I would like to get some opinions from more experienced drone enthusiasts.
I built my second Quadcopter like this:
ArduCopter 3.2.1 on MicroAPM 2.72
Turnigy Multistar 2216 800kV V2
12x4.5 Props
Micro U-blox Neo-6M GPS and Compass
Q-Brain 20A ESC
Plywood frame (10mm thick), MtM distance 42.5cm
I am having issues when descending in RTL and when switching to Loiter and hold position - I get strong oscillations. APM Log File Analiser complains about vibrations, and true enough, I get AccX and AccY values up to 5.
At first I had used a cheap frame I bought, made of carbon with plastic arms, but that was extremely wobbly and the copter was hardly able to take off and extremely unstable. Now with the plywood frame it flies well in Stabilize.
Now there is stiffness and vibrations, and I guess they are two different things - or not? Could I improve performance by making my frame more stiff? Or should I start adding foam, gel, and whatever to reduce the vibrations transmitted to the APM? Or both?
I would be immensely thankful if you could have a look at the log file attached and give me an idea what is amiss here. I am not sure what would be the next step. Am I wrong to try to use plywood altogether? On the other hand, there are toolbox-copters and cardboard-copters flying around - am I giving too much attention to the frame? I would like to get the basics right before tuning for a setup that is problematic from the beginning - or am I too perfectionist?
Replies
I Say YAY. Plywood is light and stiff.
Here is a great book on the subject:
https://books.google.ca/books/about/Low_pow/er_laminar_aircraft_str...
Plywood is in many cases better than composite (cheap/light/stiff/enviro-friendly/absorbs vibration and turns it into heat)
Plywood is better than aluminium too because it is more stiff and can be bonded without rivets.
At least that's whot the book says. - we have made 2 plywood and balsa designs. sandwich balsa or foam between thin light baltic fir ply and the structure is amazingly strong. the design was also very quiet.
Wow, thank you. Your response caught me with the aluminium bars in hand - and I decided to give plywood another try. I made a kind of Ecks-inspired frame and a test flight on a quiet day went well. With wind it is another story - I will have to retune PIDs.
Unfortunately the vibrations are still above the desired values. I might have to look at the dampening of the APM - I am using soft earplugs. Any ideas?
Today I changed the earplugs and tried to dampen with some foam from a gel/foam bike saddle cover - huge improvements. AccY and AccX are good now. I now realize that the earplugs, being made of some kind of memory foam, are certainly not the ideal material.
AccZ is still not good, between -2 AND -18. Not sure what to do about it.