pic: Magnetic Grappling Hook

[Chris Hapstack]

loading photo ...

[Chris Hapstack]

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

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

[cbale2000]

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. =/

[Chris Hapstack]

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.

[Boltman]

Originally Posted by Chris Hapstack

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.

Pretty sure the 20 second time factor would preclude that design

[Chris Hapstack]

Originally Posted by Boltman

Pretty sure the 20 second time factor would preclude that design

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.

[Boltman]

Originally Posted by Chris Hapstack

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.

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.

[cbale2000]

Originally Posted by Boltman

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.

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.

[fiona.crush1011]

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

[Rivet Man]

Originally Posted by Boltman

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.

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

[Chris Hapstack]

Originally Posted by Boltman

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.

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).

[Chris Hapstack]

Originally Posted by cbale2000

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.

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.

[Chris Hapstack]

Originally Posted by Rivet Man

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!

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.

[IronicDeadBird]

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.

[cbale2000]

Originally Posted by IronicDeadBird

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.

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