Newbi with ? (Full Version)

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Handeman -> Newbi with ? (4/19/2008 3:42:17 PM)

Hi everyone,

I'm brand new here and I will tell you right now, I know nothing about skydiving, ram air chutes, or even RC.

I'm hoping I can get a LOT of questions answered.

First off, my thing isn't RC, its rockets. As I'm sure you all understand, the higher the rocket goes, the farther the walk to recover it. There are several things that are done to assist/shorten that walk like dual deployment. That is where electronics deploys a drough chute at apogee that lets the rocket fall very fast and then deploys the main chute at a preset altitude.

I've been told by quite a number of very experience rocketeers that no one has been able to build a successful RC controlled chute for a rocket. This site has inspired me to try and I'm hoping that with the expertise here, I can get my rocket to fly back to the pad instead of drift away.

My first question is one that could kill the whole project to begin with. If the transmitter is turned on, then the reciever, (I believe that's the correct sequence) how long can the receiver be out of touch with the transmitter and still reaquire the transmitters signal again and operate correctly?



robert92679 -> RE: Newbi with ? (4/19/2008 10:53:46 PM)

That sounds like an interesting project. Depending on the size of the rocket, it may be possible to 'repackage' the electronics from the body of a jumper into the rocket. A couple things to keep in mind are the total weight of the rc equipment, plus the impact on the rocket balance. Depending on the placement, it may become top heavy.

To answer your question, there is no time limit on how long the TX and RX can be apart. I recommend using a PCM system, so you can set a 'failsafe' to prevent the servos from jittering if they are out of TX range. Failsafe will hold the servos in a pre-set position if the TX signal is lost. Servos in a non-PCM system (PPM?) tend to jitter when no TX signal is present, which might result in premature chute opening and/or uncontrolled movements.



Handeman -> RE: Newbi with ? (4/20/2008 2:12:18 AM)

robert,

Thanks...

I'm really glad to know the RX and TX can be seperated and still work when the RX picks up the TX again. If that didn't work then the whole project would be done, or headed into the ham radio world. The PCM sound like it will work quite well but as you explained it, I'm not sure it will be needed.
BTW what is PCM and PPM?

The preliminary design, if you can call a few napkin sketches a design, will be for a rocket that will be 4" diameter and should have about 18 inches of that available for RC although I don't believe it will take nearly that much. The weight of the RC shouldn't be much of a factor although it will be accounted for in final design. As for being top heavy, that's actually a good thing, up to a point. The problem in rockets is when they get too bottom heavy. If the CG get behind the CP (Center of Pressure) then the rocket just does loops.

I don't think there will be enough room to repackage the skydiver arms into the rocket, although some sort of lever may work. I was thinking about using small motors with current limiting resisters and servo activated switches to turn them on and off. The motors would have gears that drive a larger drum that actually pulls in the control lines and when the motor is shut off, the air flow pushing the chute back into shape should unwind the control lines again. At least thats the current thought.

The RC will only steer the chute. Deployment will be controlled by the altimeter electronics. A drough chute should open at apogee, somewhere around 1,500 - 2,000 ft during testing but eventually it will be in the 5,000 to 7,000 foot range. The RC controlled chute wouldn't deploy until it was back down to 1,300 ft. That is also when the RX antenna would be deployed and I would assume the RX would again pick up the TX signals.

The next question would be, how many Gs can the receiver and servos handle. The lower flights would only pull 10 - 20 Gs but the higher flights could see upwards of 60+ Gs during boost? Also, the chutes are deployed by pressurizing the body tubes with black powder charges. These can cause the parts to acclerate vigorously and snap to a stop when they reach the ends of the shock cords that hold everything together.

Any idea how large of ram-air chute would be required, I haven't dug that deep yet? I am estimating the rocket, with burned motor, would weight about 6 lbs.

Again thanks...



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