Team 539's Robot Shooting!

[DavisC]

Yesterday was the first day having the shooter and system working on the robot!
These are a few vids clipped together from yesterday of the first shots it did in 1 peice!

http://www.youtube.com/watch?v=HqF6leVKPbI

Please comment!

Ps. it's shooting at about 50+ feet and mostly consistent, just need to improve the feeder and driving over the balls.

[Alex.q]

Originally Posted by DavisC

Ps. it's shooting at about 50+ feet and mostly consistent, just need to improve the feeder and driving over the balls.

How consistent is mostly consistent? It is hard to tell in the video becasue each camera shot is from a different angle. Nice distance though.

What reduction are you using with the FPs?

One last question: In our prototype, we have a massive amount of vibration when running the motors that fast. Did you guys encounter this, or does anyone have any sugestions for this?

[Nuttyman54]

Originally Posted by Alex.q

One last question: In our prototype, we have a massive amount of vibration when running the motors that fast. Did you guys encounter this, or does anyone have any sugestions for this?

Most likely this is because the shaft/wheel assembly is not balanced. "Balanced" in this case means the center of gravity is slightly different than the true center of rotation. At low speeds or with light weight things, this isn't a problem, but when you start spinning larger objects like shooter wheels and flywheels at 3000+ rpm, you will start to notice it. At certain frequencies, the unbalanced vibration will match one of the vibration modes of the assembly, and you'll hit resonance (which is really bad).

This can be dealt with in a few ways:

1) Add some kind of damping to your system, like making it much stiffer. Stiff systems (short, stiff shafts, good bearings, etc) will have a very high first mode, making it hard to trigger a resonance. Even if you're not at the resonant frequency, getting close to it can start to cause your assembly to vibrate pretty wildly. You can see from this simple graph the effect of damping on the amplitude of the vibrations, as the driving frequency (the speed the wheel is spinning), gets closer to the resonant frequency (where it peaks).


2) Make sure you have good tolerances on your parts. This will help ensure that your system's CG is as close to the axis of rotation as you can get it. You can also have whatever your spinning be dynamically balanced by a shop that specializes in that. There are specifications depending on how close you need the CG of the wheel assembly to be to the true center of rotation. They will drill holes or add small weights at specific places around the wheel to move the CG around very slightly. Cox & Sprague's website has a good explanation of how this is done.

If you're truly interested in the physics and math behind this kind of analysis, take a look in a book about rotor dynamics, it's got all kinds of cool information and ways to calculate the critical frequencies and see if your mechanism is likely to explode.

[DavisC]

At first we had somewhat of the vibration issue since it was slightly unstable by itself, then we added a pillar block on the other side (with a free shaft) but it made a lot of resistence from not being perfectly in line. So we slighty drilled the holes wider and mounted them nicely alligned. Oh, and make sure you use plenty of lube on any freespinning part.

The main supports are 3/4" steel (square, hollow, from Lowe's) while the extra supports are 1/2".

It was the first day shooting it while mounted on the robot but at least 85% of the shots on full power landed within the same cement square.

The Banebots are 550s with 4:1 gear ratios, and they use the grey rubber wheels.

[GilaMonsterAlex]

Awesome work!! Really awesome too because this was our first brainstormed idea, and I'm really glad it works.

Sweet distance too!!