This blog covers the day to day progress of water rocket development by the Air Command Water Rockets team. It is also a facility for people to provide feedback and ask questions.

Monday, December 21, 2009

Acceleron V pressure switch

This weekend dad and I worked on the Acceleron V pressure switch. On Acceleron's last flight it did not look like the pressure switch(TDD2) worked properly, and the pressure switch(TDD) we were using before on the earlier Accelerons had been somewhat leaky.

The pressure switch is used by the primary flight computer to initiate the staging of the second stage when the booster stops producing thrust.

So we set out to try to make a more reliable one. (I think this is our 5th attempt at a simple and reliable pressure switch). In the photo below is the prototype. The hose clamps are only temporary for the first pressure tests. Also the cut off bottle neck at the end of the switch is only temporary to support the clamp.

We pressure tested the activation pressure and it was around 30 psi. That means that the switch will activate when pressure falls below 30 psi. This is a good value because the flight computer can delay the staging a little bit until the pressure is around zero.

We ran several low pressure cycles to test how well it activates. And the results were always repeatable. We are now gluing it together properly, removing the hose clamps, and when the glue has dried, we will test the switch to full operational pressure to make sure it can still hold up at the higher pressures.

I would also like to set up one of the booster segments on the thrust stand and simulate a launch with the correct amount of water and pressure. The segment will be fitted with the pressure switch so that we can see when the switch activates in relation to the thrust curve. This should allow us to then calibrate the small staging delay for the primary flight computer.

Once the pressure switch is fully tested, I'll do a full write up of how it works on the main website, but it is simple enough for most people to build.

Acceleron V has also been completely stripped down so we can start replacing the bottles with the new spliced pairs.

Deployment Mechanism development

We have also been working on a new deployment mechanism that uses in-line parachute deployment. The main criteria for this is to reduce the weight. Currently the standard nosecone and side-deployment mechanism we are using on a 90mm bottle weighs around 138 grams without the parachute, but it does include all the mechanical hardware, electronics and battery.

The new nosecone and deployment mechanism currently weigh 37 grams (including a servo motor) with the electronics and battery still to be added. The new electronics (FC V1.7) and battery will add about 20 more grams, so all together the entire nosecone should be around 60grams. The design also allows for potentially large parachutes and is also around 30% shorter than our existing designs.

When we've had a chance to test fly it a number of times, I'll again post full details.

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