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• Water Bottle Rocketeer
• Posts: 7

Hi guys,

Great news Riaan! Its always great when things come together!

As I understand it, your system is going to be used to find the rocket - thats great. The system is periodic and coupled with the powerful transmitter is a good solution. Obviously finding the rocket is a key priority.

As I have said before, the AIM XTRA is in its final stages. The hardware will undergo one more revision, before going to market. The current prototype is working well, but there are some things which need to be changed to make it a commercial product.

So, the unit/s will hopefully be ready for the big day. So, Im glad there is another unit also going along.

So, while your system will help us find the rocket, the XTRA will provide streaming data to a base station allowing us to track it in realtime and monitor all sorts of other fun things, like burnout and deployment.

It would be awesome if we could have a big screen up at the event, allowing everyone to see the trajectory etc. after it has gone out of sight.

You mentioned velocity from Doppler: That wont be necessary as the GPS gives velocity. In addition there is the pressure sensor and a 100g accelerometer providing 2 extra ways to get velocity.

So, we are going to have so much sensor information we aren't going to know what to do with ourselves.

Lets just hope the rocket doesn't blow up!

..

My current progress:

Pressure - success
Altitude - success
GPS position/velocity - success
Vertical acceleration - success

.

Still to do (all previously tested, but now for integration in XTRA):

* Battery monitoring
* Storing data in Flash
* Transmission to ground
* Receiver
* PC software for data interpretation

Some important details:

The airframe being Aluminium is ok, but the electronics bay MUST be non-conductive. ie. fibreglass or something. The GPS antenna needs to see as much of the sky as possible. 4 Satellites need to be visible. The transmitter obviously needs to have an unobstructed path to the ground base station.

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• Water Bottle Rocketeer
• Posts: 7

DAVID
How much will one of your units cost me ,me and my brother wil be entering our own rocket (Aurora) for the 10k and we need a tracking system.

I have not yet giving pricing details officially, or in written form.
I guess now is a good a time as any!

The complete AIM XTRA system, including receiver and software:

USA retail pricing: ~ $ 480
RSA retail pricing: ~ R 2900

* These prices are rough estimates, and are dependent on demand and R/$ rate.

I know those are large sums of money, but its targeted at the US rocket market.
Equivalent inferior units with less features are going for over $800, so its actually a very competitive price.

You will notice that I have chosen to significantly reduce the RSA pricing. This is because local is lekker, and I want to support my fellow SA rocketeers.

Please give me a call to discuss with me further about organising a unit for the October launch.
If you are on a tight budget (im sure you are), we can talk about ideas of bringing the price down.

Cell: ____072_466_8590____

The number above will only be available as of Monday.

All the best for your 10Km entry!

-
David

[johanngr]

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Thanks David,

the doppler-effect-method mentioned by Riaan seems to be a good addition to the current array of systems.  I feel the more data we get from the rocket the better.  It will give us experience in using a system that will work in the vacuum of space.

Many people are not aware that you cannot use pressure sensors and accellerometers outside the atmosphere.  However, the DE-method can be used to Mars!

As far as the avionics bay, If it needs to be non-conductive and have a clear view of the sky, the nosecone is the only option I see.  The nosecone has a large volume and will be made of fibreglass.  The tip might be aluminium for aerodynamic heating effects.

Also, David you mentioned the price of the XTRA, are you sponsoring a unit for our project or do we have to buy it?  I need to confirm this so we know where we stand.

Thanks for the hard work by the Electronics Team for Arrow10!

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• Water Bottle Rocketeer
• Posts: 7

Also, David you mentioned the price of the XTRA, are you sponsoring a unit for our project or do we have to buy it?  I need to confirm this so we know where we stand.

Well, this is obviously a commercial product for me, and so I will gain greatly from having tested the unit with an actual 10km attempt. The data will also be very useful for further improvements.

Having said that, it is a large amount of money for me to invest in the project.
I would appreciate it if part of the cost could be paid for by another sponsor, so that the cost is shared to some degree.

But, I am committed whatever happens!

... The Doppler measurement:

You are correct - pressure sensors wont work outside of the atmosphere. Accelerometers have a better chance as they can integrate to get the velocity, although this is not very accurate.

I have limited time at the moment., but I will try look into a Doppler measurement device.

[johanngr]

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Thanks David, I'll see what we can do to accommodate you as with the other members.

As for the accelerometer.  When an object is in free-fall there is no up or down for any device that detects the change in position by comparing the unit's casing to the spring-loaded object inside.

That said - The moment an object leaves the atmosphere it is in free-fall.  Thus any such device cannot work in space.  For now though, it is perfect.

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• Water Bottle Rocketeer
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Thanks David, I'll see what we can do to accommodate you as with the other members.

As for the accelerometer.  When an object is in free-fall there is no up or down for any device that detects the change in position by comparing the unit's casing to the spring-loaded object inside.

That said - The moment an object leaves the atmosphere it is in free-fall.  Thus any such device cannot work in space.  For now though, it is perfect.

Thanks. I would really appreciate some financial support.

As for the accelerometer and space:

Yes, the accelerometer will measure 0 when in vacuum assuming its heading vertically upwards.
But, having measured the acceleration while under boost and in the atmosphere will allow you to determine a velocity. Once in vacuum, the only force acting on the rocket is gravity. If you then integrate all the know forces, you will know when your velocity reaches 0.

So, an accelerometer doesn't "work" in free-fall, but velocity can be inferred. Another problem with accelerometers is that you are assuming the rocket will reach a close to vertical apogee. While this may be the case in a vacuum, it certainly wont be in the atmosphere.

But, a DE approach will certainly be the best and most reliable in vacuum circumstances.

.

For the ejection system this time around, I recommend pressure coupled with acceleration.
The GPS too will give a VERY accurate velocity (+- 0.5 m/s) which we can use to determine apogee. The nice thing about GPS is that it wont give any false readings, and the error margins are known.

This will of course all be tested in the coming weeks.

-
David

[Rian]

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• Water Bottle Rocketeer
• Posts: 8

Hi David,
I am much exited about the AIM XTRA. I will start to save for it now
I can lay my hands on a directional receiver which we can use to locate the rocket for a backup. Will you be continuously transmitting? If so we can use the directional antenna with your system. What frequency are you using for the down link?
I found a very good article on Doppler tracking at http://www.arrl.org/ do a website search for Doppler Tracking and download the top result.
I also think the nosecone is the best place for the GPS antenna and also for the downlink antenna.

Groetnis Rian

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• Water Bottle Rocketeer
• Posts: 7

Hello everybody,

An update on the AIM XTRA:

The first launch of the AIM XTRA was on the 30th of July.

The launch was intended to test the following:

* GPS performance and lock times.
* Would the XTRA hold lock while accelerating?
* How it would perform in terms of re-acquiring lock if lost?
* Test 100g accelerometer (with filtering etc.).
* Test low data rate link telemetry with real-time GPS and accelerometer data.
* Test receiver.

Results:

First we waited for the XTRA to get GPS lock. Only a few minutes and we had 3 satellites.
This was all monitored through the radio link to a laptop.

We waited a few more minutes. More satellite were being locked onto.
Eventually we had seven. A very good number!

It was time to launch...

Everybody stood waiting for me to push the button... 5 4 3 2 1 ... Launch!
The rocket climbed vertically and out of sight. I was watching my laptop screen closely.

The data came in showing the telemetry was working well, and the GPS was maintaining lock!
Everything was being saved to file for later analysis, and only the lat/long displayed.

The rocket reached apogee and still everything was going well. An onboard AIM USB unit popped the drogue. Still good data was being received.

The rocket came down very close to us (40m) and it transmitted its position all the way to the ground!

What a resounding success!

I have done some analysis and have included it below as two image attachments:

This data was all obtained in real-time via a custom USB interface receiver.
Live Google Earth tracking has also been tested successfully.

9 units will be produced within the next 2/3 months.
1 unit (the prototype) will hopefully be used for the 10km project.

Im still hoping to get some sponsorship, as I cant afford to carry the cost on my own.

So, I guess its time to get this thing integrated into the launch vehicle...

Tests will be performed on range in the next few weeks. All expectations are that line-of-sight above ground will be over 20km.

Lets hope that's accurate!

[johanngr]

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Whoa David!  Way to go!

I want to do flight tests of all avionics by middle September.  Motor tests will be done this month.

Johann

[twostage]

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• Water Bottle Rocketeer
• Posts: 14

Well done David

The unit looks promising
I will have to get me one of those

the line of sight range looks good 20Km is quite far