Continuing on yesterday’s update, here’s the tale of wiring Clocker up over the past two days, plus (finally!) some video of driving and testing. As of right now, I’m pretty much ready to call the bot “done”. As in, maybe not everything is perfect yet, and perhaps not everything has been tested to breaking… but if Motorama were in fact tomorrow, I’d be comfortable with pitching it into the arena.

With the bot basically having reached mechanical completion with the routing of the drive chains, I turned my attention to the wiring end of things. Clocker uses two RageBridges (And So Can You!), one for the two drive channels and the other for the clamp and fork.

In the past, I’ve bussed together the two power inputs of RB on the bottom, but since now I’m working with the boards with heat sinks, this is no longer possible. Solution? Just bus across the top. Now, “production” RBs are supplied with 4 battery wires, but this is one way to cheat a bit and get a one-input system. Yes, I know this layout is terrible.

The green board is actually one of the revision 5 prototypes which are functionally identical to the production boards – I didn’t want to consume a production board which could be sold for my own giggles if I had workable prototype ones.

Next up was making the power source of the whole bot. Originally, I was planning on an 8S2P configuration using A123 cells. However, actually assembling 16 cells together and trying to stuff them into the rear cavity with a RageBridge made me realize that it was just utterly impractical. The fit was extremely tight in CAD, and the CAD model does not include the many layers of shock absorbing rubber foam and heat shrink I coat these things with.

So I dropped to 7S. No matter – that just means Clocker goes about 17mph instead of 20! Big deal, in a 24 foot Motorama arena or a ~12-18 foot Dragon*Con stage!

This is a picture of the pack in progress. I used my usual construction technique of copper braid and split balance harness (so my fairly average hobby-grade charger can actually recognize it).

Like Null Hypothesis, I’m giving Clocker an integrated charge and switch port. There’s a Deans connection which is really just a removable link, then an XT-60 type connector which has a direct battery connection. Why do I make them different? Because otherwise you risk dropping that removable, super low resistance link right across the battery. Yum…

To test the drive, I mounted 1 RB and the battery in the rear of the bot. The “production” RB was used because it has heavier traces than the prototype and the drive motors will be stressed much more, current-wise. With only the drive hooked up, I took the bot for a spin around the hallway.

I’m very satisfied with the drivetrain. Unlike Clocker Remix and Clocker version 1 in 2008, there was no attempt to keep the center of gravity as far back as possible. Rather, it’s near the centroid of the wheelbase and track rectangle. Result? This thing handles so smoothly – almost as good as Null Hypothesis, which still wins just because it has fatter wheels – Clocker tends to drift and slide. Previously, Clocker had a particularly nasty oversteer issue because the weight was purposefully far back, causing uneven wheel dominance in turning.

A better shot of the controller installed in the bot. It’s actually raised off the bottom plate by 1/4″ spacers. The threaded standoffs act as nuts to secure the board against those spacers, and then the fork/clamp controller sits on those threaded holes. The receiver is stuffed right next to everything by the back.

And the ‘upper deck’ in the Tower of Rage is assembled.

The top plate needed a bit of filing, sanding the edges, and enlargening the waterjet-cut pilot holes to slip into place. It’s retained by the same #4-40 button head screws that I normally hate so much, but hate #6-32 even worse, think #8s are worthless, and consider #10s too big for the job. So… yeah.

With all of the electronics and pretty much all the screws in, I took the bot for its first moment of truth: the weigh-in.

Uhhhh… well that isn’t good.

Now, what on earth could I have missed? The CAD model included almost all screws and the full 8S2P a123 pack and still came in at 28.5 pounds! I’m going to just assume that things weigh more than what I could have guessed – for instance, the threaded rods binding the fork together weren’t modeled, which seems silly since they’re quite huge. Additionally, the top and bottom plates were modeled as phenolic material when they are actually fiberglass (garolite G-10). The difference in that alone turned out to be almost 0.2 pounds per plate!

Well then. Clocker has to ditch 1.25 pounds somehow.

I spent a while thinking about possible plans of escape. I had very little metal that I was comfortable with “speed holing” since it would compromise the somewhat complete armored perimeter of the bot.

Replacing said top plates with polycarbonate would save about 0.35 pounds per plate, but I did not have the material on hand at the moment, and it wasn’t enough by itself.

Dropping to 6S on the battery would only save a few ounces, and I’d have to tear the battery apart again. The final solution had to involve multiple changes.

With the heaviest of hearts, I grabbed one of the left over 7S 4.4Ah Thunder Power lithium polymer packs from the amphibious DERPA project team and replaced the A123 pack. Sadly, no matter how much I love the little white round cells, the lithium pack just has greater gravimetric energy density. I gain back what is essentially an 8S a123 voltage (25.9v nominal), with essentially the same capacity. And, it saves 0.75 pounds; even with the two G-10 plates I added to the top and bottom to make the pack simulate a hardcase battery so it isn’t as squishy.

Now, with Clocker at 30.5 pounds, knocking the rest out of metal was a possible course of action.

I always figured I was going to have to machine out these landing legs eventually. They’re solid 3/4″ aluminum. That’s almost obscene. Each slot basically netted me 0.14 pounds, so a cool quarter pound for the pair.

There’s a quarter left, still.

The rest of the quarter came out of the right side outer frame rail, which was solid 1/4″ aluminum. I hollowed it out to a wall thickness of 0.1″ on the outside, and this was able to knock out just under 1/4 pound. Since the Sportsman’s Class does not have to contend with heavy hitting cheap shot kinetic weapons, I was completely fine with this relatively thin (for a combat bot, anyway) side armor.

The final result?

Yes.

That’s as close as I want to go. Generally, big event scales only read up to the 0.1 pound anyway, and some leeway is given at the organizers’ discretion to account for not everyone owning the same calibrated scales. So I should be able to add 5 or 6 more #4 button heads on the top plate without issue.

So, the final tally of changes was a few machined-hollow metal features and a battery change. While the battery change lost me 0.75 pounds in the rear, the front leg channels and side plate pocket combine to keep the C.G. basically where it is.

Finally, the press shot:

I spent way too much time driving this thing around and practicing with the fork. So far, the driveline has been perfectly reliable. The centroid CG placement and smooth braking of the RageBridges, coupled with the ultra-tight deadband, makes for one of the most smoothest-driving bots I’ve built.

The “clock face” has been covered up with some thin polystrene sheeting that is normally used as thermoforming exercise stock. It’s just a dust cover, more or less.

One thing I experimented with was adjusting the torque clutch on the DeWalt gearboxes. My “DeWut?!” mounts have a set screw that can push in the torque clutch’s preloading spring, just like what the torque setting ring does on the drill body itself, so in principle you can create a torque limited drive. I’m glad to say that this is in fact possible in real life. I tried lifting stuff with the fork, but the motor just made angry drill sounds because I didn’t adjust out the clutch at all.

Luckily, this version of Clocker was built with serviceability in mind, and in under 1 minute I had the 4 screws undone, the motor slid out, the set screw tightened, then the motor remounted and the screws reinstalled. While I could have played the “How far do I turn the screw to lift a 30 pound opponent?” game, I elected to just let the current limit on RBs take care of maximum lift load, so I locked the clutch using the set screw.

My exercise regimen was mostly blasting in straight lines up and down the hallway. This was in fact not very easy – Dewalt must have changed their 18v motors’ windings very slightly at some point, because I have 2 allegedly identical 18v type motors that are  definitely different ages, and they are very slightly different. They are different in speed enough, though, that Clocker still pulls a wide circle. For now, I’ve been just practicing it away with the radio, but I probably want to check for matching motors next time I have the bot open. I also engaged in a few short “drive a perfect square” laps, and “do a perfectly straight J-turn” also.

But Clocker has actual weaponry, so I’ve also been practicing attacks and methods using the fork and clamp. I’m fairly sure that now with the much faster clamp arm, I can catch and lift an opponent (or at least break its traction) in under 2 seconds.

Here’s another short test video using Null Hypothesis as a fork chew toy.

Notice how Clocker can hoist a 30 pound opponent pretty much hanging off the end of the forks. I attribute this to the much longer springy legs this time around, making the 2-bot complex much  more stable as a result. I think in battle the lifts won’t be as smooth, and there will be much squirming on the opponent’s end, but it’s good to see that Clocker will no longer be as prone to faceplanting on a lift. The down side, in my mind, is that the legs are now a vulnerability because they stick out so far.

The tournament will soon tell all. Between now and Motorama, I want to get a few things done:

1. Practice sparring with some of the other area 30lbers, Null Hypothesis, or the now mostly beheaded Clocker Remix.
2. Make spare wheels. I have 6 spare wheels, and I’m probably going to need all of them.
3. Secure all internal wiring with some kind of adhesive or sealing compound
4. Take nice pictures and make an assembly guide for the DeWuts! I plan to bring several to Motorama, so they must be ready by then. They will be up for public sale on e0designs.com after the event itself.

For the T-minus updates from here on out, I’m probably going to just update on practices and anything that breaks, plus maybe an opponents analysis when the event gets closer.

 

Since the last Überclocker update, a ton of work has been done on the bot. This past weekend, I purposefully trapped myself in the shop for the duration of the Snowmageddon Snowpocalypse Snowlingrad Snolocaust Great Leap Snowward Snowtorious B.I.G. which shut down most of New England for Friday through Sunday, to get as much done on Clocker as possible. I’m proud to say that at this point, the bot is driving (but not yet lifting). This following report will basically summarize the work of the past week or so, including all of this past weekend – otherwise, there’s going to be like 90 pictures!

I began by tackling basically the only menial machining task on the bot: making the Springy Legs. The “raw forms” were waterjet-cut from 3/4″ aluminum with the intention of finish machining.

This is the stationary rear portion of my DIY shock absorbers. They just have a hole drilled through to hold a bronze bushing, which will interface with the “rod”, a shoulder screw.

The other two parts were a little more interesting. The trunion end of the shock absorber is doubly supported in the leg itself, so it meant I had to cut a roughly 0.8″ deep slot in the leg. I broke out, fortunately not actually breaking, my long-cut 1/4″ carbide endmill from the days when I collected tooling and carved it in 3 passes.

After most of the little menial machining objects were done, this is the state of the frame. I have a set of stiffer springs in case I find these too ‘soft’. If the bot lurches forward too much, it could hinder the lift by just keeling over at the very front of the legs.

From there, I moved to making the wheel hubs. These are based heavily on my design used in Clocker’s summer Gritty Reboot, but with a bigger Delrin center and larger diameter spacers for the larger sprockets. I started with a 1″ Delrin round and quickly whipped them out on Tinylathe from there.

Starting to reach Criticality (where a project can finally support its own weight)… I found a pile of nylon and steel washers to space the legs out properly. From there, plenty of blue Loctite was poured into the standoff-axles, forming the “permanent” side of the attachment. If I ever have to replace the legs, though, I’m kind of boned.

I christened this thing “Clockerboard” since I was riding it like a skateboard for a little while. The frame is extremely rigid, and the precision-ground aluminum standoff axles pair well with the Delrin hubs. The action is so smooth it might as well be on real bearings.

And the bottom plate goes on. I clearance-drilled the pilot holes in the bottom plate and made the attachment with #4 button headed screws. I normally despise buttonheads because of their super small 1/16″ hex key size, but they offer more bearing area (larger head) than the regular cap screws, which is better for the garolite’s structural integrity.

Starting from a 1″ diameter chunk of ceramic-coated (hard anodized, anyway) aluminum shaft, I drilled out the entire center with a long .75″ drill bit to save weight, then started putting the fork asesmbly together. In lieu of using retaining rings on the ends of the shaft, as originally planned, I decided to just machine spacers to span the gaps between forks in order to take up the axial slack. There was already going to be 3 different shaft collars constraining movement axially – a little snap ring wasn’t going to add that much more to the equation, and I could not be buggered to try and find the only grooving tool within 2 miles.

After cutting out some lengths of threaded rod, the fork comes together. This assembly is extremely rigid because of the sheer amount of preload I’ve put into this system through the three alloy steel threaded rods.

…unfortunately, I forgo that screws have heads.

The real story here is that the shoulder screw holding the leg on sticks out further than in the design because I added the spacing washers to give the leg a wider bearing area. I didn’t account for the extra width of a locknut compared to a regular nut, either. So the result, unfortunately, is just the hardware running into itself.

No problem – cutting the threaded rod exactly to length, and shortening the outer spacers 1/8″ each, gave enough slop room to clear the fork.

The modified clamp actuator goes on with, you guessed it, some more shoulder screws.

Mid last week’s pretend-o-bot, or thereabouts. This was just before the DeWuts showed up, so at this point I was stuck until I had motors. Luckily, Anonymous (…Chinese CNC shop) delivered.

While waiting for the DeWuts, I decided to take care of the rest of the menial machining tasks. I purchased a 1/8″ keyway broach to make the key cuts, and went to the Edgerton Shop to use a long-throw arbor press to cram the thing through the gears and sprockets.

With the DeWuts having finally shown up, here’s one of the first pictures from the mid-snowstorm robot work: one drive motor with shaft trimmed and test mounted. To be honest, I was mostly distracted by finally being able to run Landbearshark in its native habitat to get substantial robot work done…

I also went ahead and mounted up the lifter motor. It’s attached to the frame through a big U-bracket which functions as a spacer, the bot cavity being 1/2″ wider than the motor.

One issue was that the final distance between mounting holes was basically 3.00 instead of 3.05″, the original anticipated design length. I’ll have to take measurements of multiple units in order to confirm the +/- deviation from 3.00″ I should report, but the 3 on Clocker are all pretty close. Either way, much clearance-drilling was required. I basically had to open these holes up to 5/16″ to make that fit.

Drive motors mounted. By this point, I think the snow depth was already 18″ and going. The pickup truck plows had given up, and heavy equipment was starting to roll through the streets.

The last task of the night was routing the chains.

The chains on this version of Clocker are routed a little interestingly. On this (right) side of the bot, the chain wraps around the bottom of the sprocket. On the other side, though, the chain wraps over the top of the sprocket (and hence under the tensioner sprockets).

I did the chains up this way on purpose because the DeWalt motors are very heavily timed to favor one direction: the drilling/screwing-in direction, or counterclockwise. You rarely use a drill in reverse, so manufacturers squeeze a bit more forward power out of the motor by optimizing the brush timing for one direction.

In a traditional two-sided drive robot, the motors have to spin opposite directions to effect forward or backward motion since they are mounted mirrored from each other. In the DeWalt’s case, it seems to cause up to a 10% speed difference between sides – that means the robot will just pulll a huge wide turn the entire time you command ‘straight’. Clocker Remix, in fact, does this – it has never ‘driven straight’ in testing.

In practice, combat driving never really sees enough straight line travel for this to matter much, so most people just straight up ignore it.  If I had the opportunity to make the bot more symmetric, though, I was going to take it. So, to power the bot forward, both motors in fact rotate counterclockwise as viewed from their own shafts. This is the favorable timing direction and the difference in speed is both audible (faster spinning, higher pitched) and visible (the bot is definitely slower going backwards).

As for the chains themselves, I incrementally dialed in the tensioners by running the chain for a few minutes, then moving the tensioners to tighter positions. Chains stretch a few % just by virtue of wearing in the first time, so this was critical.

That concludes the first round of work. In the past day, I’ve managed to wire up half of the bot, but that will be reported on shortly. Tomorrow I anticipate being able to start doing shakedown tests and figuring out what to tune before the event.