My name is miles and I am from team 39599E in Wintees California. We have won a tournament and are qualified for states and I am getting my robot ready for states. We are discovering that a lot of robots are super fast and can still climb. Our robot is slow but we can climb with 4. Any advice? We need our drive to be only 4 motors. We want to be able to climb with at least 2 and be able to steal the neutral goal in autonomous period.
If you want to climb with 2 and win goal rushes, you’re gonna need a six motor drive, or a transmission. You can’t get competitive torque AND speed out of four motors; the more you have of one the less you get of the other.
for 4 motor drive your speed is fairly limited. Because most fast robots are using 6 motor drive, you won’t have enough torque to climb if you use some of the faster speeds that other teams are using.
I would recommend at most a 36:84 ratio on 600 rpm cartridges for 257rpm on 4" wheels. This isn’t a bad speed, and while slower than the speeds most teams on 6m are choosing, is at least faster than direct 200.
however, this isn’t really realistic with only 4 motor drive. In order to have enough torque to reliably climb with multiple goals, you have to make that speed sacrifice that will put you at a disadvantage during the goal rush.
But if you play your strategy well, you can still come out on top during the rush. Your opponents only have 2 robots, figure out which goal they won’t immediately be rushing, and aim for that one. Often times this is the center goal, but sometimes an opponent uses a trick auton that makes it look as if they’re going for one goal but turn to go for another. This might be something for you to consider as well.
Ok thanks, but I don’t think my team can install a six motor drive due to the fact we have 4 motors being used on mobile goal lifts. Is there a good gear ratio that you know of though.
Above is a chart of geared drivetrains that are physically possible without doing anything weird. The force column is generated by a non-engineer, and is super simplified. Just taking the stall torque of v5 motors at 100 rpm, adjusting the torque based on output ratio then solving for force by dividing the torque by the wheel diameter. So grain of salt and all… its mostly for comparison.
We all know that 4 motor 200 rpm 4" wheel drives can easily climb with two goals. I have seen well built 4 motor drives using 200 rpm 5:3 on 3.25" wheels or 7:5 on 4" wheels balance with two goals. I bet there are teams out there that can balance two goals with 600rpm 3:5 3.25" as an upper limit. Drivetrains built to go faster would struggle.
I have in-person testing and experience to say that 600rpm carts and a 3:7 ratio on 4” wheels (257rpm) is a very solid middle ground for a 4 motor drive. It’s fast enough to tie a lot of teams to the middle and if the robot is somewhat lightweight, it can park with 3 goals.
We have a 4 motor drive on 4 inch wheels and 257 rpm. The robot is able to platform with two mogos and rings. I’d suggest using a custom traction wheel in the middle to be able to do this.
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