- You may be looking for the robot knights from Sherwood Forest.
Irongron used the robot to attack Hal the archer, who had become a prisoner during a failed assassination attempt on Irongron. However, the Third Doctor used a crossbow to shoot the control box from Irongron's hand. This caused the robot to go on a rampage.
Later, the Doctor masqueraded as a robot knight in order to gain access to the castle. Irongron requested the robot knight to fight him, so the Doctor was forced to take part in a sword battle with Irongron to uphold the disguise. The Doctor won, but Irongron discovered it was him. (TV: The Time Warrior)