robot stops when in vertical position.

by steven
(belgium)

When I put the robot in the water, it is working fine on flat level. When it hits the wall, goes to vertical position, wheels keep on turning a little while and then it completely stops. Is there any sensor for understanding of position of the robot? If so, what is it and could this be the broken part. If so, is it normal for the machine to go in 'shutdown'? Robot is about 10 years old. Never have had any issues since this. Thanks for your reply in advance. Steven