If you keep the mass of the ram and spike down and move it very fast (low moving mass + high flow rate) then you have a chance of stabbing through something.

As mass of the spike is <<< robot mass then they shouldn't get flung apart as much but still pack a punch due to having a lot of momentum. High velocity should also reduce the time the impulse acts making for lots of force. You could try recessing the spike into your robot so it has ample time to accelerate before hitting anything.