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-   -   Poll: Reasonable and achievable, or shooting for the stars? (http://www.chiefdelphi.com/forums/showthread.php?t=154814)

jgerstein 06-02-2017 13:39

Re: Poll: Reasonable and achievable, or shooting for the stars?
 
When I started mentoring, we were a shoot for the stars team. Our ambition far outstripped our experience, our fabrication resources, and sometimes our budget. It led to frustration, burnout, and anger.

Now we go for what is reasonable and achievable for us, and we try to move that bar up a bit each year. That doesn't mean that we don't take on anything challenging during build season, but we try to make sure that we have a fallback position if new challenges don't work out, and that we're not taking on so many challenges we end up overwhelmed. We're trying new things, but keeping some things (like our chassis) simple. We still make mistakes, but now mistakes are setbacks that lead to a late night or two instead of soul-crushing, season-ending disasters.

Students still try new things, they're still inspired, and we're probably going to aim for a crazy shooter for our off-season competitions, since that's one of the skills we want to start building.

RacerX 06-02-2017 13:50

Re: Poll: Reasonable and achievable, or shooting for the stars?
 
There are some teams that scale back on their goals and ambitions due to prior results, and perceived 'failures', yet they have no idea why they had 'failures'. Automatically scaling back is limiting, especially with teams that have resources, funding and student personnel.

Wasn't there someone who said 'you learn more from your failures than you do your successes'????

The FIRST program provides opportunities for learning on a whole host of levels..... Its more than just robots..... ;)

JesseK 06-02-2017 14:00

Re: Poll: Reasonable and achievable, or shooting for the stars?
 
Quote:

Originally Posted by Kevin Sevcik (Post 1641109)
18 Ah @ 12V = 12*18 Watt-hours * 60 min/hr * 60 s/min = 777600 Watt-s or Joules. Escape velocity is 11186 m/s. So 777600 = 1/2 * m * (11186)^2 = 12.4g. Balls weigh 70g, so you'd need 6 batteries charging your ball launching system to reach escape velocity. Not counting drag, etc. A properly designed charging system could probably send a penny into solar orbit, though.

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?

Sperkowsky 06-02-2017 14:07

Re: Poll: Reasonable and achievable, or shooting for the stars?
 
Winning is a lot more inspiring than building a cool robot in my opinion. That said there's definitely an optimal balance between the two.

iyportne 06-02-2017 14:14

Re: Poll: Reasonable and achievable, or shooting for the stars?
 
As a mentor and professional innovator, I say there has to be a combination of both. It's all about risk vs. reward, innovation vs. stagnation, and being able to measure or recognize your base (which changes every year with team demographics). So:

1. Establish your base as quickly as possible...build on what you know and at least don't start with re-inventing the wheel. This should establish the worst you will do this season.
2. Aim higher. Growth requires struggle. BUT, make sure your aim is scalable meaning it can fall back to your base or go even higher. Your aim is the best you will do.
3. Allow yourself to grow during competition season.
4. If you are lucky enough to have a year-round program...keep going as if you are still competing after champs, finishing all those things you wanted to do at the beginning of the season, or new things you witnessed during the season.
5. GoTo #1 - Start next season at a higher base.


Evolution, not Revolution.

Kevin Sevcik 06-02-2017 14:19

Re: Poll: Reasonable and achievable, or shooting for the stars?
 
Quote:

Originally Posted by JesseK (Post 1641170)
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.


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