Arpa DeFault is Robot's and Gart's mother. She is a very popular figure with the social class. Her appearance is like Gart's but she has one wheel per side, hair buns, a necklace like Nessie's but it's longer, eyes that look like glasses, and she has (it's very simple) an A on her chest. There not much about her but here some things about her.
She was mentioned by Gart in Between Brothers and it reveals she likes Gart best. She appeared at the end of Grandma Day Off she was angry because she saw her mother endangered and she wanted to know who did it. Then Robot told her Gart did it then she felt excited. She told them Grandma had fun then she punished Robot for tattling.
In the other episode called The Party (which reveals she's an antagonist) she was sitting a chair with Gart and Grandma at Robot's invention and seeing the picture of Edsel Default (Robot's grandfather), Pattern (Edsel's son) and Bricklyn (Arpa's Husband) and it's unknown if Edsel married Grandma because Arpa and Bricklyn would be siblings. But anyways Arpa was sirpriced that Robot heard Gart mention their party. Then she invited Robot and threated him that she'll get rid of him if Robot misbehaved and embrassed her in front of Lady Madame. Then at the party Arpa's nephew she hated the most Gizmo came she got rid of both Robot and Crazy Cousin Gizmo.