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#1
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Re: Climb Stopping Mechanism
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That's probably a decent amount of force (at least 300 lbs) |
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#2
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Re: Climb Stopping Mechanism
Hence the need for sensors.
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#3
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Re: Climb Stopping Mechanism
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However, in this circumstance, the force applied on the rope after hitting the stop at the top isn't "the full power of the winch + the weight of the robot pulling on the rope..." Rather, it's the maximum of the two. (Which is likely to be the "at stall" torque from the winch.) Last edited by Ken Streeter : 03-02-2017 at 17:44. |
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#4
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Re: Climb Stopping Mechanism
We're using a flex-head ratcheting wrench, i.e. just an ordinary ratcheting wrench except there's a pivot between the head and the handle. In order to lower the robot, we simply undo the velcro strap holding the wrench handle in a constrained position (i.e. between two bolts) and pivot it out of the way. The wrench rotates with the winch as it unspools.
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#5
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Re: Climb Stopping Mechanism
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Quote:
Last edited by GeeTwo : 03-02-2017 at 21:52. |
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#6
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Re: Climb Stopping Mechanism
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For those who are interested, this is the wrench in question: https://www.amazon.com/TEKTON-WRN570...words=WRN57010 |
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#7
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Re: Climb Stopping Mechanism
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I'll second the comment about marking which side of the wrench needs to be facing out, or which way the switch needs to be flipped if you're using a reversible wrench. Drill it into your pit crew's and drive team's heads. You can never double-check too many times. |
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#8
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Re: Climb Stopping Mechanism
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Depending on where it is in the gear reduction and the spool diameter it'll either be completely locked and tough to remove or trivial to remove by hand. |
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#9
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Re: Climb Stopping Mechanism
The wrench is right on the spool shaft, and the spool diameter is 1.25''. It's got a nice long handle, and I seriously doubt it will be a problem though we have not tried "wedging" the robot like that yet (we will be current-limiting the climbing motor to prevent that, at any rate).
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#10
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Re: Climb Stopping Mechanism
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#11
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Re: Climb Stopping Mechanism
After reading all this, maybe it would just be better to climb early and let the robot backdrive as time expires... This seems tricky otherwise.
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#12
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Re: Climb Stopping Mechanism
Hmm... I wonder if you could build a slip knot into the Retaining Feature of the rope. It holds under tension, but after a match, make sure the robot is supported and release an inch or two of slack. It'd be all in the rope, so even the teams that show up without the slightest consideration of this issue can implement a solution.
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#13
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Re: Climb Stopping Mechanism
a prudent approach:
Decouple the winch and the sensor trigger system. Winch system needs to be powerful, sensor trigger system does not. 1. Stop the climb well short of the sensor disk. Do this via encoder or careful operator control. a ratcheting device, such as a wrench, ensures that when power is killed the climber drum doesn't unwind. Robot is now hanging a few inches below sensor. 2. Activate a low power device (pneumatic piston or a cam on a small motor with its own ratchet) that extends up and holds pressure on the sensor disk through the end of match. Or do it passively with a compression spring. 3. After match lift robot up. As long as the trigger device on robot is low power two people should be able to overcome it easily and thus easily take tension off the winch ratchet system. This type of solution has likely been covered in another thread but it seems worthwhile to emphasize in this thread that triggering the sensor with your winch system, and the trouble that can ensue, is unnecessary. The forces involved that can damage the field, your robot, and possibly you, are of such magnitude that added complexity in the form of the additional trigger subsystem would likely pass the cost/benefit test. |
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#14
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Re: Climb Stopping Mechanism
Depending on the geometry, this is likely to run afoul of the perimeter rules. You'd need to be hanging at an angle such that this extension doesn't reach past the bumpers. (Or have a smaller-than-maximum-size robot.)
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#15
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Re: Climb Stopping Mechanism
Based on tests today of our first iteration climber, it seems reasonable to (a) get the climb scored but not stall into the touchpad, (b) relieve the load on a switchable ratcheting wrench by lifting the robot further into the touchpad thereby allowing you to switch the ratchet, (c) remove the rope from the field thereby releasing the robot, and (d) remove the rope from the robot in the pit. Our tests proved that this is difficult but feasible with a manual climb, but would be much more repeatable and faster with an automatic climb. The key is to not finish your climb with full power. I would warn folks that with the high reductions many climbing gearboxes have, it could be difficult to remove rope by backdriving the winches by hand.
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