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Turning the things that turn the FFU turned out to be harder than expected

Hello Everyone!


Marci here with some news from the workshop. We are working on two major parts of the free flying unit (FFU), the magnetometer boom assembly and the reaction wheels. The magnetometer boom is the primary experiment of the mission that will conduct our measurements near the apogee of the suborbital flight. We started manufacturing the tapesprings in small workshop outside of campus as we can't work with epoxy on the main KTH campus.


The tapesprings are made out of glass fibre. They are like the inverse of that metal, light reflecting thing people put on their ankles and wrist when they go running or biking in the night. The tapesprings, if you roll them up, will open up into a beam if their rolled up state is disturbed.


The other subsystem we are putting our blood, sweat and tears into lately is the mechanical part of the attitude control system of the FFU (ADCS). The reaction wheels are responsible for actually rotating the FFU, or more accurate to me, stop it from rotating and spinning around. They work on the principle of conservation of angular momentum. But what does that mean in English? It means that when the FFU is deployed from the REXUS rocket it will be spinning around and the reaction wheels are responsible to stabilize the FFU after ejection. We had some manufacturing pathfinders for the reaction wheels from Mans that we had to measure to check their concentricity and how smooth they run, or to be precise, their axial- and radial runout.


We found that the manufacturing process has to be improved. We manufactured a soft jaw to hold the workpieces concentrically in the lathe chuck.



The new reaction wheels have shiny brass surfaces all the way across them but it does not mean they are all good, after they receive their gears they will have to pass the same tests that the first batch went through. We will see how they perform. I really hope they do well because I like to avoid machining steel whenever I can. Some burn marks on my forearm are still fully visible since the last time I had to do it.


This is the measuring table where we will test the concentricity and alignment of the flywheels of the reaction wheels by measuring their radial- and axial runout. As the not here indicates the weekend-machinists’ expectations are usually shattered by the events that take place here.



There are currently 3 flywheels that are completely finished. These will serve as test units to see if the manufacturing process is accurate enough. A set of six flywheels are on the way of which three will be used for testing and the last three will be used for flight hardware (do not touch). The mirror finish one with some care can achieve on brass surfaces truly fascinates me. Every time my hand holding the polishing paper becomes visible in the part that becomes the mirror I can’t help but smile like a kindergartener on Christmas eve. Also I kind of want to wear one of these as a necklace on a centimeter thick golden chain at Lappis beach this summer.


Be safe out there dear reader, hopefully next time we can show you results from the gravity offloaded boom deployment test and 1 or even 3 axis ADCS tests.

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