Enforce enough braking power when users set higher horizontal speeds

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -585,6 +585,11 @@ MulticopterPositionControl::parameters_update(bool force)
 		_params.hold_max_z = (v < 0.0f ? 0.0f : v);
 		param_get(_params_handles.acc_hor_max, &v);
 		_params.acc_hor_max = v;
+		/*
+		 * increase the maximum horizontal acceleration such that stopping
+		 * within 1 s from full speed is feasible
+		 */
+		_params.acc_hor_max = math::max(_params.vel_cruise(0), _params.acc_hor_max);
 		param_get(_params_handles.alt_mode, &v_i);
 		_params.alt_mode = v_i;
 

src/modules/mc_pos_control/mc_pos_control_params.c

@@ -456,7 +456,7 @@ PARAM_DEFINE_FLOAT(MPC_VELD_LP, 5.0f);
  * @decimal 2
  * @group Multicopter Position Control
  */
-PARAM_DEFINE_FLOAT(MPC_ACC_HOR_MAX, 10.0f);
+PARAM_DEFINE_FLOAT(MPC_ACC_HOR_MAX, 5.0f);
 
 /**
  * Altitude control mode, note mode 1 only tested with LPE