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Unread 05-02-2017, 22:52
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Ken Streeter Ken Streeter is offline
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FRC #1519 (Mechanical Mayhem)
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Join Date: Feb 2005
Rookie Year: 2005
Location: Team: Milford, NH; Me: Bedford, NH
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Re: Climb Stopping Mechanism

Quote:
Originally Posted by Daniel_LaFleur View Post
Hmmmm.... Not sure if I understand your why here.

As the robot climbs the rope the weight of the robot causes tension on the rope equal to the weight of the robot ... Agreed

But once the robot encounters the hard stop at the Davit, it will give an upward force on the davit equal to the torque of the winch. Since every action produces an equal and opposite reaction the Davit will push down on the robot equal to the torque of the winch. This will be added to the force of gravity on the robot, thus the rope will see full force of the winch + weight of the robot.

Please show me where I am wrong.
Quote:
Originally Posted by tig567899 View Post
The force on the davit is equal to the torque of the winch minus the weight of the robot - opposite forces cancel. The davit will push down on the robot equal to that force - thus: weight of robot (due to gravity) + winch force - weight of robot = winch force.
tig567899's reply above states it pretty well.

However, as an illustration to help think through it, consider a robot that weighs 150 pounds ('bot + battery + bumpers), and a winch that can pull with 151 pounds of force.

If the 150-pound robot with a 151-pound-pulling winch were halfway up the rope, and a bystander put a hand out and pushed down with just one pound of force, the robot would stop ascending the rope, and be able to go no higher. It would only take 1 pound of downforce to do that.

The situation is no different with the davit -- only 1 pound of additional downforce is needed to stop the 151-pound-pulling winch from hoisting the 150-pound robot.
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Ken Streeter - Team 1519 - Mechanical Mayhem (Milford Area Youth Homeschoolers Enriching Minds)
2015 NE District Winners with 195 & 2067, 125 & 1786, 230 & 4908, and 95 & 1307
2013 World Finalists & Archimedes Division Winners with 33 & 469
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