Still some way to go to automatize ball valve opening and closing
As part of the Alpha rocket plumbing, a ball valve is used to set off the flow of oxidizer (in our case, nitrous oxide) and possibly to stop it, too.
The motor control alone worked as intended, as is shown in this video.
Once coupled with the ball valve however (video here), the torque it provided, even multiplied by 2 through the gear ratio, was not sufficient to rotate the ball valve mechanism. The ball valve itself is designed to withstand 300bars, a good security margin vs the 60-70bars pressure we plan in the oxidizer tank, yet it also requires a sizeable torque to rotate. With rudimentary tests, we had calculated the torque needed to rotate it to be 0.6Nm. As the Nema 17 stepper motor has a holding torque of 0.48Nm, we expected that with the multiple given by the gear it would be sufficient to activate the valve.
It does appear, as we were warned, that "holding torque" is not the same as the torque the motor can provide to actually move something.
So the next step here, rather than going for a bigger motor, is to go for bigger gears on the valve instead. The drawbacks of this is of course the size of the full system (but not much of an issue for a static ground test) as well as the time the motor will take to rotate the valve a quarter turn - we will have to see that through experimenting.
My next action that night was to saw the whipped cream siphon I purchased earlier this month to extract the small part that opens and discharges the whipped cream chargers that one can easily source (yes, you may have nitrous oxide in your kitchen without knowing it). A small test was performed to check that despite all the sawing and grating the part was not damaged - nice effect inside the video.
The plan is now to couple this part through plumbing to the empty paintball CO2 canister I have at the lab, and transfer the content of the now 49 chargers I have in the canister. Of course the resulting pressure will not be on par with the 72 bars in the chargers, but we hope to get to 40-50 bars, which should be enough to perform a small ignition and combustion test.
This will validate the later purchase of a professionnal nitrous oxide canister - 15L for about 650€, this is of course a purchase not to make lightly!