A non-pyro version of the tender descender

[mbeels]

I was considering a parachute cannon or chute release for my latest rocket, there isn't room for a traditional DD setup. As I was mulling over possibilities, the thought of doing the following occurred to me. The altimeter is in the nose cone, and drives a servo to release the main parachute. The parachute is held in the tube by a length of shock cord with a loop on the end. pulled out of a tube by the drogue. What are the potential pit falls of trying this setup? I think that this is pretty similar to what the tender descender does, except from the nose cone.

 

[manixFan]

Honestly using a Jolly Logic chute release would be the same thing without all the added complexity. Or a cable cutter. I've seen many issues with altimeters in nose cones so I'm not a fan of that placement. It can work obviously, but it can also fail spectacularly.

It's an interesting idea and it may be worth trying just for the challenge. But assembly of the nosecone seems like it would be quite a challenge since you need access to the interior to rig the servo, yet also a good anchor point for the chute attachment. You don't show a shoulder which complicates things a bit. Just thinking it through I can come up with a couple of ways of doing it, but none are very space efficient. Keep us posted if you decide to pursue it.


Tony

 

[mbeels]

You don't show a shoulder which complicates things a bit.

Yeah, I greatly simplified the drawing, it is more of a rough schematic. I already have the nose cone prepared, with a AV bay, bulkhead, and eye hook. I'm kind of curious to try it, partly because I already have servos (and no chute release), and it might be a fun experiment.

 

[mbeels]

FWIW, the nose cone currently looks like this. The main structure and bulkheads are 1/4" ply.

 

[manixFan]

Looks very sturdy. How is the sled retained in the nose cone? And, how are you going to vent the altimeter? That seems to be the issue with a nose cone mounted altimeter if you us barometric apogee detection. Airflow over the nose cone can give false readings during ascent.


Tony

 

[mbeels]

I will use 2 small screws, one on each side of the nose cone. My intent is to have the actual nose cone be just a lightweight cosmetic cover for the frame which should bear all the loads.

The altimeter will be a Proton, which has an accelerometer as well as a barometer. I think that a barometer in the nose cone can still detect apogee just as well as one not in the nose cone, but any velocity readings derived from the barometer readings on the way up will not be as accurate. Either way, I think that the Proton will be ok with a four small vent holes around the base of the nose cone (above the shoulder).

 

[manixFan]

I do know from past experience that accelerometer based apogee can be an issue sometimes, but it may be better than baro in this case. I can see that the nosecone itself won't really bear any load, so that's good. Unfortunately it may be a while be before you can test it! But I will be interested to see how your apogee detection works with the Protron. I've got one as well but have not messed with it much.

All in all an interesting approach.


Tony

 

[mbeels]

I'm not entirely positive, but I think that the Proton uses barometer for apogee detection (or maybe a combination of the two?), and the accelerometer for event detection such as lift off and motor burnout.

Yes, and unfortunately, I'll have to be patient!

 

[neil_w]

This is my new favorite thing:




What are you building, anyway?

 

[HVArcas]

i love recovery designs where the drogue helps pull out the main.

 

[mbeels]

This is my new favorite thing:

What are you building, anyway?

That's better then the one that got squashed flat!



This is going into the rocket heretofore referred to as "Celestial Jet", but I think I have a new name in mind.

 

[neil_w]

Ah, didn't realize it was that tight in there.

 

[mbeels]

Ah, didn't realize it was that tight in there.

It's mostly the length that is an issue, and the fact that I don't want to split the rocket anywhere except at the nose cone. Now, this might be where @BABAR advocates for rear eject, but that ship has sailed. I'll probably fly it single deploy on the first flight (and something to just test the servo function), but since I have time, I'm pondering how I could do dual deploy.

 

[Hybrid33]

I did this 16 to 17 years ago. It was not in the nose cone . The servo was on the top AV bay lid . I highly recommend using a deployment bag .
I had one flight that did not deploy the main, the servo did it's job but the chute was so tight in the body tube the shock cord could not slide past the chute.

 

[Hybrid33]

If I were to use it again I think I would install a inside conduit to prevent any issues with the shock cord/tether getting past the parachute

 

[mbeels]

I did this 16 to 17 years ago. It was not in the nose cone . The servo was on the top AV bay lid . I highly recommend using a deployment bag .
I had one flight that did not deploy the main, the servo did it's job but the chute was so tight in the body tube the shock cord could not slide past the chute.

Did you machine that aluminum yourself? That looks quite stout, and quite similar to what I had in mind.

 

[Hybrid33]

Yes I machined it and the pin . Tested up to 60 LBS on a swing set . That was 5 times the weight of the Rocket .

 

[Yukon@K-9 Rocket Tech]

How about a small 3D printed device with a servo and rubber band that wraps around the main chute, and the servo releases the rubberband like the jolly logic chute release? Would decrease weight significantly

 

[mbeels]

How about a small 3D printed device with a servo and rubber band that wraps around the main chute, and the servo releases the rubberband like the jolly logic chute release? Would decrease weight significantly

That would be lighter. My plan with this one is to avoid lengths of servo wire going to the parachute, I want to try and reduce the chances of the recovery gear getting tangled and fouling. I hope with the main getting pulled out of a tube, there is a more orderly deployment. I have some parts for a mock-up, once I get it together, I'll post some photos.

 

[Not Quite Nominal]

If you're worried about the servo binding, you could use a three-ring system. You do need to make sure that nothing fouls it though.

 

[HVArcas]

It's mostly the length that is an issue, and the fact that I don't want to split the rocket anywhere except at the nose cone. Now, this might be where @BABAR advocates for rear eject, but that ship has sailed. I'll probably fly it single deploy on the first flight (and something to just test the servo function), but since I have time, I'm pondering how I could do dual deploy.

What is "rear eject", blast out a slidable motor mount that drags the parachute?

 

[mbeels]

What is "rear eject", blast out a slidable motor mount that drags the parachute?

Pretty much! Usually the motor tube extends a long ways into the body of the rocket, and the recovery gear is wrapped around that. It also has the benefit of providing some additional protection from the ejection gasses. Here is a video with some examples:

 

[mbeels]

If you're worried about the servo binding, you could use a three-ring system. You do need to make sure that nothing fouls it though.

What is a three-ring system?

 

[Kelly]

What is a three-ring system?

It's a way of releasing a load under tension, with a minimal required force. The principle is that you don't release the chute, you release something that releases something that releases the chute.
https://en.wikipedia.org/wiki/3-ring_release_system

 

[mbeels]

It's a way of releasing a load under tension, with a minimal required force. The principle is that you don't release the chute, you release something that releases something that releases the chute.
https://en.wikipedia.org/wiki/3-ring_release_system

Oh wow! That is a beautiful animation, clever! Thanks for posting this link, very elegant design.

 

[beeblebrox]

What is a three-ring system?

https://en.wikipedia.org/wiki/Ringling_Brothers_Circus

 

[mbeels]

https://en.wikipedia.org/wiki/Ringling_Brothers_Circus

That accurately describes many of my current escapades!

 

[mbeels]

Alright, I decided to try and mock this up. It turned out to be a simple concept in my head, but the devil is in the details. This is a case where 3D modeling would have been a great help. I found myself having to do lots of trimming, adjusting, filing, tweaking, and wishing I could move a few holes around. But it works.

I realized that a 1" optical post is an extremely convenient piece of hardware, it is 1/4"-20 threaded on one end, and has a nice through hole near the other. It inserts into the bulkhead of the nose cone, and a servo pulls out the release wire from behind. The pin is supported by a section of Al tubing.

The optical post has a washer under the eyebolt which sets the depth, so it can't slide in or out when the pin is engaged.

 

[mbeels]

And from the outside, without shock cords attached. The main sits in the tube, and the cap is held down by the releasable eye bolt.

 

[PatD]

It's a way of releasing a load under tension, with a minimal required force. The principle is that you don't release the chute, you release something that releases something that releases the chute.
https://en.wikipedia.org/wiki/3-ring_release_system

Back in the day it was the state of the art in skydiving for main cutaways. No idea what they are doing now.