# Control vehicle speed in Mission mode

Hi,

How can i change vehicle airspeed on demand during flight along the route in Mission mode?

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Use QGroundControl daily build

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git pullâ€™ed recently.

Iâ€™ve only found speed param in waypoint which can be set during creating route. I need to change speed during flight. Anyway it seems that vehicle ignores this value.

Also iâ€™ve found type of waypoint with MAV_CMD_DO_CHANGE_SPEED command and tried to use it. But there is absolute unclear set of parameters.

Mission Param #1 Speed type (0=Airspeed, 1=Ground Speed)
Mission Param #2 Speed (m/s, -1 indicates no change)
Mission Param #3 Throttle ( Percent, -1 indicates no change)
Mission Param #4 absolute or relative [0,1]

The first parameter is clear. Second and third are depressing me. In school i was taught that speed and throttle are linked. So more throttle as a rule means faster speed and otherwise. But how to use 2nd and 3rd parameters i absolutely canâ€™t understand. I think that you implemented something like cruize-control in automobiles, i.e. driver can set desired speed and autopilot should controls the throttle to keep vehicleâ€™s speed equal to required. But description of MAV_CMD_DO_CHANGE_SPEED shows that seems you did something different.

Another mysterious parameter is parameter 4 - absolute or relative. What absolute or relative? Speed? I donâ€™t know what terms do you use but in physics all speeds are relative because speed describes how position of object changes. And since coordinate system is relative so position is relative too and, as a result, speed is always relative. What do you mean under â€śabsoluteâ€ť speed isnâ€™t clear for me. I suppose that airspeed is vehicleâ€™s speed relatively to air and groundspeed is vehicleâ€™s speed relatively to ground.

Can anybody explain me distinctly how one can control vehicleâ€™s speed in Mission mode?

The question is relevant. Is it possible?

Canâ€™t be done through QGC. Youâ€™ll have to ask firmware folks whether it is possible to be done at all when a mission is reunning.

For a FW I was able to change the speed during a mission by modifying the FW_AIRSPD_TRIM parameter. I donâ€™t know if it is possible for a Multicopter.

Thanks! Which mavlink command is suitable for the FW_AIRSPD_TRIM parameter? MAV_CMD_DO_CHANGE_SPEED?

I modified the parameter directly with QGC. I donâ€™t really know how you would do that with mavlink commands.

To change FW_AIRSPD_TRIM and any other parameters need to send PARAM_SET message.

I would love to know the answer for his as well using Mulitrotor. We would like nudge the aircraft off the flight path during a mission as well as use the forward and backward control stick to increase and decrease speed of the MR during the mission. Any of the developers know if this is possible? We using the Cube FC.