[FTC]: Shooter Wheel Safety

[BradMello]

Originally Posted by Joyride_67_1902

Are you sure you need a 1:27 ratio?
Try to zip tie the rubber on the wheels onto the wheel thats what we did and there is no problems with it.
Andrew

Why would you need to zip tie rubber onto a 1:9 ratio shooter wheel?

And how much grip does the wheel have on the ball when it's zip ties touching it and not rubber?

[Al Skierkiewicz]

From an inspector standpoint, speed that produces even small failures in the parts should be avoided. If the shooter is running fast enough to lift the tread off the wheel, then I think you are looking at something that has crossed the safety threshold.

[JesseK]

Rick, I would recommend that the mentor in question redesign the bot. Here are some things to bring to the table:

Is the shooter single-sided? In other words, is one side the spinning wheel and the other a firm backing? If so, a team can cut the RPM need in half if they replace that backing with wheels. One of my teams had this design until they realized they wouldn't have the needed space to add the necessary gearing. The solution was to add an additional spinning wheel to the top that the balls hit once they get to the proper angle in the shooter circle.

Even at 1368RPM (1:9 ratio, which is what most of my teams are going with I think), the shooter's contact time with the ball is so small that even a large amount of motor torque applied to it will not accelerate it as much as you think -- these are wiffle balls with alot of slip. There are ways to solve that though:

• Increase contact time via an hourglass-shaped design between two tetrix wheels
• Try different wheels. I'm not 100% certain these are the same LEGO wheels a student brought in that are 3.25" in diameter, but they definitely look similar. Attaching these to the TETRIX axles is easy via cunning use of the allowed plastics as a makeshift hub. The tread attachment is a little flimsy, but we've definitely see an improvement in contact time.
• Increase the input velocity into the shooter. If you notice successful '06 designs from the videos have very speedy ball manipulation via belts, fast helixes, or other wheels that pre-accelerate the ball before it hits the shooter. It's like the merry-go-round as a kid -- once you get it started, it's easy to slap it as it goes by quickly and give it enough juice to spin faster. Actual contact time was nearly infinitesimal, yet due to its previous velocity you were able to boost it to speeds that made the onboard kids very very dizzy. Everything you need to know you learned in Kindergarten!