BattleBots Post-Fight Report #1 : Shatter! vs Witch Doctor

Wow! What a fight! If you haven't seen it yet, then go see it!

SPOILERS AHEAD! You've been warned. Full battle damage report after the jump!

So, what the heck went wrong, and what the heck went right?

We came into this fight pretty hyped. There was an amazing segment with Jenny where we went over our drive, our hammer, and our armor. They mentioned more than once our goal to fire the hammer 50 times in a match. That didn't quite go to plan :( Let's take a look by sub system: drive, hammer, and armor, and figure out why we weren't able to hit that 50 times mark.

So first off, the drive:

Look at that strafing action! It worked great, and you can almost picture Shatter! going "weeee!" as it slides around. Fun! We had a full 3 minutes of fully functioning strafe drive. That's a first for the rebooted Battlebots! Can I get a giant bolt for that? No? Darn. Still, it's always nice to see the drive working well, and you never know what's going to happen on a new floor. That said, our low pushing power (a natural side effect of mecanum wheels) was evident toward the end of this match. We could kind of push them a bit... but not like we'd like. It's on our list of fixes for next year.

Onto the weapon... which did not work so great. You may be thinking of this moment when our hammer decided to come undone:

That little titanium plate flying through the air is SUPPOSED to be bolted onto the arm with 3x 1/2" diameter grade 8 bolts. We've slammed this thing directly into multiple spinners and never lost a single bolt or even had the hammer head get loose. So what the heck happened?

Well, it's a bit sad really. One of these photos shows a properly attached hammer, one shows an improperly attached hammer. Can you spot the difference?

On the hammer on the left, which is properly mounted, you can see the bolts extending through the bottom of the nuts. On the hammer on the right, you cannot see the bolts protruding from the nuts.

When you go to a competition like Battlebots, you buy a lot of new things. We bought a lot of new bolts. The bolts we used in the hammer this fight were slightly too short, which meant we were putting too much stress on too few threads. We actually sheared all the threads off the bolts. The bolts were ok other than that, they didn't fully shear. The nuts were fine. The hammer was fine. The arm was fine. But the threads failed. Oops: 

Always check your bolts! Two dozen fights and we never did this until our first fight at Battlebots. Talk about bad timing! But, you can all learn from our mistakes. Check your fasteners!

For anyone wondering, it isn't just 3 bolts attaching the hammer. The 1/2" thick titanium arm has 4 "fingers" which extend 1.5" through the entire thickness of the hammer. Those fingers take the majority of the force of a hammer blow. The bolts just hold it "on" to the arm. You can see the fingers later on in the fight:

The fingers were fine. BUT! Even if we'd used the correct bolts, the hammer coming off wasn't a big deal, functionally. The hammer was actually already broken. What? Read on:

The online response has been focused on our hammer attachment method. I understand, it does make for spectacular TV when the weapon comes off. However that wasn't the real issue at all. Well before the hammer ever fell off we were firing at, maybe, 1/10 power. We only had one full power hit, got stuck in the floor, and then our next shot was super slow and it didn't get better from there on out. If we'd had full power, even just the arm would be a brutal weapon.

​So what happened? This:

See, that's one of our two weapon ESCs, and it's not supposed to look like that. Those three wires on the left are supposed to be connected to the controller! The controller is supposed to be in one piece! It's also not supposed to light on fire! Arg!

This happened almost immediately. We're not sure the exact failure mode, but what ended up happening is that at least two of the three wires leading from the ESC to the motor shorted. This turned one of our two weapon motors into a big e-brake. The remaining motor and ESC, which were still good, were pushing against a stuck motor with 10kw of power and over 300 amps! All that power to fire the hammer slower than a kid flailing a pool noodle. Not good! The batteries were extremely hot at the end of the fight but because they're Max Amps (thanks sponsor!) they lasted. After a bit the ESC lit on fire, and then eventually the burnt up ESC failed so badly that it blew up the weapon receiver as well, losing all function to the weapon.

​I mean look at this thing, there's more char than controller:

Oddly, the receiver only blew out on the channel we were using. The other channels still worked. I mean... what? We switched it anyway.

Due to our new foam and internal structure (which we'll go over in a future post), the fire was also contained and didn't spread past this controller. So... that's some positives at least.

Teammate Paul Gancitano wired up a new one in record time and we were fixed on this front (after adding to our shock mounting as well, just in case).

So, it came down to those darn electrical gremlins. It was a 3 year old controller, and perhaps it was just his time. No one lives forever, and at least he went out doing what he loved.

Onto the armor performance! Check out some gory post-fight photos:

Those photos look pretty brutal! But they're actually not bad. We planned to replace these pieces after any big spinner fight (of which Witch Doctor certainly qualifies, I mean did you see the Re:Mars Twitch steam?). It's designed to dent, ding, tear, rip, shred, etc, and dissipate all that energy to save the frame behind it and keep us from flipping. It's key that these panels tear, and not crack in half, which is exactly what they did! Also, check this out:

That right there is a direct, full power hit into our side. It's about 2" deep into the UHMW-PE ablative armor. I love this photo.

We've taken full power vertical spinner hits to the side before, twice in fact. It's been an Achilles heel for us. No matter how well you drive, eventually you get hit in the side, and this doesn't usually end well for us. The first time this happened was against Team Toad, at Robogames 2017, which did this:

This broke a gearbox shaft, bearings, baseplate, and side. The wheel actually ended up being salvageable. It also hit the frame hard enough to warp it, and busted an ESC due to shock as well as popped a lot of bearings out of our hammer assembly. We lost by KO on this hit. 

The second time this happened was against 2BBQ at the first KoB later in 2017. It did this, while sending us 20 ft across the arena through the air:

Clean through our 1" thick 6061 frame rail, which then busted a bunch of electronics located directly behind this side rail. We kept going, since we had better internal shock mounting at this point, but we ended up losing as a direct result of this hit.

It's annoying to replace these frame rails. Everything is bolted to them! It's really annoying when your gearboxes break and you need to use an angle grinder to get the wheel off. It's even more annoying when your baseplate breaks and you need to unbolt every single freaking component! Losing because of one badly placed hit is frustrating. It's not even the money lost as much as it is the fight, and the time to repair it.

We'll be doing a big segment on ablative armor on the blog in the future, but let me say this;

I love ablative armor.

Replacing 4 bolts and a panel of plastic is WAY better than losing a fight immediately, and replacing near every component. Let me just show that side hit image one more time:

That's a master power switch directly behind this hit. Without the ablative this would have been very bad. With the armor, the frame rail was fine and so was the switch. Also, thank you Witch Doctor for not hitting either mounting bolt, which would have made this panel pretty annoying to replace...

We also took multiple hits to the front as well, and we never flipped over. Going the distance against a vertical spinner as powerful as Witch Doctor, with multiple full power hits to your armor, and NOT flipping... I was happy with that. We may not have won this fight, but the armor at least gave us the chance to.

EDIT June 25: I wanted to clarify a point which was brought up a few times online after this article was published: we did not velcro on the ablative armor :) The sides are each bolted on with 4x 1/2" grade 8 bolts, and the front is attached with 9x of them. The only parts which are velcro'd on are the hollow 3D printed decorative top panels (which are attached to the actual armor underneath, which for this fight was 1/2" polycarb). Due to the editing of the tech segment which combined a few things I said, it sounded like the ablative panels are velcro'd on.

Also, we did a bit of damage to Witch Doctor too:

We were really, really close to getting their belts when we kept jamming our weapon into theirs. It didn't work, but we did eventually kill their weapon with our armor. I wonder, would they have even lit on fire if we'd cut the belts early? As for what that fire was, we never heard. Some sort of wiring short that lead to half the drive cutting out.

EDIT June 25: I've been told by Andrea from Witch Doctor that it was a burst (shattered?!) fuel line that caused the fire (and they were purposefully venting the fuel, hence all the green fire in the lead photo for this article). The cause of the burst fuel line is still up in the air.

I will say this: the fire was localized directly below this chip our arm put in their lid. Coincidence?

​Either way, a memorable fight, with some sick photos:

Maybe we'll make the 2020 calendar? One can dream :)

For our next match, we used proper-length hammer bolts (doh!), improved the weapon-ESC shock mounting, replaced the busted weapon ESC and receiver, and swapped out the ablative armor panels. Keep watching to see if it all works out!

I would also like to say that the Witch Doctor team is amazing. They built a top notch robot and are top notch competitors. They really deserved that victory at the Re:Mars event. Their non profit community makerspace is also pretty amazing:

https://www.makemia.com/

They do a lot for promoting STEM to kids and it's awesome. Follow them on instagram too!

Anything we left out you'd like to hear about? Let us know!

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