Setting Throttle Mid (aka Hover Throttle)¶
Copter-3.4 (and higher) includes automatic learning of hover throttle which means manually setting the parameter is generally not required.
If you have a slightly overpowered or underpowered copter the throttle required to keep the vehicle in a stable hover may be under 40% or over 60%. Although this is fine while flying purely stabilize mode it can lead to a rough transition to autopilot modes (Alt Hold, Loiter) where having the throttle outside of the 40% ~ 60% deadzone will be interpreted as meaning you want the copter to climb or descend.
For this reason it is a good idea to adjust the Throttle Mid parameter (also known as THR_MID) so that your mid throttle while in stabilize mode is closer to 50%.
Please follow these instructions to adjust your manual throttle to so that your copter hovers at 50% throttle:
- Fly your copter in stabilize mode in a stable hover for at least 30 seconds
- Disconnect your LiPo battery and connect your APM/PX4 to the Mission Planner
- Go to the Terminal screen and download your latest dataflash log file (more details on working with dataflash logs can be found here)
- After the download has completed, close the “Log” window and push the “Log Browse” button and open the latest file in the log directory (it’s last digit will be the Log number you downloaded so in the example above we downloaded Log #1 so the filename will end in 1.log)
- When the Log Browser appears, scroll down until you find any CTUN message. Click on the row’s “ThrOut” column and push “Graph this data Left” button.
- While referring to the scale on the left of the graph, estimate
approximately what the throttle level was during the hover. In the
example above (which was an unnecessarily long flight) the mid
throttle appears to be about 550.
- Note: if the average throttle is below 300 (i.e. 30%) then you have a very overpowered copter and it would be best to add a some extra weight (i.e. a bigger battery perhaps) or reduce the power in some other way (smaller motors, move from a 4S to a 3S battery, etc)
- If the average throttle is above 700 (i.e. 70%) then you have a very underpowered copter. You should consider increasing the power of the motors and ESCs or use a higher voltage battery (i.e. switch from a 3S to a 4S battery).
Open the Mission Planner’s Software > Standard Params screen and update the Throttle Mid Position (THR_MID) to the value estimated above (you’ll find it near the bottom of the list)
Push the Write Params button
- On your next flight you should find the throttle is closer to mid while flying in stabilize mode
Automatic Learning of Hover Throttle¶
Copter-3.4 (and higher) includes automatic learning of mid throttle (aka “Hover Throttle”). The MOT_THST_HOVER value will slowly move towards the average motor output whenever the vehicle is holding a steady hover in non-manual flight modes (i.e. all modes except Stabilize and Acro).
If you wish to manually set the MOT_THST_HOVER value, it is best to download a dataflash log and set the value to what is seen in the CTUN.ThO field. The value should be between 0.2 and 0.8.
If for some reason you wish to disable learning, you can set the MOT_HOVER_LEARN parameter to 0.