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-   -   JVN Build Tip: Mechanism Loading (http://www.chiefdelphi.com/forums/showthread.php?t=91461)

Rosiebotboss 11-02-2011 08:37
Re: JVN Build Tip: Mechanism Loading
 
Quote:
Originally Posted by dtengineering (Post 1020304)
I want a video of the hot-dog roast taking place over the drive train at the end of the day! :)

I wonder if anyone has actually smoked a CIM... maybe they ARE indestructible in an FRC context.

Jason
Yes, 190 has. I do not remember the year, 2004 maybe. They did a mecanum drive and were overheating the CIMS big time. The robot rule that says "thow shalt not modify motor housings" belongs to 190 because they cut a window in the CIM housing and had small muffin fans on the other side/end pulling air through the windings. a really neat solution, actuallly.

JesseK 11-02-2011 10:36
Re: JVN Build Tip: Mechanism Loading
 
Great post John; it should add a bit for knowledge to many varying levels of experience.

For our lift, I've done some math. We too will be using some surgical tubing to aid in the lift. We're using a 5/8" thick 2"/turn threaded rod at 50% of its critical speed -- we can increase that if we decrease its load. The hope is that we can use only 1 RS-775 to power it, yet we may still add a second one just to be on the safe side if we have weight to spare.

The surgical tubing serves a second purpose too, however. At the top and the bottom of the rod's range of movement, we've lathed off the threads in order to prevent the nut from getting ripped apart should the programmer's 3 safety pieces fail. At the bottom the tubing will combine with springs to lift it out of the bottom dead zone, thereby enabling us to continue scoring even sensors/code fail.

(Yea I know, threaded rod is heavy -- but we 'got a guy' who knows what he's doing with it, so I'd rather error on the heavy-but-quality side than try our multiple failed winch ideas again...)

Foster 11-02-2011 11:16
Re: JVN Build Tip: Mechanism Loading
 
Quote:
Originally Posted by ThirteenOfTwo (Post 1020376)
We learned passive assistance in VEX, specifically last year when we wanted to design a 254-esque arm to fling the game objects without any pneumatics. We actually gave our basket "negative weight". Footballs flew. Since then, passive assistance on every arm we've done, including on the VEX robot that made it onto JVN's blog. :D It's that useful.
Most of our VEX robots this year have passive assistance on their arms. The rack/pinion on a slider is great, the ability to "up gear" to move the arms faster is a must. The latex tubing makes this possible since there is less weight for the motor to move.

Nice post John, is this the famous "Subsystem 0" we keep hearing about on your blog?

Lil' Lavery 11-02-2011 11:52
Re: JVN Build Tip: Mechanism Loading
 
Related question:

Does anyone have a stress-strain curve for surgical tubing? Anecdotal evidence suggests that it's possible to exit the linear-elastic region under FRC conditions. While it's generally not that big of a deal, given how FIRST teams use surgical tubing, I'm still curious.

artdutra04 11-02-2011 12:03
Re: JVN Build Tip: Mechanism Loading
 
Quote:
Originally Posted by Lil' Lavery (Post 1020548)
Related question:

Does anyone have a stress-strain curve for surgical tubing? Anecdotal evidence suggests that it's possible to exit the linear-elastic region under FRC conditions. While it's generally not that big of a deal, given how FIRST teams use surgical tubing, I'm still curious.
Calculator here: http://www.primelineindustries.com/tools.html

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