Posts Tagged ‘nosecone’

 

H2 Reassembly and Nosecone testing

The weather is predicted to be fine this weekend so we are looking forward to launch day 7. Our Modular H2 rocket was put back together after the hydrostatic test. We have used the Robinson coupling that didn’t have the slow leak at 125psi so all should be well from the propulsion part of the wrocket.

We made a new launch release flap out of corrugated cardboard. After many tests the old one wasn’t holding its shape well. A new one fixed that. These weighs in at 1 gram.

Here is a pic of H2 put back together.

H2 ready for launch day

H2 ready for launch day


Nosecone Testing and Calibration

As with our last timer we have tested the number of turns on the new tomy timer to find out how many turns equate to what number of seconds. We want to get the deploy near or just before apogee.  The results were

Number of Turns .     Seconds
1.0 3.2s
1.5 4.4s

These timings are fine for H2 up to a 120psi launch which is what we will test up too.

Here is a video of the new nosecone and side deploy in action. The video is 1 turn of the timer, you can see the parachute get kicked out the side. For the video the wrocket is sitting unpressurized on the launcher.

Posted by on September 20th, 2008 Comments Off

Nosecone Mk II

After our recent parachute deploy failure it was back to the drawing board for the ping pong nose cone (PPNC)  and side parachute deploy. Having built the first version there were a number of things I wanted to fix. These were

  • The placement on the nosecone of the timer
  • Want to use a single rubber band to not wind past the timer – this reduces the chance of being caught up on the timer itself.
  • The size of the door probably needs to be a little smaller and lower (dont want it near the pointier point of the nosecone, this makes the door not close properly
  • The vertical height of the nosecone support structure may be too high based on our parachute size.

The PPNC shell and support structure were largely based on our original design

Timer Placement
This is probably the most important thing for the new nosecone. We think the root cause of the parachute deploy failure was that the elastic band when it wrapped around the nosecone got caught up on the timer itself and wouldn’t allow the door to open. Nosecone Mk II has the timer located just before the door hinges. This gives the elastic band enough space to be stretched but not too much that it will wrap back past itself or the door. Hard to explain , so here is a pic.
Door hinge and timer location

Door hinge and timer location

The door has 2 wire hinges. The door is made out of the same diameter bottle, just put on backwards, so that the natural curve of the bottle will fling the door open by itself. The parachute deployment plate is just visible on the right with its two elastic bands that eject the parachute. The timer is to the left mounted on the side of the nosecone support structure. A hole is drilled in the side of the bottle to allow the handle of the timer to extend beyond the rockets diameter.

The little green guy is our fearless pilot. The tape is on the inside to ensure the nosecone structure doesn’t snag on the hinges when it is removed.

Nosecone Door

Nosecone Door

Above you can see the door in the open position, notice how it curves the opposite way when open, also the one elastic band on the door which is enough to keep it closed and connects to the timer.

We added an extra section at the top of the nosecone support structure, this was to keep the top of the door below the curve in the nosecone (although it doubles as a pilots cockpit), this will help keep the door closed properly as it will sit flatter against the side of the nosecone. The size also fits our parachute better, not too loose, not too tight.

New Timer

This nosecone had a proper Tomy timer, sent to me by Trevor in Cairns (thanks again). These are available from Toy stores. I will have to find them here in sydney. This is what the packaging looks like. They are about $3 each.

Tomy Timer Packaging - Front

Tomy Timer Packaging - Front

Tomy Tomer Packaging - Back

Tomy Timer Packaging - Back

The timer is much better than the previous fish swimmer in nosecone Mk I, as it has a built in regulator. This means that when you cut the wheels off you don’t need to put any weight back on it to stop it from just unwinding quickly.
Here is the timer ready to go into the nosecone. The wheel you can see on the front was cut off.
Tomy Timer ready for installation to nosecone
Tomy Timer ready for installation to nosecone
Ready to Fly
Here is the final configuration, parachute is packed, elastic band is connected to the timer (far left), the speed flap (launch detect) is attached and the nosecone is attached to the top of the pressure bottles.
Ready to Fly

Ready to Fly

Also our fearless pilot is strapped in and readyfor launch

Posted by on September 8th, 2008 Comments Off

Air Flap Launch Detect & Deployment Timer Calibration

Air Flap Launch Detect

The Air Flap detects launch and releases the timer that in turn releases the parachute. I modified the Air Flap to make it longer and narrower. I expected that the original one which was shorter and wider would probably have been pushed down by the air resistance at launch, but I couldn’t make it release by blowing hard on it.

Its possible the original one would have worked but I cant be sure it would be at or just after (less than 0.5s) launch . The new one is able to be released by blowing hard on the end of it. The longer flap uses mechanical advantage by making the lever of the flap longer so it takes less force to push it back against the body of the rocket and in turn start the timer off.

Here is the flap in the ready to launch position . It is made from a section of corrugated plastic

Air Flap in launch position

Air Flap in launch position

The Air Flap is glued against the side of the nosecone and also has 3M strapping tape to help keep it against the side of the nosecone. I found when the timer is wound up a lot that the edge of the flap attached to the nosecone was starting to lift. This solution keeps it in position.

Close up of Air Flap attachment

Close up of Air Flap attachment

When the rocket launches the air flap is held back against the side of the rocket causing minimal aerodynamic disturbance, I think :) Here it is ready for launch.

Launch configuration

Launch configuration

Deployment Timer Calibration

In order to have the parachute deploy at the right time I needed to know how many turns of the timer would equate to how many seconds. This way as I increase the pressure in the rocket and the apogee height increases, I can tune in the right amount of delay in the timer so the parachute doesn’t open too soon or too late.

To do this I setup the rocket in launch configuration and timed how long it took from launch detect until the chute door opened and the chute was ejected from the nosecone. I can use this time and add another second or so to give me the time when the chute should open.  The results were

Timer Turns Seconds to Parachute Eject

4

3.5

5

4.2

6

4.6

7

5.4

The results were not linear possibly due to the non-linear spring mechanism or the varing tightness of the elastic band, however these are in the ballpark that I need.

I will use the water rocket simulators like Cliffords to approximate the apogee of the rocket prior to launch at a certain pressure and water fill, then dial in the number of turns on the timer to hopefully get the parachute ejection time correct. I will take this table with me on Launch day to use as I increase the pressure.

Posted by on August 28th, 2008 Comments Off

Nosecone Reliability Updates

I have been working on trying to increase the reliability of the release mechanism on the nosecone over the last day or so and have disassembled and reassembled the nosecone a few times.

I found today that the cardboard L brackets holding the nosecone support structure together had separated and the ‘V’ shape of the nosecone was narrower and as such the elastic bands on the deployment plate didn’t have enough pressure to kick out the parachute. I think this was probably caused by 3 things

  1. The glue I’m using isn’t strong enough. I’m using a Sellys “shockproof” superglue but I don’t think this is going to cut it. I’m going to have to try to get my fingers on something better.
  2. It didn’t like being assembled and disassembled a few times
  3. The elastic bands on the deployment plate were possibly strung too tight

I decided to strengthen the structure by wiring the uprights of the nosecone support structure to the circular top and bottom plates. I used what I had available which is some tin (I think) wire which is about 2mm thick and while able to be bent with your fingers, retains its shape very well. To do this I made 4 big staples out of the wire and wired each upright in 2 locations to the base and top plates.

Bottom uprights wired with 4 wire pins for top plate ready to go

Bottom uprights wired with 4 wire pins for top plate ready to go

Its easier to do all 4 at once, I found out when doing the bottom plate. You can see here the 4 pins are ready for the top plate to be wired on.

4 Pins in place in uprights

4 Pins in place in uprights

The top plate is put on, i pushed a piece of the wire easily through the corrugated plastic beforehand so the holes were in the right locations, then the wires are just bent to either side and trimmed to remove access

pins in place and bent over (excess not trimmed yet)

pins in place and bent over (excess not trimmed yet)

here is a pic from the inside section where the parachute sits when its ready to be deployed

pic inside the parachute area before deployment plate is put back in

pic inside the parachute area before deployment plate is put back in

I did realize that I now had things that the parachute could possibly snag on .. (Murphy’s law at work) .. so I covered all of the exposed wire with tape to make it smoother and eliminate (or reduce as much as I can) the chance of the parachute snagging while being deployed.

exposed wire taped up

exposed wire taped up

I taped the wire at the top and bottom of the plates so there was nothing to snag on.

Another small change to increase reliability was to invert the wire I had holding the door onto the nosecone. When the elastic band unraveled it caught on the exposed ends a couple of times during testing, so I took them out and reversed them so the bent sections were inside. I covered these with tape as well on the inside.

inverted wire pins

inverted wire pins

An additional change was to remove a small amount of corrugated plastic I was using to mount the timer on. I found that during testing the bolt on the timer would hit the inside of the plastic nosecone and in some cases stopped it. I only noticed this issue when I first packed the parachute. Removing the extra piece moved the timer closer to the middle of the nosecone and allowed more room for the bolt on the timer to spin freely.

Further testing showed an improvement in the reliability of the parachute deployment. I realize the extra wiring will add weight to the rocket and reduce the height it will reach but the nosecone support structure is very solid and can easily handle the tight rubber bands on the parachute release plate.

I think the increased reliability will be worth a little less height :)

Posted by on August 22nd, 2008 Comments Off