Curiosity Style Egg Drop Lander

[christheman200]

The analog altimeter has the potential to be perfectly accurate and work every time. It would save the weight of having onboard sensors to do the task as well.

However, a system of accurate height measurement to control the descent is still needed. This makes the analog system fairly redundant, although redundancy is usually considered good in these systems.

I know that this could be done in a much simpler manner, but I am trying to give myself a very hard challenge on purpose. If I can overcome this obstacle, I will have learned a lot more than if I had taken on a smaller task. In general, I would like the rocket to be as simple as possible yet be within my rules, and if the rules can't possibly stick, they can be adjusted.

Edited July 7, 2014 by christheman200

[Duxwing]

The analog altimeter has the potential to be perfectly accurate and work every time. It would save the weight of having onboard sensors to do the task as well.

However, a system of accurate height measurement to control the descent is still needed. This makes the analog system fairly redundant, although redundancy is usually considered good in these systems.

You would also need sensors to read the weighted probes, programs to interpret the sensor readouts, etc: just receiving a signal would be simpler.

I know that this could be done in a much simpler manner,

Therefore do "this" in that "much simpler manner": engineering is about elegant efficacy.

but I am trying to give myself a very hard challenge on purpose.

If you want a "a very hard challenge," then give yourself one instead of arbitrarily complicating the one you have accepted.

If I can overcome this obstacle, I will have learned a lot more than if I had taken on a smaller task.

Go ahead, take that big task--and don't complicate it once you've taken it! And should this task be easy, take a bigger one later and enjoy your success. Whereas from your current alternative--making a seemingly-simple task so difficult that you spend days thinking and calculating instead of doing--you will learn a terrible engineering lesson rendering useless any skills you might learn during this challenge. That lesson is what I wrote before: engineering is about elegant efficacy.

Anyone engineering is trying to solve a problem. Anything that is tried and works is a work of engineering, which is elegant if minimally-complex. Anything that is tried and does not work is junk, which, obviously, cannot be elegant. An effort to solve the problem also is a thing: if it endlessly creates more work--however interesting or edifying--without solving the problem, then it also is junk. Therefore distinguish interesting and difficult problems from interesting and difficult solutions.

Fear you success and the end of this fascinating, exciting application of rocket science? Fear not! Such applications as it abound! You just probably won't get to look cool in front of your teacher and class...

In general, I would like the rocket to be as simple as possible yet be within my rules, and if the rules can't possibly stick, they can be adjusted.

Therefore ditch the MatLab and onboard sensors and just use a cheap, light receiver powered by a capacitor: you can buy both from an electrical store.

-Duxwing

[Creature]

What I meant with the drop height thing was concerning more about the testing phase. When you're doing the real thing, go as high as you can of course Like I said when coming down with a parachute you could just as well drop it from an airplane (which I don't recommend doing).

In any case it's awesome that you're not afraid of a challenge, but be mindful of time constraints and plan the desing process logically. Right now your top priority is getting a throttleable rocket engine to work. This is pretty much the thing that's gonna dictate your error margins and the amount of control you have, everything else is just paper rocket science for now and not a top priority. If you really want to hover-drop the egg, you need to have some pretty fast and accurate controls on the throttle plus all the engines need to have a steady, reliable thrust curve. This is why I strongly suggest you keep the landing legs at least as a possible option somewhere on the back of your mind because truthfully I'll be flabbergasted and positively bamboozled if you can pull off the precision you need to get the egg to come to a halt within 2 centimeters of the ground. I really have no idea if this is possible or not but once you have some real data on the engine we can start speculating. Everything is always easy on paper but in real life engineering you need hard data and all equipment operates within a certain range of tolerances. This margin is something you need to find out by doing SCIENCE! on it.

The other important part is the actual control logic and circuitry. So you need a unit that can receive sensor data and send out a command to a servo to adjust the throttle. A good place to start here is the gyro. The most basic thing is keeping the craft level. Once you have that logic in place, you can easily add other inputs. I don't know how R/C helicopters or arduino quadcopters do this but that's probably a good place to start.

I'm really fascinated by this project just for the sake of knowing if it's possible to do this. Even if it doesn't work as planned you'll still win and get a very good learning process from this. Also take anything I say with a grain of salt, I have no experience in mechanical or electrical engineering. What I do know is project design, data analysis (at least as long as we don't go too heavily on the statistics) and labwork in general (also bioengineering but you probably don't need that). Some things I recommend you do is get a lab book and take notes of everything. Second thing is to get dirty with the engine and throttle control right away, that's your primary component that defines your operational capabilities. Third thing you could consider is starting a blog about your project once you have something substantial to show for it.

[christheman200]

The weighted probes are not likely to be implemented.

The reason behind this whole project is to come up with a working automated landing system. The egg just incorporates it into a school project. For the sake of simplicity, it may be a good idea to ditch the egg and just create a lander. However, if possible, it would be really cool to land an egg safely with the craft. Perhaps an automated system should be created first, and then an upgraded version could carry the egg?

[christheman200]

In any case it's awesome that you're not afraid of a challenge, but be mindful of time constraints and plan the desing process logically.

Right now your top priority is getting a throttleable rocket engine to work.

This is why I strongly suggest you keep the landing legs at least as a possible option somewhere on the back of your mind because truthfully I'll be flabbergasted and positively bamboozled if you can pull off the precision you need to get the egg to come to a halt within 2 centimeters of the ground.

I'm really fascinated by this project just for the sake of knowing if it's possible to do this. Even if it doesn't work as planned you'll still win and get a very good learning process from this.

Some things I recommend you do is get a lab book and take notes of everything. Second thing is to get dirty with the engine and throttle control right away, that's your primary component that defines your operational capabilities. Third thing you could consider is starting a blog about your project once you have something substantial to show for it.

I have at least to the end of summer holidays plus one to two months to "finish" the project for school. In all likelihood the project will be due some time next year. As well, if it isn't finished by the school project due date, that doesn't bother me at all, since I can keep working on it during my spare time. Just keep bugging me on this thread to do more work so that I stay motivated!

I will put together the design for a test rig right after writing this message.

Perhaps on the first iteration of the craft there will be no egg.

Yes, I agree with you on the learning aspect. My father is blown away by what I've been learning in the past few days. I can't imagine what I'll be like in two months. Even if I don't get near to completion on this project, it drives me forward to learn advanced topics.

I have assembled all of my notes into my favourite binder, which has a drawing I drew of the space shuttle, pre-launch, on the cover. Any pieces of paper without binding holes have been put into sleeves.

I should start a blog, shouldn't I?

[Creature]

Keep the egg! You need a mission objective, don't you?

The way I see it, you need a craft that can slow down to a halt first and then lift off again. This can be to a hover or to ground, for now it doesn't matter. Just build in enough thrust time to facilitate a short hover for egg landing if it seems plausible. If you can do this then it's all up to control finesse what else you can do.

[christheman200]

OK, I'll keep the egg!

Since the pressure varies over time, I'm going to need to recalculate my tolerances for landing.

I've researched the construction of a thrust test stand, and I've come up with a solution.

Two good resources among others are:

http://www.instructables.com/id/Arduino-Load-Cell-Scale/

http://www.nerdkits.com/videos/weighscale/ - this company also sells the sensors for ~$10 in-case you don't want to take apart a scale

In short, the load cell inside of a bathroom scale is hooked up to a signal amplifier, which is read by an arduino and logged to a computer.

Finer details will come in the morning when I'm actually awake.

[Skyler4856]

Why not just do a Yutu style landing, with a craft that has a TWR less than one, and just stabilize using gyroscopes...

[christheman200]

Well, landing the egg in a similar manner to that of the Yutu lander demands just as much technologically as it does to land on rocket power.

As well, the parachute will only slow the craft to a speed of some odd 5m/s. If the craft has a TWR<1, the egg will come down at >5m/s. That is far too fast.

If you are talking about using gyroscopes as in KSP, those don't really work very well in real applications.

[Navy2k]

My approach would be a mix of engine types.

Pressured Water for the descent. If you can have the same amount of deltaV every time you could calculate a function at what hight at what speed to launch the system for a suicide burn. That should bring you to 0m/s exactly at touchdown. When the egg touches the ground ignite some sort of escape tower solid fuel seperator.

Stays the problem of keeping the craft leveled.

Greetings

Ben

[Skyler4856]

Well, landing the egg in a similar manner to that of the Yutu lander demands just as much technologically as it does to land on rocket power.

As well, the parachute will only slow the craft to a speed of some odd 5m/s. If the craft has a TWR<1, the egg will come down at >5m/s. That is far too fast.

If you are talking about using gyroscopes as in KSP, those don't really work very well in real applications.

Not really, you simply find store bought SRB's that give a TWR<1 and enough burn time to lower the rocket down far enough. And A gyroscope option could involve spinning a mass with Servo motors...

[christheman200]

It seems that you did notice my comment regarding the egg coming down at >5m/s.

Your servo motor option could work if it had a fast enough response time.

[Skyler4856]

It seems that you did notice my comment regarding the egg coming down at >5m/s.

Your servo motor option could work if it had a fast enough response time.

You wouldn't even need the gyroscope to go off in mid-air, in fact it would be optimal for the gyroscope to fire whilst on the roof, or whatever the OP is planning on launching it from...

A fact I would like to add to my original plan which may either needlessly complicate, or simplify dramatically, depending in how the OP goes about figuring out the feature. I would suggest having multistaged SRB's with an accelerometer based decoupling system....

[christheman200]

I've been playing around with a reputable on-line water rocket simulator, and my numbers aren't adding up to those of typical low power water rockets. I've now come to realize that I have been overestimating the weight of the craft by a factor of ~2.

I have found that it may be considerably easier to construct a SpaceX Grasshopper style lander, using a single gimbaling engine with a throttle. For now I will assume that the engine is somehow gimbaled via servos.

A conventional pop bottle weighs 49 grams, and with a 5 water bottle system, including a 50 gram egg, 3 50 gram servos and a 100 gram solenoid valve, the weight will tally to ~550 grams.

At 120 psi, according to the following simulator, such a rocket will produce a delta-v of >28.6m/s.

The simulator: http://polyplex.org/rockets/simulation/simulate.cgi

This project is looking much more feasible now.

[B787_300]

just a couple of notes...

1. Metal for the pressure tank. make it to a FS of 2. IE if you are shooting for 150 PSI, make the tank able to take 300 PSI

2. Talk to your schools FRC team if they have one, they might have some good experience in working with pneumatics

3. definitely use a chute on the way down to reduce the amount of water needed. water is HEAVY

4. see about using delaval nozzles on the thrusters... might help increase the ve of the water

[QuesoExplosivo]

de Laval nozzles won't work with water, as it can't expand.

[christheman200]

^Yes, a common misconception with water rockets is that they are more efficient with convergent-divergent nozzles.

I've managed to push a pop bottle to a pressure of 120 psi before, albeit I reinforced the bottle with plastic around the outside. However in retrospect it was a very bad method of reinforcement, and I expect that the bottle used could have withstood the pressure.

If you want to hold 120 psi with a small metal tank, it can be incredibly thin. The problem with this is that it is very hard to form the metal this thin. Realistically, it is possible to make your pressure tank as thick as the plastic in a pop bottle, which will make it too heavy.

One of the most important things about making metal tanks is that they are much, much more dangerous than plastic bottles. If the tank explodes, you'll have deadly shrapnel going everywhere, and cut metal is very sharp.

Yes, chutes are crucial.

I'm on our school's FRC team. I can't wait for school to start up again.

[B787_300]

ah water does not expand but steam and water vapor do... and there are other ways of getting water into steam with out heating, think of the IGL

[shynung]

ah water does not expand but steam and water vapor do... and there are other ways of getting water into steam with out heating, think of the IGL

That means superheating the water, which needs more heat resistant materials to contain it (I'm not sure a 2 liter PET bottle would do). Plus, superheated water is very sensitive to contamination; if a single speck of dust gets in, it'll be enough to blow the whole thing to smithereens.

[Creature]

Are you using the solenoid for throttle control between the water tank and nozzle? I don't know how it would work in practice but would it be possible to have a separate pressure tank connected to the water tank with a valve in between as throttle? It would be easier to control the air flow than the water flow. Depending on the nozzle size you might still be able to cut the throttle completely. But it would change the dynamics a lot so I have no idea if this is feasible at all.

[christheman200]

Creature,

your idea is very logical but I'm certain it won't work.

Once any air pressure is released into the water tank, that pressure will stay in the tank until it can leave, and if your rocket is pointing down that is when all of the water has exited.

I'm trying to comprehend the arrangement of the nozzle, valve, and gimbal point at the moment. It seems that if the throttle is before the gimbal point, the standard size of the nozzle after it would reduce pressure as the thrust is decreased, lending to a lower performance. It seems like a tough challenge to control the added mass of a solenoid valve after the gimbal.

[Creature]

Well to be precise it would keep thrusting until the pressure inside the tank is equal to outside atmospheric pressure. After that the ambient pressure will start working to keep the water in the tank. But you're right though, once the valve is opened and the air flows in, you can't cut the thrust fast, the pressure must equalize first and that might not happen before all the water is out. Additionally the response time for air throttle would be slower and less precise so if you can make the direct throttle to work it's a better solution.

[christheman200]

I've gone ahead and spliced together a few pop bottles, which should be sealed in one week.

Now I'm trying to set my mind on creating a gimballing nozzle. I've found what seems to be an almost perfect design here:

I've sent the designer a message, and asked what he used to give the nozzle its degrees of freedom, perhaps a ball joint or piece of tubing.

That's where I'm stuck at the moment.

Another conundrum I have regards the use of solenoid valves and exhaust velocity.

If I throttle the flow with a solenoid valve by pulsing the flow on and off, the pressure in the nozzle should be less than it is inside the tank. And if the exhaust pressure is lower, the exhaust velocity must be lower, and there will be a considerable delta-v loss. Is my reasoning valid?

[K^2]

Why do you need gimballing nozzle? And at any rate, it will not have the time to actually adjust.

[christheman200]

The new idea is to use a SpaceX Grasshopper style rocket, which is much easier to construct, and can be used for a number of purposes.

Hobby servos can slew around 60 degrees in 0.24 seconds. The fastest can do that in 0.04 seconds. I don't have much experience working with servos, however, so I suppose their may be a considerable time delay until rotation. Other than time delay, I don't see the servo speed being much of an issue, if fast servos are used. A stable rocket would ideally need very little corrective control as well.