Hello,
My team is building a NBN robot for funlink text. We currently are using a single 4" flywheel driven by 4 vanilla 393s, and 25:1 gear train. According to our math we should be reaching 2500 rpm. The robot currently can’t shoot a full court shot and bogs down some after each shot. The compression is around 0.125 inches.
Would any NBN veterans be willing to save us some work? Can you recommend a proven motor/gear train combo? What is an ideal rpm?
We are thinking of using 6 turbo motors with a similar gear train. That would do 6000 rpm which is probably overkill but would be really fun outside of the arena.
For my robot that shot from the bar only, more or less, we had a theoretical 2160 RPM (9:1 with two turbo motors) using 5-inch wheels. At maximum power, it shot from a bit closer than half field. I would recommend closer to 4000 RPM, since you are using 4-inch wheels. 3500 could do. You should be able to get that to work with four motors.
I don’t know if shooting full field is different, but I’m not sure about compression… Just try decreasing the compression until it doesn’t fire anymore and then go back a notch. If you have any issues with too little compression, you will notice, trust me. I’m not sure how drastic 1/8 of an inch is without actually seeing it’s effect on the ball… It sounds reasonable, though.
By going up in gear ratio there is more strain on the motors causing them to give out faster, so going up in ratio with theoretically make the ball go farther but in actuality the ball may fall short cause the motors aren’t reaching max speed.
Changing your flywheel motors to speed should fix most of your issues. Some of the best single flywheels from NBN were 4 motor 25:1 on speed for a final ratio of 40:1, and had about 1/8" compression, and 4x 4" wheels with rubber bands on them. IIRC that’s pretty similar to what VCAT (VexU World Champions that year) had, and then I know for a fact that’s what Disco was running (I think the compression might have tapered out a bit, so less compression at the end, but I don’t really remember). We also had anti-slip mat on the hood and had a wide Lexan hood that put some flex into the system to adjust for ball density. Make sure to account for the slip mat thickness in the compression. The fastest I ever saw any of that flywheel design go was about 3.5 balls per second FC accurately. If you don’t have code, Bang-Bang or TBH will work just fine, minimal tuning required. If you want a coding challenge, my NBN robot (400x) had about the same rate of fire as the other Disco’s who just used Bang Bang but would stabilize at the shooting RPM a lot more cleanly. Almost no performance increase, but it did sound very nice ;p. If changing it to speed doesn’t work, then something is wrong somewhere in the build. Check everything for friction, especially the flywheel shaft. Ours would spin for 25ish seconds when I spun it by hand and it was disengaged from the gear train.
Also, don’t forget to add a speaker and make it play a tone as a multiple of the flywheel RPM.
It’s hilarious very important.