LaunchPad AlTImeter Technical Support Forum

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

Post by uberpixel »

U.S. Water Rockets2 wrote: 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.
Thanks for the feedback. I think I will need to rebuild my payload section with a circular bulkhead that isolates the servo side with its large (3/8") rubber band pass through hole from the altimeter side. I see that as a necessary step to more carefully control the pressure port geometry. My current design has a rectangular, longitudinally-oriented piece of Coroplast that does not isolate the servo hole from the altimeter...

I plan on doing a few more launches tonight with my current design, so we'll see how it goes.

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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 »

uberpixel wrote: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).

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


That's a nicely made modification. It looks like you got the size way down. We have also done some work on a smaller version that is custom made for FTC rockets. Have a look at one of the prototypes.
FTC AlTImeter
FTC AlTImeter
ftc2.jpg (227.11 KiB) Viewed 41 times
Testing FTC AlTImeter
Testing FTC AlTImeter
ftc3.jpg (82.03 KiB) Viewed 41 times
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Re: LaunchPad AlTImeter Technical Support Forum

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U.S. Water Rockets1 wrote:We have also done some work on a smaller version that is custom made for FTC rockets. Have a look at one of the prototypes.
Wow. That looks very professional compared to my garage hack job...

-uberpixel
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Re: LaunchPad AlTImeter Technical Support Forum

Post by uberpixel »

So, I had a bit of a mishap on Friday that resulted in an unfortunate lawn-dart landing which subsequently destroyed my payload section. I won't go into details, but it was not an altimeter failure that resulted in the crash... :oops:

So I rebuilt the payload yesterday (for radial deploy) with the hopes of providing better static pressure ports and also making it idiot proof (ouch) so I don't have another lawn dart landing.

Question is, with the size of the payload, are my four 1.5mm diameter holes going to be appropriate for the altimeter? I had much larger holes with my first version which worked successfully (but with some false triggers as mentioned earlier). It's a bit challenging when the only way to test the system is to launch it - unless anyone has any alternative ideas. Also, I haven't sealed the coroplast bulkhead to the side of the bottle that separates the chambers. Is this necessary? I'd like to leave it unsealed so it can be easily disassembled if necessary to access the servo. I got lucky and found 2 different sizes of bottle diameters that sleeve over each other perfectly. I just need to figure out which bottle came from which store/brand...

Here are some pictures of my new payload section:
New Payload
New Payload
140720_083514.jpg (92.92 KiB) Viewed 39 times
Separated into two halves:
2 pieces
2 pieces
140720_083557.jpg (102.48 KiB) Viewed 39 times
Closeup of the 1.5mm pressure ports (4 in total):
pressure ports
pressure ports
140720_083319.jpg (97.22 KiB) Viewed 39 times
General component layout:
layout
layout
140720_083329.jpg (95.67 KiB) Viewed 39 times
Servo cord passthrough:
servo passthrough
servo passthrough
140720_083423.jpg (65.99 KiB) Viewed 39 times
Ping-pong ball nose-cone for easy pull apart of halves:
nosecone
nosecone
140720_083357.jpg (57.22 KiB) Viewed 39 times
Will this work?

Thanks,
-uberpixel
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Re: LaunchPad AlTImeter Technical Support Forum

Post by Blenderite »

Would adding more holes in the parachute cone allow the pressure to equalize faster, making it not be set off by wind or slight leaks into the bay?

You could try putting the device into one of those 10mm film canisters, assuming they are big enough.
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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 »

uberpixel wrote:
U.S. Water Rockets1 wrote:We have also done some work on a smaller version that is custom made for FTC rockets. Have a look at one of the prototypes.
Wow. That looks very professional compared to my garage hack job...

-uberpixel
Your design is the kind of thing that everyone can make themselves. It is great in that it doesn't require special skills to make. You did a great job with it.
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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 »

DogLover wrote:Would adding more holes in the parachute cone allow the pressure to equalize faster, making it not be set off by wind or slight leaks into the bay?

You could try putting the device into one of those 10mm film canisters, assuming they are big enough.
There are a lot of very carefully tested experiments that people have done to determine the correct number of holes and the hole size/area. We took a good consensus from many sources to come up with the recommendations in our user manual. You really cannot just add lots of big holes to compensate. too much vent hole is just as bad as too little.
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Re: LaunchPad AlTImeter Technical Support Forum

Post by uberpixel »

uberpixel wrote: Will this work?
I wanted to provide an update that I had several successful deployments this weekend with my updated payload design.

It was very sunny however, and I did encounter the sunlight related false trigger several times. After putting a sunshade over the pressure sensor, everything worked perfectly!

This is just further confirmation that if you follow (all of) the instructions provided by USWR for this Altimeter (including the pressure port size recommendations and the sun-shade for the pressure sensor) it should work very consistently.

One other thing, my max altitude was reportedly 252 feet. This was somewhat disappointing since the simulator here (http://polyplex.org/rockets/simulation/) predicted a flight of 445 feet for my 9.6L rocket @ 80psi. Not sure how my rocket may differ from the idealized design used for the simulator but there would appear to be either a significant discrepancy between my rocket and the ideal, or the altimeter is wrong. I just watched the latest video on USWR site showing the AlTImeter's performance vs. a commercial option to be very similar. That has me thinking that my rocket must deviate from the design assumptions used by the simulator or my pressure sensor is faulty. Maybe I'll try dropping a "Standard Altitude Marker" streamer to see if I can confirm the altitude.

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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 »

uberpixel wrote:
uberpixel wrote: Will this work?
I wanted to provide an update that I had several successful deployments this weekend with my updated payload design.

It was very sunny however, and I did encounter the sunlight related false trigger several times. After putting a sunshade over the pressure sensor, everything worked perfectly!

This is just further confirmation that if you follow (all of) the instructions provided by USWR for this Altimeter (including the pressure port size recommendations and the sun-shade for the pressure sensor) it should work very consistently.

One other thing, my max altitude was reportedly 252 feet. This was somewhat disappointing since the simulator here (http://polyplex.org/rockets/simulation/) predicted a flight of 445 feet for my 9.6L rocket @ 80psi. Not sure how my rocket may differ from the idealized design used for the simulator but there would appear to be either a significant discrepancy between my rocket and the ideal, or the altimeter is wrong. I just watched the latest video on USWR site showing the AlTImeter's performance vs. a commercial option to be very similar. That has me thinking that my rocket must deviate from the design assumptions used by the simulator or my pressure sensor is faulty. Maybe I'll try dropping a "Standard Altitude Marker" streamer to see if I can confirm the altitude.

-uberpixel
Thanks for the praise of our documentation and pointing people at the recommended setup. That's good to hear from a 3rd party launcher.

Regarding the altitude readings. There is a very good chance that the altitude is accurate. Wayyyyyyyy back when we first started launching, we were making FTC rockets that we simulated and thought we were going 700-800 feet high. We bought our first altimeter and launched it and were stunned to find out that the rocket was actually going 400 feet. It sure looked to use from the ground like 800 feet. The simulators were saying it went that high. The rocket was not cooperating.

We got a second altimeter from a different source, and while the two never agreed exactly, they were within 25 or 30 feet of one another and were in the 400 foot range. There will always be a little bit of error between two barometric altimeters unless you have really super tight controls on all variables (sunlight, wind, power supply, CPU oscillator calibration, etc. but the readings were showing the simulator and our calibrated eyeballs were way off.

What we did from that point on was to play with the drag coefficient and other simulator parameters until the simulator agreed with our launch, then we tried launching and simulating with different pressures and found that the simulator was a lot more accurate once we dialed in the exact drag coefficient of the rocket.

We also discovered that the simulator did not do a good job with restrictions to air flow like tornado tubes, even if they were above the water line. Those were hard to calibrate and tune out, so we stopped using rockets with multiple segments, because it hurts the max altitude.

Hopefully, you will be able to dial in your rocket simulator and get better matching results and then be able to work on improving the rocket apogee height maximum.

We enjoyed that part of the project as much as building the rockets. But we're weird like that!

Have fun!
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Re: LaunchPad AlTImeter Technical Support Forum

Post by Blenderite »

If you start manufacturing these things USWR, let me know. I will be one of the first buyers! :D Also have you considered starting a KickStarter so you can develop it even more, or do you even need that?
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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 »

DogLover wrote:If you start manufacturing these things USWR, let me know. I will be one of the first buyers! :D Also have you considered starting a KickStarter so you can develop it even more, or do you even need that?
It's a large investment in resources to make and deliver a finished product to many people like this. Even setting up a kickstarter is a lot of work that doesn't guarantee success. We have a lot of people downloading the firmware and designs and making this themselves already, so what you suggest is there are enough people out there who don't want to build it themselves to justify the effort. Do you really think there are enough customers for the work involved? How would we know? Only one other person other than you has suggested this. If there was a way to get the word out to people and have them show they supported this ides, we would definitely give it some consideration.
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Re: LaunchPad AlTImeter Technical Support Forum

Post by Airhinson »

Tried locating battery from parts list at hobbyking. Cannot duplicate. Which are the important parameters?
From photo in instructions I saw Turnigy 1s 3.7v 138mah. Found similar batteries but not exact. What are minimum requirements?
Would a 130mah battery work? Or could I go to the next highest mah rating?

Thanks
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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets »

Airhinson wrote:Tried locating battery from parts list at hobbyking. Cannot duplicate. Which are the important parameters?
From photo in instructions I saw Turnigy 1s 3.7v 138mah. Found similar batteries but not exact. What are minimum requirements?
Would a 130mah battery work? Or could I go to the next highest mah rating?

Thanks
Pretty much any battery that has an acceptable voltage for the servo is good. The servo we recommend can take up to about 6V, so any battery or pack that puts out between 3.7V and 6V would be fine. Even a plastic battery holder from a toy that takes four AAA alkaline batteries would work too. But if you want to use a LiPo because they can be easily recharged then any 1S battery should be fine. We usually suggest the smallish ones because they are very light and we really only need power for a few seconds per flight.

We've used this one a lot in the past: http://hobbyking.com/hobbyking/store/__ ... _Etc_.html

Also this one: http://hobbyking.com/hobbyking/store/__ ... _Etc_.html
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Re: LaunchPad AlTImeter Technical Support Forum

Post by Airhinson »

Thank you very much. I've only launched Gardena-nozzled rockets to date. Using the tutorials on USWR, I've put together an o-ring launch tube and am acquiring materials for the parachute deployment system. Thanks for the info.
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Re: LaunchPad AlTImeter Technical Support Forum

Post by U.S. Water Rockets1 »

Airhinson wrote:Thank you very much. I've only launched Gardena-nozzled rockets to date. Using the tutorials on USWR, I've put together an o-ring launch tube and am acquiring materials for the parachute deployment system. Thanks for the info.
Thanks for the nice plug for our designs! We hope you have a lot of fun with them.
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