Posts Tagged ‘nosecone’

 

Water Rocket Car R/C Development (continued)

This week we have been working on the development of the Water Rocket Car’s remote control steering and fixing a few smaller issues with the launcher.

RC Steering
We realized a more powerful servo was needed. Thanks to George for his suggestion of reducing the arm length to get more power out of the existing servo. We gave did try this but it still wasnt working well enough with the weight of the car on the wheels, it also seems to have centering issues on one side when the steering arm is connected that low. The new servo has worked perfectly since we have put it in so we will go with that, we can always use the other servo to release a parachute or pull a brake lever …  :)

The HITEC HS-985MG servo we are now using is an analogue servo which has 12.4kg/cm torque which is 3 times that of the previous servo. It weighs 62g which is a little heavier than the 46g of the previous servo, but has practically the same dimensions.

We have performed a few un-powered tests and the car seems to behaving well. Here is the video

Servo Mount & Second Level
We put together a stronger (metal) servo mount to secure the servo to the base of the car and secured the second level to the car with three screws.

New Servo Mount

New Servo Mount

The second level is to hold the battery and radio receiver above the steering arm. We decided to leave it this way to maximize space on the car for the pressure bottles. We have put a piece of wood between the first and second pressure bottles which will stop the pressure bottles from crashing into the servo or second level in case of a crash or under high acceleration.

Second Level for Receiver and Battery

Second Level for Receiver and Battery

The battery clip we had didnt have an on/off switch built in, so after rummaging through some electronic spare parts we made found a switch and soldered it  in-line so that the power can be just switched on and off without having to pull the power cable from the receiver. The switch is mounted just under the second level by the right front wheel.

Battery on/off switch

Battery on/off switch

Fliptop NoseCone
We also realized we needed some protection for the receiver and battery in case of a roll over. This was accomplished with a new extended nosecone. The nosecone is a “table tennis ball” nosecone we already had plus and extended section from another bottle. These are glued with PL Premium. The nosecone is held in place to the base by wire at the front, which allows it to flip up to access the battery and receiver without needing to take it off the car. The other end is taped to the last pressure bottle.

Fliptop Nosecone

Fliptop Nosecone

We also decided to paint the nosecone black … it looked a bit ordinary when it was clear with the glue and multiple bottles … it looks good in black. Any heat soak on the nosecone shouldn’t have a detrimental effect on the pressure bottles.

Nosecone in place

Nosecone in place

Front Bumper
We also needed better protection for the front wheels and subsequently the gears on the servo in case of a crash. We have seen from previous launches what a crash does to front wheels. We have fitted another section to the front to take the impact of a crash if the need arises. Better to sacrifice a piece of plywood than a wheel or servo. we will probably replace this with a front wing once its working properly.

General Fixes
There were a few things that needed fixing from previous crashes and issues.
– One of the front wheel bolts /bearings was bent, so we replaced it.
– The gardena quick connect had developed a leak and the 1 way valves inside them were sticking in the on position. This wasn’t allowing pressure into the bottle. When we pulled them out they had some rust on them, we decided to replace them both.
– We made a new holder for the launch string, have been meaning to do this for a while, it just makes it easier to setup and pack up the string to the launcher.
– We had a few stickers that came with the servo, so we added these to the car .. why not :)

Addition of string holder to the launcher

Addition of string holder to the launcher

Replaced Gardena Qucik disconnect for launcher

Replaced Gardena Quick disconnect for launcher

100m Here We Come
The only thing left to do now is a final pressure test for the nozzle, then head out to the test track to try some pressurized tests and break that 100m distance record we have been threatening to break for a while. Just need the weather to co-operate :)

Posted by on October 8th, 2009 Comments Off

PPNC Dummy Nosecone Module

One of the downsides to crashing a wrocket with the PPNC Main Parachute module is that the nosecone itself in almost all cases needs to be replaced. This usually means redoing the door and holes for the tomy timer. Whilst this is not overly difficult, on a flight day if we have a crash like this it usually means the end of testing the parachute mechanism as its usually damaged enough not to work.

With this in mind we have come up with the dummy PPNC nosecone module. If on flight day we have a crash most of the damage will be to the dummy nosecone and the thinking is we can just put another dummy PPNC nosecone on and fly with the parachute again. These PPNC Dummy nosecones take literally 5 minutes to make, so we can have a few of them at the ready.

Here is the dummy PPNC nosecone with its bubblewrap padding.

PPNC Dummy Nosecone

PPNC Dummy Nosecone

Its a bit smaller than the normal size PPNC simply because this is what we had left after making the door for the Drogue Chute Module.  We may decide to make it full size in future. Here is a pic next to the PPNC Nosecone module and main chute.

PPNC Dummy Nosecone v's PPNC Nosecone with main chute

As with the other modules it fits snuggly onto the shrunken bottle bottom undernearth, wether this is another module or a pressure bottle. Here is the PPNC Dummy module with the Drogue Chute Module and a shrunken pressure bottle

PPNC Dummy Module + Drogue Chute Module + Shrunken Pressure Bottle

PPNC Dummy Module + Drogue Chute Module + Shrunken Pressure Bottle

We have added this to the module weights page, the PPNC Dummy Module weighs in at 22 grams (0.776 oz)

Posted by on October 10th, 2008 Comments Off

Dual Deploy Nose Cone – Part 2

Rethink
After building the SSPPNC and thinking about the servicing problems I was facing, I came to the realization that this SSPPNC didnt really fit with our philosophy of a modular approach to water rocket construction. Rather than building a SSPPNC that could deploy both chutes we decided to leave the PPNC as it was and build a drogue chute module. The idea being that this module could be added or removed from the rocket based on the requirement of the launch.

Bottle Shrinking
One problem we have found when fitting and aligning the parts of the rocket was the fact that the diameter of the PPNC is smaller than the bottom section of the PET bottle, not by much but enough to have it not fit on straight and sometimes having to be realigned after taping.

We decided to use George’s method (http://www.aircommand.com) of shrinking the bottom of the bottle. This ensured the PPNC slides over the bottom of the bottle underneath it in the rocket. See Georges video about the 4:00 minute mark for how to shrink a bottle. We didnt quite have the water boiling but Im guessing around 80 degrees C. We immersed the bottom of the bottle a few times until we had it the size we wanted.

Here is a pic of 2 x 1.25L bottles. The bottle on the left is a standard bottle, the bottle on the right has had the bottom shrunk slightly.

Shrunken bottom of 1.25L bottle (right)

Shrunken bottom of 1.25L bottle (right)

Although they look very similar there is a big difference when connecting the modules together. This is best shown with a video. So here one is. In this video I am connecting the new drogue parachute module to one of the rockets pressure bottles. First connecting to one I have shrunk, then to an untouched bottle. You can see the difference.

Drogue Parachute Module
In part one of this article we showed the nosecone structure for the drogue deployment module. As we have now decided to make a drogue module that can be added or removed from a rocket, we needed an enclosure that would allow this. The obvious choice was to use the bottom section of a shrunken bottle.  This will allow the PPNC module to fit over the top of it, it also allows this module to fit over another module (a future payload module) or the bottom of the pressure bottles.

Drogue Chute Module

Drogue Chute Module

We have used bubble wrap as fill in the top section (its lighter than sponge), the size of the structure and door opening is smaller, to take smaller chutes, but the tomy timer configuration and air flap is the same as the PPNC module

Putting The Modules Together

The modular method we have used to shrink the bottom section of the bottles allows the modules to be easily put together to form the rocket combination we desire. Here is a video of the PPNC module, drogue module and out pressure bottle being assembled. For liftoff they are taped together. This method makes module alignment much easier.

I have weighed the modules and shown it here for those interested. You can always get to this from the Menu section of the site then under categories then weights.

Dual Deployment
Here is a test run of both chutes deploying, the modules are connected to H2. We will do a bit more testing prior to launching this configuration, however so far so good. The air flaps detect launch and will sit closer to the rocket body during acceleration

Posted by on October 7th, 2008 Comments Off

Dual Deploy Nose Cone – Part 1

The last week we have been busy building a PPNC nosecone that will deploy 2 parachutes using tomy timers. The idea is to have a smaller drogue chute deploy at apogee and the main chute when its closer to the ground.

Drogue Chutes
We have used some simulators to try to work out how big to make the drogue chute, but ended up with mixed results. So we decided to make 2 drogue chutes and see how they test. These were 10cm in diameter and 15cm in diameter respectively. We used the same procedure as we did when making the main chute except reduced the number of chute lines to 4 and 6.

Drogue Chutes

Drogue Chutes

On initial testing, the 10cm chute is just too small and doesn’t get enough air into it . The 15cm chute might be ok, but the hole in the middle is too big. We can just sew a patch over it and give it a further test. Worse case a 20cm one may be called for.

Longer PPNC Nosecone
The two chutes and release systems wont quite fit in a standard 1.25L body section we make the PPNC nosecones out of, so we have made a super sized PPNC (SSPPNC) by adding an additional 1.25L body section.

Super Sized PPNC Nosecone

Super Sized PPNC Nosecone

The bottom section was from a different 1.25L bottle manufacturer and is just used for the mockup, we will use a P&N bottle for the final nosecone.

There join is not perfect and the nosecone structure gets stuck a little. We will need to be more careful when fitting the final bottom bottle as we need to be able to get the nosecone structure in and out for servicing.

Nosecone Structure
The nosecone structure needs to have 2 elastic band powered pressure plates to push out the chutes. To accommodate this we have built another smaller structure as well as a section to join the two chute deployment sections. We needed this to have enough space between the two so they was less chance of lines being caught up.

Here is the drogue deployment structure (pressure plate not fitted yet)

Drogue chute deployment structure

Drogue chute deployment structure

You can see we use wire to join the sections together, this makes it very strong which allows for tighter elastic bands which help throw the chute away from the rocket body better, as well as having a better chance of survival during a crash.

Here is the structure how it will fit inside the super sized PPNC.

PPNC Dual Deploy Structure

PPNC Dual Deploy Structure

From the top down the pieces are

  • Pilot capsule – its main use is to ensure the main parachute deployment structure is below the curved section of the top of the nosecone. This helps the door close better if its flush against the side.
  • Main Parachute deployment section and pressure plate
  • Extension section – This is to position the drogue chute deployment structure down below the join of the two bottles in the nosecone. Having the door across the join is not a good idea
  • Drogue Chute deployment section (note the pressure plate is not fitted yet)

The two doors will be on opposite sides of the SSPPNC. The idea for putting the drogue lower than the main chute is so that when the drogue deploys it will be connected to a lower part of the rocket nearer the CP than the CG, the rocket will orient itself with the nosecone down position and drogue trailing behind. This gives a lot of room for the main to deploy and open being furthest away from the deployed drogue. The main chute will be connected close to the CG so that the main and drogue dont tangle .. well thats the theory anyway :)

Tomy Timers
We received our order of 5 tomy timers yesterday which is good. We also managed to destroy the one we had when glueing it to the structure, too much glue and we managed to glue up the gears … Lucky we ordered a couple of extras

The work for the rest of the week will be assembling the nosecone, testing the dual timer and getting some calibration numbers on the timers.

We will report part 2 later in the week

Posted by on October 1st, 2008 Comments Off