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

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

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

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

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

Yeah. It’s kind of trashed.

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

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

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

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

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

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

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

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

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

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

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

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

überclocker

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

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

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

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

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

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

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

RazEr rEVolution

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

…

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

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

Segfault

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

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

land-bear-shark

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

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

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

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

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

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

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

It has begun.

While I seem to be in “build season” mode year-round, it is during long breaks with little in the way of academic or life obligations that I get the most done. Last summer, I began work on LOLrioKart and built Überclocker, Pop Quiz 2, and Nuclear Kitten for Dragon*Con.

… which sort of sucked horribly for everything. Except NK, but only by about *this* much.

So what’s coming down the projectubes this summer?

Mostly the same thing. D*C is my biggest bot-celebration of the year, so once again the combat robot fleet takes high priority. Since there’s really just one robot that needs rebuilding, I also have the usual pile of small electric vehicle projects, of which only one is actually urgent.

Übercløcker RЭmiχ

I started redesigning Uberclocker some time in the fall of last year, hoping to get it done by Motorama 2009. Of course, due to scheduling concerns and logistics, this didn’t happen. But what that presented me with was the chance to put it away and not look at it for several months.

This is pivotal. The basic design has already been hashed out, but now I get to return to it after not thinking about it for a while. I am now in the process of analyzing the 3d model for any “impossible objects” that I might have included, or Really Bad Ideas. Such design flaws plagued the real life Uberclocker 1.0 at D*C last year.

Planned upgrades from 1.0? Well, besides EVERYTHING, the primary focus is on drivetrain reliability, center of gravity, and the upper clamp arm.

As a member of the pushybot school of combat robotic thought, I value maneuverability and driving above jawesometacular weaponry. Uberclocker 1.0 had a strange serpentine timing belt setup that seemed like a really awesome idea at 5 in the morning, but… wasn’t.

The robot also suffered from “centrally located center of gravity” syndrome at the event. While a CoG near the geometric centroid of the robot is good in practically every other case, the fact that the bot’s sole purpose was to grab another opponent and lift it off the ground meant that it just sort of faceplanted every time I attempted a lift. Not a very impressive show. The redesign lengthened the wheelbase of the bot, and selective weight reduction moved the CoG back about 4 inches, without additional ballast.

Oh, that’s right, Uberclocker 1.0 weighed in at an incredible 22.5 pounds out of 30 at the event. I’ll fix that too.

What I didn’t really get to (properly, anyway) in the redesign was the upper clamp arm. The previous arm was both weak and structurally unsound. While I think I took care of the “unsound”, I still have my doubts as to the clamp mechanism’s effectiveness. In the past, clampbots have used pneumatics to actuate the upper half of the clamp. This is advantageous because a pneumatic actuator requires no “holding power”, unlike an electric motor, which has to be continually powered to produce torque. Pneumatics also have a certain amount of spring-back ability that a solidly coupled electric actuator doesn’t.

But robot-heaven forbid that I make Überclocker even more complicated by incorporating a pneumatics system for the one actuator that might need it. Thus, I’m still partial to a (spring-coupled) leadscrew-type mechanism, over the current design candidate’s motor-on-a-weird-gear. Except this time it won’t be driven by a beetleweight motor.

I intend to keep the “Chinese puzzle” frame, and will be refining it for ease of assembly. I devoted a few weeks to just fabricating the frame parts last time – no, never again. That’s what computer-controlled machine tools are for.

Pop Quiz 2√2

Incidentally, 2√2 is about 3. Not quite there, which also describes this planned rebuild of Pop Quiz 2. It’s not quite a complete conceptual revision, but there will be significant upgrades all around.

PQ2 is one of the (if not the) flattest 1lb class robots around that has an active weapon. It hits lower than some undercutters. The problem is that going the extra 1/8″ down in this current design meant that I had to ditch practically all the well-known, battle-proven parts – Sanyo gearmotors, SPEKTRUM 2.4ghz receivers, etc.

It was a fun thought experiment come to life, but the robot had a horrific reliability record, almost no reception due to the FM ground-band receiver, and a 5 minute chopped hack of a master power switch that ended up disintegrating after exactly 1 hit at D*C 2008. Pop Quiz had about 15 seconds in the arena.

Not cool. For ’09, I am INCREASING the height of the bot. Me, making a robot taller. How many times does THAT happen?

The robot height will be increased to about .400″, enough to cram in a set of real Sanyo micro gearmotors. The rest of the robot’s electrical system is sound, and so is the weapon motor. I’ll most likely end up reusing the electronics anyway, minus the cheesy little FM park flyer receiver. Instead, it will be swapped out with the latest Spektrum DSM offering, and I will run one transmitter between all the robots.

There’s no current virtual model for PQ2.8284171, but just imagine the current bot 0.025″ thicker.

Nuclear Kitten 5.1 Digital Surround Sound Edition

I’m actually satisfied with the performance of one of my combat ‘bots for once. NK needs very minor rework to take another run at D*C. The weapon motor needs some magnet reglued, and the weapon pod pivot axle is slightly bent and needs to be made better anyway. Past that, I have a spare blade to replace the faceplant-into-steel-bumper bent blade.

The only point of concern with NK is the drivetrain. Despite having a mechanically isolated weapon, I’m still blowing drive gearboxes, just because the bot is that much more powerful. I might switch to something like the 50:1 Copal motors || redesign the motor mount || use softer wheels.

No frame changes are necessary, since the bot escaped D*C rather unscathed.

LOLrioKart

Since I discovered that the main battery pack was leaking voltage all over the place (somehow, through an eighth inch of rubber?), I stripped down the entire electrical system and tested all the batteries. It turns out that the steel casings of the cells are live, something which I’m fairly certain should never be the case. While it’s fairly common for the battery negative terminal to also be the casing, the errant voltages are always somewhere between 0 and 1 volts.

This case voltage doesn’t seem to have negatively affected the cells, but I’m fairly certain it’s the culprit behind stray frame voltages. Somehow.

The focus for LOLrioKart work will be the electrical system. I intend to complete and test the ginormoFET controller and possibly implement dynamic (or regenerative!) braking using the upper leg of the half-bridge. Mechanically, the kart is fine.

Well, except for the brakes, but they’ve always been undersized and insufficient.

Ultimately the goal is to run it for longer than 1 minute on all 54 volts, or the full pack voltage of whatever eventual power system I might come into. I’m heavily considering crating up LOLrioKart and shipping it down when Dragon*Con comes around, so I can drive it in the parade. This could possibly be the worst idea I have ever thought of.

Project RazEr

It’s been hanging on a utility hook since the last controller fire. Everything works and the batteries are still charged, so all I need is a BLDC motor controller. Since everything still technically “works”, I don’t intend to touch the scooter that much, if at all. Any work on it will be replacing the shell of the wheelmotor with something more substantial (and better engineered, and more reversably built).

Time to get crackin’.

Equals Zero

robots are dumb

Category: Pop Quiz 2

It’s Time for Shenanigans