Hi guys, I was wondering why teams have extremely intricate base designs this year. I see alot of teams externally gearing their base and I am unaware of the purpose. What are the advantages of making a really multiplex base? I was planning on just building a two motor chasis where the front wheels would be powered by chain and sprocket.
It really just depends on what you need your robot to do. Last year a lot of teams used power transfer mechanisms or 2 stage drivetrains but in the end its just ways to make your robot do its tasks better.
Many teams used geared up drivetrains to have a speed advantage on their opponents. If they could get to the neutral goals faster than their opponents, you could win the goal rush, which would put their alliance at an advantage going into driver control.
Later on in the season, many teams started realizing that if they were able to shift into a torque gearing, they could pull back with more torque than their opponents, and therefore they could have a batter chance at wining the goal rush (or at least force an awkward clamp or drag them to their side of the field). This is why many teams in China, although lacking dedicated goal rush mechanisms, put dual speed transmissions on their drivetrains.
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A geared chassis is not complicated, and many teams use it to control speed or torque. For example, a chassis geared 3:5 on 600rpm motors 3.25in wheels is what many teams use, and they find it a good balance between speed and torque, but this requires 6motors as 4 motors can burn out. 5:3 on 200rpm motors gives an output rpm of 333 which is also good but gives less space to place bracing along the bottom of the chassis. All of this usually depends on what kind of game it is. Pushing will be important for this years game so I doubt that 2motors will be enough to create a competitive bot.
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So what do you guys think would be an ideal gear ratio for the chasis for this year’s problem?
3:5 600rpm 3.25 wheels is personally the best but as a good alternative you can use 257 on 4in wheels
600 rpm on 2.75in is pretty good and even better with 6m
depends on the weight of the bot, Im not sure if you can run 600 direct 4m on a heavy robot 2011D ran 600 4m direct on their changeup bot but only because it was very light, pretty sure like 10-13 pounds or something
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Having selected a 4 motor tank drive, we have opted for a 257 RPM drivebase on 4 inch wheels. We wanted to have more speed than a regular green cartridge bot when getting to discs to shoot, but at the same time remaining competitive in roller fights as well as having the edge in roller fights against speedier drives (which many teams are going for) as well as X-drives.
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Thank you so much for this suggestion for this gear ratio; however, I do not have 3.25 inch wheels. Do you know a gear ratio that would work well with 4 inch omni wheels???
common gear ratios on 4" wheels are 257 (600 geared down 3:7) and 280 (200 geared up 7:5). I would not recommend 280 with only 4 motor drive, though it can work if done very well, just won’t have much torque. 257 is a great ratio for both a 4m or 6m drive, and will have decent speed but also nice snappy acceleration.
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Drivetrains are just as important as other essential functions on the robot, your drivetrain can be the deciding factor on how competitive your robot is. Tipping point really took this to the next level with goal rushing in auton being the deciding factor for who wins a lot of the time. In tipping point it was so important teams on top of making fast drives, also added other features just for the beginning of the match like kickstands and boomers. While those might not be neccessary for spin up, having a drivetrain that designed for your robots play style whether it be offensive or defensive can make a big difference. Personally I think using a two motor drive is not a very good idea, I think the minimum for any kind of competition is 4 motors. Using just 2 motors makes the drive slower and also weaker. You could have a really good flywheel and intake but without a good drive it wouldnt be put to good use because your robot reaches disks slower or because it aligns to fire with the goal slower.
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Why would a torque base be good for this year’s problem, wouldn’t it be more effective to have a fast chasis so you can get to the discs and other scoring objects faster than the other alliance.
257 is generally considered to be a decently fast drive. Sure, you can push it much faster if you want to, but the reason 257 is such a common ratio is because it provides a very good balance between speed and torque/acceleration. 280 is somewhat faster, and is also a good choice, though with 4m drive you will have less acceleration and weaker pushing power, which might not be worth the speed increase depending on what you want to do in a match.
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What is the external gear ratio needed to reach a 257 gear ratio and what type of gear cartridge should i put in the motor to rach this gear ratio.
Use the search bar. This is quite the common ratio and will be easy to find.
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If your doing 4m drive, another important thing to consider when choosing gear ratios is how long the motors will last. I’m tipping point, my team didn’t have access to pneumatics so we had to use a 4m drivetrain. Initially we had 280rpm and this had a few problems - the acceleration was slow, not much torque, and the motors would burn out quickly (really inconvenient for practicing driver/programming). We chose to redesign before worlds to a 257rpm drivetrain, and this was much better. Even though it wasn’t as fast overall, the faster acceleration times kinda made up for it. This drive was also able to last longer during practice and worked out fairly well for us against 6m drives at worlds (goal rush vid)
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So just to be clear, it would be worthwhile in designing, building, and programming a chasis that is geared to 257 rpm for this year’s problem.
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you have to decide that for yourself
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