Challenger is around 65 lbs if I'm not mistaken. I pick it up and go up stairs without too much trouble. Not as easily as 10 years ago, but not bad. I don't know about the orbot but without the spray tank I wouldn't think it's much different. Challenger has a 3/8 inch steel motor base which I think is heavier than orbot but the motors are probably about the same weight.
Orbot is probably a bit more awkward to pick up and carry, but has those 10 inch wheels.
Orbot is probably a bit more awkward to pick up and carry, but has those 10 inch wheels.