Pseudo-platform movements — ladder movement

I’m working on a weird little game for a game jam (so this is pretty urgent!) Basically I need a character to move as if in a platform game, but controlled by the programming instead of the player.
After a day struggling with the non-physics movements, I’ve switched to physics because that’s the only way I can figure out how to make the character fall. I don’t understand the physics elements very well at all, but so far I’ve got the character walking nicely along platforms, falling when there’s no platform, and being flung appropriately by the spring. The walking is done very simply with Physics Bouncing Ball movement (progressing in a straight line with no bouncing).
What I can’t manage is getting him to stop when he collides with a ladder, and then climb up it. The program doesn’t seem to recognise any collision with the ladder at all.
I’ve also tried using a Physics Rope/Chain object instead of a ladder (in hopes that the physics character might interact better with another physics object), but again there doesn’t seem to be any collision detection with the rope.
Any help would be very helpful! If I can’t get some kind of climbing into the game, I’ll have to abandon the project.