- You may be looking for the robot knights from Sherwood Forest.
Irongron used the robot to attack Hal the archer, who had tried to infiltrate his castle. 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)