View Single Post
  #21   Spotlight this post!  
Unread 06-02-2017, 14:19
Kevin Sevcik's Avatar
Kevin Sevcik Kevin Sevcik is offline
(Insert witty comment here)
FRC #0057 (The Leopards)
Team Role: Mentor
 
Join Date: Jun 2001
Rookie Year: 1998
Location: Houston, Texas
Posts: 3,761
Kevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond reputeKevin Sevcik has a reputation beyond repute
Send a message via AIM to Kevin Sevcik Send a message via Yahoo to Kevin Sevcik
Re: Poll: Reasonable and achievable, or shooting for the stars?

Quote:
Originally Posted by JesseK View Post
According to JVN's Spreadsheet, if we can get the load on the motors down to 0.04 lbs of resistance using some space-age materials on the wheel it is theoretically possible to power a ball to terminal velocity using just 8 775PROs and a wheel that is 30' in diameter.

So 6 batteries it is! If we stick a bank of capacitors in there, maybe that will prevent RoboRIO brownout?
See, the problem is that the back of the envelope calculation assumes all the energy goes to the projectile. You'd have to figure some way to transfer all the rotational energy of the wheels into the fuel. And honestly, if you're getting the rim of a wheel up to escape velocity already, your best bet is to attach the fuel to the rim of the wheel, and let it go as the correct moment.

The good news is you wouldn't need the bank of capacitors for this setup, since your flywheel at escape velocity is a mechanical capacitor. The bad new is a 4.5m radius wheel spinning at 11.186 km/s rim speed develops a centrifugal acceleration of (11186)^2/4.5 or 27.2e6 m/s^2. So the centrifugal force on the 70g ball is 1.9MN or 427000 lbf. I suspect the crush load is somewhat lower, so this solution is much harder to analyze since it significantly deforms the projectile during launching.

Also this is why the centrifugal pumpkin catapults are so terrifying to watch and don't have a hope of catching the air cannons.
__________________
The difficult we do today; the impossible we do tomorrow. Miracles by appointment only.

Lone Star Regional Troubleshooter
Reply With Quote