Chaos 2 (series 3, heat E, final vs. The Big Cheese - The Big Cheese almost self righted itself in the same fight but the engine powering the hydraulics was down to half throttle so the arm didn't have she speed)
Mortis (series 3, heat F, first round vs. Ming)
(X-Terminator in series 3, heat K, final vs. Panic Attack doesn't count in my opinion since if I recall correctly PA was already lifting and driving forward with enough force to cause the robot to roll over and back onto its wheels.Your mileage may vary of course )
Prizephita (series 3, heat N, first round vs. Thing II - in the interests of being an incredibly sad git and winning the qu...um...not that...accuracy and a strong sense of fair play, I found the episode in the annals of YouTube - at half past two in the morning - and confirmed that Prizephita's boxing glove srimech did indeed see use once or twice before getting wedged in the side rail)

There is a grey area with robots like Stinger, Armour Geddon and Pussycat that have no real 'right' or 'wrong' way up and so could be seen as self righting before, but I've assumed those don't count?