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Date:  27th March 2011 4:20pm - 5:20pm
Location: Denzil Joyce Oval, NSW, Australia
Conditions:  Breezy and overcast. Temp ~20C
Team Members at Event: PK, Paul K, Jordan K and GK

Servo Timer II

After a couple of weeks waiting for the weather to clear up, we took the Servo Timer II out for a spin this weekend. We want to trial the timer under various flight conditions and on board several different rockets before we get the PCB boards made up. This first set of tests was designed for small rockets with lower pressures using small nozzles.

We've also been tweaking the firmware to filter the G-switch to help prevent false triggers and adding another trigger mode that allows for manual arming.

We fitted the servo timer to a new nosecone and hooked up a couple of the small 70mAh LiPo cells for power. The whole nosecone now weighs 86 grams compared to the 154 grams of the previous version. This represents about a 45% weight reduction. 

New Ejection Plate

One of the biggest problems with the side deploy mechanisms we use has been the reliance on rubber bands to eject the parachute. Because they stay somewhat stretched even with no parachute in the bay, they end up deteriorating over time. After 2 weeks they have to be replaced because they loose their elasticity and break. The rubber bands also don't provide a lot of ejection force.

So for the Servo Timer II tests we replaced the rubber bands and ejection plate with a bent piece of PET bottle.

The attachment method is designed so that once the parachute is in the bay, it does not require a lot of force to hold it in. But when the parachute starts ejecting, the force is magnified and the parachute is really kicked out. This concept is similar to the compound bow in that it doesn't take a lot of force to keep it pulled back, but provides lots of force for the arrow once released.

The ejection plate is attached further back from the edges to allow it to bend easier. Other than the ejection plate itself, all other components of the deploy mechanism remain the same.

Building up inventory

We have also been processing quite a few bottles from our bottle collection. We are trying to build up our inventory of spare parts so that we can concentrate on flying rockets and experiments this year without having to go and do repairs between launches. About 72 bottles were cleaned, trimmed, sanded and some glued to make up 10 x 110mm spliced quads and 11 x 90mm spliced quads. This is the first time we have tried making the 90mm versions. The capacity of one 90mm quad is 3.12L. These will be reinforced with fiberglass.

We also made a couple more 9mm nozzles, 3 more 90mm nosecones with deployment mechanisms, and a number of fairings.

I've also bought another uMAD from Whooshtronics to serve as a backup deployment mechanism on some upcoming projects.

Launch Day Report

We went down to the local park on Sunday afternoon to do the test flights, but when we got there, there were a couple of football games happening. I mean who plays organized sport on Sunday afternoon? So we shifted operations to the neighbouring field, but because it's quite small and there was a cross-breeze we had to limit the pressures to 100psi to keep the rockets in the park.

We flew 3 different rockets over 7 flights at 100 psi using a 9mm nozzle. 2 of the flights used the uMAD to trigger the deployment at apogee. This way we managed to fly all 3 servo timer prototypes at least a couple of times. One of the timers used 2 x LiPo cells while the others used a 9V battery.

All seven flights went great and parachutes deployed when they were supposed to. All rockets landed without damage. The timer also didn't trigger when the rocket popped up in the launcher while pressurising. This is what the launch detect filter was designed to filter out. Pressurising vibration also wasn't an issue. I will probably go back and add the filter to the firmware for FC V1.6. The new ejection plate also worked well on all it's flights.

The next set of tests will focus on medium sized rockets and foam launches where we get slow acceleration. We'll also do some high-G flights to see how the timers behave. We would like to do another 10 to 15 flights to see if any issues come up.

Here is a highlights video from the launch day:

Day 102 - Highlights

Servo Timer II Operation

Flight Details