Ahoy! On our last episode of HyperShock How-Do's, we discussed the armor and chassis design, specifically focusing on the "Billettes" at the front end of the robot. These large CNC'd aluminum chunguses basically attach chassis to the weapon. They also provide a mounting point for front attachments like forks and wedges, and give us a spot to mount some bunny ears (also referred to here as horns) to keep the weapon from hitting the ground when inverted.
Well, there was a problem. When you make everything stiff, impact loads spike quite high. So high, in fact, that baby HyperShock getting dropped on its noggin would bend 1/4" Grade 5 Titanium no problem, 3/16" AR500 like it was made of pudding skins, and anything stiffer just stripped the 3/8"-16 bolts right out of their stubby little holes. Looking sick? Check. Working? uh.....
We needed a dampener. something "squishy". At least, squishy on the scale of a BattleBot. Urethane suspension bushings had done us well so far in mounting the front forks and wedges, so let's cram some into the bunny ear mounts!
A few solutions were considered, varying from "wow, who's mean enough to make some poor sucker machine this" to "no, absolutely not".
Attempt 1 - Complicated and Weak: Perfect!
This was the first attempt with off-the-shelf urethane bushings. You can tell I got a fair amount of CAD disease here with some of the features. It's neat and gets the point across, but a mission to machine, unnecessarily complex, and not nearly as robust as I'd like. You can see the intent here: thru holes for the urethane bushings and a massive clearance pocket on the back for a thick & flat rubber gasket that goes between the Billette and another complicated machined part that the screws holding the horn in bolt into. Like I said, complicated.
Additionally, I'm trying to avoid making this thing so heavy that we have to find a bunch of weight elsewhere to magically remove. So....
Attempt 2 - Like 1 But More Complicated
I managed to keep the weight in check thanks to even more complex pocketing and skeletonizing, and adding a HyperShock logo definitely helped make it stronger, but it's going in the wrong direction if our goal is robustness.
Attempt 3 - Cooking with Gas
I stepped back and looked through urethane bushings again to find a slightly longer one (thicker, and therefore requiring stronger, supporting material). I found one I was happy with and started the process with the intent of simplifying the silly pocketing I'd been adding and eliminate that complicated new machined part I'd stuck myself with in previous embodiments. It instantly started to look more real and plausible, and much more robust in my mind.
Final Design
As you can see here with the final* iteration, 6 stubby urethane bushings press into the Billette, a female threaded part with a large flange (sometimes called a sex bolt, not kidding) presses inside, and 3x 3/8"-16 bolts thread into the sex bolts holding in the horn. Tada! Simpler, beefier, slicker. Oh and we theoretically also have the option of putting the horns on the outside, or doubling up (outside and inside).
There's lots of opportunity to explore by having some solid shock mounted attachment points up front. Special Top armor for Quantum or SawBlaze? overhead keep-away stick? the world is our oyster!
Horn Positioning - Inverted Drivability
Another historical issue was drivability when inverted. The weight distribution of the robot is veeeerry front-heavy, so the robot was prone to tipping forward while driving upside down. We experimented with some funky horns at re:MARS which theoretically brought the weight on the driven wheels while inverted up from 65lbs to 100+lbs. They came forward another few inches, almost looked like bull horns. Alex thinks the Bull Horns definitely helped drivability at re:MARS, but they still bent (see above mitigations) and one seems to have been ripped off when we rode up the screws inverted.
A pleasant side-effect of the new horn mounting was I ended up moving the mounting positions further up and forward for enough clearance on the urethane bushings. This alone pushes the original horn shape 1.5" forward, as well as upwards a bit for added ground clearance when inverted. This alone puts another 13lbs on the rear wheels when upside down, and we can play with horn shapes to find a balance for improved drivability and durability.
Fun Fact: We thought this would help us with driving, but we ultimately went back to a further back contact point on the ground. It turns out that stability and better driving upside down made it nearly impossible to gyro-flip when inverted. So your options were A) stable upside down and drives less bad, or B) make it unstable upside down and get back on all four wheels ASAP with a little flip. We went with option B.
Billette Bonus Round - Axle Retention
At re:MARS, we ran into an incredible frustrating situation where the bolts on either end of the weapon axle were stuck and we couldn't get them both out because the axle kept spinning.
A quick and simple fix for this is to put a small flat on one end of the axle and a mating flat in one of the Billettes (I chose right because we've formed a habit of inserting the axle left-to-right for whatever reason) to restrict rotation. I particularly like this solution because it doesn't add any extra pieces or screws, to lose or break, and if we decide it sucks we can just machine that material out and use it like before. And since we're already having new Billettes machined, it's basically a free fix that will be a massive quality-of-life feature.
Conclusion
These updates have stuck with the robot through Season 7 a visit to BattleBots: Proving Ground against Magnitude, and a very scary weekend of BattleBots: Faceoffs against Tombstone, Valkyrie and Orbitron. All in all, the latest Billette design is holding up quite well even with giant hits and massive flights through the air (courtesy of other robots). We knew the bunny ear problem was solved when Riptide sent us to the ceiling and we landed without a bent ear, so we'll call that a "win". What will we do next? find out on next quarter's episode of HyperShock How-Do's!
