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…

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

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.

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?

They’re done!

Well, one of the new drive motors for Überclocker is, anyway. The bot edges closer to being reassembled and rewired. I’m going to devote this week to getting Clocker running, and bringing Arbor as close to it as possible. The next week, which is essentially the last one, will go to finishing Arbor as well as packing the robots up for shipping to Atlanta. That’s right – I can’t bring 2 full robots and all their support equipment with me on the plane. It’s not a TSA issue, and never has been – I’ve been flying with robots since the 2006 RFL Nationals. Instead, it’s a matter of Airtran billing me up to the sky for very excess baggage. Clocker by itself last year ate up to the second category of oversize and the first category of overweight baggage, which cost me a pretty $95 or so. Add to that a second robot and I might be forced to shove them on air cargo. Instead, I can build two small shipping crates and load them up to 50 or 60 pounds, then send it all UPS ground.

What this means is that I have to physically send away the robots several days early, lest they not make it in time for D*C. We’ll see how this goes.

In the mean time, a lathe chuck.

…holding one of the gearbox end plates. No matter how many times I complain about it, I always end up coming back to the square chuck. It’s simply the quickest way to turn out revolute-symmetric parts on noncircular substrates. This is the motor mounting end.

And this is the gear holding end. The needle bearing assembly from yesterpost presses into the bottom-most bore.

The ring gears press in like so.

The original second stage shifter ring gear gets pressed all the way to the bottom of the cavity, at the second shoulder from the top. The trimmed first stage ring sits at the first shoulder level. All of these are \m/etalfits, which is a variant of the Beast Fit, which is an extension of the 20-ton-hydraulic-press-fit.

In the above picture, I have also installed the needle bearing. I took more care on this bore because compressed bearings reduce to the degenerate case of a solid chunk of metal.

I dropped the DeWalt gears in to confirm axial spacings and diameters. Result: splendid.

The first stage gears actually sit about 1/8″ below the surface of the gearcase. This is by nature of the DeWalt motors, and is something I just compensated for with a 1/8″ tall boss on the motor mounting side (visible in the first picture).

Repeat ad nauseam and add in a bit of mill time, and here are the gearcases with drilled holes. Because these parts were again square and rotationally symmetric by 90 degrees, I was able to pull off the Pop-Lock-Flip-It-and-Reverse-It to great effect. Who needs to move machine axes when you can just move the part around?

Now with more tapped holes!

Something disturbing that I noticed on Überclocker during its Motorama showing was that the DeWalt motors were starting to come apart at their crimped seams. These motors were designed with ease of manufacturing in mind, and feature rolled-crimped-and-folded sheet metal everything. The face plates in a motor are normally retained by bolts or are one-piece constructions, integrated with the can itself. But these are crimped together – or rather, were, since the mounts I used only held them by the faceplate.

Solution: tack weld! I dropped a small bead in 4 locations midway between the crimps. This ought to hold them…

The big moment!

Because I replaced (forcibly, and irreversibly) the pinion on Clocker’s 14.4v DeWalt motors with a HF drill pinion, I actually had to break out my two stock 18v motors to use on these gearboxes.  The combination of lower gearing but higher voltage motor will actually cause Clocker’s top speed to remain roughly the same.

To my relief, everything fits. There’s about a millimeter of axial slop in the gearset if I loosen the retaining ring and just let all the internals slide. I find this slop to be totally acceptable, since even if I engineered it to be spot on, after the first match it will be off by a millimeter anyway.

Finally, the new drives mounted in the robot.

The increase in length by about 1/8″ means that the endcap of the DeWalt motor is now tangentially contacting the supports in the back.

What’s left to do on Überclocker? Surprisingly little. I need to make one more hollow gear carrier for the other side, but that’s it. All of the other work on the drivetrain is just putting it back together. However, I might make some hubs for the McMasterBots wheels that are compatible with the existing hub structure.

I ripped all the wiring out of Clocker such that I can’t effectively put it back together the same way, so the robot will be rewired from scratch. It’s better this way, because I felt like I could have routed quite a few connections better than the first time around.

Arbor is currently hanging in limbo as I wait for parts to get cut, but depending on how many drill gears I can salvage, I might not actually make a replacement DeWalt drivetrain for it. Arbor never had a gearbox stripping issue at Motorama – in fact, I harvested a working gearbox from it to fix Clocker up.

TO DRAGON*CON!