Ball Centering Video (Team 846)
 

Hello everyone,

Welcome to a shameless promotion of our new shooter design video! It covers different roller types (single, double, crown, and flat to be exact), and whether or not each type is able to align a ball to its center while spinning. This is useful if you're looking to, say, I don't know, have your shooter consistently score accurate shots into a goal (cough cough). A decentered ball introduces an unknown variable in your procedure, and unknown variables have a tendency to spectacularly ruin your day.

So why not un-ruin your day? More videos like this are in the works, where we analyze a robot-related topic (so you don't have to!) and present our findings to you in bite-sized chunks. We're calling the series "Monkey Box," so stay tuned!

Again, here's the link to the video.
https://www.youtube.com/watch?v=pF8A1ElLQks
Oh, and feedback is greatly helpful to us in developing future episodes, so do consider dropping a thought or two below.

Happy viewing! :)

Re: Ball Centering Video (Team 846)
 

Really interesting results. I didn't expect the double wheel to shift the ball off center.

Now do you think with how most backings of shooters will have a central angle less than 180 degrees, that the flywheel profile may be negligble? These tests seem to have results that can be observed after several rotations, i.e. the robot has a theoretical shooter backing of central angle greater than 360 degrees.

Considering our intitial conditions being the position of the ball center relative to the center of the flywheel, these conditions seem to change significantly in a backing exceeding 360 degrees, but do they change enough in a backing of central angle less than 180 degrees, or even 270 degrees?

If I play and pause the video for each wheel and pause after about 180 degrees of rotation, I don't notice much difference in the shift of the ball until several more rotations, so does my hypothesis of negligibility between wheel profiles hold true in a backing of less that 180 degrees?

Or am I wrong, and the shifting is more dramatic in a smaller angle backing when using higher speeds where the ball may slip on the wheel while being accelerated as opposed to being perfectly gripped in the slower speed of the small scale model?

Also, a foam ball was used in the scale model. I'd like to know if there are different results using more rigid and less "grippable" balls, or even balls with more intertia or irregular surfaces. For example, it would be neat to see the differences between a small foam ball, a ping pong ball, and a golf ball. Also, does the amount of compression affect the rate at which the ball shifts? There may be plenty of variables associated with this.

Re: Ball Centering Video (Team 846)
 

Hi! I'm James (the host, on the right in the video)

You are completely right in the sense that it does take awhile until noticeable change has occurred. However, both me and Jing-Chen were very surprised that the ball climbed climbed onto the roller relatively quickly. This means that the ball is indeed shifting when it passes through the shooter, and such a small change may have an effect on where the ball lands. Whether or not this change is negligible or not, or whether centering is actually desired, is up to the viewer to decide.

As for the variables you've mentioned, I'm glad that this video got you thinking! After all, this is merely a simple test built out of LEGOs, so we couldn't account for all of those.

Re: Ball Centering Video (Team 846)
 

What was the specific wheel you guys used for the shooter last year?

Re: Ball Centering Video (Team 846)
 

Nice work, guys. Thanks.

Re: Ball Centering Video (Team 846)
 

Good stuff! Enjoyed the video.

Re: Ball Centering Video (Team 846)
 

Interesting results, but makes sense if you understand crowned belts, the double peaked rotor, really gives you two crowns to track to, but only one can win.

https://woodgears.ca/bandsaw/crowned_pulleys.html

Re: Ball Centering Video (Team 846)
 

Hi, I'm James (the host in the video)

The flywheel we used for design shown in the video is an aluminum flywheel with a diameter of 1.875" and a mass of 2.5 lbm. As you can probably see we cut grooves into the flywheel (using our CNC) with the hopes that it would grip the ball better. As it turned out aluminum is still a very slippery material against the ball, so we ended up wrapping it with surgical tubing.