Character jumps out of a ramp instead of sliding down it

I'm attempting to simulate stairs by using ramps, and the character seems to go up them just fine, but there's a problem when it tries to come back down. Instead of sliding down when I input the direction, it just jumps out of the ramp using its speed (This is what it looks like).

Although I understand what's going on, I'm not exactly sure how to go about fixing it.

(My script is just basic movement by input and I've got a rigidbody attached.)

Thanks.