sounds like you had low batteries...I suggest using reciever hump packs...less likely to jar the battery loose then running AA's...a failsafe dosnt kill then engine...it locks up your brakes when either you run out of range or you have low battery....it however does not activate your brakes if you loose battery power to the reciever (battery jumps out of the holder)....if you are using AA's in the reciever I would wrap a rubber band around them