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  #16   Spotlight this post!  
Unread 18-01-2017, 15:56
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Re: How Fast Can you Safely Climb?

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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Unread 18-01-2017, 16:04
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Re: How Fast Can you Safely Climb?

Quote:
Originally Posted by Chris is me View Post
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.
If they react too early, you don't hit the plate... If they react too late, you've potentially loaded up the entire system w/o breaking anything and it'll be a real pain to remove from the field (or you devastated the touch plate).
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Unread 18-01-2017, 16:06
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Re: How Fast Can you Safely Climb?

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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Unread 18-01-2017, 16:10
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Re: How Fast Can you Safely Climb?

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Originally Posted by Koko Ed View Post
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.
^ QFT.

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.*
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*See "Bill and Ted's Excellent Adventure."
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Unread 18-01-2017, 16:16
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Re: How Fast Can you Safely Climb?

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Originally Posted by Bruceb View Post
ok I am not a programmer but isn't there a way to sense current draw and shut the motors off when it spikes?
The answer is yes, but you want to do this as a backup, not as a primary stop feature. I say this as a team that used this method last year, and was having anxiety attacks all season about burning out that motor.
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Unread 18-01-2017, 16:16
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Re: How Fast Can you Safely Climb?

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Originally Posted by AdamHeard View Post
If they react too early, you don't hit the plate... If they react too late, you've potentially loaded up the entire system w/o breaking anything and it'll be a real pain to remove from the field (or you devastated the touch plate).
Well, the plate has a bright light on it, so the "too early" thing isn't a huge concern for me. Too late is a problem, depending on your design - any design is going to need a way to relieve the rope tension or stop at exactly the right time to work. Depending on how fast the hanger goes, you can have a second button to run the winch more slowly when you're near the top.

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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Unread 18-01-2017, 16:17
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Re: How Fast Can you Safely Climb?

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Originally Posted by Ginger Power View Post
Are there any other options that can be utilized on a robot?
Ultrasonics and other distance sensors could work. My team is toying with the idea of running the whole operation on a loop that's activated by the on-board gyro sensing a change in the robot's angle.
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Unread 18-01-2017, 16:46
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Re: How Fast Can you Safely Climb?

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Originally Posted by Eric Scheuing View Post
Ultrasonics and other distance sensors could work. My team is toying with the idea of running the whole operation on a loop that's activated by the on-board gyro sensing a change in the robot's angle.
Could also use the accelerometer in tandem with that to stop when you reach a certain height.
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Unread 18-01-2017, 16:55
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Re: How Fast Can you Safely Climb?

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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Unread 18-01-2017, 16:57
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Re: How Fast Can you Safely Climb?

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Originally Posted by zinthorne View Post
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.
The issue would be if a team only had a motor keeping the robot up, it would crash to the ground immediately.
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Unread 18-01-2017, 17:08
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Re: How Fast Can you Safely Climb?

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Originally Posted by Lireal View Post
The issue would be if a team only had a motor keeping the robot up, it would crash to the ground immediately.
You could argue that it would also crash to the ground at the end of the match anyway if all they had was a motor holding it up.
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Unread 18-01-2017, 17:08
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Re: How Fast Can you Safely Climb?

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Originally Posted by RoboChair View Post
Never enough.

Looking at you Team 900....
6-CIM climber you say?

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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Unread 18-01-2017, 17:13
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Re: How Fast Can you Safely Climb?

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.
  • Knot slips/rolls completely off the bitter end of the rope. Rope slips through tabs and channel.
  • Knot tightens or compresses enough to slip through tabs. Rope slips through tabs and channel.
  • Rope breaks. Robot falls, only custom rope is damaged. I suspect this will be disturbingly common with teams using mostly velcro for a rope. I expect field crew to have a trophy wall of 4" long ropes, since they'll likely break at the 90 degree bend.
  • Knot wedges between tabs and bends them outwards. Depending on size, knot may get stuck in channel.
  • Steel channel buckles under load. I'm not bothering to calculate this, but it seems like it's less than the following.
  • One or more tabs shear their welds.

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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Unread 18-01-2017, 21:06
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Re: How Fast Can you Safely Climb?

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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Unread 18-01-2017, 22:58
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Re: How Fast Can you Safely Climb?

Quote:
Originally Posted by Ginger Power View Post
What happens when the retaining knot is solid, the gear ratios are low, and the rope is rated to ridiculous tensile strengths? Is there a realistic possibility that something on the field could break?

What recommendations do people have so teams

1. Don't burn out climber motors
2. Don't break the field
The pilots can see the field, and they can communicate to the drive team with hand signals.
I don't see why that would be prohibited...
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