi 775 size (Speed 700) motors share a common bolt pattern.

Aha, a candidate motor arrives!

These HTI units are commonly found in the surplus channel. They appear to have been manufactured en-nutty-masse for some kind of small vacuum cleaner. Regardless, AllElectronics has them for $3.75, MECI for $3, and the Robot Marketplace for $Jim, are you fucking serious?

Downside: They’re not neutrally timed. The timing appears to be 5 to 7 degrees in the CCW direction. This means Überclocker will be tracing a hell of a big circle all the time, but, as the laws of mathematics dictates, under small arena-sized deviations, a curve can be considered straight.

To actually be useful, the weird brass ring had to be removed from the motor shaft, and the whole thing needed to be shortened.

No problem, let’s just chuck the whole motor in the lathe and carve it all off in one setup. Again, this is one of those things that I put up just to make shop instructors cringe. Do not actually do this.

All done. The 15 tooth (rare!) pinions from the toasted motors were pulled off and reinstalled on these, with a dot of Loctite for trimmings. I say rare because only the 24:1 drill gearbox has a 15 tooth pinion, a gear large enough to actually bore out for the 5mm shaft of the Speed 700 motors.

The 24:1 drill gearbox is extremely uncommon in cheap drills. So uncommon that I have had trouble locating more for spare parts.

All mounted and ready. I’ve already cut the D-flats into the output shafts. These will engage D-flatted bores in the (still to come) final drive gears, and be retained by a single end screw.

Once I get said gears cut, the drive base can be assembled and theoretically tested. Next, to make a Siamese twin version of this gearbox – the Integrated Dual Frakenb0xen.

Überclocker Remix: Round Three; Pop Quiz and NK unofficially canceled

Aug 18, 2009 in Bots, Project Build Reports, Überclocker Remix

And the beat goes on.

The wire’s coming up fast.My summer internship with iLolbot ends this Friday. After that, I have a solid week where the only damn thing I’m going to do is plug on ‘clocker day and night. In precisely two weeks time, I’ll have to have everything wrapped up and shipped down to Atlanta. Lack of 24/7 tool access means that the state of the robot as of midnight on September 1st is pretty much going to have to be final.

At this point, I doubt I’ll have time to get to Pop Quiz at all. I thought Nuclear Kitten had required only a re-magneting, but it turns out the motor needs a total rework. Additionally, I need to reconsider the drive motors, since I went through two gearboxes last year and do not have any spares at the moment.

The insect status for Dragon Con is therefore tenuous.  NK is a second priority after Überclocker, and only if I think the design is going to be solid. Two events of last-minute rushing have sent me the message that last-minute rushing makes robots not fun.

Hell, if Überclocker doesn’t make it, I’m just going to D*C for the sake of going to D*C. Maybe I can actually take some pics this time.

Überclocker Remix

The build has pretty much reached the point where I’m the only bottleneck. That is, I have to fab all the rest of the part, and I’m slow compared to a CNC anything.

Yeah, I consider that “slow” now.

It’s time to start filling in the pretend-o-bot!

The “shocks” for the springy front legs. These are, like on Überclocker 1, post-op’d waterjet parts. I actually had to rework this design on the fly because I ordered the wrong kind of shoulder screws – 5/16″ diameter instead of 1/4″. The problem was that my springs had a 1/4″ rod-fit size.

Ever machine a spring? It’s not pretty, but a 5/16″ carbide endmill chucked in a lathe tailstock made pretty short work of it. I was expecting some epic disaster with the spring unwinding or just exploding out of the chuck.

This is the leg arrangement with the ‘shocks’ in place. I thought 100 pound/inch springs were going to be too stiff, but the high lever arm ratio of the linkage means the whole thing is still pretty bouncy.

More little shiny round things are now appearing around the robot. These are the drive “standoffs”, which function as dead axles. I formerly made these part of the robot structure, but it was an epic pain undoing the screws which held the body rail/panel to the standoff. Therefore, I just made a shoulder which sits in a bore on the outside walls of the robot. It’s not entirely structural, but will resist cave-ins (from impacts) to a degree.

I did end up putting a threaded hole on the outside end just in case I changed my mind.

The standoffs were made from 12L14 steel, which is something like two beans and a lollipop per six foot rod on McMaster. I have a new appreciation for this stuff – it’s like… steel, but it machines like aluminum.

Then again, how much should I be trusting steel which machines like fucking aluminum?

Hubs!

Well, these are actually functional prototypes of hubs. It was easier to pop four off in one cycle than to switch back and forth between machines, completing one at a time.

Completed hubs, with sprockets. Remember those sprockets with the weird double-D shaped bore? Now you know why.

Simple retainment and power transmission with the aid of the DD and a snap ring. I used to hate retaining rings (snap rings, C-clips, etc…) with a flaming magnesium passion. But after getting a set of snap ring pliers I realized they were the most compact and cheapest way to keep something axially where it should be.

So now I love snap rings. The cool thing is that the sprockets are easily removable, so I can press the wheel on later. This was just an assembly test.

… but wait, what do you mean the chain doesn’t go in my sprocket teeth?

I highly doubted it was a pitch/scaling issue, since some times the chain was able to wrap all the way around and other times not. I suspected that it was more a building up of small incremental errors made by the waterjet as the c hain went around the circle.

The solution was as simple as giving each tooth a really quick flick over the open section of a belt sander. After that, it was still sort of rough, so…

… this is TOTALLY LEGIT GUYS I PROMISE.

I am under no circumstances endorsing this kind of behavior.

Yeah. Right. Anyways, chuck one hub in a powered spindle of some sort (I had a convenient one 10 feet away), and put the other hub on a little axle that you can grab onto.Link the chain between the two sprockets and power the machine on.

Assuming you haven’t been sucked into the spindle yet, pull on the axle, hard.

This sort of grinds the chain into the sprocket teeth and forces it to round out imperfections just by virtue of being under balltastic tention. I was only limited in the pull force by the fear of the whole lathe rolling over onto me.

The sprockets ended up pretty smooth.

So I take back every mean thing I have ever said about 4 jaw chucks. They are wonderful, wonderful creations of man. More epic than the discovery of naturally-occuring sliced bread and the invention of the solar system.

But they’re still a bitch to use. However, it’s totally worth it for some situations.

Such as when you want to square off a section of barstock and insert a symmetrically-located circular feature in one setup! In fact, for situations (not speaking from personal experience at all) where your choice of barstock-portioning implement somehow makes an angled cut in two axes at the same time on both sides, the easiest way to get a known square end might be to cram it in a 4-jaw using the flat sides of the barstock and perform facing cuts.

I was only able to find tutorials on how to center round things online, but not square ones, so I had to invent my own little method first. Essentially it boils down to comparing the minimum deflection of a dial indicator on opposite sides and adjusting the jaws associated with those sides until they are the same. “Minimum deflection” refers to the location where the indicator tip is exactly perpendicular to the surface of the part. Any rotation would cause it to extend more.

…did I mention that 4-jaw chucks are a bitch to use?

Here are the results of a night bitching around with Bitch Chucks. These are embryonic drive gearboxes – more or less repackaged drill motors.

I discovered an annoying feature of one of my digital calipers which caused bore measurements to be .007″ under what they actually are. Imagine my surprise when I discover that a 0.944″ OD bearing passes through a 0.936″ hole.

It turns out the ID-measuring points were bent inwards such that they overlapped slightly.For future measurements I’m reverting back to an older (but less grunged) set.

This probably happened that one time they fell off a moving bike. Don’t ask why I have digital calipers mounted on a bike.

The Eternal Tragedy of the LOLrioKart

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

The saga continues.

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

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

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

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

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

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

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

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

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

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

…yet.

Zip tied to the kart.

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

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

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

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

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

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

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

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

Finished a few hours later.

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

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

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

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

So did it work?

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

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

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

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

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

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

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