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LaunchPad AlTImeter Technical Support Forum

Discussion about deployment systems including altimeters, timers, air speed flaps, servo systems, and chemical reactions.
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LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 » Sat Jun 28, 2014 11:07 pm

Hi everyone! We started this topic so that people could ask Technical Support Questions about the LaunchPad AlTImeter. Since this is a "Do It Yourself" project that you will assemble from the FREE plans and software available on our Website, we would like to keep the support questions in one place where everyone can read them. That way, if you have an issue that was handled before, it should turn up in a forum search and save you time and frustration.

Before posting a question here, please make sure it is not already discussed in the manual, which you can read on our home page: http://www.uswaterrockets.com/documents ... manual.htm

Thanks for your support!


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Re: LaunchPad AlTImeter Technical Support Forum

Post by Tim Chen » Sun Jun 29, 2014 11:16 pm

Wow, this is awesome!!! I am going to make this!! Thanks guys!!! You rock!


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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 » Sat Jul 05, 2014 10:34 pm

Tim Chen wrote:Wow, this is awesome!!! I am going to make this!! Thanks guys!!! You rock!
Thanks, Tim!


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Re: LaunchPad AlTImeter Technical Support Forum

Post by uberpixel » Mon Jul 07, 2014 12:44 am

This looks like a really cool project.

I was just getting ready to build a ServoChron but I may change direction and build this instead (already have the MSP430). The pressure sensor is a bit expensive with shipping but the added feature set certainly helps offset the price.

One question - how are you keeping your electronics dry? It looks like you have a wet test range and with the requirement for static pressure vent holes, it would seem that sealing your AlTImeter would be a no go. I'm thinking the servo arm could also be a point of water intrusion. I'd like to be able to launch over a lake for extra space but I'm concerned about ruining my electronics.

Any hints?

Thanks,
uberpixel



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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets » Mon Jul 07, 2014 11:48 am

You are correct that the inclusion of the static pressure vent holes and the servo hole are areas where the water can come in. What we have found is that when we make the rocket from soda bottles, the main pressure vessel is very buoyant and floats very much on top of the water. The water line is usually less than an inch from the lowest point submerged in the water.

With that in mind, if the electronics bay is connected to the top of the rocket, and it has holes in it that let the water in, because of the low water line you can be sure that only 1 inch or less depth of water will fill the electronics compartment. By mounting the electronics 1" or more away from the sides of the compartment, the water level never actually comes in contact with the electronics, as long as you are careful when recovering the rocket you allow the water to drain out and not slosh around inside the compartment.

Also, for what it is worth we can add that during testing we had some mishaps that resulted in the altimeter getting totally submerged. We used the trick often suggested for drying wet cellphones (place it in a bag of uncooked rice) to dry it out and it recovered just fine.

Of course, in some of our smaller diameter rockets, it is not possible to keep the electronics away from the water that comes in the holes, so we use baffles inside to prevent the water from coming in contact with the electronics. You can do something similar if you have concerns.

Good luck!



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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets » Tue Jul 08, 2014 9:01 pm

Hi everyone!

We've just released two videos showing the process of building and programming the software into the LaunchPad AlTImeter. Please take a couple of minutes to review these videos, as these should explain the entire process in enough detail that most questions are already answered in the videos. If you still have questions, you can ask them in this topic. We're here to help!

http://www.youtube.com/watch?v=lG6LBraU-Qk

http://www.youtube.com/watch?v=OrcEw346bdA



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Re: LaunchPad AlTImeter Technical Support Forum

Post by The Mooseheads » Tue Jul 08, 2014 10:01 pm

Nice and clear instructional videos! Great work, USWR!


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Re: LaunchPad AlTImeter Technical Support Forum

Post by uberpixel » Sat Jul 12, 2014 5:12 pm

I just received my pressure sensor from Sparkfun!!!

Just need a couple more parts and it will be time to get to work...

A couple of questions:

First, does the pressure sensor need to be present on the MSP430 Launchpad when the firmware is programmed into the chip? I have some mini Altimeter standalone plans in mind.

Second, any tips on where to find PET sheets big enough to create the payload cover? I'd rather not splice rockets together to make a big enough piece if I don't have too. Maybe another material would work?

-uberpixel



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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 » Sat Jul 12, 2014 10:08 pm

The Mooseheads wrote:Nice and clear instructional videos! Great work, USWR!
Thanks, Rick! When are you going to build it now?


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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 » Sat Jul 12, 2014 10:14 pm

uberpixel wrote:I just received my pressure sensor from Sparkfun!!!

Just need a couple more parts and it will be time to get to work...

A couple of questions:

First, does the pressure sensor need to be present on the MSP430 Launchpad when the firmware is programmed into the chip? I have some mini Altimeter standalone plans in mind.

Second, any tips on where to find PET sheets big enough to create the payload cover? I'd rather not splice rockets together to make a big enough piece if I don't have too. Maybe another material would work?

-uberpixel
No, you can program the chips at any time. You can program them on a regular unmodified LaunchPad if you like. It doesn't make any difference. Just know that without the sensor, the software really cannot do anything, so it will not begin to function until the sensor is present.

You can use any plastic you have available for the parachute cover. It shouldn't matter as long as it's flexible enough to wrap around the bottles. You can probably find sheets of plastic at a craft or hobby store, or use a plastic sign. Something like a thin plastic "No Trespassing" sign would work. It just won't be transparent. That shouldn't matter.


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Re: LaunchPad AlTImeter Technical Support Forum

Post by uberpixel » Wed Jul 16, 2014 3:14 am

Success!!!

I can report a successful build of the AlTImeter with servo deploy option.

I decided that instead of going the easy route, I'd build a standalone version that doesn't need an MSP430 launchpad (other than for programming). It would also allow me to fit the unit in the FTC rocket if I decide to give that type of rocket a try down the road. In the end it was definitely harder and more expensive than the stock build, but since when should that matter!

My fully optioned version came in at 27g including buzzer, pressure sensor, LED's, switches, battery and servo. Additionally, the board including pressure sensor fits inside a 3/4" x 7/8" x 1 5/8" rectangular prism. Even though it is stacked on top of the MSP430 IC, the pressure sensor can be easily removed to allow access to the MSP430 IC for future program updates (if necessary).
140715_233721_s.jpg
140715_234448_s.jpg
I can share my parts list, board layout, and build pictures if anyone is interested. Let me know if this should go in a separate thread or if I can include it here.

Can't wait to stuff it in a rocket this weekend and see how it really works!

Thanks for creating this fun project and sharing the plans and firmware, although my wife is less thrilled...

-uberpixel
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Re: LaunchPad AlTImeter Technical Support Forum

Post by Jamie5335 » Wed Jul 16, 2014 4:12 am

Hello uberpixel,

Wow, thats a nifty little altimeter you have built yourself there- nice work! I presume you are using the same PIC as used on the MS340 Launchpad?? Are you using USWaterRockets's firmware??

I know that It feels great to make your own PCB layout and hats of to you there!!

Jamie B


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Re: LaunchPad AlTImeter Technical Support Forum

Post by uberpixel » Wed Jul 16, 2014 10:23 am

Jamie5335 wrote:Hello uberpixel,

Wow, thats a nifty little altimeter you have built yourself there- nice work! I presume you are using the same PIC as used on the MS340 Launchpad?? Are you using USWaterRockets's firmware??

I know that It feels great to make your own PCB layout and hats of to you there!!

Jamie B
Thanks!

Yes, this uses the stock USWaterRockets firmware and the same IC from the MSP430 Launchpad. For all intents and purposes it is identical to the stock design.

All I've done is layout a compact/standalone configuration for the circuit that doesn't require the entire Launchpad board. It's built on a cut-down (off the shelf) pre-drilled IC board from Radio Shack and a handful of parts from Digi-key. I used some creative sharing of traces and hookup wires to make the connections. I'm sure it could be done smaller and more efficiently on a custom PCB but I don't have the skills for that.

-uberpixel



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Re: LaunchPad AlTImeter Technical Support Forum

Post by uberpixel » Fri Jul 18, 2014 2:33 am

More success!!!

Tonight I successfully launched and retrieved my mini version of the USWR AlTImeter on top of a 2 chamber 2 liter using the USWR radial parachute design.

The AlTImeter properly detected apogee and activated the servo to initiate the parachute release.

It sure is fun seeing the parachute come out and fill with air...

I can report a problem however. Several times while pressurizing the rocket, the altimeter falsely detected launch and would deploy the parachute. There was a bit of a cross-wind, but not more than 10mph - I'm wondering if it caused a pressure fluctuation in the payload section. I have two holes in the payload section, one 3/8" hole for the rubber band and one 1/4" inch hole for static pressure. Is this a problematic configuration? It's somewhat embarrassing to have a crowd of curious onlookers watch as the rubber band slowly unwinds as the parachute plops onto the ground. Not to mention unnerving as you try to re-load the parachute on a pressurized rocket... Eventually I would just get the rocket pressure about half way before arming the altimeter. Not the greatest safety margin.

Also, I have a feature request. Would it be possible to create a parachute deploy test mode? It would be nice to initiate a 30 second delay and then have the servo actuate in order to test the release mechanism. As it stands the only way I could do this was to blow on the sensor to trick it into thinking it had launched.

There was one other problem. I think the accuracy of the altimeter must be off. It reported that my highest flight was 252 feet, but I'm pretty sure my last flight topped out at 2045 feet. Razz:

All in all, I can't be happier with this project. And would like to again say thank you to USWR for their efforts in developing this project.

-uberpixel



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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets2 » Fri Jul 18, 2014 10:26 am

Hi Uberpixel,

It is great to hear that you are enjoying success with our little project. It is nice to hear from 3rd party people who are adapting the design and making it their own personal modification.

Regarding your experience with unintended deploy, there are a great many factors which can cause this. You have speculated that wind gusts can cause this, and you are correct that this can be the problem. We made a lot of test flights and experimented with multiple ground tests in various wind conditions to try and come up with an algorithm to detect launch that was immune to wind gusts yet sensitive enough to detect a slowly accelerating rocket like a small nozzle rocket that uses foam for the reaction mass. We think we have come up with a good compromise that works well under all conditions, but being a compromise it may not be the best at all situations when compared to a single purpose design.

To reduce the wind effect on any rocket means that the recommendations for the pressure port sizes and locations detailed in the manual are very critical to the performance. If you ignore the recommendations, it will increase the chances that there will be unintended deploys and/or error in the apogee readout value. So, the size and location of the holes leading into the chamber housing the altimeter should be as carefully designed as you can make them.

There are a couple of other factors that can cause a deploy while on the launcher:
1) Light striking the pressure sensor. Believe it or not, the sensor is so sensitive that it can detect the pressure of light hitting it. If the sensor is exposed to sunlight or strong reflections, it could detect a false launch.
2) Swelling rocket effect: Water rockets tend to swell up when the air is being filled into them, and this expansion can create pressure changes inside the payload compartment. Rapidly filling a rocket from a tank is most likely to cause a false pressure fluctuation, so be careful how fast you fill the rocket.
3) Pressure leaks in the water rocket: We've seen where a leaky joint or a loose bottle cap or tornado tube seal will let air escape from the bottles and into the altimeter compartment and these fluctuations can cause a false launch detection. You need to be aware that this can also be a contributing factor.

We will look into adding a deploy test mode in the future releases. Thanks for the suggestion!



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