This upcoming month, my POE class is having a Mario Kart Balloon Battle competition. You have four 9" balloons strapped to your robot and you drive around trying to pop other robots’ balloons. You get 10 points for each balloon you pop and five points per unpopped balloon at the end of the round. The robot has to start out no larger than an 18" cube, but it can expand once the round starts. We have access to the standard vex parts, but no pneumatics, and can modify them as needed.
I was thinking about using a six bar lift to raise the balloons in the air. Could I use this and still drive around with reasonable speed and stability? I need ideas for the driving mechanism, popping mechanism, and defenses. Any help is greatly appreciated.
If you can see what your competitors are doing, try to make the lift about a foot taller than your tallest opponent. A one- or two-motor lift will probably suffice, since you’re not lifting anything too heavy.
For offense, you can build a second lift, probably the same type, so you don’t need to lower your balloons to attack another robot’s balloons, with, again, two motors, and a moderately low gear ratio (if you have aluminum, try 1:5 with torque motors). This is higher than Skyrise lifts, but Skyrise game piece are not as light as balloons. Build basically a claw with c-channels and attach a motor, so you can pinch the balloons to guarantee popping them. This also means that your opponent cannot move while you are holding his/her balloon, or it will pop.
As far as a drive goes, speed and maneuverability are probably important, especially if the field is moderately large (standard Vex field or larger). I would recommend an X-drive.
I’m assuming you want to leave the lift up while moving, so you might need an expanding drive. It adds complexity, but if you can pull it off, you will impress your professor, and it will be very effective. Perhaps try using linear slides with the green inserts (if you have them, the ones that fit inside the metal slides), with a slot cut for a bendy plate. The drive motors can pull the inserts along the linear slide, until they hit a screw to prevent the inserts from sliding out, then a bendy plate can drop into the slot in the slide to keep the inserts from sliding farther into the slides, reversing the expansion.
I’ll try to build an expanding drive over winter break starting this weekend, but I’m not making any promises.
You can probably get away without an expanding drive if you are careful, but the lift will definitely reduce stability. I would definitely recommend making the drive as heavy as possible and the lift as light as possible if you choose not to build an expanding drive. This keeps the center of mass as low as possible, reducing the lift’s negative impact on stability.
The only downside to that is that 4 9" (diameter, I assume) balloons will occupy most of your 18" cube, leaving little room for the rest of the robot and severely hindering your ability to pop other balloons. If you are eliminated when your last balloon is popped, then you can simply protect one balloon and be extremely offensive. You earn more points for popping a balloon than protecting one of yours. If you do no offense, then you can only score 20 pts (4 balloons x 5 pts per). A primarily defensive box robot, then, will likely only score 40-50 pts with a good driver and an excellent use of limited space, which can be offset by popping 4-5 balloons.
Thanks for all of the great ideas. DanielIW26, that makes me feel a lot better about stability. lpieroni, all we have is the plain 2.75" and 4" wheels, but I think we can make do there . I will look into the claw idea, and see about adding sharpened screws to the pincers. TeamTurboTech, a shooter would certainly look neat, but I don’t know what it could shoot. Our teacher won’t let us modify the drive shafts but anything else is fair game. Xiphas, I asked my teacher about that and he said they wouldn’t all fit in the 18" cube. I will make sure to post a video when it is done.
For defense Make linear slides that go SUPER high and attach your balloons to the top. For offense you may want to try to bump the enemy into falling down then crush the balloons with your wheels but I don’t know what the ramming restrictions are… (Please let me know) if ramming is illegal then try a pellet gun if you can detach parts. If both of these are illegal try a flywheel chain saw on a long arm.
@OverlyOptimisticProgrammer, we will receive the official rules when we get back from break, but I don’t think there are any restrictions shy of breaking the opponents robot. I was thinking of a forklift or arm that flipped the other bot on its side, but I think I will already have stability issues with a lift.
Update: We have completed the competition. The our robot and the competition underwent several changes. We scrapped the idea of a lift, used the idea of a box, and we won. The first couple of rounds, our teacher had us driving around on different surfaces (concrete, carpet, and gravel) trying to pop each others balloons. We did three rounds this way, and our teacher let us make changes in between. One team built a lift, so we started out with a flipping arm. They were to heavy, so we attatched a spinning popper to the arm. It was just barely able to reach their balloons. For the last round, our teacher marked out a small racetrack and we raced around, still trying to pop balloons. We new our robot was to bulky to go fast enough to win, so we quickly built a smaller robot. It had a 1:3 gear ratio on the wheels and a similar popper. I do not have any good pictures of the finished robot, or any short video of it in action.
That sounds like a really cool competition. My team will have to try this in May, after Worlds. That’s actually a great way to introduce new kids to Vex without putting all of them on one team. We tend to get at least 5 freshmen a year, plus a few sophomores, juniors, and/or seniors who are either new or newly active, and we don’t have the resources to give each group of 3-4 new kids a mentor and a team and still have a robot with multiple Vexterans. My only other idea for doing so was forming a few larger teams (maybe 6 people per + a mentor) and have them each work on their own project, like a car chassis (with differential) or a humanoid walking, balancing robot (programming would probably be headed by the mentor student in conjunction with our RobotC understudies). That would get really frustrating, and they would basically be jumping into the deep end, which may or may not be effective.