My friend and I are working on a NBN robot to be used in one more competition. It uses a single flywheel, which the ball will roll over and out of the robot. Five motors with regular-speed internal gears drive the wheel, and the gear ratio is 0.4 (I’m not the best with gear ratios. Each motor drives a regular strength 30-tooth, and then the last motor in the train also driver a HS 60-tooth, which drives a 12-tooth attached to a regular strength 60-tooth, which driver a 12-tooth attached to the flywheel. Sorry for the poorly worded explanation, I don’t know how else to word it.)
What we want the most is to be able to shoot many balls off quickly into the high goal. Making full-court shots would be helpful, but it is more important to be able to shoot the balls quickly and accurately from a relatively short distance at this point. The problem we are running into is with compression. We are using plastic to press the balls up against the flywheel, and we can get it to either shoot the balls straight up with little momentum or almost straight forward with a decent amount of momentum. Either way, the ball isn’t going to make it into a high goal. We have tried adjusting the compression of the plastic, creating guides using standoffs, and making ramps using aluminum straps and steel plates, but nothing has worked effectively.
Any suggestions would be greatly appreciated. I’ve attached a video of the robot in operation, as well as some pics of the flywheel. If any additional information is needed, I will do my best to provide it. Thanks in advance.
Okay I’m not too experienced, but there’s a few things I see that can definitely be improved.
Firstly, it looks like your hood is not mounted securely enough. This means there is hardly any compression at the top, hence the ball flying straight up. Since you’re trying for a curved hood, both the top and the bottom of the plastic need to be screwed in. I would look at some reveal videos of other teams to find out how they mount the hood. One common method is having standoffs mounted at angles from the flywheel using shaft collars. Another method I think 2131E had was a vertical channel on the back of the robot with the plastic mounted to that. And if I remember correctly, 2915C used curved metal, and the 169 teams had a cool sprocket mounting system. Try to find one that works well for your robot.
Also, for the hood, I would try to match the curvature of the flywheel more. Right now, it looks like the one mounting point for the hood is well above the actual flywheel. Try moving that mounting point to the center, if not a little lower, of the flywheel.
Lastly, do you know how fast your flywheel is spinning? It would definitely help to have an optical shaft encoder somewhere on the gear train and some form of RPM control for consistency during matches.
First of all, I would increase the gear ratio between the motors and the flywheel. It appears that you have a 9:1 ratio. In our robot we used a 28:1 ratio. That may not be the perfect ratio, but I would at least increase to 21:1
Are you sure? It looks like a 25:1 ratio to me. With 4 inch wheels though, you could definitely still increase it. You could change out the torque motors to high speed motors for a net ratio of 40:1, which is what we use.
For the hood, we used a rectangle of Lexan secured directly to the metal on the bottom and to standoffs on the top. To get the top of the hood at a good angle woth the standoffs we used shaft collars and the coupling screws (the flat of the collar is touching the metal with a screw going where the shaft normally is and then the coupler screw into the threads). Sorry if that’s not very clear; ask again if that’s not good enough of an explanation.
Sorry, I forgot to mention that the hood was detached during that video. I had to film it quickly, but I should have mentioned it in the original post. It skipped my mind. The positioning of the plastic hood was one of the things that we played around with the most, and ultimately decided if the ball would fly up into the air, or in front of the robot.
I did check out 2131E, and I noticed that their flywheel was mounted higher, rather than between the two pieces of metal like ours. Is it possible that doing this would allow the ball to gain more momentum on its way up? I also watched 2915C, I really like how the hood is concentric with flywheel. I might try that if we don’t run out of time.
My friend and I will be sure to play with the gear ratios tomorrow, along with the compression. Thanks for all the amazing help from everyone!
It’s interesting because I think 2131E might have changed their flywheel during worlds, since it’s a little different from their reveal video. I don’t think mounting it above the metal with pillow bearings makes too much, if any, difference.
Also, if you haven’t already, you should definitely check out the Discobots. Their flywheels are incredible. Good luck with your competition!