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Live Gimbal Test 4

A project log for Project Rockoon

Actively stabilized model rocket by means of a motor gimbal, originally designed for launching a rocket from a high-altitude weather balloon

Julian CostasJulian Costas 08/24/2016 at 16:121 Comment

Today I conducted a test of the gimbal from a launch rod using extra long tethers. I was hoping that the launch rod would keep it straight during the initial thrust spike, and that the gimbal would take over from there. At the moment, there is no recovery method, or even a nose cone for that matter, so the tethers will keep the rocket from being destroyed.

Over the past week I've made some notable improvements. I've realized that the small differences in the tolerances of the solenoids meant that the engine was not being angled equally in all directions. I really wanted to calibrate the position of each solenoid with some sort of adjustment screw, but with a mechanism/rocket this small, there's really very little space for something like that. I ended up making a plate the sits behind the solenoids that has small elevated ridges for each solenoid to sit on. The ridges for each solenoid can be individually filed down so that the right height can be achieved. It only took about half an hour to calibrate this piece so that solenoids sat in the right position. I'm thinking that I could make a few of these plates to test different angles of deflection.

The code has remained unchanged for this test, but the test itself was changed quite a bit. I put a launch lug on the COM harness, and launched the rocket from a 3/16" x 3' steel rod mounted on top of a garbage can. I positioned tethers roughly 4 feet out and 8 feet up (from the ground). One tether was attached to the top of a ladder, and the other was wrapped around the trunk of a tree. The plan was to pull out the trash can with a rope when the rocket left the launch rod, so that as the rocket swung back down, it wouldn't hit the launch rod or the ground. If the gimbal sent the rocket in a wild trajectory, it would still come out unscathed.

Here's a clip of the test:

Overall, I couldn't be happier with this test. It looks like the rocket started tumbling when the tethers tensed up at the end. I had some bungee cords inline, so I was hoping to minimize this, but I guess it still imparted quite a bit of shock. Regardless, Everything before that went well. In the video, you can even see the gimbal making small corrections. Super cool to watch!

This test was done with a tiny C motor, so the next step will be to do some static engine tests with an E motor, and start working on developing a recovery mechanism. After that, a test will be done with an untethered rocket with fins, with subsequent tests using smaller and smaller fins. In order to go totally finless, I will either have to make or buy a motor with a thrust profile that would produce a small amount of thrust for stabilization through the coast phase.

Discussions

Mike Maluk wrote 08/26/2016 at 08:27 point

That looks fantastic, looks like it's doing it's job really well!

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