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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Eggtimer Quantum altimeter

Discussion about deployment systems including altimeters, timers, air speed flaps, servo systems, and chemical reactions.
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anachronist
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Eggtimer Quantum altimeter

Post by anachronist » Mon Aug 07, 2017 1:58 pm

Currently I'm building a servo-deploy rocket because I bought (and built) an Eggtimer Quantum which has a built-in servo controller and built-in WiFi for data transfer and configuration over your phone. The only other altimeter with wireless capability is the Jolly Logic Altimeter Three, but it doesn't have deployment and it's more expensive.

But my all-mechanical design is still there, ready to build. I'm kinda stuck on the best way to do a trigger release (that is, a small weak movement of a part inside the rocket triggers a larger release of energy, sort of like a mousetrap release, or hair trigger on a handgun). Basically my problem is, the movement of a weight or a magnet should trigger the parachute release mechanism. I've got a few ideas, but nothing I'm really happy with yet.



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Re: Eggtimer Quantum altimeter

Post by addstogether2 » Mon Aug 07, 2017 6:15 pm

Good to see I'm not the only one to use the Eggtimer Quantum. I also purchased the Classic as well. I still have to put it together though.

I was going to use a micro servo to release the chute with a bottle section as the ejector.

Al


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Re: Eggtimer Quantum altimeter

Post by anachronist » Tue Aug 08, 2017 3:04 pm

addstogether2 wrote:Good to see I'm not the only one to use the Eggtimer Quantum. I also purchased the Classic as well. I still have to put it together though.
I've finished putting together my Quantum. I made a couple of modifications. Instead of that big fullwave bridge, I substituted a LiPo S2 charging socket - it's lighter and fits perfectly in two of the bridge holes. To make it work, you need an additional jumper wire to connect the negative bridge pad (which is diagonal from the "+" pad) to a ground pad; there are a couple different posi This has 3 advantages: I can use my S2 battery with its standard balance connector, I can swap out batteries easily, and the socket guarantees the battery polarity is always correct.

With apologies for posting this in "non electronic parachute deployment" thread, here's how it all looks. In this picture I haven't yet made the final white servo wire connection. I was still deciding whether to use the MAIN or DROG deployment channels.

You can see the battery socket with the center pin pulled out so that it would fit on the board. The extra jumper required for this is actually part of the black servo wire, connecting DB- and the nearest empty battery terminal. This completes the connection between the empty negative fullwave bridge pad and the negative side of the S2 socket.

Also you can see a little 3x5-hole breadboard I made for the servo. The Quantum manual says these extra 3 components on the servo wire are required. The big capacitor is 220uF.

The battery is a small 120 mAh S2. I got 2 of them. I intend to swap them out after each flight, although so far in my tests it looks like a battery charge will last for at least 2 flights. Those batteries came with a non-standard balance connector, so I replaced it with a standard balance connector so I can plug the battery into my charger.
altimeterservo.jpg
addstogether2 wrote:I was going to use a micro servo to release the chute with a bottle section as the ejector.
I'm looking for ideas on release mechanisms. I'm not keen on using a side-door parachute ejection. I prefer an axial arrangement where the nose cone pops off... but I am still mulling over the best way to release it with the servo. I'm thinking of having the servo pull in two rods, one on each side, that penetrate the wall of the rocket where the nose cone wall overlaps the electronics bay wall (and that overlap I still have to figure out). Whatever mechanism I come up with, will also be applicable to the non-electronic mechanism I'm working on.

-A
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Re: Eggtimer Quantum altimeter

Post by addstogether2 » Sat Aug 12, 2017 1:29 am

Have you managed to calibrate the eggtimer quantum against any other altimeter yet. If you want to use it in a record attempt you will have to use a commercially built altimeter.

I haven't come up with the solution yet but working on it.

Al


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Re: Eggtimer Quantum altimeter

Post by anachronist » Sat Aug 12, 2017 2:49 am

addstogether2 wrote:Have you managed to calibrate the eggtimer quantum against any other altimeter yet. If you want to use it in a record attempt you will have to use a commercially built altimeter.
The Quantum uses the same pressure sensor as other commercial altimeters. There is a 2015 post from WRA2 about the LaunchPad AlTImeter (also a home-built altimeter) clarifying: "Since that altimeter is built using 'off the shelf' commercial products ... we can assume some measure of accuracy as far as the hardware goes and each one will be using the same software makes it similar to a commercial altimeter and that it should be allowed." The Quantum uses an off-the-shelf pressure sensor and all of the Quantum altimeters use the same software, so I'd say it's OK too. The Eggtimer folks use their altimeters in pyro competitions too.

I'll also point out that there aren't any model rocket altimeters, to my knowledge, that have any sort of calibration traceable back to a NIST recognized standard reference, unless the pressure sensor is already calibrated by the manufacturer of those sensors. Therefore, calibrating it "against any other altimeter" may be meaningless. I'm fairly confident that any altimeter accuracy is far better than the tire pump pressure gauges people are using for these record attempts. Those gauges have huge errors, my newest tire pump is off by 20%. No way I'd rely on that gauge for a record attempt.

I should ask Cris at Eggtimer about altimeter accuracy though.



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Re: Eggtimer Quantum altimeter

Post by addstogether2 » Sat Aug 12, 2017 5:59 am

I do recall that post. I agree It still won't be a bad idea to check with Chris at Eggtimer anyway just to be sure.

Al


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Re: Eggtimer Quantum altimeter

Post by anachronist » Sun Aug 13, 2017 2:51 am

addstogether2 wrote:I do recall that post. I agree It still won't be a bad idea to check with Chris at Eggtimer anyway just to be sure.
Here's what Cris wrote:

"Digital altimeters are factory-calibrated, but like watches no two altimeters will read the same. I have flown multiple altimeters many times, they almost always agree within a fraction of a percentage. NAR recognizes this, which is why altitude records require a +2% difference from the old record."

Cris added that the Eggtimer used Bosch digital sensors before they were discontinued. Now they use Meas-spec sensors made by TE (this one).

Cris also said "Before digital altimeters came along, you'd use an analog part with an A/D converter (or the A/D convert in your processor chip), and you'd have to calibrate them against 'known' altitudes." I believe the competition rules were written back in those days, which is why WRA clarified a couple years ago that the Luanchpad AlTImeter kit was acceptable.



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Re: Eggtimer Quantum altimeter

Post by addstogether2 » Sun Aug 13, 2017 3:09 am

Thankyou for checking with Chris and sorting that out.
I have 4 days off work next weekend and will build mine then.

Regards Al

I also have re titled my posts
Re: Eggtimer Quantum altimeter


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Re: Easy non-electronic parachute deployment

Post by WRA2 » Sun Aug 13, 2017 10:49 pm

The reason for the need for the rule to limit altimeters to "mass produced" and "commercial" was simple. The accuracy of the altimeter is solely based on the firmware that reads the pressure sensor and converts the output to feet or meters. The eggtimer falls in the same category as the Launchpad altimeter from USWR. The end user (or the rocketeer flying it does not have access to the firmware source code.

Consider a clever rocketeer out to set a record constructing their own altimeter (from scratch) and writing the firmware code to do this conversion. Now consider that their rocket is a little short performance wise so they modify their own firmware code to add a bit to each reading before logging. We would have to analyze the firmware source code for every submission.

The USWR altimeter firmware is obtained by the end user in it's compiled form and cannot be modified by the end user. Also everyone uses the same firmware. USWR also validated their firmware by flying their altimeter alongside a commercially available one (perfectlite if I remember correctly). That was the reason for its approval. The eggtimer also appears to meet that same criteria so it would also be allowed.

Hope that helps.


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Re: Eggtimer Quantum altimeter

Post by anachronist » Mon Aug 14, 2017 11:29 am

WRA2 wrote:The reason for the need for the rule to limit altimeters to "mass produced" and "commercial" was simple. The accuracy of the altimeter is solely based on the firmware that reads the pressure sensor and converts the output to feet or meters. The eggtimer falls in the same category as the Launchpad altimeter from USWR. The end user (or the rocketeer flying it does not have access to the firmware source code.
Well, in the case of the Eggtimer, the firmware isn't accessible even to the Eggtimer folks. It uses a commercially-produced pressure sensor that already includes its own processor and firmware, calibrated by the manufacturer -- not only for pressure, but also with temperature corrections. The pressure sensor outputs millibars of pressure altitude through a serial interface. After that, the firmware in the Eggtimer simply does a unit conversion, to express the pressure altitude as actual altitude using a standard formula. It isn't much different from converting pounds to grams. The Eggtimer firmware doesn't need to do any calibration because that's already included in the sensor.
WRA2 wrote:The USWR altimeter firmware is obtained by the end user in it's compiled form and cannot be modified by the end user. Also everyone uses the same firmware. USWR also validated their firmware by flying their altimeter alongside a commercially available one (perfectlite if I remember correctly). That was the reason for its approval. The eggtimer also appears to meet that same criteria so it would also be allowed.
Thanks for the clarification. I wanted to point out that the firmware in the pressure sensor is not only inaccessible to the end user, but also to the Eggtimer manufacturer. The Eggtimer firmware appears to be more for managing the configuration settings and pulling in the data from the pressure sensor.

I kinda wish the last few posts could be moved into their own thread

(Update - looks like that was done - thanks WRA2 - so I've retitled all my posts in this thread "Eggtimer Quantum altimeter")



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Re: Eggtimer Quantum altimeter

Post by anachronist » Mon Aug 14, 2017 12:01 pm

I can't speak highly enough about the Eggtimer Quantum, by the way. It has features I haven't found anywhere else: built-in servo controller, WiFi connection for configuring and downloading data, dual-deploy if you need it. I don't see that combination of features in other logging altimeters.



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