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Unread 16-01-2014, 07:56
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ToddF ToddF is offline
mechanical engineer
AKA: Todd Ferrante
FRC #2363 (Triple Helix)
Team Role: Mentor
 
Join Date: Apr 2011
Rookie Year: 2011
Location: Newport News, VA
Posts: 600
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Re: Creating pneumatic launchers

Quote:
Originally Posted by billbo911 View Post
As long as you are taking my comments out of context, then you are right.
Sorry, Mr. Bill. I wasn't calling you out at all. Your example was right on the money. I was reacting to this post.

Quote:
Originally Posted by AustinShalit View Post
Anytime you use a large bore the speed is going to decrease. ...

In order to have an equal amount of force, use multiple cylinders with smaller bore rather than a single large bore for greater speed.
This design advise is correct in the context of FIRST robotics, assuming both cylinders are fed by valves with the max allowable Cv. But, it's not what you would normally do in industry.

At this stage of the design process, the students are coming up with a lot of different ideas for how to execute different concepts. Some of those are great ideas in the "real world", but not in a FIRST robot, because of the restrictions imposed by the rules. Some of those ideas are great for a FIRST robot, but are not what you would do in industry. I always take great pains to explain the difference because I don't want a student to internalize a "lesson learned" from the world of FIRST robotics and apply it to real world engineering when it might only be true in the context of the FIRST robot rules.

Whether it's because of imprecise language or because they have learned the wrong lessons, you see a lot of half-true design rules quoted by students (and occasionally mentors) on CD. I think as mentors we're responsible to explain to the students how these design rules are context dependent, and how the underlying assumptions affect their design decisions.
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Todd F.
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