Tuned and connected down estimator.

Change-Id: I2182af89a664a376103b49c54b96e0a2368ffb3c
diff --git a/frc971/control_loops/drivetrain/drivetrain.h b/frc971/control_loops/drivetrain/drivetrain.h
index a9541b7..69e9794 100644
--- a/frc971/control_loops/drivetrain/drivetrain.h
+++ b/frc971/control_loops/drivetrain/drivetrain.h
@@ -48,6 +48,9 @@
   PolyDrivetrain dt_openloop_;
   DrivetrainMotorsSS dt_closedloop_;
 
+  StateFeedbackLoop<2, 1, 1> down_estimator_;
+  Eigen::Matrix<double, 1, 1> down_U_;
+
   // Current gears for each drive side.
   Gear left_gear_;
   Gear right_gear_;