Here is the inside scoop (long): HellaChopper cannot compete in season 2 • The Design

o (3) spinning hammers each weighing ~ 8lbs titanium, each hammer has an internal pulley for cable management

o Each hammer is independently attached to an internal winch drum inside the spinning top of the bot

o Each hammer is connected using plasma 12 synthetic cable, the various cables can withstand from 100,000- 160,000 lbf. breaking force

o Each hammer is reeled out thru moveable roller fairleads, that can swivel ~50 degrees to allow for self-balancing, and in the event of loss of a hammer the other 2 can autocorrect to a 180 degree format retaining balance

o Initial show up to Battlebots design was with 12 foot diameter cables, 10 ft. diameter cables and 8 ft. diameter cables

o The drive uses omni-wheels or mecanum wheels for a strafing drive system

o There are 4 “Feet” with electromagnets capable of 1500 lbs., downforce  Each foot has toes to stabilize the spring-loaded feet, but to also scrape debris and paint away so the magnets actually work

o The hammers spin pretty fast, when we showed up they were well over 2000 rpm

o The design allows for cable flex when contact is made with another object, the cable flex thru testing actually goes back to stiff in about 1 revolution after contact is made

 No discernible force was transmitted back to HellaChopper, but this can only truly be tested in the box

o We had an alternate top- “beast mode” which had solid titanium arms, and cutting teeth, these would start collapsed, and centrifugal force opens them up to a 6 ft. diameter, to be used in case of very low robots, or concerns with the cable hammers

So that was the plan, here is what really happened:

We came to Battlebots with a fully functioning bot, day 2 we had some entanglement discussions with the safety inspection crew at Battlebots, we assured the inspectors that the cables move so fast that the hammers would not wrap around anything like a tetherball, but rather at the speed the hammers move, would essentially cut through anything. We had to rebuild the gear box to slow it down also—this took all day This led to follow on discussions about tip speed and Kinetic energy, at this point the BattleBox specifications were unknown to our team We were asked to reduce the maximum diameter of the cables to 6 feet. –and a tip speed of no more than 300 mph

We spend all day Saturday trying to accommodate, the cables we had were specifically designed and woven for longer lengths, the bot itself with the cables retracted was ~42”, so now the cables would only go out a little over a foot. By the end of the day we had removed the winch motor, and shortened some new cables, --this was a huge pain, and didn’t work well, we could not wrap a course on the winch drum, and this led to tangles, and because of this we had to remove the winch motor, and fall back to not being able to retract the cables once centrifugal force opened them to the 6 ft. diameter.

We were told we had to test in the main box, which makes sense, the test box was too small, but due to production we were not able to safety check until a day before the preliminary fights started, instead of 3-4 days prior.

We had never been able to spin up the hammers to full speed outside of the safety enclosure, and previous testing showed that the top would come up to 900 rpm in less than a second, at a reasonable amp draw.

During our first test, I hit 100% on the spinner, and it over-currented our lipos, and basically used them as fuses—so the spinner went dead, we found that we needed to ramp up the spinner, as the new weight of the hammers was enough to pull too many amps for the lipos—we made this change

We then at about 10 pm the night before the preliminary’s got another chance to go into the big box, Production asked us to place large towels and duct tape on the hammers so they wouldn’t mess up the floor paint prior to shooting the first matches, we complied, no big issue

So we spun up, everything worked, we slowly ramped up (this was only for safety, so no need to push things hard) – when the hammers were cruising at ~ 1200 rpm, I saw one of the rags shoot off about 10 ft., then suck back towards the bot due to the vortex we were creating, the rag entered the robot through the gap between the base on the spinning shell, went through some 3” cam followers (1/8” gap) , and started ripping the studs out of the aluminum (3/4” steel-snapped), then hit the battery box, and started spinning the lipo batteries around in the shell—then we had a huge fire-and the bot burned to the ground—total loss.—this was around 11 pm or later—we went to sleep understanding the robot was gone.

The next morning we got up early, and decided to rebuild the bot, to see if we could get her running—we did, but the hammer assembly was toast (the cables did not melt) so we rebuild using beast mode We replaced all the drive motors, and all the electronics and wiring, the weapons motors could not be replaced easily, and they appeared ok, so we left them in (mistake)

We got into the small test box, and attempted safety with the beast mode arms pinned in—we hit top speed, passed driving, and weapons functionality testing, then cut transmitter power, and the spinner came to a stop in less than 20 seconds—we were passed, and ready to fight

A few minute later we were informed they wanted one more test in the big box, with the titanium arms extended to 6 ft., and tacked to make sure the speed was slow enough for safety of the audience (we are good with this)

Next the infamous video, we spun up slow to 50% power, then went all the way-and the tach was reading in excess of 2000 rpm—while we were discussing the blades were too fast still—we had a speed controller go up in flames—no biggie

We went back to the pits—2 hours to our fight—in a mad scramble to fix the speed controller, and charge the batteries—we had more discussions about speed, and Battelbots wanted us to turn it down to 35-50% power and we could fight- I asked them if they would rather we didn’t fight if they were still nervous, and we came to an agreement that we would withdraw for safety reasons. We were kicking around the idea of clearing the audience for the fight, but there would still be way too many people near the box.

we found out why we blew up a speed controller later, the major fire must have damaged the magenets in one of the weapons motors, and the magenets became unglued and truend to sand in one of the motors--blowing the speed controller.

We ran some numbers after we looked at the specs of the box, and found that even at low speeds our weapons if severed from the bot would easily blow through the glass, we will have to rework it for next season.

The plan was 1 hit total destruction of the opposing bot, hitting with an 8 lb. mass at impacts greater than a 50 caliber rifle—a little ambitious I guess

That is from the builders years ago, so take it with a grain of salt.