Continuing my alliterating-c tradition of robot names is Cannon, an antweight version of Lolcat. On paper (and in CAD), Cannon looks like it’s going to be a lot of fun.
Very rough, yes, but it still lets me visualize everything and make sure the parts fit.
Here are the specs I have planned out:
Weapon motor: Turnigy Aerodrive SK3 2826-1240. It is rated at 150W and will provide more than enough weapon power. The old “Beloved Shardy” undercutter I built simply did not have a powerful enough weapon motor, and this one will be sure to suffice!
Weapon ESC: Thunderbird-18. It’s tried-and-true, and the weapon motor is rated at 16A continuous so a fire seems unlikely right now. Unlikely.
Battery: Turnigy Nano-tech 3S 460mAh LiPoly. I love the idea of three cells, and in theory, a 460mAh can supply about 14 amps for an entire two-minute fight (throwing out any drops/inefficiencies). I think I will have bigger problems than the battery if the robot requires 14A continuous for two minutes!
Drive ESCs: Fingertech tinyESC v2.1, the same kind used in Lolcat. I can’t say I’m wild about these controllers; I killed five or six of them before I learned that I’d discovered a hardware issue. They now seem to work okay, and I do have to say that Fingertech customer service is phenomenal!
Weapon: 3.0ish ounce 2.5-inch diameter titanium eggbeater spinning at about 9200rpm. It will be supported by ball bearings and connected to the weapon motor by a urethane belt with a gear ratio of 3:2. The weapon shaft will be hardened S7.
I already ordered some of the parts, and I was actually very impressed by how much higher-quality everything appears. Just look at the packaging.
Look at those beautiful graphics. It’s almost worth the huge premium over normal Turnigy products for the SK3…
Actually, just look at the motor and battery!
These motors are actually a little bigger than I expected but feel very solidly built.
Speaking of big, these batteries are HUGE for their capacity. Maybe I’m just used to dealing with Lolcat parts.
I do have some small quips with these parts.
Both the battery and motor are enormous. It’s a good thing I have minuscule drive ESCs because I may have a hard time getting everything to fit, and the body I designed for Cannon is fairly large.
The brushless magnets don’t feel very strong, though the motors feel very precise when you turn them. My feeling is that I am mistaken and when I actually wire the motor up, I’ll be in for a pleasant surprise.
The motor wires are small and flimsy.
The battery came with a JST connector on it. The battery is rated for 25C (11.5A) continuous, 40C (18.4A) burst. JST connectors are rated for 5A. That’s a waste of plastic.
Still, despite my minor complaints, I am happy with my purchase so far. I can’t wait to see that motor spin.
The motor isn’t the only part of Cannon I am excited about. I learned a lot about building eggbeaters well with Lolcat, and I believe most of it will apply in the antweight class as well. For one, protecting your belt is very important. Lolcat’s belt almost got sliced twice at Bot Blast, so I’ll try to get the side rails to cover up the pully. However, the bottom of the side rails is far more important. Tracked Terror kept getting underneath Lolcat and flipping it over. I worry that wedges could do the same with Cannon, but I have devised a fix of sorts.
Side view of the above image.
Notice that the sides are swept back. The beater extends way forward of the front of the supports. I am concerned about what effect this will have on stability. Since the beater, likely the heaviest individual part of the robot, will be centered in front of the support, the entire robot will act even more front-heavy. It could lead to some flipping over on hits; only time will tell. I am also concerned by how small the bottoms of the supports are, but they will be 3/8″-thick UHMW so antweight weapons shouldn’t be able to completely wreck them.
The only way we’ll see how this plays out is in the arena. I will continue to post progress updates on this blog as Cannon comes together.
Coercion’s blade needs a lot of work – I think the video of Ripto bending it 30 or so degrees proved that. The question is how to change it. I know Coercion is a good bot, but I have noticed some continual flaws. First of all, the blade is too heavy. It spins up too slowly and it takes way too much work to get up to speed (thanks to losses all over the place), so the weapon motor runs hot and pulls something in the 30A neighborhood. I thought I had more or less fixed the problem before Bot Blast, but running my robot on 7.4V made it far more sluggish than I anticipated and I still wasn’t getting ideal blade performance. The blade is also so heavy that it tends to flip over its nose, which provided a loss at Boy Blast. I have decided to apply some physics to make Coercion more hard-hitting and hopefully more efficient than ever.
Where omega (henceforth referred to as w) is angular velocity, E is kinetic energy, and I is moment of inertia.
Awesome, so based on that, we can do one of two things to increase the kinetic energy of the weapon:
Increase the angular velocity (how fast the weapon is spinning). This will be the more effective of the two methods because it is a squared term, so if we double the angular velocity, we quadruple the kinetic energy.
Increase the moment of inertia. MOI is the sum of the masses of the particles that make up an object multiplied by the radii from the center of rotation squared. In other words, the heavier something is, the greater its MOI, and the greater something’s diameter is, the greater its MOI.
So there we have it. To make Coercion’s blade work better, we make it heavier and spin it faster. Great physics lesson, Einstein. The problem here is that to make weight for better wheel guards, a better weapon motor, new batteries and the other improvements I have planned for Coercion, I need to make the blade lighter. Remember that MOI is also based on the distance the particles of an object are from its center of rotation. Thus, if I can concentrate the mass as far away from the center as possible, I can “cheat” (not really) a little bit: the blade will hit harder while not weighing in any more.
My target weight of the blade was 11ish ounces, which is about a big reduction over the old blade. I had to make the inside as skinny as possible while making the outside part as wide as possible. I kept the same blade dimensions – 11.75″x1.50″x0.19″ – and I plan to have this blade waterjetted out of S7 and then hardened (I learned my lesson at Bot Blast!).
10.35oz, far lighter than the old, nearly-one-pound blade.
The plan is to spin this blade at 10,000rpm with a 3S LiPoly and a new weapon motor in the 1500-1900kv range (and a new, 2:1 weapon gear ratio). If I recall correctly, Coercion’s blade was spinning at about 7000rpm at Bot Blast, and according to the MOI differences I saw in Solidworks (the new one has about a 22% lower MOI than the old one), the new blade will actually store about 50% more energy. Not bad for saving three or four ounces, huh?
Having not competed since Motorama (and not competed in a Mall for five or so years), I was very excited to fight robots at the Columbia Mall in Bloomsburg, PA. We woke up around 7:30, had a terrible breakfast (why would you serve one egg by itself on a plate with an orange?) at Cracker Barrel, and were at the venue by 9:00ish. I was pleased to see that Bot Blast has a wooden floor because it would not interfere with Lolcat’s radio reception. Wooden floors are also a bit quieter and more forgiving.
This event report contains some fight videos, but only for the interesting ones. I have only included one Lolcat vs Tracked Terror fight and did not include any Amatol fights.
With the guys.
We got through safety inspections without much of a hitch. Coercion was a tiny bit overweight (as was Amatol) but apparently the scale was off by a bit so I didn’t have any issues. We sat around and waited for the event to start. Fights kicked off around noon, which is way earlier than they would at Motorama. We were all impressed.
The first fight of the day for us was with Coercion against Kyle’s fearsome vertical spinner, Ripto. I knew it would be a tough match for Coercion (especially in an eight-foot arena like the one at Bot Blast) but I never imagined it would be as tough as it was. We both spun up and Coercion went flying into the ceiling. The S7 blade (which I did not have hardened for some unthinkable reason) was bent about 30 degrees upward. I tried to push Ripto, hoping that the belt would come off the weapon, but it was no use. I quickly tapped out.
I do not have any images of the bent blade because I was so concerned about getting it fixed. I can tell you that it took some vice smooshing and beating with a hammer to get it back into shape. I did, however, get Coercion fixed.
The next first-round match was between Amatol and another wedge bot. After about thirty seconds of pushing, Amatol ended up stuck on the wall and was counted out. Amatol’s wedge wasn’t getting it done and I lost because of it. The next version will need a bent back. 0-2!
At this point, I was running seriously low on robo-mojo. It was Lolcat’s turn to fight a small undercutter called Baby Box. Undercutters have always scared me with Lolcat ever since Jeremy Campbell’s Rebound broke the eggbeater twice at Motorama 2011. I was hoping that it would not be able to cut my belt or worse, rip the eggbeater out of its supports. After accidentally hitting the blade a few times, I felt like my robot would hold up. I eventually removed the other robot’s weapon. Unfortunately, I did not remove either of Baby Box’s wheels (there seemed to be some foam padding helping there) and I was unable to cut Baby Box’s exposed battery connector. But still, I won the match on a judges’ decision.
With some of my mojo restored, I set my sights on my next antweight opponent, Mateo. I had to postpone my match because of connector issues (which would come back to haunt me), but when we finally got in the arena, the match was boring. We pushed each other around and Mateo wound up stuck on the arena, and after being left on the wall twice, I decided not to risk freeing it. I felt horrible but won by knockout.
With two wins under my belt, I started to calm down a little bit. I had been seriously worried at the beginning of the event, but I chalk it up to a combination of bad luck, poor foresight and great opponents. My next fight was another with Lolcat. This time, it was against Hedgehog, which was the fairyweight I thought had the best chance of breaking Lolcat coming into the event.
The fight began and we both spun up. Hedgehog tried to attack my wheels as I moved to attack its wheels, so our weapons ended up making contact. After seeing that my beater could stand up to Hedgehog’s large, direct-driven blade, I became a little more aggressive. My strategy worked – one hit sent Hedgehog a good foot or so into the air and the next sent us both flying. The second hit broke Hedgehog’s weapon motor in two and Lolcat won by tapout.
The damage to Lolcat from this fight was actually a lot worse than it appeared. Lolcat’s weapon shaft was a little bit tweaked, the pulley had a big gash taken out of it, the right weapon bearing’s dust covers were broken off, and alarmingly, the weapon belt was nearly sliced in two! I made a new belt but chose to keep the shaft as it was since it did not appear to impact weapon performance. A quick spin up test confirmed that, and Lolcat was ready to go once again.
My next opponent was a beetleweight vertical spinner called Lezlee. Considering my blade had just been re-straightened, I was happy to just be fighting. I noticed that Lezlee had thin aluminum armor, and since Coercion appeared to be on its last legs at the time, I decided to just go all-out. I spun up and chaos ensued. I chewed away at the front of Lezlee (somehow while avoiding the blade), and one hard hit jarred its LiPoly free. Jeremy is smart enough to know a one-pound piece of spinning steel could do bad things to an explosive battery, so he called the match. Coercion won by knockout.
The next fight was Amatol vs Kyle’s Cutter, an antweight spinner. I was confident heading into the fight because Amatol was built to fight spinners, not wedges, so I was looking forward to testing my robot’s strength. Unfortunately, I box rushed Kyle’s Cutter, hit the wall, and one of the battery connections in the speed controller came loose. Amatol was dead in the water and I tapped out less than three seconds into the match. I thought some very non-PG words after that fight.
With Amatol out after two stupid, preventable losses (AGAIN!), it was Coercion’s turn to continue carrying the Team Slammers banner. It was matched up against Play ‘n Krazy, which was fighting as a lifter at Bot Blast but is usually a vertical spinner. I was looking for revenge for my three-second match, and I got it in the form of a nine-second one. Coercion spun up and delivered a hard hit to the front of Play ‘n Krazy. The hit removed a wedge panel, a wheel, a wheel guard and a receiver and Play ‘n Krazy tapped out.
Lolcat was up next in the fairyweight winners’ bracket semifinal against The Tracked Terror. This was the first of three straight matches between these two robots. The Tracked Terror beat Lolcat at Motorama, so I was out for revenge. We traded blows for two minutes but Lolcat won on judges’ decision. More on these matches later.
The next fight for us was Coercion vs Counter Shock. Counter Shock was a very well-built beetleweight drumbot, but the drum wasn’t working so all I had to do to win was to keep the weapon running and not get stuck on the wall. I only accomplished the weapon part. I spun up and hit Counter Shock hard, but unfortunately, the hit also flipped Coercion over. It was too tall to hit Counter Shock, and got pushed up against the wall. Counter Shock gave Coercion one final shove, and the wheels could not get traction. Coercion was counted out, leaving Lolcat as our only robot still in the tournament.
Despite being out, Coercion still had one trick left up its sleeve – the beetleweight rumble. Although it ran out of battery at the end, it was crowned co-champion of the rumble along with mantisweight Dead Metal (since there was no mantis rumble). I think it had something to do with the flying around everywhere thing (see the video) combined with my exuberant cheering at the end of the match.
Lolcat was in up next against The Tracked Terror in the first fairyweight final. This match did not go as well for Lolcat as the semifinal did. I kept getting flipped over and according to Jeremy, lost on aggression. The good hits were also 3-2 in favor of Tracked Terror. I was worried – I was very close to finally getting a win with Lolcat, but it was going to come down to an all-or-nothing final. I charged my batteries and decided that no matter what, I would keep chasing Tracked Terror. Lolcat uses 50:1 gearmotors instead of the 30:1 ones used by Tracked Terror, so it was at a major speed disadvantage.
Nearly two years of work came down to one final match. I wanted to win really badly. I stayed aggressive. I followed the game plan. Luckily for me, it all worked out. Lolcat won on a judges’ decision and was crowned fairyweight champion. Congratulations to Chris on building an awesome robot! Lolcat could barely scratch it.
So, with the event over, what did I take away?
Lolcat is too slow and 30:1 HP Pololu gearmotors instead of 50:1 Sanyo gearmotors would do it a lot of good.
Coercion’s blade is too heavy and needs to be hardened. At Motorama, I plan on using an 11-12oz blade spinning at closer to 10,000 RPM. I will keep the MOI as high as I can while designing it.
Amatol needs… improvements. It is very strong but keeps failing in dumb ways. I will make some adjustments to keep it from getting stuck on the wall and hopefully the robot lords will smile upon me at Motorama.
Due to SATs, we won’t be able to make it to Franklin Institute this year. Any changes we make won’t be tested for a very long time!
Another big thanks goes out to Jeremy Campbell for putting on a great show. We will definitely be back next year!
I’ll be attending a robot competition in Bloomsburg, PA this Saturday (July 21st). If you live around there, it’s in the mall gazebo at the Columbia Mall. Fighting should start by 11:00 and we’ll be done by 7:00. 150g fairyweights, 1lb antweights, 3lb beetleweights and 6lb mantisweights will be fighting. It’s worth driving a couple hours to see. I understand that it’s a very fun event for builders and spectators alike. I’ve only fought in a mall once but it was one of my favorite events of all time.
I’ve been working hard over the past few days to get ready because just like every other robot builder, the 1-week mark seems like a good time to start prepping to me. Luckily, I didn’t have much to do. Here’s a picture of the three robots I’m taking:
I promise they won’t look this good on Saturday night.
Here’s the lo-down on changes I’ve made to my robots since they last competed (at Motorama in February) and how I think they’ll fare:
Complete redesign of sides. They are now taller and the front beater support has been swept back slightly so wedges will tend to hit beater first instead of support first. They are also made of polycarbonate now, so they are lighter and do not cause radio interference.
Upgraded from a custom 2S 160mAh LiPoly to a ready-made 2S 180mAh LiPoly that is capable of 40C burst current. The new battery seems to work much better and fits better as well. It can also be balanced.
New wheel guards provide more wheel padding so the plastic has time to absorb more energy. They are also swept back more and will hopefully be less flexible. The screws are farther from the edge on the new ones, too.
Because of the height, all components now fit inside the robot.
The current lolcat is running extremely well. If it does not suffer from any radio issues (receiver failures or interference) it will place in the top three.
Replaced a drive motor that was taken out at Motorama for use as a spare.
Remarkably unchanged. Hopefully this robot will have better luck at Bot Blast!
There are a lot of antweight wedges going to Bot Blast, so winning will come down to driving and having a lower wedge. Amatol does both well, so it should pull off at least two wins and if it gets a lucky draw, could place in the top three.
Weapon is now supported by ball bearings which reduce friction and allow for a tighter weapon belt.
Weapon belt has been tightened significantly to prevent slippage.
Weapon can now be fully tightened which should reduce flexing into the weapon pulley like what happened at Motorama.
1Ah 3S LiPoly has been replaced by a 1.3Ah 2S LiPoly to meet the increased current demands of the motor with a tight belt driving a 1lb blade and to combat the increase in power consumption by lowering the voltage.
Grease has been removed from the robot to reduce belt slippage.
Polycarbonate wheel guards have been fashioned to use instead of the ABS ones that fared so poorly at Motorama.
I have purchased sparemotors and wheels! The motors can also be used in Amatol.
Drive motors are now protected with foam to prevent the magnets from breaking during big hits.
The beetleweights at Bot Blast are excellent. Coercion hits very hard (it will go through quite a bit of aluminum and bend titanium) but is unproven in the arena, unlike the rest of our fleet and the rest of the beetleweights there. Assuming it holds together, it could do very well, but that can be said for any robot. Coercion is a tough call but placing in the top three is highly unlikely.
I am extremely excited for Bot Blast. I’ll post an event report, videos, and pictures when it’s done!
John Parsons' Blog About Robotics, Programming and the Search of Knowledge