Aug 31, 2012 in Reference Posts
As promised, here is the presentation in full: http://etotheipiplusone.net/stuff/whereget.pdf
And the link to the EV Cheat Sheet: http://etotheipiplusone.net/stuff/evsheet.pdf
Thanks to all for coming.
Aug 31, 2012 in Reference Posts
As promised, here is the presentation in full: http://etotheipiplusone.net/stuff/whereget.pdf
And the link to the EV Cheat Sheet: http://etotheipiplusone.net/stuff/evsheet.pdf
Thanks to all for coming.
Alright, here we go. The post where I have to fix everything, because I have to leave for Atlanta and Dragon*Con 2012 (and its associated Robot Battles) in 8 hours. After assembling 2 more Ragebridge boards, finding that all of them had Resetting Regulator Disorder, I tried several increasingly desperate hacks to get the boards reliable before discovering a small nuance in the datasheet. In all, I managed to blow up another board (due to a slight… assembly problem), but I believe I have finally found a stable operating plateau for the Ragebridge boards.
Oh, and Clocker works. Here’s a recap:
One of the first problems I had to solve before actually getting to work on the Ragebridges was how to mount them. Formerly, Clocker’s “eBays” held 2 Victor 883s each. I wanted to group the Ragebridge boards on one side of the bot to avoid having to have long runs of distribution wiring, and because mounting two mostly bare PCBs horizontally greatly increases the risk of robot grunge getting places they shouldn’t.
I couldn’t really stack two of the Ragebridge boards horizontally, though, because they were slightly too tall to accommodate the thickness overhead of mounting standoffs. If I had shorter capacitors, this could have worked fine, and I was planning on building a small enclosure around the boards with fan cooling.
Then I realized that the boards are just short enough to mount vertically. I still needed a way to retain them, though, so cooked up very quickly this “rack” that has slots which the boards fit in. This was whipped out on the Lab Replicator™ and the standoffs made with a lathe.
First tries always reveal where parts run into eachother. On the upper board, the capacitors on the underside touch the standoff above them. And on the lower board, the Arduino Nano’s ISP headers touch the standoff below them.
The second revision moved the boards a little closer together and away from the standoffs. With the mounting solution taken care of, it was time to attack the boards themselves. I first had to attach wires to them:
Instead of soldring wires to both battery inputs and then joining them in parallel, I used a single 12 gauge input wire and then a 16 gauge ‘jumper’ which brought power to the other half of the board. The constraints of rack-mounting my controllers this time meant I couldn’t make big Y-cables.
After populating the boards, I began to run into regulator drama yet again. With my Spektrum receiver (Clocker’s receiver for 3 years now) attached, the LM2594-based switching regulator wouldn’t. This was worse than it was on Null Hypothesis (details in the middle) where it seemingly had a habit of not wanting to power cycle. The 15v rail was totally unstable, and the 5v power LED on the Arduino nano would flicker as the regulator kept latching up and resetting.
Even with the Arduino Nano but no receiver, it was still erratic, taking several seconds to stop resetting the microcontroller. The whole time, the regulator was also getting hot. Extremely hot.
Both boards displayed the same symptoms. When the regulator was in latchup mode, the switching frequency was audible and also very unstable. Basically, it seemed that any load was causing the whole thing to go crazy. I began attributing it to being a design error on the board or in the layout – maybe I had crossed my grounds somewhere else?
I began pulling desperate hacks suck as capacitance in places where it really should not have needed capacitance (i.e. where a slightly out of spec component value should not have a first-order effect on functionality), and even hacking a 7815 linear regulator onto the board to test if it worked at all (Result: Yes, the board itself is fine, and the linear regulator would be also fine if I wasn’t wanting to run 30+ volts).
Defeated for the night and about to switch Clocker back to Victor 883s, I read once more through the datasheet hunting for possible thermal limitations or some indication that I had totally fucked up the component layout and selection. The datasheet had a section on inductor selection, which I’ve handily ignored in the past. Within it was this equation:
Okay, sure, let’s try it… For my setup, with Vin = around 25 volts and Vout = 15 volts, I got a V-us value of 38. Now let’s see the inductor selection table:
For as long as I’ve used the LM2594, I’ve just tossed a 100uH inductor onto it because it was cheap on Digikey for the package size I designed with initially. And for as long as I’ve used the LM2594, it’s always been a nervous wreck.
My voltages and load clearly put me in 330uH territory. The microcontroller and receiver combined generally draw 50-70mA combined, with the beefy Spektrum receiver demanding 100mA when it is searching for a transmitter. So for the purposes of modelling, 0.1A is a good number to use for load current.
So what does too-small an inductor do to the system? Several possible things. First, current can change (ramp up or down) faster – there’s less “mass’ to it, so to speak. Second, as a result, the regulator can enter “discontinuous” mode, where the energy needed by the load per switching cycle results in a duty cycle so small that the current (which can now change faster) falls to zero instead of continuing to flow (“continuous” mode). The LM2594 should be able to handle discontinuous; but next, because the current can change faster due to the inductance being too low, it could very quickly reach a level which throws an overcurrent fault in the LM2594 regulator. In other words, it wakes up, turns the inductor on, goes OH FUCK, enters shutdown, wakes up, turns the inductor on, goes OH FUCK….
This really all speculation, but the observation that most supports the inductor-too-small theory is the fact that the LM2594 only reduces its switching frequency if it is in the overcurrent condition. I shouldn’t be able to hear it otherwise. I tested this by finding a voltage input which would run comfortably at 15v out and 100uH – about 17 to 18 volts seemed to do it. And there were no problems whatsoever. As soon as I crested about 20-22 volts, though, all hell would break loose.
Could I have been defeated by just not reading the datasheet? Let’s find out. Luckily, I had some 330uH through-hole inductors left over from the construction of Segfault’s controller long ago:
Through hole, surface mount, same thing… just some bent legs.
This was the only change I made to the whole regulator circuit – all of my other hacks had been undone by this point, because I wanted to make sure there were no other layers of mods that needed to be made. Surely just an out-of-tolerance component value cannot be the root cause of my controllers’ undoing!
Except it was.
Whatever, I’m just gonna stuff it in the robot.
I’ve yet to experience another hiccup or reset since replacing the inductor. At all – the only thing which causes a reset is a sudden applied load on the logic side – plugging in the Spektrum receiver when the board was not doing anything previously, for instance. In *that* case, certainly more buffering capacitance could help, but if the receiver is suddenly plugged in during battle, something has gone very, very wrong.
I test drove Clocker for a few minutes in this configuration (only the drive – the other controller isn’t installed) just to test the robustness of the fix. This test included several power cycles both “hot” and “cold”, to see if the thermal issue could have been part of the problem. The regulator does still get hot, but it seems to be a normal hot.
It’s time to install the next board! By this picture, I had already pulled the 100uH inductor off every single Ragebridge board current in existence and replaced them with the 330uH thru-hole ones. I was now test lifting various chairs and handtrucks with Clocker.
Playing with the current limit setting, I got the main output gear clutch tuned to the point where the bot could quickly lift 30 pounds on top of the fork, but if I stalled the fork against the frame, there wouldn’t be enough current to do any damage. The way it was accidentally tested was by wiring up one lift motor backwards so the two motors were fighting eachother the whole time, while I stared dumbly on and went “Hmmm, I wonder if something’s jammed”. I am vaguely glad for the existence of (my and only my) current-limited controllers.
The prescribed current limit for the fork is 30A, at which point the two motors will produce 50lb of upward force at the tip of the fork.
Alright! I’ve fixed the electrical problem, so let’s bounce the problem back to mechanics. That is my right side output gear, not being where an output gear is normally found.
How did this robot *ever* work?
Remember at Dragon*Con 2010, the left-side output shaft of my custom DeWalt frakenboxes lost its shoddy press fit, leaving the bot mostly immobile. That side was repaired by knurling the output shaft where it meets the planetary gear carrier, and it hasn’t been a problem.
I’ll admit that the discovery of this problem was just a little unconventional:
Hey, if it has a current-mode, I’m riding it, okay?
Definitely a useful way to stall-test your drivetrain. Each drive side’s current limit is set to 55A, which actually seems kind of low for the DeWalts. They definitely want more when spinning up. Maybe I should have double-bypassed the current sensors to get peak 90A limits, but then I’m pushing the board’s physical layout in terms of current density in the copper layers.
During some enthusiastic turning, the right side suddenly stopped producing torque, and I heard the dreadful sound of “motor spinning up unloaded”.
How did this robot EVER work?
Clearly the answer is it never really worked, if I’m hammering out one problem after another. I repeated the knurling and re-fitting operation on the right side, and all was good.
Now let’s return to the electronics.
During another driving and lifting stress test, something exploded in the bot.
Crap. It’s already like 3 in the morning by this point, and I’m wondering if now that the fundamental disability of the controller has been solved, the problems have moved down the line to the next weak link. Now, the controller that bit it was the drive controller, a.k.a the one I did all the nasty experimentation on before finding the inductor issue, so maybe it’s just weakened from being an experimental subject.
The failure was just indicative of massive shoot-through. Aren’t my gate drivers supposed to prevent that? What could possibly cause the FETs to suddenly overlap with disasterous consequences, besides like, leaving half of the gate drive chip unsoldered because I forgot to go back and solder all the pads after anchoring it?
Oh, it was that? Okay, carry on.
Here’s the final wiring arrangement for Clocker. It looks kind of like the same jumbled mess as it has been, but the wiring runs are alot better packed.
I made another spare battery afterwards, because this pack is getting high in years (and in number of dents in the cells – a little disturbing). Not only that, but Clocker has no less than 3 550 class motors and two DeWalt motors now, so it’s more stress on the battery than ever. It’s not going to run back-to-back matches for sure, so I need to have a swappable battery.
Here’s the bot all closed up for this year!
And now, a bit of test video, showing some more handtruck yoga.
So that’s where all those dents in the cells are coming from.
And here’s a shot of the 2012 fleet: Null Hypothesis and Überclocker Unicorn. Sorry, the nickname just kind of stuck – and it was also partially inspired by the fact that Gundam Unicorn is a real thing.
So that’s it. 30lbers only this year for me, with none of the ants and beetles returning. Instead, I have become the arena; more on that later!
Observant attendees will notice that I am a panelist in the Robotics & Making Things & Engineering & We’ll Find a Snappier Name For This Next Year track. It’s been a long peeve of mine to go to conventions only to discover that all the panels suck, so I’m out to fix it. In the past 2 years, I’ve been complaining that nobody really had a panel focusing on the where to get and how to use (not to mention the even go want to do look more like) – the resources of engineering projects, which for me at least was perhaps the number 1 contributor to actually being able to get nice stuff done. What to buy, where to buy it, where to scrounge and salvage it if you can’t buy it, and why it doesn’t work the way you think it does.
So I’m proud to announce the MAKER RESOURCES panel, which will probably be something like all of my Instructables slammed into an hour. Focusing primarily on parts procurement and fabrication resources for the non-shop-endowed maker, I’ll also touch on design software and design methodologies.
Next is the ELECTRIC VEHICLE TECH panel, co-hosted by real EV guy Adam Bercu. My role on this panel will probably be dealing with the smaller end of rideable objects, discussing the nuances of using hobby R/C parts and shitty e-bike controllers. We’ll likely cover basic EV drivetrains and power system choices as well as math for estimation and calculation of drivetrain properties. Basically, 2.00scooter in an hour except probably more 2.00motorcycle.
I’ll also be on the DIGITAL FABRICATION AND WATERJETTING panel along side long-time robot buddy Simon Arthur (some of you may know him as Big Blue Saw), in which we’ll touch on ways to abuse the waterjet and laser cutter, and the coolness of digital fab in general.
The 1100-mile haul begins soon.
Hmm, well that ain’t good.
T-minus right about 48 hours before I be trippin’, and Clocker has just begun its journey back into one piece. I suppose this is really nothing new.
Here’s what the bot looked like at the beginning of this week. It’s not exactly complete… In order to finish up, I needed to remake several parts and wait on McMaster. Luckily, neither of these processes takes very long. The parts to be remade included the drive wheel assemblies from 0.25″ steel and aluminum, the top fork parts and new lower fork ‘tines’ from 1/4″ aluminum, and new sprockets from 1/8″ steel…the same piece of 1/8″ steel I’ve made Clocker’s previous sprockets and Cold Arbor‘s drive sprockets from, incidentally. It finally reached the end of its waterjettability with this round.
The first part up for rework is the top fork:
I played with the geometry a little more after the CAD images last time. The fork is now 2.5″ taller in the “gullet’ section, allowing it to park a bot up to 7.5″ tall (if the robot’s small enough to fit totally in past the grabby bit, that is). To reduce weight of the forward part of the bot, I’ve went back to standoffs for this part, as the .25″ side plates provide most of the stiffness.
Here are the new front and rear wheel parts, in super-convenient pile-o-plates form. I machined the Delrin bushing from round stock on the venerable tinylathe. The wheel holes were drilled in-situ after a layer of sprockets has been piled onto the hub, since the hub plastic is
dense air polypropylene and exceptionally soft. The weird flowery cutout in the steel is for weight reduction only.
One issue that came up is that these wheels are manufactured….not very consistently. The hub on the one I used as a model seemed to be a few hundredths thinner than this set that I’ve gotten, with the result that my cap screws protrude further than the plastic hub. This meant they would have ground against the frame instead of letting the bushing take up the thrust load.
Maybe it’s my bad for designing something so close in a combat robot, but whatever. A quick hit with the appropriate diameter drill let me “counterbore” the holes enough to sink the bolt heads down below the bushing.
Yep, it fits.
Once I made a full wheel, then I repeated the process production-line style for the rest.
Again, what the hell are with these wheels? They have excellent traction and predictability on smooth ground, but they are so inconsistent. There are also massive voids in the molding near the center. Someone either just does not care at all, or they know their industry well enough to know what costs to cut…
The sprockets were “rotationally filed” to achieve the tooth chamfer that is critical to making your chain not explode off.
Here’s the chassis on all 4 wheels as a fit test.
SO MUCH GROUND CLEARANCE. A whole 3/4″ of it. That’s alot for one my bots – Null Hypothesis itself was my first design to venture above 0.5″ on purpose. I’m a fan of low and wide bots because of my arena combat history.
Onto the fork actuator. Again, this thing is Cold Arbor’s old saw actuator, which I saved for this exact purpose.
There was one problem with the actuator, though. The spacing of the sprockets did not result in an integer number of chain links in the chain pitch circle – this was one of those design oversights I’m unfortunately too prone to. The end result is that the chain has always been extra floppy. Cold Arbor used to regulator ditch these chains because they would bunch up at high speeds and then get ripped apart by the drive motor when they got jammed against the side of the actuator frame.
I decided that there was no real value in trying to move the output center up a little, which would have resulted in me needing to machine some kind of weird adjustable linear bushing. Instead, I elected to add these ninja standoffs to act as crude chain tensioners. They’re made of some random steel round and screw onto the protruding motor mounting bolts. They keep the chain squeezed around as much of the sprocket as possible.
It’s worked beautifully so far.
Now with the leadscrew cut to the correct length.
And installed in place – note the former plate spanning the two inner tines now replaced by the motor mount.
Say hello to Clocker Unicorn (or perhaps Clocker Cyclops). The big rubber bumper doesn’t look as out of place as I had anticipated, and it’s very squishy – good for hanging onto people.
One problem I discovered was that the higher ground clearance meant the fork no longer got anywhere near the ground. The front structure of the lifter gearbox mount was just getting in the way. I counter-milled (milled with a countersink…) a chamfer onto the front and also took the height down a little bit. The amount is set such that the front fork will just barely not scrape the ground – I don’t want to deal with it potentially impeding the robot’s movement.
Starting to put everything back together now…
To reassemble just this part of the robot requires at least 2 sizes of ball-ended hex wrenches. Design win.
And holy shit those chains. No wonder I lost both of them alternately!
The solution is a set of miniature eggy-cam chain tensioners. Unfortunately not roller, but Delrin’s slippery tendencies should make up for it. These can be adjusted on their mounting bolts to press down on the chain in varying amounts. Way better than my very non-adjustable failed tensioner attempt of yestercon.
A full set of installed eggy cam things (more formally just called cam tensioners) totally removes the slack from the chain, with plenty of takeup capacity left. If it stretches more, I might as well throw out the chain.
Alright, it’s time to test if my totally refreshed lifter parts can do anything! I clamped the robot to the table and hooked up the still assembled electronics deck to the fork. The bot’s 7S battery was reconnected, and…
… well then.
Okay, so I did managed one successful lift. Then this happened on the way back down when the fork hit the frame and the gearboxes kept torquing, even though the clutch slipped when that happened. The failure of the pins was entirely brittle – the break is clean across the diameter and there was no bending seen in the pins at all. The sound I heard from the outside was quite an impressive series of cracks.
Alright, alright. I get it. I suck at the mechical engeerning. A little more thought and analysis (and reading of the Chief Delphi forums of archived Banebots 56mm carrier plate threads) led me to decide that whatever the pin is made of and whatever the shaft is made of is simply too disparate in carbon content and possibly other alloying components to consider as one unit. One thing I could have done was to heat treat the shaft separately – pop the pins out, carburized/case harden the low carbon steel shaft to gain some strength, and shove the pins back in.
For now, however, I’m going to restore the system back to the way it was before I tried to fix it. When the gears are pushed tightly together as they are inside the gearbox, loose pins aren’t as much of a problem as them just shearing the fuck off.
I took apart two of my older spare HF motors for these replacement shafts. They have a carrier plate that is a full millimeter thicker than the ones I used, and which are more commonly found in newer cheap drills. Damn cost cutting measures – really, it’s an extra millimeter of length of a shaft that is machined from a single piece of steel and is over 50mm long so it’s not like that much material is actually being saved compared to what is being removed to get the shaft diameter itself.
And damn these pins if they come loose inside.
I put the gearbox back together with the output stages submerged in grease so at the very least there’s hydrostatic pressure keeping the gears in line (Not really, but if the pins do loosen, the gear face sliding against the previous carrier stage provides alot of support to the whole assembly).
One more mod I made to Clocker today as I rage-reassembled it was some stiffer springs on the ‘front shocks’. The old ones were actually way too soft and didn’t provide much support for the bot as it lifted an opponent, so Clocker faceplants were a more common occurrence than I would have liked. These are about twice the spring rate of the old shock springs.
Clocker is now mechanically back together and alot less jiggly than it was before. What is it time for now?
It’s serious Clocker time!
I’ve spent some time practicing my TIG wielding ability on small steel objects as well as reading back up on ways to make steel less temperamental (or perhaps more tempered). The results have not been scientifically verified nor even experimentally confirmed legitimate, but at least it looks kind of cool.
Last time, my TIG welding adventure left off with my little pins breaking off one by one because of my muscle-memory water quenching. I wrote those off to practicing the technique itself. Doing these pins was relatively easy, I think, because it didn’t actually involve trying to hover the tungsten over a path – just kind of wiggling it in place. Some kind TIG advice from friends also helped. After I went through 2 more scrappy shafts, I decided to do the real things:
Oh man, those just about don’t even need any machining to flatten the upper face. I had to cut short my desire to TIG WELD THE EVERYTHING such that I stand a chance of finishing the bot on time. These shafts were both preheated to the “nice golden brown” stage (260C or thereabouts), welded on 80 amps, then quenched in cold water. I then tossed them in the convenient MITERS tiny heat treating oven (interior dimensions of a 4″ cube) set to about 300C, for a nice blue finish, wherein they baked for about 2 hours before being quenched once more.
Now, it’s important to point out that there is absolutely no scientific basis behind the choice of temperatures. I don’t even know what steel these things are made off, past a crude scratch test with some known 1018 steel plate. The shaft itself is definitely a really really mild steel, and I’m hard pressed to believe the pins are that much higher carbon. Remembering some rumors and gossip on the CheifDelphi forums from my 2007 FIRST Robotics season when the Banebots P80s (back when they were just called “56mm” gearboxes) had carrier plates made of what was found to be essentially 1006-1008 (very low carbon) steel, I think I’m not far off base.
I based the preheat on the assumption that they at least resemble a medium carbon (.40% to .60%) steel in some industrial applications, as well as the tempering temperature, figuring that the mildest of mild steel shaft body wouldn’t do anything noticeable.
I really, really should take these things to the materials lab and do a real hardness test if they ever break. Even I’m a little curious now.
The next stage after my brownies baked to perfection was to machine the taper. Luckily, the taper turning attachment for the trusty Old Mercedes (the MITERS 1953 model South Bend 10L) has not disappeared since I made these shafts the first time 3 years ago. There’s not much I can say to explain the taper turning doohickey besides pointing to this video which shows a very similar conceptually (but different in layout) device.
I discovered after finishing these pieces that my previous tapers were not only not the size the drawing said they were, but were actually 2 different sizes. The gears apparently had different bores. Fortunately the bores were smaller than indicated, so I had to just keep making small passes while trying the gears on every once in a while.
Different setup, different machine, once again.
Tinylathe was used to make the retaining ring groove on the nontapered shoulder because its tiny adorable .040″ parting tool is precisely the width of one of the snap rings I’m using. The only parting tool available for the bigger machine was .125″ wide, which I really do not like – it’s really too wide for the machine’s age-induced lack of alignment and the tool holder’s non-stiffness. I regularly machine on the big 10L and then part off on Tinylathe now.
Luckily, the “3 degrees” I eyeballed this time is the same “3 degrees” I eyeballed in 2009. I did quite a few verification fits to make sure the distance between the gear and housing was close to 1/16″. A little sandpaper-polishing was involved to very finely bring the diameter of the tapers down at the end.
Fully assembled and packed with not only grease but fresh gears!
I think this is the first time in 2.5 years that this gearbox has not made terrible grinding sounds when the lifter was being run.
Unfortunately, Clocker will only get more taken apart before it gets put back together at this point.
Several major changes will be happening to Clocker this time around, things which I should have done immediately after discovering it wasn’t doing the robot thing properly, but were neglected due to lack of roboner.
The first, and most simple change which could make it far more effective, is moving to 3 inch wheels:
Clocker was originally designed with 2.5″ wheels because I was still totally into flat robots then, and the ground clearance afforded by 2.5″ wheels, half an inch, was enough for the Robot Battle stage at the time. Unfortunately, wheels get smaller over time, and stages also get torn up (on purpose) – last year, it got to the point where Clocker had too little ground clearance margin to even move around reliably. In a game where there are no arena walls, moving around reliably is like 90% of the match.
Going to 3″ “McMasterBots” 40A wheels will up the native ground clearance to 3/4 inch. While having your bot higher off the ground may make it more prone to getting wedged, it’s also easier to get away, and there will likely be very few wedges where I’m going anyway (cept mine of course)
I’ve designed a new hub which is made of a convenient stack of plates with a Delrin bushing in the center. This time, everything just bolt through the whole wheel instead of transmiting through the aluminum hub body and into a press fit as the current hubs are set up.
Going up in wheel size is going to require me to make some changes to the robot’s frame, as several elements were designed only with 2.5″ wheels in mind. The front ‘shocks’, for instance, have to be moved inboard more and the shoulder screw head can’t stick out any more. This is fairly simple – I’m just going to mill down that portion of the rod end. The ‘plate’ at the left which bridges the two front leg halves will also have a little chunk milled out of it.
The rear ‘corner block’ in the frame will also need to have its thickness reduced, since a 3″ wheel will be exactly rubbing on it.
These were the simple changes.
I’ve been dissatisfied with Clocker’s upper clamp arm since I built the thing. Two major reasons: First, the actuator I used on it is just a little 400-class motor feeding into a 20:1 Banebots 28mm gearbox (of which production has been stopped for several years, leaving me with no practical spares), driving a leadscrew. It has no real clamping force whatsoever, nor can it help the robot recover if it flips over while body-slamming an opponent (this has happened a few times).
Last, and worst of all, the motor is the hard stop for its own range of travel! The separation distance between the motor axis and the leadscrew axis, for some reason, was made as small as possible ,meaning the motor is the first thing to run into the leadscrew anchor by the main fork. This has happened once, and I literally bent my motor. This actuator was one of those things that I look at later on and can only go “…” at.
So why not just flip the motor around so it sticks out foward? Then it would have stuck straight up in the air above the clamping fork (and been the first thing to hit the ground when the robot gets flipped), or it would have stuck really far into the ‘clamping volume’ and been the first thing to land on the opponent when the fork came down.
Stuck between a rock, hard place, and its own leadscrew anchor.
All of this lead to a night or two of thinking of, sketching out, and just manipulating solid part models around a new upper fork and motor layout.
Here’s what’s going on. This is arrangement candidate number 1, top actuator with motor facing away from main pivot point.
Notice that the motor is actually Cold Arbor’s saw actuator? I decided this early on that I wasn’t going to make yet another new custom linear actuator when I had a perfectly workable one already kicking around. The 550 will add alot more force to the grip, and I’m going to use it as a chance to test out asymmetric current limiting on the Ragebridges – stronger release/lift current than grab/lower.
This arrangement was created purely as an iterative design step. It’s really quite terrible. First, the motor’s really exposed and if I grab an opponent, an edge of it might just punch my motor from below. Second, the center of mass of the very heavy actuator is quite far out from the fork’s main pivot. I’d want it as close as possible in the best case.
Finally, notice the much deeper fork. Clocker was designed pretty much to grab only flat, boxy pushybots, so it really could not grab anything over 4 or 5 inches. Well, there’s lots of bots that are 6″ and taller, so the deeper fork is designed to accommodate them now too. This, too, was on its first iteration and the following screenshots will show little geometric changes.
Part of the reason Clocker couldn’t grab taller bots was because the clamp could only open so far before, again, the actuator ran itself into the leadscrew mount balls first. I aimed to resolve that problem in the new geometry – here’s a shot of the new top clamp beign able to reach about 55 degrees of swing. This is actually physically impossible because the clamp arm would run into the main fork axle parts – but it can reach 45 degrees with no problem. Previously, the maximum angle attainable was only about 35 degrees…
Here’s arrangement candidate #3 (Number 2 was just a variant of #1 with the motor turned around). Now we’re getting somewhere.
The motor is mounted very low and aft, meaning my C.G. remains where it should be. The motor no longer travels a significant amount linearly when raising or lowering the clamp arm, since it is mounted to the fork instead. The leadscrew anchor, formerly at the end of the egg-cam looking thing on the right (in the profile of the main lifter gear), is now directly installed on the clamping arm.
And here’s how far back the arrangement can push the clamp arm. I briefly considered adding an ‘indent’ to the clamp arm so it can partially overlap the pivot hubs, and this may creep back into the design later on.
The motor, while it does intrude a little on ‘clamp space’, can be better shielded from things landing on it in this configuration. I like it alot.
A better shot of how the clamp motor will be mounted. Notice it now has its own little roo-bar structure in front of it – this will be a ‘hard stop’ for incoming robots. It won’t protect too well against other robots’ pokey things, so I may turn it into a plate (or have it swappable with a plate) for very pokey robots.
The summary of these changes is:
Here’s what else has changed.
Why? I bought replacements for them yesterday and I hit the wrong part number on McMaster. The ones I ordered are 1.25″ diameter with a huge 3/8″ threaded stud. I’m definitely not using 2 of those, because while the thought of force-teabagging your opponent with double huge rubber knobs is hilarious, it would be impractically wide. Also, using 1 is lighter and allows me to save some weight from the most important location – the very end of the long arm.
I’ve already done most of the preparation machining such as preparing the frame for new motors and modifying the Cold Arbor saw actuator for its new home. Clocker’s pretty much been broken down into component molecules, and I just need to cut out the new arm and drive pieces. It needs to come back together by Monday night.
With Null Hypothesis pretty much squared away except for the occasional motor detonation, and no real leads on that regulator problem besides “wait more than 1-2 minutes before turning it back on”, I’m going to start fixing up my current ‘flagbot’ (like flagship, I suppose) Überclocker Remix.
And I’ll start off like I always do:
Having been mostly neglected during my focus on building more silly vehicles than silly robots, Clocker has always been on the receiving end of last-week hacks and fixes to address only the issue that came up in the competition previously. In 2010, to fix the problems from 2009, I replaced the shitty 775-type motors with DeWalt drill motors. In 2011, to fix the issue of the DeWalt motors being used with improper torque transmission methods, I just press fitted harder. And in 2012, to fix the problem with the chain falling off now that the motors are relatively reliable, I’m gonna…
Fuck, I need to make actual upgrades to this bot. Changes that should have occured in 2010.
The actual story, though, started a few days ago when I wanted to spar Clocker against Null Hypothesis just to shake down the bot a little more to see what else might have been creeping up on it. Long story short, I couldn’t get the lifting fork to actually lift anything – something, it seems, was slipping before the big gear clutch. Having seen this problem before, I quickly decided it was the tapered gear shaft on the Integrated Dual Frankenb0x – the retaining screw probably loosened or stretched or something. But it was an excuse to open the robot up and examine it completely.
Often times, what you don’t know and can’t see is better off being undiscovered.
Alright, so here’s the bot. It’s just looking worse and worse too – dirt and grime has settled into all the little metal dings and gashes. Shiny new cuts in aluminum look ballsy and cool, but dirty oxidation does not.
Clocker is a great example of one of my bad habits of designing things very sequentially. In order to take out the lifter gearbox, I have to execute the following sequence of events:
Basically I unbuild the robot to replace a critical component. If I just dive in and go, it takes about 10 minutes to go one way.
And after all that is said and done, it pops out!
…with one of the bearings permanently fused to it. Hurray?
Ah, the IDF, one of my finest machining examples. Combining the parts from what must be like 6 cordless drills, it’s a twin 3-stage 216:1 reduction all made of shitty sintered iron and maybe steel.
When I test ran the motors still attached to the gearbox, something sounded bad. Really, really bad. Time to take those gears out…
Gearbox 1 is missing all of the pins ever on its output stage. This is a known failure mode of the cheap drills when overtorqued, because the carriers are seemingly made of mild steel and the press fits just explode instantly, causing the pins to fall out. Some times, if the loads are light, wiggly pins are enough when backed by the intermediate stage to not cause much noticeable trouble.
Not good at all.
Gearbox 2, unfortunately, displays the same failures.
The funny thing is, I bet these gearboxes have been running like this since at least Motorama 2010 when Clocker might have experienced the highest shock loading forces on the fork. I’ve literally never touched this gearbox since when I closed it up in 2009 and now.
I went from possibly having something which was still working now to either a few hours of machining to replace just those shafts (which might just fail once again), or cooking up a new and potentially way more expensive solution.
Time to take apart the gearbox some more.
I really liked the tapered shafts for these gears. They take some amount of screw pressure to transmit a ton of torque using the full width of the gear box (unlike, say, a pin or partial keyway), and in the worst case they just let loose and slip. They took a lot of effort to get back off – I had to carefully secure the gears by their teeth in a vise and tap on the shaft with a hard punch and hammer.
After getting the gears off and appraising the condition of the carriers, I spent a little while brainstorming about what to do from here.
Solution 0: Just remachine the damn thing from one of n drill motor shafts I have sitting around. Prone to failing in the same fashion? Yeah, definitely, because cheap drills are cheap drills. It would take less than 30 minutes because taper-cutter.
Solution 1: Machine a tiny Wubba-wubba drive! Prone to failing: Probably not. Probability of me actually getting it right: Ummm….
Solution 2: Overnight myself some Banebots P60s and emergency-redesign the whole system to accommodate them.
Solution 3: Attempt to weld the pins to the carrier plate, just the way they are.
I decided to try solution 3 first, since it involved 1. trying to use our TIG welder because this is a very precise and delicate piece, and 2. The shafts were already broken and could only get broken even more in the name of learning and practicing TIG welding, or fixed.
Say hello to the blob.
I’ve only used our cheap Harbor Freight TIG exactly once, and it was to weld the tungsten to the random plate of scrap practice steel 15 minutes after we set it up for the very first time. This was going to be fun!
Since MITERS is used to MIG and very few people (save for Amy) had aptitude with the TIG machine, it was a little neglected. I resorted to using a chunk of mild steel MIG wire as the filler rod, and it definitely took a few tries to not weld the tungsten. But after practicing on some more angle scrap, I began to like it better than MIGing. It’s quiet. Deceivingly quiet – just an eerie blue glow. There’s no disgusting splatter and crackling.
Next, I practiced on a scrapped drill shaft from some project I can’t recall, but it was in my little baggie of drill parts.
Taking Solution 3 can actually have very indeterminate results depending on what kind of steel the Shady Chinese Power Tool Co. Ltd. had lying on its shop floor when the shafts were made. Welding different alloys, especially a very hard high-carbon alloy like the pin (….presumably) to a low carbon soft alloy like the squishy shaft steel will most likely cause cracking in the heat-affected zone. Welding high carbon steel is just terrible in general.
But the pin steel, as tested with some pliers anyway, didn’t seem to be that hard. I’m not exactly surprised – given how shitty the shaft steel is, I wouldn’t expect nice hardened pins. I decided to preheat the whole mysterious assembly to a nice golden brown color (approx. 250 celsius) based on this site’s recommendation for a medium carbon steel.
The results of my first practice run is shown above. It’s definitely blobby – I didn’t let the puddle form for nearly long enough. I started with a fairly low current of 40 amps, too, so it took a little while to reach even that stage. I might as well have MIG’d it.
Attempt number 2. I think I’m getting a little better at this. I upped the current to 60A, and it just looked better. The liquifaction starts at the top of the pin (where I aimed the electrode) and propagates to the body. Once the puddle became a few millimeters in diameter, I dipped in a little MIG wire.
Since the IDF runs with just 1 0.5mm shim of clearance between the carrier and bearing, I decided to machine down this weld to see if I made it reasonably far into the steel. Interesting effect – the pin’s weld puddle is much harder than the surrounding steel.
Here’s 3 attempts on 3 scrappy drill shafts, all machined down. The first one on the left clearly shows some porosity and lack of filler, and I’m really starting to like the 3rd on the far right. Overall, I’m liking Option #3 as a potential saviour technique for my drill shafts (as well as preserving them from being damaged in the first place). While it may be metallurgically unsound and may earn me cold stares from certified welders, I’m going to guess that any metallic inteference is better than a slouchy press fit.In the best case, the metals join reasonably strong and I up the failure ceiling a few more ft-lbs and I win. In the worst case, I’ve made a mushroomed metal head on the pin so at least it can’t just slip out backwards, and I…. win?
Enough practice – hows about some production parts? These are the two drill shafts after welding and machining. The one on the right I kind of skimped on surfacing a little.
Unfortunately, my joy was short lived. I’m now going to admit a slightly embarassing mistake I made with all of these practice pieces: they were water quenched. Like straight off being red hot and into the sink.
Anything I’ve welded in the past has been gigantic, ugly gorilla welds in mild steel which can’t possibly heat treat in any way, and dunking the parts in water just became second nature to cool them down quickly. Well, with alloy steels and medium to high carbon steels, I think that was a dumb.
The pin there broke off after I put two stages of planetary gearing back into the gearbox and turned it by hand. Sadness.
Alright, it looks like I’m going to have to remachine these shafts anyway. However, before I do so, I will weld the pins in place and then more gently cool them down, possibly even applying a proper tempering process. MITERS does have a tiny oven which has been used by some members to cast aluminum.
So, how’s about them TIG welders?