08-04-2016 12:31

Chris Hapstack

Re: pic: Magnetic Grappling Hook

Latching: https://www.youtube.com/watch?v=G6oYBItYZrU

Firing: https://www.youtube.com/watch?v=v3PiLsyRn10

08-04-2016 12:39

cbale2000

Re: pic: Magnetic Grappling Hook

I like the idea, definitely looks like it would help the claws engauge, though it does not appear to fix the problem of having to be basically perfectly lined up for it to catch. =/

08-04-2016 13:00

Chris Hapstack

Re: pic: Magnetic Grappling Hook

Oh yeah it's definitely more of an amusing prototype at this point rather than a finished product. I was hoping the magnets would have a more dramatic effect, so we might end up going with something entirely different.

08-04-2016 13:18

Boltman

Re: pic: Magnetic Grappling Hook

Pretty sure the 20 second time factor would preclude that design

08-04-2016 13:24

Chris Hapstack

Re: pic: Magnetic Grappling Hook

In what way? This (or a different grappling hook) would be entirely contained within our frame perimeter until the last 20 seconds of a match.

08-04-2016 13:29

Boltman

Re: pic: Magnetic Grappling Hook

The acceleration applied to get magnet to engage on bar is relatively slow. So to properly position (big one) , then engage, then collapse then winch seems like that would be troublesome to say the least in 20 seconds. Don't see how the magnet helps much.

08-04-2016 13:36

cbale2000

Re: pic: Magnetic Grappling Hook

I'm pretty sure the cables used to engage the winch clamps would also be used for the lift so the whole thing, so the grasp and lift portion of the process would be done in one action. Sure, positioning would take time but could be done before the 20 second mark. Winding in the winch could be done quite rapidly depending on the motor and gearing used (a decent PTO could probably climb in less than 10 seconds).

IMO the biggest issue with these types of designs is accuracy, if you can get past that, you probably have the most effective type of climber out there.

08-04-2016 13:43

fiona.crush1011

Re: pic: Magnetic Grappling Hook

Do you have any close-up pictures of the real mechanism?

08-04-2016 13:57

Rivet Man

Re: pic: Magnetic Grappling Hook

Hi Chris Hapstack,

I'm going to agree with my friend Boltman on this one.

This design sure looks entertaining but it reminds me a lot of those arcade games where you try your best to win a stuffed bear but always end up dropping them even though it looked like you lined 'em up (Sorry Linda!).

I guess the positive here is that you could have your driver practice hanging by trying to win toys out of those machines. Just 20 dollars of practice and they'd be pros!

On another note, all that stuff still comes under 1 pound? Do you guys design these robots out of air or something? If I bought a clamp like that at Home Depot it'd weight at least 5 pounds!

Best Regards,
RM

08-04-2016 14:00

Chris Hapstack

Re: pic: Magnetic Grappling Hook

I took two separate videos to showcase the two actions of the grappling hook (firing and latching), but in reality they would all happen in one fluid motion. We would pull up on the batter, fire the grappling hook, and then immediately start winching in the attached rope. Pulling on the rope is what actually causes the hooks to latch closed, so the time between firing the hook and the robot starting to lift off the ground is controlled by the slack in the rope. Even if we wanted to be conservative and leave a couple feet worth of slack, the robot would start rising a couple seconds after firing the hook. If you’ve seen 118’s or 842’s climbers, we’d be shooting for a similar motion. It shouldn’t take appreciably longer than theirs.

The magnets were an attempt to help the hook align itself if the firing position was slightly off. They seem to have a small effect in testing so far, but it’s not significant enough that we’re stopping here.

Here’s a different view of the grappling hook firing upwards. This test was without the polycarb hooks attached, so it was lighter and thus went higher. Even with the hooks attached, though, the assembly went from release height to bar height in under a second. https://www.youtube.com/watch?v=FsrqKvVxamk

When it comes to the actual acceleration of the grappling hook, we didn’t calculate it, because knowing it is unnecessary. What we DID calculate was the spring size and displacement needed to launch the hook to the height of the bar (done by setting the potential energy of a compressed spring equal to the gravitational potential energy of the hooks at the height of the bar). This allowed us to have “getting the hooks to stop around 6ft in the air” as our goal, and we could size our spring to meet that goal. Because the hooks are thus reaching the top of their projectile path right at the height of the bar, you can assume it takes as much time to reach the bar as it does to fall from the bar to the height of the launcher. Using the equation t=sqrt((2*s)/g) where t is time in seconds, s is height above the ground in feet, and g is the acceleration due to gravity (32 ft/s^2), you get 0.61 seconds for the hooks to travel upwards (if the bar is 6 feet above the robot).

08-04-2016 14:02

Chris Hapstack

Re: pic: Magnetic Grappling Hook

Yes, the same cable both engages the clamps and lifts the robot. Our winch is designed to run at 12 inches/second under the load of the robot's weight, so we could ostensibly complete the climb within 4 or 5 seconds of firing the hook. Accuracy is definitely the biggest hurdle yet to go.

08-04-2016 14:05

Chris Hapstack

Re: pic: Magnetic Grappling Hook

Delrin, polycarb, and a little aluminum! I can't promise it'll lift much more than a robot, but it's looking like it will support ours.

08-04-2016 14:27

IronicDeadBird

Re: pic: Magnetic Grappling Hook

Oof I'd be careful with that I've seen a few magnets explode when they collide with something too hard. It is quite a spectacle unless said magnets are expensive rare earth magnets you just recently purchased.

08-04-2016 14:30

cbale2000

Re: pic: Magnetic Grappling Hook

Any magnet with a metal coating would work as well I would think.

08-04-2016 14:37

IronicDeadBird

Re: pic: Magnetic Grappling Hook

Then I guess my only real concern is if it accidentally went off and it happened to land in another robot.

08-04-2016 14:46

Chris Hapstack

Re: pic: Magnetic Grappling Hook

Shattering the magnets was definitely a concern. The purple side guards shown in the picture (actually made out of polycarb) extend 1/16" above the faces of the magnets, so the magnets themselves will never actually contact the bar.

08-04-2016 16:02

pmangels17

Re: pic: Magnetic Grappling Hook

If you decide you don't like the magnets, you could always try (using the same launch mechanism) to use a purely mechanical system that latches itself upon contact, and could be made a bit more forgiving with regard to aim, like this design from this thread.

EDIT: The linked robot is from 2013, but the hook concept is the same.

08-04-2016 16:13

Chris Hapstack

Re: pic: Magnetic Grappling Hook

I like it, I like it

08-04-2016 16:36

pmangels17

Re: pic: Magnetic Grappling Hook

So do I. I should correct myself though. In my earlier post, used the phrase "purely mechanical system," though the system you've designed already satisfies that criteria. I should have said a system where the grappling and latching are all accomplished in one passive (no actuator needed) motion. In any case, the system you designed is pretty sweet, I hope y'all have success with whatever you decide to use.

08-04-2016 16:40

Pretzel

Re: pic: Magnetic Grappling Hook

I have one thing to note about using magnets, and it has to do with paying attention in the pits.

Team 1619 last year used strong magnets (I believe that we used two 75 pound magnets) to hold our canburglar in place for the rest of the match after their initial use. As one of the people who was always in the pit moving around the robot, I lost count of the number of times my driver button or a small team pin attached to my shirt became affixed to the magnet and either tore my shirt or forced me to manually detach the button/pin to prevent my shirt from tearing. We also had to be careful with electronic devices. If we used a phone for a flashlight you had to be careful not to set it near those corners of the robot (the magnets were positioned on the top of our robot's "roll cage", a generally ideal location for an overhead light to be placed). Tools and nuts/bolts also became attached to the magnets when they were passed over or near the magnets.

If you decide to continue to use the magnets, I would recommend you have the claw stored someplace in the robot that is somewhat out of the way of other items in order to minimize these inconveniences. Our magnets were positioned at perfect pin/button height (right above your belly button) on an outside corner of our robot, which made for a hassle at times in the pits.

Not a huge thing, but something to consider when using strong magnets on your robot. Make sure everyone who works on the robot understands that they are there and how large their area of influence is so that they can prevent accidents and inconveniences.

08-04-2016 20:21

JesseK

Re: pic: Magnetic Grappling Hook

With all of these flashy quick-release and speedy grappling hooks that are iterated on throughout the season, is anyone else having flashbacks to the minibot races of 2011?

08-04-2016 21:26

fargus111111111

Re: pic: Magnetic Grappling Hook

I am noticing a lot of people concerned about being able to quickly align the hook, but could you not put the hook and launcher in such a position on the robot that it would be properly aligned when the bumpers were pressed against the castle wall? This is what 118 did and once they had it working they hit the bar every time. I heard they missed some on practice day at Huntsville, but once matches started they were climbing very frequently.

08-04-2016 23:12

RogerF

Re: pic: Magnetic Grappling Hook

Watch team 2341, The Sprockets, at the world championship. We have perfected a magnetic grapple that works every time. Very similar to the one you have posted. Ours is delivered by a spring loaded arm.

Good luck all!!

Roger. Mentor