Archive for August, 2010

 

Dragon*Con 2010: It’s a wrap

Aug 30, 2010 in Bots, Cold Arbor, Events, Nuclear Kitten 5, Project Build Reports, Überclocker Remix

cold arbor

First, I would like to say that I finished Ninjabridge.

It looks like this:

Yup. Back to a relay.

Ninjabridge worked briefly after extensive noise-reduction and ground loop prevention surgery. Sadly enough, it suffered a gate drive failure and subsequent Epic Shoot-Through at almost full saw speed. Nothing was particularly happy.

And so with the sun rising yet again, I pitched together this 12v SPDT relay assembly. It’s triggered by the previously mentioned R/C switch.

At least the saw works. Some more drive testing confirmed that my fears about the saw’s startup and running current pulling down the entire system were unfounded. Here’s a video of Arbor nibbling on some wood.

And a “pre-event” picture (not that D*C is a destructive enough event to warrant it, but hey.)

Überclocker

After putting all the screws on Arbor, I turned my attention back to Clocker to address one last detail that hasn’t proven fatal, but isn’t very healthy to ignore.

The bot’s drive chains have been getting increasingly looser as matches passed. The left side, in fact, has become so loose that the chain hits the ground on the bottom side of the frame. This is just begging to get snagged on something, or to make the chain walk right off the sprocket.

I’ve been meaning to put a chain tensioner on the drive since I built the bot, but never got around to it until now. The tensioner is just some simple bits of milled Delrin that has holes for perpendicularly tapped screws. I freehanded the vertical holes with a cordless drill, which brought back memories of before I was saved from a life of meager tools and hand fabrication. It was a heartwarming moment.

With the tensioners, the drive is substantially quieter. I would also venture as far as to say the bot is a little more responsive, too, since before the tensioners, the front wheels could spin 30 or more degrees before engaging.

If the chains ever get looser (Robot Jesus forbid) the Delrin sections can be milled more to compensate.

So now it’s time for a Clocker photo – I cheated a bit here, and actually took the picture before adding the tensioners.

And an everyone shot:

boxxy

No, not that boxxy.

This year, I’m going to be shipping down the bots ahead of time – which really explains why I’m working on them now and not, say, next weekend. Last year, taking Überclocker and support equipment as baggage cost me a cool $90 or so for overweight, oversize, over-the-top baggage fees. For essentially the same price, courier services will ground-ship an excessively large “package” from here to Atlanta in about 3 to 4 days.

Now, I’m defining “package” as “giant 2-foot wooden cube weighing 135 pounds and loaded with two (and a tenth) deathbots”, which might be stretching the definition some. But here’s the wooden box.

It’s made of some cheap Home Depot plywood (the same plywood, in fact, that Arbor was nibbling on. That panel became the bottom.

This time, I have enough overhead such that I’m actually bringing SPARE PARTS.

The bots go out in several hours and will hopefully arrive Thursday…

Nuclear Kitten 5.1: Start to Finish

Aug 27, 2010 in Bots, Nuclear Kitten 5, Project Build Reports

Something that very few people (myself included) have seen is the inside of NK’s weapon motor. About the time I built it in 2008, my camera decided to consume itself. So all I had from that time were grainy cell phone pictures because I’m compulsed to post build reports, but those pictures didn’t really show anything worthwhile.

NK’s motor was the third hub motor that I’ve ever built, period (after the original RazEr motor and the second iteration). It is also hands-down the most cleanest wound and carefully terminated motor I’ve built. This was back when I actually had patience for making motors. All the winding layers are clean and the termination is perfectly symmetric like a LRK should be.

After this, it all went to hell because I just stopped caring about how neat my motors looked… or even how concentric and wobble-free the cases were because it was fine as long as it could MOVE, dammit.

In International Crazy R/C Airplane Guy Notation, this motor is a 5205-14D. 52mm diamter stator, 5mm stack, and wound 14 turns per tooth in Delta termination.

I bought replacement magnets from Superdupermagnetgeorge to fill back in the 25% or so of the rotor that had become detached. The original magnets appeared to have been retained solely by superglue.

That’s kind of not legit at all.

In recent days, MITERS was given several large jugs of epoxy and hardener. While cleaning out a back shelf for the new EPOXY section, I found alot more adhesive accessories from years ago. Of most immediate interest was several cans of epoxy filler in different flavors in types. There was a can of West System 403 fiberglass-based filler, a bucket of phenolic microspheres, and wood flour.

I decided to do something that every other custom motor builder seems to do – fill in all the gaps and seams in the magnet ring with some hybrid epoxy. Adding filler gives the glue volume and more bonding area to the magnets. The fiberglass-based filler came out rough and lumpy, so I tried mixing up a cup of phenolic microballoon epoxy. It came out looking sort of like epoxy-flavored Nutella.

Now those magnets shouldn’t be going ANYWHERE.

weapon pod pivot

One of the gimpiest parts of NK5 is the weapon pod’s rear pivot. The disc is mounted on an assembly that can swing up and down, letting the bot drive inverted if necessary. The issue is that I made the last pivot in like 5 minutes. It was just a piece of sandpaper-cleaned Home Depot aluminum tubing and some roughly cut spacers. It flexed all over the place, and by the time D*C2008 was over, the tubing had crumpled from the impacts.

This was inexcusable. And so, in the middle of the night, I hopped on the lathe and just started making something. Above is the first 100% designed on the fly part I’ve made in a very long time. On one end, a snap ring groove. And on the other side, a 1/2″-28 thread machined so a thin panel nut can thread onto it. It basically functions as a very complicated but specialized bolt, holding the two halves of the bot together with some preload.

Originally I had intended to pick a random snap ring from the hardware bin, but a bit of digging around located me these weird e-clip-like things. A bit of research on McMaster showed me that they’re called “poodle rings”, presumably because of the big ears.

They had a much large diameter and thus potential contact area, so I remachined the groove slightly to fit them.

I also recut the UHMW spacers (using the same stick of UHMW) so they fit better and were also much large in diameter. The larger in diameter they are, the better they can resist side forces.

The old disc was warped from NK faceplanting into the steel arena bumper at full throttle. As a result, I dug out the spare disc I cut in 2008 and gave it the heat-to-orange-and-dump-in-oil treatment. It’s a crude method of heat treating, but it gives decent hardness for 4130 in bulk (don’t try this with a tube frame…) Afterwards, I reassembled the weapon motor and gave the teeth a touch up on the grinder.

With the important part of the robot done again, I begin refilling the internals. Pictured is the 1.3Ah Li battery I bought as a replacement for the old 2008 battery, now featuring a very dead cell. I actually got two because they’re too cheap for their own good.

And here’s the beauty shot:

While I had the lid open, I added a green LED next to the blue. Because funky colors are totally a priority.

NK handles just as well as I remember it from 2008. The right side drive motor is making some weird noises, but it doesn’t skip or feel crunchy. Regardless, I should probably get some replacement motors and have them dropped in Atlanta for next week.

Total robots finished: 2.999999999996842178 / 3

Dragon*Con 2010: Cold Arbor Impending Shenanigans

Aug 27, 2010 in Bots, Cold Arbor, Project Build Reports

Cold Arbor is now at a stage of completion where if necessary I can rig everything else together in 30 minutes. By this, I mean that the only thing missing from the bot is a means to control the DC saw motor. Interestingly enough, I’m well-stocked when it comes to brushless DC controllers, but now I want a single-direction 24 volt brushed ESC and that’s apparently asking a little too much.

The past few days have been filled with intensive Arbor work. After recutting and remaking the front sheet metal assembly, the rest of the robot came together quickly; as did the wiring. I’ve driven the sawless base around using the Hobbyking radios, and have pretty much confirmed their legitimacy for myself. It’s also just as fast and squirrelly as I remember it being.

The updated sheet metal work strengthens the area around the Slot of Saw Clearing (+1). The drop down flange extends farther in both directions from the slot, and more importantly, envelops the tabbing on the top and bottom flanges. I’ve also gotten rid of the ridiculous holes in the mounting ears that stick out backwards.

The whole show was, again, assembled using the weird aluminum-zinc solder-braze-weld alloy, then cleaned up on the belt sander.

The casualty rate for this piece was unusually high since I brushed the alloy in with far more pressure than I usually do. I’m hoping this will make for better adhesion.

After everything cooled down from the operations, I began remounting the saw. Arbor is assembled in a very linear, single-track fashion. In order to get the front off, all the sides had to come off first.

Also, in order to replace a motor, I have to use 3 different sizes of hex wrench on 4 sides of the robot at once. Once the saw arm assembly was refixed, I went ahead with steps to mount the Preduction.

Everything would have gone smoothly if I had remembered that there was actually no way of inserting the shaft collar into the assembly unless it was a two-piece split one. I didn’t, so I bought a bunch of normal 1/2″ collars.

Sadly enough, a 1.125″ diameter collar will not fit down a 7/8″ wide gap.

Solution: Just turn the thing into your own 2 piece collar. Step one is to mill a counterbore for the screw on the non-split side. Then drill a tap hole, tap the threads, and drill a clearance hole a little bit past halfway down.

Then viciously hacksaw the thing in half. Clean up the carcass on the grinder, and mezzopiano, a two piece shaft collar.

Perfection.  Here’s a little bit of saw flexing – overall, the travel is the same as before the actuator mods.

That’s it. The bot is mechanically complete. All the actuated systems move to my satisfaction, and the drive motors both work.

I discovered that the saw drew an absurd 33 amps just cruising, no load, at the full 24 volts. The cause for this was traced to the worm gearbox input shaft bushings. When the Preduction was added to the system, its ball bearing output and the two shaft bushings formed an undesirable overconstrained shaft. Essentially, the shaft has to bend at the first input bushing because the major end constraints are the very frontmost bushing and the Preduction ball bearing.

This might have been tolerable (and therefore a hidden problem) if the worm box came with ball bearings too, but with bushings, this causes massive friction. Just removing that bushing dropped the no-load amps to 17. Still high, but the MEV-alike draws 7 amps no-load already, and the rest I can realistically say is disappearing somewhere in the geartrain.

electriclulz

It’s time for that part of a project where everything usually goes horribly wrong.

The first thing to go wrong is my discovery that the fully loaded bot weighed only 27 pounds. With the greatly increased current demands of the saw motor, I elected to balance the weight by putting in a larger battery pack.

Above is the planned 6S2P arrangement of 26650 cells. The whole thing just barely fits between the drive wheels, the motor, and the front claws.

Going down to 6S relieves the motors of alot of strain. The 700 size drive motors already get pretty toasty, and the MEV-alike is a 12 volt motor. Things were really unhappy on 24v, and the single-parallel pack was being drawn down pretty quickly at Moto. Therefore, I’m also using 2 cells in parallel, each group forming a single metacell like on the METALPAXXX.

First thing to do is to put the cells together in bricks. I went my usual route of using Automotive Goop adhesive between the cells, then binding them with electrical tape and leaving the adhesive to set. Also pictured is a spare 7S1P pack for Clocker.

The 200th Cold Arbor build pic is of the infant Arborpack. I performed my usual grounding braid assembly method here – nothing particularly special

And here is the complete pack, with balance leads and after being double bottleshrunk.

Because the new battery arrangement precludes the use of the existing 1/8″ polycarbonate armored battery box, I elected to give these cells an extra layer of protection… or two, rather. I bought (and subsequently emptied to the detriment of my health) more cheap 3-liter sodas and cut up the bottles. With some quality heat gun time, the bottles shrink around the battery pack and then harden into a thick plastic shell.

Once again, in anticipation of the potential for high pulsed current demands from the saw motor, I threw a diode-capacitor buffer in line with the receiver’s power source, a cheap Hobbyking BEC. The diode sits between the main battery and the BEC input and essentially makes sure a sudden voltage dip in the rest of the system cannot upset the BEC. The large buffer cap should carry the BEC demand through transients.

I built the “check valve” system because I was planning on using a giant relay and a receiver-controlled switch to turn on the DC motor.

Loading the electronics back into the bot!

Rewiring Arbor was simple because the controllers were not stripped of their wiring, and the motors all had pigtail leads. So this process in total took maybe two hours, with plenty of wanking time allotted.

And a quick finishing shot from the front.  By this time, I had already taken the bot on a (sawless) test drive or two. The McMasterbots wheels wear pretty quickly – I’m going to have to order spares. Not for D*C, but later on.  As of the picture time, the RCS order had not yet arrived, so the saw wasn’t up and running.

ninjabridge

A relay-controlled weapon motor. Really? A relay? Really now, I think I can do better than that. If I couldn’t buy a forward-only, 24 volt compatible, variable speed DC motor controller, can’t I just build one?

These thoughts were cycling through my head as I was assembling the most impulsive electronics project ever – Ninjabridge.

Ninjabridge is composed of a Pro Mini Arduino, an IR(S?!)21844 synchronous half-bridge gate driver hidden under the Arduino, and four IRFB3006 FETs. It is (will be, after I add wires and software) a foward-and-brake controller with inherent synchronous rectification. With two 3006s per leg, I should get at least 40 or 50 amps continuous out of this thing with no additional heat sinking. Modern silicon is niiiice.

I’ve actually been in the design stages of a full robot controller – 4 channels of H-bridge DC motor drive and one single direction half bridge for weapon work, up to 36 volt operation at 40-50 amps continuous, all featuring implicit synchrec. I originally wanted to get the boards made and the whole thing ready for Dragon Con for use in this very robot, but decided against risking everything when I had otherwise functional controllers.

But there exists a “controller gap” in the medium power (12-36v, 30 to 60 amps)  range as of right now. Above this range, you have the venerable IFI Victors, and below this are the popular small robot controllers like Scorpion XLs, and the Dimension controllers that Arbor uses on its actuators. I’m not intending on striking out in the market with anything, but I want to see what’s possible with modern semiconductor and IC technology. And to this end, I think the above features are fully reasonable to pack into a space the size of at most two Victors (which are pretty large controllers).

I’ll track down more 12 gauge noodle wire for Ninjabridge and then spend a few weeks…err… hours coding up a basic single channel R/C compatible controller. Then maybe Arbor can actually damage something.

Dragon*Con 2010: Cold Arbor Speedplugging

Aug 23, 2010 in Bots, Cold Arbor, Project Build Reports

So there’s now a week left to go before the robots have to be packed up and shipped out. Nuclear Kitten is awaiting express-mailed parts from Hobbyking, and I’m just going to play it by ear in the time that remains. And now with Clocker done, I’ve primarily shifted efforts to Cold Arbor.  Arbor is actually most of the way ready to be reassembled. The grunge-machining, which has essentially been me making gearbox after gearbox, is finished. I now have to turn my attention to the front of the robot and appraise the condition of the brazed sheet metal assembly.

But first, pictures of gearbox after gearbox, because that’s apparently what I’m cut out to do in life.

Cold Arbor’s right drive gearbox was cannibalized for Überclocker during Motorama 2010. Arbor uses the now exceedingly rare (and expensive for) cheap drill gearbox with 700 size motors, so replacement parts for the intermediate stage are hard to find. Clocker promptly ate the second stage carrier, leaving me with no parts left to fix Arbor.

Or so I thought – while rummaging through my drill parts box, I started hitting 15 tooth gears, one after another. I figured I cannot have so many 15 tooth gears and not at least one more carrier plate. If I could find another carrier, then I wouldn’t have to remanufacture Arbor’s drives, and the whole bot could be put back together in 10 minutes.

I found a carrier which was wider than the others. Since the 15 tooth first stage has a wider planetary engagement circle than the standard 36:1 drills with 18 tooth first stage planets, I thought I had found the mythical lost carrier. Too bad, it was just a wider 18 tooth carrier.

I was not happy.

And I took my anger out on the carrier plate by… turning it into a 15 tooth carrier by drilling the damn pin circle into it. This was done on my haute usinage fixture, the rotary indexer.

Afterwards, I punched out the existing pins and moved them over into the new holes. This was actually a nontrivial exercise, since the pins were very small and demanded the straightest entry possible, something which I could not readily provide, even with a press.

After a bit of wiggling, the right gearbox is repaired. Why didn’t I just convert my carriers before?

I pumped the gearbox back full of grease, then threw it on the robot again. It will probably fail again during test driving, like everything else I build.

preduction

This is the junkyard parts-car equivalent of a Banebots P80 gearbox. Quite a long time ago, we bought one at the Media Lab to investigate planetary gearboxes for steering the embryonic Transformer that is the Citycar. It was experimentally determined that no, in fact, you cannot run a long Magmotor through this thing. And so it sat disassembled in a bag for the past few academic terms. Seasons passed and people graduated, and a few weeks ago I remembered that we had this thing and I needed a replacement for Deathrunner.

The motor pictured above is the Mini-EV-alike that I last remember seeing some time in 2007 before I left for the great northern wasteland. I guess I did end up bringing it with me. I literally have no numbers or performance data (or even a part number) on this motor, so I can only assume that it performs like a standard Mini EV. However, it’s a MEV with Magmotor-sized brushes, so it has to be more hardcore than the average MEV.

Regardless, I can’t have a 18-24,000 RPM motor feeding into the worm drive. So this is where the scrapped P80 comes in. I’m going to harvest one stage, the output shaft, and output carrier in order to make a 4:1 “preduction” gearbox for the motor.

There are three major machining steps in chopping and screwing the P80. The first is to cut down the ring gear so it’s sized for a single stage. It turns out that the ring gear is actually steel, and not brass or Shitluminum 9000­™ that the smaller Banebots gearboxes are made of.

Next, I made the motor mounting plate using some 2.75″ diameter aluminum. The holes were processed on my indexer once more (which was conveniently zeroed in already from drilling the new drive carriers).

Finally, I bored out a spare 4:1 planet, which has the same number of teeth as the legitimate sun gear, to press on to the 6mm motor shaft. I used an “A” size drill bit, which had a nominal diameter of 0.234″, and just shoved it through the gear. Then I shoved the gear onto the motor with an arbor press.

Proper manufacturing of interference fits actually involves math and factors in material properties, thermal expansion coefficients, allowable stresses in the material, and some magic numbers. My method is to just shove with a bigger press.

The protruding motor shaft was ground down.

The front bearing carrier plate was a waterjetted protoform job. I originally specified double 6801 bearings, but I didn’t have any on hand and ordering some would take a week (or cost more than it should from McMaster). In lieu of double thin-section bearings, I elected to just hammer the 6001 medium-section bearing out of the stock P80 faceplate.

The P80 had a 1/2″ diameter shaft that I decided to take advantage of. I drilled the center of the shaft to 5/16″, enough to slip over the worm gear input. At that point, the bottom of the stock keyway in the shaft was a few hundredths of an inch away from breaking through to the internal bore, so I cut it out with a Dremel.

The result will be yet another clamp coupling, like Clocker’s former arm drive and my funky die holder. And Fankart!’s propellor mounts. I love these things too much.

Here’s the Preduction drive, assembled but without hardware. I approve of how clean the whole assembly is.

Compared to Deathrunner, Preduction drive is about 1/2″ longer and unfortunately not that much lighter.

framing the issue

Here’s that “bent frame” issue that I described back during the first Cold Arbor situation sizing.  Essentially, this part of the frame is the most highly stressed point in the entire robot because of the thin cross section and its location right next to the saw mount.

Yet it’s also really poorly designed. My tabbing and slotting didn’t reach all the way across the gap, as the fracture failure on the lower right portion of the dropdown tells.

Additionally, where the saw connects on the other side, there’s huge weight-reduction holes. Thus, when this area inevitably experienced bending loads, the flanges just bent away.

Fail. I have a few front assembly cut out of 1/8″ aluminum that addresses both of these problems, so all I need to do is braze it together and throw every component back on.

Oh – there’s one more problem. The bottom fingers of each claw are attached using Impossible Standoffs – meaning standoffs which I threadlocked on both sides. Now, how the hell do I get those OUT?

Dragon*Con 2010: Überclocker is Done, Cold Arbor in the Mix, and the Nuclear Kitten 5.1 Blitz

Aug 20, 2010 in Cold Arbor, Nuclear Kitten 5, Project Build Reports, Überclocker Remix

In 2008, I had a Pre-Dragon*Con Botgasm. Last year, with only Überclocker, I didn’t have enough robots on deck to be finished in order to properly botgasm. Therefore, this year, I’m going to have to make up for it with now three bots that need completion!

Well, let me interrupt myself before I even start: Überclocker is done. I closed the bot up (well, minus battery cover, which I physically lost some time in the past 6 months) this afternoon and have been driving it around relentlessly trying to uncover hidden driveline mechanical flaws that could come and bite me in two weeks.  With Clocker asymptotically functional, I set it back up on the shelf and am now turning my attention to Cold Arbor…and a a revival of the Nuclear Kitten.

Überclocker

Two days ago, I left the FrankenWalt gearboxes about 95% finished. I made both gear cases, both sets of ring gears, both motor mounting plates, even both output stub-shafts… but only one output spindle. I just didn’t feel like machining the teeth off another gear that night.

But I returned later, having re-educated myself on the importance of finishing robots, and attacked that last remaining part.

Now here’s the reassembled drive base of the robot. I essentially took apart the entire outer metal structure, cleaned everything, then put it back together with the motors in place. Significant amounts of dirt, arena grunge, and metal chunks and flakes (!) made it into the corners of the robot, so as long as I had it in the open, I might as well clean it all out.

The outer chains have experienced some pretty serious stretching, and I expect that I’lll need to make a tensioner for them soon, lest they snag on something.

A couple more screw later, and the fork structure is remounted. While I had the fork apart, I took the time to make a few minor tune-ups and adjustments; mostly line items on the laundry list of upgrades that I keep intending to do (since they would technically take little time), but never get off my ass to do so. Such as:

…grinding the tips off the fork shaft set screws. These were formerly normal cup-pointed set screws, but I was dissatisfied with the way the cup point was gouging and digging into the flat on the (relatively) soft aluminum lifter shaft.

One way to resolve this is to just make a more legitimate power transmission medium, such as a keyed hub. But we can’t have that, since I’m lazy and therefore always vigilant for hackarounds. To obtain a wider contact surface with the aluminum shaft, I ground the tips off. Now, the contact circle is much closer to the 1/2″ screw diameter.

It won’t prevent gouging, but it should increase the shock torque handling ability of the fork a little more.

I kept the electronic bays intact, so dropping the Victors back in was a quick job. Since most of the wiring was on connectors, I didn’t have to rewire much from scratch.

Bonus: There is something very, very bad in the above picture. First one to name it wins….

… something. For what it’s worth, I fixed it.

A quick power-on confirms that the system is still functional.

Well, functional to the degree that I somehow managed to solder both drive motors in backwards.

Oh yeah – also on the list of stupid hacks I never get to is rearranging the actuator layout of the robot. Historically, Clocker has ran with the clamp actuator slung under the clamp arm itself. This location protected the motor itself from direct impact from opponents and also made the wiring path simple.

However, it severely constrained how far up the clamp could move, because the way the linkage is set up, the motor would just back itself into the aluminum fork hubs. This essentially limited Clocker to gripping opponents less than 8 inches tall.

I’ve toyed with the idea of flipping the actuator around so the motor is mounted above the clamp. This arrangement gains the bot another 2 or 3 inches of “grip” and also helps the leadscrew clear the truss that forms the forward portion of the clamp arm, which means the clamp can close to just over 1″ gap.

The only downside is that the motor is now open to damage. I’ll make an aluminum plate cover for it or something, but I think I’ll keep this setup.

All of this said and done, here’s some test driving video of Clocker, chasing Twitch, Jr. Everything goes well until the robots collide head on.

Hint: The robot that weighs three times as much and is essentially an uparmored Humvee in terms of structural durability fared better. Sorry Twitch :<

However, test driving revealed a critical flaw in the right side FrankenWalt – the first one I made. When I hard reverse planted Clocker into a corner, the right side completely lost coupling. I was completely unsure of what it could be, since the whole thing was made of Beast Fits and Loctite. As it turned out, the second stage ring gear’s press fit was in fact not a press fit at all. I probably only thought it was because I was pushing through burrs. The gear was actually pretty free to spin inside the gearcase. Solution: Drill down into the ring gear through the aluminum case just deep enough to insert a dowel pin. I used a #14  drill at 0.182″ diameter to make a gouge for a 3/16″ pin.

And by pin I mean lathe tool stock. Hey, it’s hardened steel and polished. Give me a break.

(The pin was cut flush with the gearbox surface and ground smooth, just for the record.)

It’s good that I found this out now and not, say, Monday morning of the con.

Overall, that does it for Clocker. I still need to cut out a replacement battery cover, since it being a nondescript cut-up-looking chunk of black plastic, it probably fell on the floor and got tossed during a shop sweep. At this point, Überclocker weighs 27 pounds – more than it did originally, but not surprising after the addition of the much bigger drive motors.

I’ll actually be making the replacement battery cover out of some very thick steel just to use up the last 3 pounds and push the robot’s CG back another millimeter.

cold arbor

Arbor has reached its own apex of entropy – after this point, I should be putting the robot back together more than taking it apart. Hopefully – I still haven’t addressed the drive motor issue yet. I kind of don’t want to make another two FrankenWalts, but I doubt I’ll be able to use the 24:1 gearboxes any more.

The designed parts of yesterweek have materialized into 1/4″ and 1/8″ aluminum plate. I managed to find a good deal on 2024 aluminum panels on eBay several weeks ago, and the 1/4″ parts here are made of that plate. Featured above are the new claws, the new saw motor mount, and new actuator mounting points for both front and rear actuators.

A little bit of sanding later and the rear actuator mount is in place. This is a very visible use of “thickness buffers” in the art and science of T-nutting. The original 1/4″ aluminum struts were 1.75″ apart, but the saw actuator is 2 inches. So between the back of the bot and the saw actuator, the spacing needed to widen up an eighth inch on each side and still had to hold T-nuts at the back.

So the solution is to stack two 1/8″ plates: one part which is purely a T-nut anchor, and another which is identical in that regard but also has the actuator mounting points – and make sure it’s on the outside of the stack.

The mounting plate is bolted to the thickness buffer plate using a handful of 6-32 cap screws. I thought about riveting it, but I couldn’t find our rivet gun.

The actuator drops in place like so. The only thing changing on this part of the robot is the leadscrew, which I’ll remake using a longer piece of Acme rod stock.

electr(on)ic mayhem

One of the downsides of possibly running two robots in the same class is that they might have to fight eachother in the tournament. If this happens, you either have to make sure you’re awesome at dual-joystick driving two robots at the same time, or have two radio transmitters.

I don’t. I only have my (outdated and obsolete) Spektrum DX6 radio. The same type that I ran back in 2007, when DSM1 was still in style. I have multiple BR6000 receivers for the transmitter, but only one Tx, and I don’t intend to get more obsolete equipment.

So what do I do? A real Spektrum rig is going to cost me another $2-300, which I could swing, but it would be kind of a waste of money given that term is about to start.

Luckily, like every other problem I have, Hobbyking has a solution.

On the left is my Spektrum DX6 (not even the i version). On the right is the HK-T6A 2.4Ghz 6 channel radio.

It costs all of $25, and includes a receiver. However, it also comes with no displays whatsoever (it’s the most bare-ass radio I’ve ever seen with more than 4 channels), no onboard switches for calibratoin, and the worst, buggiest we-made-this-with-a-trial-version-of-VB6 calibration software ever. Oh, and you can technically only get 5 of 6 channels working at any one time if you enable V-tail (& elevon, Delta wing, etc.) mixing for single-stick robot driving.

What it does have, though, is an established userbase and numerous “upgrade” hacks and replacement calibration software, such as Digital Radio.

The most important thing, though is that IT WORKS. For $25, I can deal with some shortcomings and rough edges. I’m tempted to tell Horizon Hobbies to just fuck off, but I also understand that HK is playing with alot of home field advantages, and would still spring for a real Spektrum rig any day.

The bottom line is that Arbor is getting its own radio for the con and for future events. This receiver setup has been determined to output “Bot-safe” signals i.e. none at all when the radio link is lost, so Arbor ought to still pass every failsafing test there is.

For what it’s worth, here’s a slightly junky shot of the inside. The difference for me between Chinese equipment and “established” well known manufacturers is that I never feel bad tearing into the former without even using it beforehand. Usually, I know that at least some kind of engineering has gone into the latter, and that me picking at it is only going to make things worse. So I satiate my curiosity on cheap parts and equipment.

The main MCU in the radio is an Intel 8051 knockoff that appears to share the same instruction set and pinout. Otherwise, the radio module itself is a bit more sophisticated, and features a 2.4G Taiwanese transceiver (Amicom A7105) and some kind of custom ASIC from Flysky (FS8004, which I can’t find a datasheet for anywhere).

My first mod to this radio is to make the left stick (throttle) spring-return to run the saw and clamp actuators. I didn’t have the correct part, but I chopped a spring lever out of a dead DX6 transmitter and sanded it down until it fit in the same slot. I also used the spring from the dead Tx.

There you have it – for $25, which is something like the cost of two burgers from Five Guys or how much Mountain Dew money I run through per week, you can get a 2.4Ghz 5.2387 channel radio that is essentially intereference-free, does not require channel crystal diggling, and has all the features you might need to control a basic robot. A word to robot n00bs: it did not use to be this easy. Get building.

nuclear kitten 5.1 surround sound edition

It’s back!

NK5 has been sitting idle on my robot shelf since Dragon*Con 2008 after it was first built. I’ve practically not looked at it, since I assumed it had taken significant damage at DC08 and was essentially not worth repairing.

After some egging by friends, I found out that I was pretty wrong.

Here’s the robot after I stripped everything down to prepare for rework. The overall appraisal:

  • The two drive gearboxes I thought were destroyed are actually working fine. No stripping or weird noises
  • The motor is functional, doesn’t have crunched bearings, or shorts in the windings. It just needs some magnets replaced.
  • The weapon pod swingarm is pretty heavily damaged and will need rebuilding to a beefier specification.
  • The 3S 1.3Ah lithium polymer battery is toast. D’oh.
  • Why the hell did I use 12 gauge wire on a beetleweight?

I’ve ordered replacement magnets and two replacement lithium packs from Hobbyking. Hopefully, with the magic of express shipping, they will arrive next week. NK fundamentally needs maybe two or three hours of work to be back to competition-spec.

How long will it actually last? I have no clue. It’s built to barely 2008 spec, and the brushless masculinity contest has grown in magnitude sine then by far. But, expect NK5.1 at Robot Microbattles on Sunday.