I am trying out different DIY, cheap approaches to be used as alternatives to expensive carbon plates. When you need strong, rigid plates that are light enough for a Quad, you're stuck with either fiberglass which is not so light and has the unconvenience of being not so rigid (except in higher thickness wich is than even heavier), either with carbon plates that have other disadvantages : price, it is a conductor material and therefore gets in the path of radio waves. They are also difficicult to shape, cut and drill (plus their dust is toxic).
Therefore, I was wondering how we could find alternate materials, which would replace the above described GF/CF plates by having a good compromise on these criteria : to remain light, strong and rigid, to be cheap, to be able to home build them with basis off-the-shelve components, to not interfere as much with radio waves as full carbon plates.
I experimented previously succesfuly with a DIY plate, baptised Hugues'plate in the following excellent post of Frantz :
The result was this:
In this first version I used two thin balsa plates, with in the middle a sandwich of epoxy, and a cotton fabric (cotton provides very strong fibers in all directions, therefore reinforcing the linear fiber pattern of balsa wood). It gave pretty good results.
However the fact of having the external sides of the plate as balsa wood was not a good idea, because we all know in the boom theory and practice that the most external layers of a boom support the tension of the load. Therefore to obtain a more rigid plate, you need the most external layers of the plate to be stiffer and stronger than the inner core.
Solution is easy : reverse the sandwich.
This is what I tried herebelow but experimening other materials. I used still a 1.5mm balsa plate as the inner core. Then on both sides I applied first some UHU epoxy:
This is slow cure epoxy. Very messy but very strong. Even stronger when you heat it up during the drying phase. What is also a good trick to apply such epoxy in thin layers on a plate : mix well the two components in a heat resistant cup. Then take the air dryer of your wife (I already took her cotton fabric so she's getting used to my experiments) and blow hot air on the mix. You will get a very liquid exposy that you can apply with a paint brush quite easily on large surfaces.
Secondly, I applied kind of pultruded carbon "fabric", it is less than one mm thick and comes in rolls covered by a plastic sheet, very convenient to apply in laminated construction, without the epoxy coming through on your fingers:
The result is a balsa plate covered with this carbon laminated thing. Problem is that these are fibers aligned in one direction and it is very brittle if you flex it perpendicular to the fiber's direction.
Therefore I applied a second layer of a kind of very light cotton fabric that we call here "Japan paper"; it looks like this:
As I did not have anymore epoxy, I reverted as a second choice to wood glue to apply this fabric. I used that one:
I like this wood gllue because it is very fast set and quite strong. Much more than the usual white wood glue.
The plate was then put under pressure for a night.
The final result looks like this (close up of the sandwich):
Now some numbers:
Dimensions are : 2,9mm thick - 13 cm by 14,5 cm.
Mass is 26 grams.
Volumetric mass (Density) is thus : 0,47 grams per cubic centimeter.
Rigidity is excellent and I will use it as an attachment plate between my X8 and my brushless gimbal.