Turns out that the Arducopter library for quadcopter operation doesn't translate to rockets that well or at least not as easy as I thought. So almost full April was spent on getting this running and have at least basic position control working. There is still much left to do, but I don't want to spend another month on this area right now. It's time to make some more visible progress also in other areas. After all, it will take some time until SpaceX are going to try their first catch attempt. We can wait until then to further improve landing.
Anyway, total for this month was 325 bucks - new best month again!
There has been just one new builder, which is anonymous for the time being.
I didn't invest into anything, apart from the usual Patreon subscriptions to modelers and info people, as I just worked on the controller most of the time.
Thank you all very much for the support! :)