Sumo Bots C

[M-E-T-H-O-D MAN]

I wonder how difficult it is to build one of these...

Building one is easy. Now building a good one, that's where it gets tough.

Go to your local hobby shop, and tell them what you want to do. You'll probably want to go with a 2.4GHz system, which means you can get a radio intended for helicopters and use it for your bot instead. (I find that it's much easier to control a sumo bot with two sticks rather than a pistol grip system.) Get some servos, motors, and wheels, and then come up with a killer design. Simple.

Hmm, sounds like this might be something I could actually bring myself to dedicate some time and effort too. Something I do on occasion.

[Primate]

I wonder how difficult it is to build one of these...

Building one is easy. Now building a good one, that's where it gets tough.

Go to your local hobby shop, and tell them what you want to do. You'll probably want to go with a 2.4GHz system, which means you can get a radio intended for helicopters and use it for your bot instead. (I find that it's much easier to control a sumo bot with two sticks rather than a pistol grip system.) Get some servos, motors, and wheels, and then come up with a killer design. Simple.

Hmm, sounds like this might be something I could actually bring myself to dedicate some time and effort too. Something I do on occasion.

Absolutely; it's a lot of fun. Just whatever you do, don't use a kit. I think about half the bots at our regionals use Vex, and another quarter are shoddily made custom bots. So if you can build a decent custom bot, that's easily top ten.

(Not that there aren't really good Vex bots--we had one beat our bot at regionals--but they're few and far between. This guy had laser-cut his blade and upgraded the motors, and it was pretty impressive.)

[harryk]

If you can try and avoid using a kit, but on the other hand building a custom bot is expensive, mine cost approximately $400 and I didn't realize how expensive it had gotten till it was done
Go to your hobby store for radios and motor controllers but try and buy other parts such as motors online, you'll be able to find a better selection at a better price

[Primate]

If you can try and avoid using a kit, but on the other hand building a custom bot is expensive, mine cost approximately $400 and I didn't realize how expensive it had gotten till it was done
Go to your hobby store for radios and motor controllers but try and buy other parts such as motors online, you'll be able to find a better selection at a better price

Yeah, Sumo is definitely one of the more expensive events. I'd say $500 would buy you everything you need for a states-winning bot--everything beyond that point is engineering and driving.

Even if you don't go the custom route, the starter level Vex kits cost a good $300. And you're paying for all-purpose motors, all-purpose wheels, sensors you don't need, etc.

[old]

OK, let's try to put these two issues to rest so that the thread can return to discussing robots and strategies:

1. Impound: I have been judging/running impound events since 1997 at the Regional, State and National levels. I've been involved with the vehicle events (wheeled vehicle/scrambler/battery buggy), the bridge/towers/boomilever events, the robot events (robot ramble/robo cross/robo billiards), storm the castle/trajectory, and I'm good friends with the people who run Mission/Junkyard and Bottle Rockets at the State level. I have never been involved in an impound event where just the device was impounded and the competitors were allowed to bring ANYTHING (other than safety goggles) to the competition. If you were to allow students to come back with boxes of tools, spare parts, or anything else, then you'd have to spend time all over again going through those boxes to make sure that everything in them was legal. As stated before, EVERYTHING that you will want to have available to you during your competition in Sumo Bots needs to be impounded. If you need to use power tools, then they will have to be powered by the batteries that run your bot or the transmitter, as those are the only batteries the rules allow you to impound. This is just September, most teams won't compete until January at the earliest, so you have plenty of notice about this.

2. As I (and others) have stated several times, it is possible to build a championship level sumo bot that does not need to have batteries replaced after every bout. In fact, I believe that all of the winners of the event at the New York State competition and the National competition did so without ever replacing their batteries. Having said that, it is possible to design a robot that meets the specs and has very good batteries that needs to have those batteries replaced once or more during the double-elimination tournament. THAT IS YOUR DESIGN CHOICE, AND YOU ARE MAKING THAT SPECIFIC CHOICE WITH THE KNOWLEDGE THAT THERE WILL BE NO RECHARGING FACILITIES AVAILABLE. If you choose to do so, then you will have to bring enough spare batteries to get you through the competition. As I stated before, at the Nationals, the maximum number of bouts anyone could participate in is 12, requiring you to have enough battery power to operate your bot for a maximum of 24 minutes. Just make sure your coach understands when you tell him/her how many spare batteries you need, that this cost is because you chose to design your bot so that it needs this many replacement batteries, and there are other designs that don't require this additional cost.

3. The object of this event is to push your opponent out of the ring. It is not to avoid being pushed out. There are stalling penalties for bots that simply try to run and hide and never engage their opponent. In addition, in the scenario that you describe, the bot that runs up to make contact then quickly backs away is violating the spirit of the competition (they aren't making any real effort to push their opponent out of the ring) and they would forfeit the bout (depending on the level, I would probably stop the bout and give one warning at the Regional level, and at the State and National level I would give that warning in the opening instructions at the start of each hour). Just keep in mind that the stalling penalty is applied if you haven't tried to make contact for 15 seconds. If your opponent is VERY slow and you simply rush to the center of the ring and then sit there waiting for them to make contact, you could be charged with a stalling penalty (if, in the judges opinion, the opponent was trying to get to you as best as their bot could and you were just sitting in the middle of the ring not doing anything).

1. Just for the sake of upholding my credibility, but not that it really matters regarding this event, I looked over the rules from 2009 C division. In the Junkyard Challenge event 4.b.ii it states that "Tools may be brought in a separate container, which need not be impounded." I knew that I had been involved in at least an event that allowed certain materials to be brought in but did not require those materials to be impounded. You had me questioning my own memory.

2. I am sure that there are many ways of building a great SumoBot, some of which cost much more than others, but it is very difficult to know without seeing them perform if they are as good or better than others. Last year this was a trial event so the competition was potentially less serious than it will be this year. I am also sure that some high performing Sumobots will use much less power than others, but since power consumption is not a design criteria (no points awarded for using less), other than cost and the fact that we will have to bring enough batteries to finish the competition, I can't see why we would design for low power. In addition, mass is a tie breaker so all things being equal we would want as little battery weight as possible. Of course we will have to be careful to design the SumBot in such a way that battery changes are quick and easy, and if we end up needing extra ballast to get more pushing power we can certainly add batteries rather than dead weight, and thereby possibly eliminate some battery changes.

3. I think you pretty much cleared up my questions about the stalling penalty. The last time I saw this event it was a B division trial event, and it was a long time ago, so I am just having some trouble picturing how it all works. I think I had read some trial event rules from the past where they said that the two SumBot had to go to the center, but I see this is no longer in the rules. I was just trying to figure out if our bot needed to be fast enough to chase down a potential competitor, or if his refusal to meet us in the center would be considered a stalling tactic. I suspect that it isn't going to happen but your scenario of a very slow SumBot could be interesting if two opposing bot were both so slow that they took more than 15 seconds to even reach each other.

I don't mean to ask outlandish questions it's just that this is my 7th year in SO. I have been fortunate to be on teams that made it to Nationals every year, and I have seen a lot of unexpected things at all levels of competition over those years. Sometimes the picture in my mind of how the event will be is very far from the reality at competition. I have also found that sometimes it is difficult to be truly competitive without really understanding, not just how the rules are written but how they will be interpreted by the event supervisors. Thank you so much for all your time answering these questions.

[Flavorflav]

Impounding tools was not required for Electric Vehicle the last time it ran, either. Old, you haven't told us what batteries you are using yet. If you are using a decent battery pack and are sucking it dry then you are right, but frankly those of us with experience in this event (i.e., New Yorkers) are finding that hard to believe.* Are you willing to share that information?

As for your third question, I would say that speed matters but only up to a point, and then it can actually hurt you. Modified RC cars are often too fast for their drivers to control in a 5' ring, but slowpokes get taken on the flank.

ETA: The reason for the skepticism is that any halfway decent battery pack should have at least a couple of amp-hours of charge, and the good ones hold much more than that. While there are motors small enough to fit in a Sumo that would pull that much in two minutes of solid pushing, hardly any Sumo bouts actually amount to that. Most bouts are over pretty quickly, and the long ones usually involve either a lot of dancing around or wheel spinning, which means the motors are running closer to their no-load draw for much of the time. Are you draining batteries in actual bouts, in some kind of pushing test, or are you estimating drain time from the stall current spec of the motors?

Also, for your second point, actively avoiding contact would definitely count as stalling, so you don't really have to worry about chasing him down. Generally, the faster your bot is the better your driver has to be, since the converse of what I said above is that a fast bot driven skillfully can take its opponent on the flank, which is usually easier to get under.

[M-E-T-H-O-D MAN]

Sounds like it really should be fun if I can get some direction on building since I've never done anything with robotics before. Of course, in Maine we'll probably be the only ones with a bot.

[old]

Impounding tools was not required for Electric Vehicle the last time it ran, either. Old, you haven't told us what batteries you are using yet. If you are using a decent battery pack and are sucking it dry then you are right, but frankly those of us with experience in this event (i.e., New Yorkers) are finding that hard to believe.* Are you willing to share that information?

As for your third question, I would say that speed matters but only up to a point, and then it can actually hurt you. Modified RC cars are often too fast for their drivers to control in a 5' ring, but slowpokes get taken on the flank.

ETA: The reason for the skepticism is that any halfway decent battery pack should have at least a couple of amp-hours of charge, and the good ones hold much more than that. While there are motors small enough to fit in a Sumo that would pull that much in two minutes of solid pushing, hardly any Sumo bouts actually amount to that. Most bouts are over pretty quickly, and the long ones usually involve either a lot of dancing around or wheel spinning, which means the motors are running closer to their no-load draw for much of the time. Are you draining batteries in actual bouts, in some kind of pushing test, or are you estimating drain time from the stall current spec of the motors?

Also, for your second point, actively avoiding contact would definitely count as stalling, so you don't really have to worry about chasing him down. Generally, the faster your bot is the better your driver has to be, since the converse of what I said above is that a fast bot driven skillfully can take its opponent on the flank, which is usually easier to get under.

I am going to use the smallest battery pack that will put out sufficient current to drive the motors for 2 minutes. So for example if our motors use 20 amps then I need a 700mah battery with a 30C rating. Of course you are right that if we finish a bout in 15 seconds and/or don't have to run full power, then our battery will not be fully discharged. The problem is that I don't want to go into competition counting on not needing the full 2 minutes of full load. It may well be that I will end up with 10 batteries with 90% of their charge left at the end of competition (and that is even assuming that I make it to the end, or even that we win States) but I would much rather have a bunch of batteries with most of their charge left than a bot that stops moving in the middle of a bout. If we decide that we need or want extra weight then I would certainly consider adding that weight with a larger than necessary battery rather than simple ballast, but I hoping to build a bot that is all muscle and as little unnecessary weight as possible.

I can't explain why our bot uses a lot of energy. We have what we believe to be a unique feature, that uses a bunch of power (no it is not a 100 watt diode laser, although that would be way cool, and dangerous, and wouldn't even use a tremendous amount of power). OK, OK we have a high power infrasound generator that drives the competition crazy, but since nobody can hear it, no one will know. Oh, oh, wait, no really we got one of the jammers off an old B-52 and we are going to selectively jam all the frequencies except ours, and our jammer is so good that it will make it seem that the other team is stalling rather than just out of control.

Our experience with Sumo Bots is limited. The only competition I ever saw was when it was a trial event at Nationals about 4 years ago. I assume that is has gotten substantially more competitive and sophisticated since then. Back when I saw it the team that won had nothing but a converted, and relatively small, RC car that was very fast. He was able to get behind his opponent and push them (sort of ramming actually). I didn't see any fancy flippers or grabbers or much of anything else on any of the bots that year, just basic RC vehicles that moved around the field. What's the hot ticket now?

[ichaelm]

I can't explain why our bot uses a lot of energy. We have what we believe to be a unique feature, that uses a bunch of power (no it is not a 100 watt diode laser, although that would be way cool, and dangerous, and wouldn't even use a tremendous amount of power). OK, OK we have a high power infrasound generator that drives the competition crazy, but since nobody can hear it, no one will know. Oh, oh, wait, no really we got one of the jammers off an old B-52 and we are going to selectively jam all the frequencies except ours, and our jammer is so good that it will make it seem that the other team is stalling rather than just out of control.

I'll assume that's a joke. Right?

That sounds like it's going to be super-expensive, if you'll need more than 10 battery packs, each rated for extremely high currents. For me, cost is a big issue. If I were you, since we both have very "limited experience" with sumo bots, maybe you should start with a simpler bot to get the hand of things, and then, afterward, work on your super-awesome maximum-performance bot with that special feature. That's what I'm doing now (but without a vision of what to build afterward). Just my opinion.

If mass is such a big issue that you're worried about using batteries that will last longer, have you looked into carbon fiber?

[Flavorflav]

I assume that you are planning to conserve mass in order to make room for your doomsday device. I'm afraid that if you stick with that plan, you will have no alternative but to bring a lot of spares. You seem to know what you are doing, but I will warn you that ambitious designs tend not to do very well in Sumo.