Say you have a copter that drops a substantial payload. How can one maintain adequate control after the payload drop without clipping the motor signal on the low end? Is the answer to slightly reduce max thrust-to-weight from like 2 to 1.75? Or is the only answer to increase the aircraft size/weight relative to payload?
or perhaps increase thruster ‘stiffness’ e.g. higher kv, higher pitch
how does that help with clipping on the minimum side, given that 0.15 for example is pretty low?
I wonder if something like ADRC (see ADRC: Active Disturbance Rejection Control by MichelleRos · Pull Request #20243 · ArduPilot/ardupilot · GitHub, GSOC 2022 - Custom Controller Implementation Update - Adding New Controller By Hand Coding, and https://github.com/ArduPilot/ardupilot/files/8202606/Jiachi_Zou_Thesis.2018.ADRC.UAV.Github.pdf) might be useful for this scenario.
Wow, I had never heard of ADRC, and it does look like it could help, by reducing undershoots. Looks like you can use ADRC by simply modifying the config parameters. I wonder why I havent seen this before? Have you had experience with this? Does it require exceptionally low noise?
Also its stated in the PR thread that PID + ESO might be better due to noise sensitivity
There is a 3-part series on YouTube:
Custom Controller #1
I have no experience with it. Just read about it a bit and remembered it when you talked about dropping payloads.
I would say you need to be able to test and tune without any payload at all.
Maybe if the copter is very overpowered, add a small permenant payload or go down a prop size.
What are your requirements and current design?
are you essentially suggesting reducing the max thrust / weight ratio?
I am currently building a scaled-up octo version of the following, but the relative weighting should remain the goal:
1.9kgf weight w/ payload
x-quad with 10"x4.5 rotors
0.85kgf weight w/o payload
it would be great to achieve the above without having to add ballast, just seems like a waste…
Quality of props will definitely help. Check Master Airscrew for example.
It’s going to depend a lot on your motors too. For example there can be a vast difference between motors that all have the same KV rating.
I’d say spend quite some time in ecalc to select components and see what happens when you add or subtract your payload.
In ecalc batteries are defined with a per cell weight, so if you weigh your existing battery, divide by the number of cells when you put its weight in ecalc.
It might be better to allow for a heavier base build (larger motors, battery) that will cope with your payload much easier. This will have other advantages too, like better resistance to disturbances (wind) and changing payloads , longer missions or being re-purposed.
But still it will come down to a flight test - test and tune with your minimal set up (no payload at all) and then assess what might happen with the payload.
Apart from motor outputs bottomming out (as you mentioned) and possible stability issues because of that, Arducopter copes very well with payload release.