Pam,
One of the diagnostics for these gadgets when they aren't working perfectly is to turn OFF the filter while it's running. The moving water can offset and upset how the robot finds its way around the pool. They don't actually seem to have sensors in them--so my guess is that the controlling computer reads a change in power requirements from the motors (voltage/amperage draw changes) and figures it's run into something and then uses THAT as its senser information. Clever and logical!
Having had my Dolphin apart, and the Blue Diamond being more open inside, I see that the B/D has three drive motor each 3x the size of the ones in the Dolphin, yet it's a much lighter unit. So far, it's been much better for me.
Happily, my Dolphin is now my friend's Dolphin and it's working much better for him.
The Aquabots have a good rep, too.
Bookmarks