Enjoy these photos!
Enjoy these photos!
Hej! In the last week we worked a bit on the last composite shell we made.
First of all we removed, using a laser cutting machine, the extramaterial. Once this was done we were able to check if, with the last manufacturing technique, we were able to obtain a perfect hemisphere (sometimes fibers are not well aligned…and the result is that instead of a hemisphere you can have a hemi-egg…). Good for us the result is a nice hemisphere! =)
Secondly we cured completely the epoxy. This required other 16 hours in the oven (8 at 150°C and 8 at 215°C) but guarantees that the shells will keep 100% of their mechanical properties till 220°C. After the curing the color of the hemisphere change: from white to caramel!
Thirdly we did a vacuum test. The epoxy that we use is very stiff, but also brittle. We were afraid that, in vacuum, the tiny air bubbles trapped in the epoxy might have ruin our precious outer surface. So we took a small vacuum chamber and performed the test. The results is that after almost 3 minutes in the vacuum there were no deformation or cracks in the shell!
Here you can find some pics!
I have good news! Two weeks ago I told you that we were looking for some new reinforcement for the Upper Hemisphere (Link). Today we finally assembled the first of those reinforcements to one of the FFU and we tested the deployment system of the parachute. So far it is working very well and we are really happy about this!
Here you can find some CAD model of the reinforcement and some pictures that we took today while we were gluing the reinforcement and a metal ring to the Hemispheres.v
In the next days we will go through the design of the Ribs of the Upper Hemisphere. We want to redesign them since we have had couple of failures during the drop test.
The Ribs are the vertical supports attached to the Upper Hemisphere of the FFU.
The Ribs act as a lateral and rotational constrain and prevent any rotations or movements of the Upper Hemisphere with respect to the Internal Metal Ring. Thanks to the Ribs it is possible to screw together the Upper and the Lower Hemisphere. The Ribs are also crucial for what concern the Deployment System of the Parachute.
During the drop test we had two main problems concerning the Ribs.
First, all the failures have occurred because the Ribs were not well glued to the Hemisphere, this is due to the fact that they were made using PVC. Unfortunately it is not possible to glue properly PVC using Epoxy, and this led to the failures.
Second, since every Rib is glued by hand, the alignment between each Ribs and the Spikes of the Metal Ring were “adjusted” using sanding tools. This solution was good enough for the first prototypes tested in the drop test, but we have to find a better solution.
The new concept design will be based on the idea to add one ring, made by the same material of the sphere, at the border of the Upper Hemisphere. The Ring, that will have all the functions of the Ribs, must be designed in order to fit perfectly inside the hemisphere avoiding all eyebolts and screws.
Since the Ring will be made using the same material of the Hemisphere gluing it with Epoxy will not be as problematic as it was with the PVC. Moreover the ring will be cut using by laser cutting, so the positions of the holes will be precise and the holes will match perfectly with the Spikes.
Pictures of the new Ring will be published soon! Bye!!
Hej! As you might have noticed tomorrow we are going to perform the Drop tests using an inflatable balloon that will help us to drop for the FFU (Free Falling Unit) from approximatively 500 meters.
The two prototypes of FFU are almost ready. Let me introduce you the last components manufactured: the Battery Cage and the Thermal Cutter.
The Battery Cage as you can imagine is a simple cage that will keep the battery attached to to Bottom PCB.
The Thermal Cutter is a small device that will cut a small wire that will deploy the parachute.
Here you can see the Thermal Cutter in action, this was the very first test performed.
Here you can see other pictures of the components and how we manufactured them.
Hej everybody, last days were pretty exiting since a lot of stuff happened. The most important news is that the Metal Rings have arrived! Yes, after a lot of time spent in designing, reviewing, editing…re-designing, re-reviewing, re-editing and so on, we finally have the very first mechanical components of the FFU (Free Falling Unit).
We immediately assembled a set of rings with the components we have right now and then we tried to screw and unscrew the rings. All worked perfectly!!
The FFUs are moving from the sterile environment of CAD softwear to the living real world.