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sauhaarda 26-01-2017 21:48

Climb Stopping Mechanism
 
What strategies are you using to stop climbing the rope after the button is pressed at the proper pressure? Are you planning on a manual stop? A pressure plate stop? A stop based on stall torque? It seems to me that there is a very small window to stop the robot from applying to much pressure on the plate. How are you teams trying to address this issue?

ollien 26-01-2017 21:48

Re: Climb Stopping Mechanism
 
Honestly the best option seems to be driver control. It's a huge light. If they can see the rope well enough to grab it, they can see the touchpad light.

Billfred 26-01-2017 21:52

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by ollien (Post 1636915)
Honestly the best option seems to be driver control. It's a huge light. If they can see the rope well enough to grab it, they can see the touchpad light.

I tend to agree with the conclusion, but I don't agree with the methodology given that one davit is on the far side of the airship from the alliance. That will require a pilot to spot, or some kind of smarts. I had it backwards.

beijing_strbow 26-01-2017 21:59

Re: Climb Stopping Mechanism
 
Our plan so far is to use a gyro to detect when the robot is angled up at more than, say, 5 degrees. Then we'll use an encoder on our climber winch to find our height, and stop when we hit the pad. The issue we've come up with is that the rope won't always wrap in the same path, so the distance you climb on each revolution will vary slightly. We're planning on using a velcro strip though, so this shouldn't be too bad. If it does end up being intolerable, we'll probably put a limit switch on the front of the robot to detect when we hit the plate and use the encoder to then climb another inch or two.

NShep98 26-01-2017 22:04

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Billfred (Post 1636916)
I tend to agree with the conclusion, but I don't agree with the methodology given that one davit is on the far side of the airship from the alliance. That will require a pilot to spot, or some kind of smarts.

If I'm looking at the manual drawing correctly, one of the davits is directly facing the alliance, not away from it. The other two are on the sides adjacent to the ladder, which is on the far side of the airship.

cmwilson13 26-01-2017 22:14

Re: Climb Stopping Mechanism
 
There is a 1 second delay between triggering the plate and the light activating.
that is plenty of time to break components at stall or burn up motors.

i don't have any testing to support it but i assume that with the can talons it will be super easy to detect the current spike once you hit the plate and then shut down the motors. it appears like a simple solution to me until testing proves otherwise

Fusion_Clint 26-01-2017 22:21

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Billfred (Post 1636916)
I tend to agree with the conclusion, but I don't agree with the methodology given that one davit is on the far side of the airship from the alliance. That will require a pilot to spot, or some kind of smarts.


I think you are looking at it wrong. Each team has a clear view of one of the davits. Teams just need to climb the rope that corresponds to their view.


mman1506 26-01-2017 22:24

Re: Climb Stopping Mechanism
 
Don't, if you gear a CIM motor for optimal climb speed you should be able to stall for at least 30 seconds. The pressure plate has a metal U channel that should prevent you from damaging it anyway and while you may worry about it I'm sure FIRST knows plenty of other teams will test its limit. No need to over complicate things.

Billfred 26-01-2017 22:43

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by NShep98 (Post 1636921)
If I'm looking at the manual drawing correctly, one of the davits is directly facing the alliance, not away from it. The other two are on the sides adjacent to the ladder, which is on the far side of the airship.

Quote:

Originally Posted by Fusion_Clint (Post 1636926)
I think you are looking at it wrong. Each team has a clear view of one of the davits. Teams just need to climb the rope that corresponds to their view.


You were right, I was wrong. Enjoy your rep. :)

Chris is me 26-01-2017 22:54

Re: Climb Stopping Mechanism
 
The light doesn't turn on until after you've pressed it for one second.

Going to just have analog manual control of the speed of the climber, slow down as you get to the top, press it down firmly, not really worried. This shouldn't be hard.

Jamesa47 26-01-2017 23:56

Re: Climb Stopping Mechanism
 
A suggestion someone on my team had was to measure the current draw from the climber motor, and when it spikes past a certain point, you know you've hit the top of the rope and are pressing the button down.

ollien 27-01-2017 01:10

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Jamesa47 (Post 1636952)
A suggestion someone on my team had was to measure the current draw from the climber motor, and when it spikes past a certain point, you know you've hit the top of the rope and are pressing the button down.

If you do this, make sure it's a timer to make sure you've pressed for >=1s.

messer5740 27-01-2017 08:48

Re: Climb Stopping Mechanism
 
You got to make a stop mechanism so you don't slide back down after time is stopped. One the match is done the rope points are calculated, so you got to keep up until the points are GIVEN to the team.

cad321 27-01-2017 09:00

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by messer5740 (Post 1637020)
You got to make a stop mechanism so you don't slide back down after time is stopped. One the match is done the rope points are calculated, so you got to keep up until the points are GIVEN to the team.

According to Figure 3-21 in the manual, teams only need to be touching the touchpad for a split second once the match finishes (assuming you were pressing it for longer than one second) in order to receive the points.

JesseK 27-01-2017 09:28

Re: Climb Stopping Mechanism
 
Step 1: If your climber is a winch, get rid of all of your sensors and use the PDB's built-in current sensors. When Current / Applied Voltage > a ratio (we're using 60A & 12V, so ratio of 5) then disable the motor from going in that direction for N milliseconds.
Step 2: Test
Step 3: Test Some More.

Current through the motor is responsive and reliable to read and react upon. Getting it from the PDB is one of the best things added to the control system in recent years.

Chris is me 27-01-2017 09:36

Re: Climb Stopping Mechanism
 
Depending on what T=0 means, you don't NEED to hold your robot on the button after power is cut, just as power is cut, provided you have already held the button for >1 second. If your mechanism can't do that, it's not like prior years where you can't get the points at all, it just requires more commitment in advance and eliminates last-second scoring.

Kartoffee 02-02-2017 09:47

Re: Climb Stopping Mechanism
 
Our team is using a hex shaft, so we will include a 1/2" ratcheting wrench to help us climb. This was seen to be effective from Ri3D 1.0 and our team is worried that our bot might fall after the buzzer (or at least glide down, which still isn't safe).

I've changed my opinion since the reveal. I thought that it would be stronger to use a single grabbing motion (like the 2013 pyramid climbers), but I've noticed that you would need to dedicate a huge portion of your bot to that.

Our team is using a type of winch. It's not an original idea, but our testing shows its effectiveness. We are quite excited to be climbing this year.

Good luck all!

mentorDon 03-02-2017 14:53

Re: Climb Stopping Mechanism
 
According to the 2015 FRC motor information sheet, a CIM motor pulls 133 amps at stall. Well above the allowed 40 amp breaker allowed per motor under rule R56 Table 8-3.

Chris is me 03-02-2017 14:55

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by mentorDon (Post 1639977)
According to the 2015 FRC motor information sheet, a CIM motor pulls 133 amps at stall. Well above the allowed 40 amp breaker allowed per motor under rule R56 Table 8-3.

133 amps at stall at full voltage. If you stall the motor at much less than full voltage, it will draw significantly less current as well. This can allow you to hold position while the robot has power (but not after power has been cut).

MrForbes 03-02-2017 15:11

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by JesseK (Post 1637034)
Step 1: If your climber is a winch, get rid of all of your sensors and use the PDB's built-in current sensors. When Current / Applied Voltage > a ratio (we're using 60A & 12V, so ratio of 5) then disable the motor from going in that direction for N milliseconds.

I'll get our programmers on this....

thanks!

We were going to just slow down at the top, and stop after we visibly moved the touch pad up as much as it takes to get the light to go on (practice day, you know). But the current thing looks like a fun way to keep a few students busy for a few more days

tr6scott 03-02-2017 15:14

Re: Climb Stopping Mechanism
 
We have an encoder integrated into the climber. We plan on monitoring the current to detect when the climb starts, and set a stop distance based on that start point. The operator will have the ability to jog higher if we stop too soon, but hoping this approach leads to automatic climbing.

Still untested theory at this point. Fingers crossed. Would like to have working repeatable solution by week 1, we are going to need it.

6101 Robert 03-02-2017 15:20

Re: Climb Stopping Mechanism
 
I think the easiest solution is to simply use the motor controllers to sense when the motor is stall. This is what 6101 is doing. The Davit has a C-channel piece to protect it in brief high-stress situation and the 40A breakers wouldn't pop immediately. I don't see any reason why this wouldn't work.

To prevent gliding, we are using a ratchet head on the winch similar to Ri3D 1.0.

waialua359 03-02-2017 15:33

Re: Climb Stopping Mechanism
 
This shouldnt be too hard.
Once you see the light go on, dont drive the lift anymore.
We plan to use a simple ratchet to prevent it from backdriving.

AdamHeard 03-02-2017 15:37

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by waialua359 (Post 1639989)
This shouldnt be too hard.
Once you see the light go on, dont drive the lift anymore.
We plan to use a simple ratchet to prevent it from backdriving.

Will you have the ability to disengage the ratchet under load?

If not, what keeps you from effectively clamping onto the field when waiting the 1 second?

waialua359 03-02-2017 15:58

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by AdamHeard (Post 1639990)
Will you have the ability to disengage the ratchet under load?

If not, what keeps you from effectively clamping onto the field when waiting the 1 second?

Sorry, I'm slow. I dont quite follow?

Daniel_LaFleur 03-02-2017 15:58

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by waialua359 (Post 1639989)
This shouldnt be too hard.
Once you see the light go on, dont drive the lift anymore.
We plan to use a simple ratchet to prevent it from backdriving.

The light does not go on until a full second after the plate is pushed.
Hope your knot holds.

waialua359 03-02-2017 15:59

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Daniel_LaFleur (Post 1640002)
The light does not go on until a full second after the plate is pushed.
Hope your knot holds.

Yes, that part we knew and it will hold.:)

JesseK 03-02-2017 16:00

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Daniel_LaFleur (Post 1640002)
Hope your knot holds.

I'm missing something here - isn't this something everyone has to worry about?

Daniel_LaFleur 03-02-2017 16:03

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by JesseK (Post 1640005)
I'm missing something here - isn't this something everyone has to worry about?

Yes, but if you wait to stop your winch until AFTER the light comes on you will be putting the full power of your winch + the weight of your robot pulling on the rope for that second.

That's probably a decent amount of force (at least 300 lbs)

waialua359 03-02-2017 16:04

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Daniel_LaFleur (Post 1640008)
Yes, but if you wait to stop your winch until AFTER the light comes on you will be putting the full power of your winch + the weight of your robot pulling on the rope for that second.

That's probably a decent amount of force (at least 300 lbs)

Hence the need for sensors.

AdamHeard 03-02-2017 16:05

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by waialua359 (Post 1640001)
Sorry, I'm slow. I dont quite follow?

When you hit the wall on top, your motor will go to stall (unless you're current limiting) and push very hard on the top.

Now imagine everything in the system is a spring, you're going to compress/stretch parts of the robot/field and load everything up.

Now there is a ratchet on there preventing you from backdriving (and you can't go forward any more as you're already loaded pretty firm into the field).

Now that's how you lock yourself onto the field.

waialua359 03-02-2017 16:12

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by AdamHeard (Post 1640016)
When you hit the wall on top, your motor will go to stall (unless you're current limiting) and push very hard on the top.

Now imagine everything in the system is a spring, you're going to compress/stretch parts of the robot/field and load everything up.

Now there is a ratchet on there preventing you from backdriving (and you can't go forward any more as you're already loaded pretty firm into the field).

Now that's how you lock yourself onto the field.

In 2010, we created a simple ratchet pawl system that worked for our climber. It should release if we at least carry the robot, releasing weight tension.

AdamHeard 03-02-2017 16:15

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by waialua359 (Post 1640018)
In 2010, we created a simple ratchet pawl system that worked for our climber. It should release if we at least carry the robot, releasing weight tension.

You won't be able to release weight tension as you're literally clamping the field. Can't go the other way because of the ratchet as well.

s_forbes 03-02-2017 16:16

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Daniel_LaFleur (Post 1640002)
The light does not go on until a full second after the plate is pushed.
Hope your knot holds.

I'm expecting at least one case where a robot yanks its stopper knot out of the davit this year, especially with the crazy ratios that people are putting on their climbers.

waialua359 03-02-2017 16:18

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by AdamHeard (Post 1640021)
You won't be able to release weight tension as you're literally clamping the field. Can't go the other way because of the ratchet as well.

Well, I guess we shall see.:)

llung 03-02-2017 16:19

Re: Climb Stopping Mechanism
 
The current measuring method works very well. We've used it in other instances in the past and plan on using it this year for the climber mechanism.

JesseK 03-02-2017 16:20

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by AdamHeard (Post 1640021)
You won't be able to release weight tension as you're literally clamping the field. Can't go the other way because of the ratchet as well.

Interesting point. How is 973 dealing with this?

AdamHeard 03-02-2017 16:24

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by JesseK (Post 1640025)
Interesting point. How is 973 dealing with this?

If you have a ratchet and are planning on stalling against the top for the full second, it needs to be able to disengage under load OR you need some way to remove the load.

Cory 03-02-2017 16:39

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by waialua359 (Post 1640023)
Well, I guess we shall see.:)

Prepare to be disappointed. There's nothing special about the scenario Adam has outlined. Any system with a ratchet and pawl is going to behave exactly as he's explained. We had this happen multiple times in 2010 with our kicker and our hanger. It's a HUGE PITA when it happens. We had to use a giant flat head screwdriver and apply major force to the pawl to lever it to disengage. This is assuming you have a pawl that's actually accessible. If you're using a ratcheting wrench you're totally screwed.

Imagine trying to release a ratchet strap that has been ratcheted to significant tension. If you try to pull the release with your fingers without taking up some of the load with the handle, you will never get it undone. You have to release tension off the release bar in order to move it. This is exactly what will happen in the scenario outlined above.

Poseidon5817 03-02-2017 16:43

Re: Climb Stopping Mechanism
 
It is legal to remove the rope from the field without removing the robot from the rope. So couldn't you have two team members support the robot, while another team member releases the rope from the davit?

Cory 03-02-2017 16:46

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Poseidon5817 (Post 1640040)
It is legal to remove the rope from the field without removing the robot from the rope. So couldn't you have two team members support the robot, while another team member releases the rope from the davit?

No. Read the above. You have nowhere to support the robot to. You can't force it up because it's already pushed the touch pad to it's hard stop. The rope will be under hundreds of pounds of tension at that point. You cannot push the robot higher and therefore cannot relieve the tension.

waialua359 03-02-2017 16:49

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Cory (Post 1640043)
No. Read the above. You have nowhere to support the robot to. You can't force it up because it's already pushed the touch pad to it's hard stop. The rope will be under hundreds of pounds of tension at that point. You cannot push the robot higher and therefore cannot relieve the tension.

This is a good point. I had assumed the same also as an alternative without carefully thinking about it.
I do recall your 2010 robot and didnt realize you had those issues also.

waialua359 03-02-2017 16:53

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Cory (Post 1640037)
Prepare to be disappointed. There's nothing special about the scenario Adam has outlined. Any system with a ratchet and pawl is going to behave exactly as he's explained. We had this happen multiple times in 2010 with our kicker and our hanger. It's a HUGE PITA when it happens. We had to use a giant flat head screwdriver and apply major force to the pawl to lever it to disengage. This is assuming you have a pawl that's actually accessible. If you're using a ratcheting wrench you're totally screwed.

Imagine trying to release a ratchet strap that has been ratcheted to significant tension. If you try to pull the release with your fingers without taking up some of the load with the handle, you will never get it undone. You have to release tension off the release bar in order to move it. This is exactly what will happen in the scenario outlined above.

Ours is accessible so looks like we will have to bring that large flat screwdriver head.:p
Or we can also do the other suggestion earlier with the current draw. Lots of time left to figure this out since our climber already made and it works.

AdamHeard 03-02-2017 16:56

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Poseidon5817 (Post 1640040)
It is legal to remove the rope from the field without removing the robot from the rope. So couldn't you have two team members support the robot, while another team member releases the rope from the davit?

Read what I posted again, you're literally champing the field and that rope will be under significant tension. Good luck.

Ken Streeter 03-02-2017 17:36

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Daniel_LaFleur (Post 1640008)
Yes, but if you wait to stop your winch until AFTER the light comes on you will be putting the full power of your winch + the weight of your robot pulling on the rope for that second.

That's probably a decent amount of force (at least 300 lbs)

Just FYI, I agree with your point that teams need to have a solution to the problem.

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.)

Hitchhiker 42 03-02-2017 17:38

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by AdamHeard (Post 1640021)
You won't be able to release weight tension as you're literally clamping the field. Can't go the other way because of the ratchet as well.

You could have it so the ratchet is easy to take off. Then you could unwind the rope.

orangeandblack5 03-02-2017 18:21

Re: Climb Stopping Mechanism
 
Wait... if you're using a ratchet wrench, could you not just reverse the direction the wrench is ratcheting?

antman 03-02-2017 18:23

Re: Climb Stopping Mechanism
 
If you use a ratchet wrench you could clamp the non-ratchet end with a bicycle quick-release lever that can slide in a slot to drop below the wrench when the lever is opened.

AdamHeard 03-02-2017 18:26

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by orangeandblack5 (Post 1640078)
Wait... if you're using a ratchet wrench, could you not just reverse the direction the wrench is ratcheting?

Please, go try this with 150 in-lb (or more) on the ratchet.

Cory 03-02-2017 18:27

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by orangeandblack5 (Post 1640078)
Wait... if you're using a ratchet wrench, could you not just reverse the direction the wrench is ratcheting?

No...that's the entire point of the discussion above. If you have a ratcheting wrench, attempt to tighten an already tight bolt. While applying a tightening force, try to flip the ratchet switch. It won't work. The pawl is under tension as well and you can't overcome it without significant force...far more than your fingers could apply.

orangeandblack5 03-02-2017 18:39

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Cory (Post 1640082)
No...that's the entire point of the discussion above. If you have a ratcheting wrench, attempt to tighten an already tight bolt. While applying a tightening force, try to flip the ratchet switch. It won't work. The pawl is under tension as well and you can't overcome it without significant force...far more than your fingers could apply.

Ah, thank you for explaining.

Nuttyman54 03-02-2017 20:34

Re: Climb Stopping Mechanism
 
I've been mulling over whether or not it's legal cut the rope to release the robot. It's legal for your robot to damage team provided ropes (G15) as long as it doesn't leave debris on the field, and once the rope has been removed from the Davit it's no longer considered part of the field (R08 blue box).

As far as I can determine, it would not be legal because up to the point where the rope is cut and the robot is released, it's technically a person damaging part of the field (even though that part of the field is legally allowed to be damaged by a robot. Just not anything else). But it was an interesting read through the rules.

*Apex Robotics is not planning to release our robot in this fashion. But it did make me curious if it's a quick fix for teams who haven't planned around this*

Oblarg 03-02-2017 21:30

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.

GeeTwo 03-02-2017 21:44

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Oblarg (Post 1640147)
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.

Wow. I was at Lowe's shopping for ratchet wrenches this evening, and thought of essentially the same thing when I looked at the flex-head wrenges. I was thinking of using a non-flex head, non-reversible wrench, wedging it in a piece of aluminum channel (similar to your two bolts), and lifting it out parallel to the shaft. If you do this, be sure to mark the ratchet wrench as to WHICH SIDE FACES OUT, or you'll have a useless climber for a match or three.

Quote:

Originally Posted by Nuttyman54 (Post 1640127)
I've been mulling over whether or not it's legal cut the rope to release the robot. ...

I concur that with the rules as currently written, it would not be legal (Drive team damage vs robot damage). However, given the preamble to the answer to Q299, I suspect that a question on this topic would get a finding of legal even if it meant a rule change.

Oblarg 03-02-2017 21:50

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by GeeTwo (Post 1640153)
Wow. I was at Lowe's shopping for ratchet wrenches this evening, and thought of essentially the same thing when I looked at the flex-head wrenges. I was thinking of using a non-flex head, non-reversible wrench, wedging it in a piece of aluminum channel (similar to your two bolts), and lifting it out parallel to the shaft. If you do this, be sure to mark the ratchet wrench as to WHICH SIDE FACES OUT, or you'll have a useless climber for a match or three.

The nice thing about the flex-head wrench is that we can constrain the head in-place to avoid that exact problem (though we probably ought to mark it anyway).

For those who are interested, this is the wrench in question:

https://www.amazon.com/TEKTON-WRN570...words=WRN57010

Karibou 03-02-2017 22:02

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by GeeTwo (Post 1640153)
Wow. I was at Lowe's shopping for ratchet wrenches this evening, and thought of essentially the same thing when I looked at the flex-head wrenges. I was thinking of using a non-flex head, non-reversible wrench, wedging it in a piece of aluminum channel (similar to your two bolts), and lifting it out parallel to the shaft. If you do this, be sure to mark the ratchet wrench as to WHICH SIDE FACES OUT, or you'll have a useless climber for a match or three.

From my experience, that is much easier said than done (with the non-flexible non-reversing). The wrench always wedged itself pretty tightly against the stop and we still needed to lift or rotate the robot slightly to get it out. There needs to be pretty much no load on the wrench to be able to slide it along the shaft to get it off (or far enough along the shaft to not be impeded). Granted, I've always done it using two bolts/screws as the stop, never channel.

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.

AdamHeard 03-02-2017 22:02

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Oblarg (Post 1640147)
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.

Have you tried this after crashing into the top and holding full stall?


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.

Oblarg 03-02-2017 22:07

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by AdamHeard (Post 1640168)
Have you tried this after crashing into the top and holding full stall?


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.

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).

CalTran 03-02-2017 22:48

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Oblarg (Post 1640170)
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).

Might as well test "catastrophic failure mode" while you get a chance to do so in a more friendly environment.

Chris is me 03-02-2017 23:31

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.

Cothron Theiss 04-02-2017 03:39

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.

James3245 04-02-2017 08:48

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.

AveryLevin. 04-02-2017 11:25

Re: Climb Stopping Mechanism
 
Out team will be using a ratcheting winch that will shut off once our Vex bumper switch is pressed. The shut off is on a delay so our robot will be able to push the pad more than an inch before we stop climbing.

Daniel_LaFleur 04-02-2017 19:39

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Ken Streeter (Post 1640060)
Just FYI, I agree with your point that teams need to have a solution to the problem.

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.)

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.

dirtbikerxz 04-02-2017 20:23

Re: Climb Stopping Mechanism
 
We just tested a few ideas today, and settled on a process. So we put a standard socket wrench (locked in place) on the end of the climber hex shaft. Our climber is very close to the bottom of the bot. Two drive team members than lifted the bot enough so that tension of the rope was taken off the hex shaft, and since the climber is close to the bottom of the bot, the person on that side of the bot, was able to flick the lever easily with one hand, while holding that side of the bot with the other hand, and then both drive team members guided the bot slowly to the ground, and the rope just unspooled.

JesseK 04-02-2017 20:48

Re: Climb Stopping Mechanism
 
I found this in Q&A and it may help a few teams. While it it legal for a PILOT to assist in removing the ROPE from the DAVIT, the laws of physics likely wouldn't allow it in the 'clamping to the field' scenarios above. https://frc-qa.firstinspires.org/qa/381

We're going to pneumatically actuate a vice grip into a brake off the gearbox of our winch. We'll probably add some cushioning to our contacts to make sure the touchpad stays engaged if we drop a few tenths of an inch. Anyone know alternative names for them?

AdamHeard 04-02-2017 22:27

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by dirtbikerxz (Post 1640515)
We just tested a few ideas today, and settled on a process. So we put a standard socket wrench (locked in place) on the end of the climber hex shaft. Our climber is very close to the bottom of the bot. Two drive team members than lifted the bot enough so that tension of the rope was taken off the hex shaft, and since the climber is close to the bottom of the bot, the person on that side of the bot, was able to flick the lever easily with one hand, while holding that side of the bot with the other hand, and then both drive team members guided the bot slowly to the ground, and the rope just unspooled.

Did you do this after crashing into the top and holding full stall for 1 seconds?

dirtbikerxz 04-02-2017 22:39

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by AdamHeard (Post 1640573)
Did you do this after crashing into the top and holding full stall for 1 seconds?

Oh... nope. Ya now that you mention it, I can see how that may be a problem, lol. *sigh* back to the drawing board

tig567899 04-02-2017 23:07

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Daniel_LaFleur (Post 1640493)

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.

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.

Basel A 05-02-2017 18:21

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.

JesseK 05-02-2017 18:30

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Oblarg (Post 1640147)
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.

We tried this today. We climbed with 130lbs attached to our climber's production frame using production motors & gearing. Rope touch to Touchpad was about 4 seconds, so it wasn't a 'crash' into the top - but we did intentionally stall the motors at the top for a second or two. The ratchet wrench was held in place by one 1/4-20 bolt - the threaded end, no less. While under load we popped it loose with a large flathead screwdriver very easily. During further tests and refinement, we added a string to pop it out at the end of the tests. It also worked very well. We climbed about 30 times, and it worked every time. We'll put a 3/8" steel stud around that bolt in the future.

Karibou 05-02-2017 18:54

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by JesseK (Post 1640783)
We tried this today. We climbed with 130lbs attached to our climber's production frame using production motors & gearing. Rope touch to Touchpad was about 4 seconds, so it wasn't a 'crash' into the top - but we did intentionally stall the motors at the top for a second or two. The ratchet wrench was held in place by one 1/4-20 bolt - the threaded end, no less. While under load we popped it loose with a large flathead screwdriver very easily. During further tests and refinement, we added a string to pop it out at the end of the tests. It also worked very well. We climbed about 30 times, and it worked every time. We'll put a 3/8" steel stud around that bolt in the future.

We ran a test today using around 150lbs and a flex-head wrench held in place in some 1x1 c-channel about halfway down the wrench. Worked like a charm; wrench folded up with no problems!

electronicsdude 05-02-2017 21:07

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by sauhaarda (Post 1636914)
What strategies are you using to stop climbing the rope after the button is pressed at the proper pressure? Are you planning on a manual stop? A pressure plate stop? A stop based on stall torque? It seems to me that there is a very small window to stop the robot from applying to much pressure on the plate. How are you teams trying to address this issue?

1/2 inch ratcheting flatwrench for retaining. Use the onboard current sensing of the PDP to kill the motor when it reaches a load higher than just lifting, aka semi-stall instance.

Ken Streeter 05-02-2017 22:52

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by Daniel_LaFleur (Post 1640493)
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 (Post 1640587)
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.

BethMo 05-02-2017 23:04

Re: Climb Stopping Mechanism
 
Quote:

Originally Posted by James3245 (Post 1640232)
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.

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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