Designing an electrical-mechanical interface

In my previous blogpost I briefly touched upon the electronics that are in the works for our next flagship rocket Stratos III. Stratos III will feature multiple electronic systems made by the electronics department, but of course oftentimes multiple departments work together to design, realize and test a subsystem.

So aside from pure electronics topics, like printed circuit board (PCB) design, we are also involved in the design of things like physical mounting structures for antennas or our own PCBs. In this blog I will talk about one of such mounting structures that I have been working on, together with another member of the electronics team: the bleed valve controller mount.

To give some context, Stratos III will have a large tank (30 cm diameter, 4.7 m length!) to hold the oxidiser, which is nitrous oxide in our case. During filling of this tank with nitrous oxide, we need to have the capability of “bleeding”: that is, releasing gaseous nitrous oxide to make space for the liquid nitrous oxide to take in more volume of the tank. And when things go wrong, the bleeding process should slowly release the gas over time.

For this reason, Stratos III has a solenoid bleed valve. When the valve is powered, a magnetic field is generated that closes the pathway for gas to bleed. This behavior is known as normally-open, since the pathway will remain open when there’s no power. For controlling and powering the valve we decided that we needed a control PCB and a separate battery. We luckily didn’t have to start from scratch: the valve was readily chosen and someone else already had a PCB design.

However, the mounting of the valve, PCB and battery were still undefined! We also wanted to have a larger area for the PCB so that we could add functionalities. So, we remeasured the valve and discussed on the allocated space in the rocket that we are allowed to use. From this moment on we started with 3d modelling the mounting in CATIA. CATIA is 3d modelling software like Solidworks, something you normally do not do use during your BSc EE – it was quite tough to get acquainted with using this software.

Catia model.

We started out by building a fitting case around the valve 3d model. Attached to this case, we modelled a baseplate to be able to mount the structure to the rocket inside. Finally, we created some “columns” to hold the pcb itself and a pocket for the battery. All-in-all we ended up with a complex design, that we 3d printed to check its feasibility! We can now continue with a second iteration and pcb design.

3D printed part.