Advanced Grabbing Unit: What am I doing wrong?

[AmoebaMan]

Before I start, let me say that I'm a noob. I picked up this game a few days ago. Best practice is not something I'm currently concerned about.

I recently sent out my first manned mission to the Mun's surface. I've sent orbiters to both the Mun and Minmus previously, and returned them safely, but I'd been wary about actual landing missions until now, out of fear that I wouldn't be able to pack enough fuel to bring my Kerbals home. Today, however, all that potential Science became too damn tempting (I'm playing science mode), so I put together my biggest rocket yet and launched it into the sky.

And, of course, didn't have enough fuel to bring my Kerbal and all his research back home.

Not entirely, at least. I came close. Right now he's in a pretty slick orbit just about 1,700km above Kerbin, just chillin' with all that research. I probably wasted more fuel than I needed to on the approach and landing, but the fact of the matter is that right now he's stranded up there, just a few seconds of fuel short of a happy reunion with terra firma. I don't want to waste Science by transmitting his research, and I also don't want to leave him up there because space is lonely. So I mounted an operation to return him home.

Which, of course, was complicated by the fact that his lander wasn't designed for this kind of operation. It's got no docking ports (I don't actually even have them unlocked). All I've got to work with is the Advanced Grabbing Unit, which I barely had enough Science to buy after a few pointless ground excursions on Kerbin sampling biomes and such.

"Whatever," I thought, "I can make this work. Send up a rocket with plenty of spare fuel, grab it with a Klaw, push it out of orbit, and let it fall to the ground." I even made sure the booster/rescue rocket was unmanned so I could safely ditch it if necessary.

So I sent up the rescue rocket. Blue skies. Beautiful trajectories. Everything went perfectly. I intercepted the stranded lander within 300 meters. Lined up with the RCS thrusters, deployed the claw, drifted slowly towards my target, and...

...bounced off.

Huh? I did this in the asteroid retrieval tutorial, it should be...grabbing? Nope. Maybe too fast? No, to crooked? Wrong again.

I've been bumping at this Munar lander for the past half hour with this gorram Klaw trying to get it to latch on. The wiki page says I should only have to make contact. It ain't working.

Can somebody help me out? I've got plenty of liquid fuel, plenty of RCS, and way more electricity than I need. I've got no clue what's wrong here, and I'd really like to get this buddy home. Or his research, at least...

ANSWERED: Apparently the Klaw can't grab things if it's approaching too slowly. I retried with an approach velocity of ~1.0-1.5m/s (as opposed to <0.5m/s previously) and it worked perfectly.

Edited February 13, 2015 by AmoebaMan

[AlexinTokyo]

Did you 'arm' the claw through its right-click menu?

[SaturnV]

It should work, you can confirm that on ground. As for your case, I suppose you just do another slower catch?

[Starwhip]

Sounds like either a bug or you didn't arm it.

Does it look like a claw or a rounded fuel tank?

[AmoebaMan]

Did you 'arm' the claw through its right-click menu?

Sounds like either a bug or you didn't arm it.

Does it look like a claw or a rounded fuel tank?

It's definitely armed. Visibly looks like a claw once the canister opens.

It should work, you can confirm that on ground. As for your case, I suppose you just do another slower catch?

I'm approaching at less than a tenth of a meter per second using RCS thrusters. I don't think it's physically possible for me to come on any slower.

[AlexinTokyo]

Thinking about it, I remember seeing somewhere that there was a minimum speed below which the klaw wouldn't grab (although I can't recall ever having experienced this myself). Perhaps try a slightly faster approach, rather than a slower one, and see if that helps?

[archnem]

I'm approaching at less than a tenth of a meter per second using RCS thrusters. I don't think it's physically possible for me to come on any slower.

This might actually be your problem. With the klaw, I've found that a faster approach is better (at least personally). I usually come in at 1-1.5 m/s.

[AmoebaMan]

This might actually be your problem. With the klaw, I've found that a faster approach is better (at least personally). I usually come in at 1-1.5 m/s.

Damned if that makes any sense to me, but it worked. Came on approach at exactly 1.0m/s and it hitched on the first try!

[Sidereus]

Damned if that makes any sense to me, but it worked. Came on approach at exactly 1.0m/s and it hitched on the first try!

Eh, it makes a bit of sense. If pressure is what triggers the claw to close, then you need to have enough force to trip it. So going too slow wouldn't work.

[Vectura]

Think of it like this: the claw arms have to puncture into whatever they are grabbing, and they need some speed to do this (forgetting the fact that would be rather damaging irl)