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How Fast Can you Safely Climb?
There are going to be some extremely fast climbers this year. How fast can you reasonably climb without putting the Pilots, the field, and your robot in danger?
For example, say a team can climb in 1 second. Their robot is going to be traveling very fast... they are going to hit the field sensor very hard... how much abuse can the field take? |
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Looking at you Team 900.... |
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I'm even more concerned hen the winch doesn't stop at the top of the climb |
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I could see a team that runs into the touchpad and continues running their winch until one of two things happens:
They burn out their motors OR Their gearing is reduced enough that they yank the retaining knot of their rope through the davit and fall to the ground. Teams should plan on having a way to stop climbing when they reach the top that doesn't consist of stalling motors. |
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ok I am not a programmer but isn't there a way to sense current draw and shut the motors off when it spikes?
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What recommendations do people have so teams 1. Don't burn out climber motors 2. Don't break the field |
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You know, the rope and target are one of the few things on the field you can be reasonably sure you'll be able to see. Just have the operator stop hitting the "winch up" button.
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If you design a robot that breaks the field again and again you are going to get on the FTA and head refs bad side really quickly and you don't want to reside there.
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The fun part is that the touchpad dome does not illuminate when the robot contacts it, it waits a second....
I love control challenges like this |
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Obviously the operator can let go of the trigger when the robot reaches the top. My point was that if a robot is climbing very fast, it's going to take skill on the operator's part to stop the robot in a reasonable amount of time. I was looking for reasonable methods of stopping the robot that would be automatic. Limit switches and current sensing are two good options. Are there any other options that can be utilized on a robot?
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The first time your robot does this, your team will have violated G15-H. Penalties: FOUL; if extended or repeated, then YELLOW CARD; if Head Ref deems that further damage is likely, DISABLED. There had better not be a second time, because if so your team will have violated T03, and will fail most egregiously.* ------------ *See "Bill and Ted's Excellent Adventure." |
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Alternately, put a vex bumper switch on whatever mechanism is doing the plate contact for you. Edit: Apparently the touchpad only illuminates when you've reached the 1 second threshold. Thanks, GDC... |
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This may sound really dumb, but FIRST could put it in the field programming to stop robot communication if the pressure sensor is held for 1 second in the final 5 seconds. I realize this takes the drama out of holding for one second to end the match, but it could stop a lot of problems with motor burnouts. Most mechanisms wont break if stalled for ~one second. Just an idea, but will likely never be implemented.
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As a serious contribution, perhaps the human players have some use here since they might be able to see what the driver might not? |
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Starting from the bottom, the rope goes through a steel U-channel, which it's held in by 2 pins. Then it makes a 90 degree turn, runs across the top of a square steel tube, and through 2 steel tabs welded on the sides of the tube. There's a pin through the top of these tabs to hold the rope in, the knot rests on the far side of the two steel tabs.
Failure options for winches will too much torque that don't stop at the top.
After playing with the touchpad, I think it's unlikely to get damaged. First, there's the channel sticking down that your winch will run into. Please design your climber to jam against this channel before the touchpad. Second, the plate is 1/4" lexan, the bolts it hangs from are relatively well pivoted, and I'm nearly certain you can shove it against the steel plate it hangs from with no ill effect. The most likely failure mode would be shearing the screws that hold it to the channel on the davit, I think. |
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Assuming someone does not have it geared 10,000:1 so it crawls up an inch per hour, motor current may pop the snap breakers/fuses. There is only so much power available, and since it needs to be geared in a realistic manner that limits how much force can be expected. Still hundreds of pounds and even thousands, but I expect the damage to be done to the robots because of ill designed systems.
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I don't see why that would be prohibited... |
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The rules say that as long as the button is pressed through time 0 and it is pressed for over 1 second, it will count. I'd therefore recommend that you run your winch a little more than the minimum requirement to make sure that even if it does begin to slip or unravel, the button will still be pressed enough to credit the points. If you're referring to the robot damage, that could be a serious issue. I talked about this with my sister and she said to use an airbag-type system to prevent robot damage. I would LOVE to see someone build an airbag-type system that is FRC legal. Either way, I hope this helps. |
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My back of the envelope calculations tell me a 2.5 second 1-CIM climber at motor max power point is very doable. Half that for 2 CIMs.
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The only sensors 1538 added to their bot for the 2015 season were encoders. They used current sensing for limits. Even with all of its complexity, this is what their wiring looked like. It takes time to develop current-based limits. They don't work if a team decides to try them out for the first time on the robot in week 6. |
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Just have the drivers stop pushing the "climb" button, when the bot slams into the touchpad. Since climbers this year (most likely) will only have to be turning in one direction, a simple solution to avoiding having to stall the motors to stay up is just sticking a ratcheting socket wrench on the end of the climber shaft. That should keep the bot from coming back down without having to stall the motors.
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When I read the rules, it appeared that if your robot contacts the touchpad, but then goes back down the rope enough that the touchpad is no longer activated, then you can't get the climbing bonus.
It might be that you want to spend a little time on the control system for your climbing mechanism? |
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I actually can't find anything in the rules that suggests that these two operations have to be done in the same instance of touching the button; I could have missed that though. Point being, if you touch the button at zero seconds, and you've already touched it for 1 second or more beforehand, you don't need to stay up there. Any number of really simple control system things can ensure you don't immediately fall back down once you touch the button - it could be as simple as a feed-forward gain. |
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As for control, the easiest way is to (a) press the touchpad using something springy like a bumper and (b) have something mechanical like a ratchet keeping you from moving downward. This combination means you can stop all power but will still be exerting some small amount of force on the touchpad. |
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"If a ROBOT causes a dome to illuminate, but disengages from the TOUCHPAD, the dome turns off and the associated points are removed from the real-time score." Let's see what the Q&A has to say about this! |
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