Thread: How many robots on the bar in one match?
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Unread 23-06-2002, 22:39
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#0047 (ChiefDelphi)
  
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Ungh
Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 1/17/2000 2:02 PM MST


In Reply to: Re: How many robots on the bar in one match? posted by Quentin Lewis on 1/17/2000 10:50 AM MST:




: I am not a Mechanical Engineer, and I suppose it depends on whether they grab the bar closer to the center, or towards the ands....but I wonder if the bar could actually hold about 500 pounds? (Anyone know?)

Four 130 lb robots hanging from the center of the bar would deflect the bar about 1.6 inches and induce a peak stress in the pipe (at the center) of about 53,000 psi. That might be enough to cause a plastic (permanent) deformation of the bar, depending on the grade and quality of the steel in the particular pipe (it's not real highly specified material). The stress comes down quickly for less conservative cases, like with four bots hung 2 by 2, fewer than 4 bots, etc. I think FIRST's position that they'll replace the bar if it bends is probably a reasonable gamble. The peak stress would come down to about 43,000 psi if they used SCH 80 (heavier wall) pipe, which I suspect they would do if one does get bent.

So I say we all take it as a challenge to BEND THE BAR! It might help if at least one bot in the pile built in the capability to bounce while they're hanging. Right about 2.5 bounces per second (quicker if we can't all pile in the middle) gets everything resonating and the bar is toast.

Dodd


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