HHWRSA

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.

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.

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.

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.

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.

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

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

Regulars to the blog would know that I do a lot of testing / building late at night. One thing I like to do prior to launch is a pressure test of the wrockets pressure bottles, especially where there are multiple bottles and robinson couplings.  Even though these are not burst tests, it is loud when the abort valve is opened, not to mention spraying a lot of water around.

We needed a solution that would keep the place kind of dry and let us test at night without waking the neighbors. We had some good suggestions from the water rocketeers on the Water Rocket Forum and came up with the Hydrostatic Silencer

Our launcher has a gardena style quick release (that has a one way valve in it) as well as a abort valve. Here is the setup

The launcher itself is not used, one side of the quick release plugs straight to the pressure bottle being tested (this opens the small 1 way valve in the gardena), the abort valvue has had an extension piece added (which is removed when launching) on the output of the abort valve and goes into a bucket of water

The attachment is 13mm black poly hose which is quite rigid and strong, the end was sealed up with reinforced tape and the end 10cm perforated with approx fifty (50) small 3mm holes.

Here is the extension by itself. I cable tied some metal to the perforated end to make it sink in the bucket of water

Here is the video of it in action, you need to make sure you have your audio on to hear what it sounds like.

Its makes a lot less noise. I just have a piece of wood over the top of the bucket to stop the water splashing out, but I will invest in a new bucket with a lid

It works well for our purposes. Now on to testing more bottles

Launch Rail
After the ground hugging cruise missile on our last launch day due to wind knocking the wrocket off the launcher, we decided for safety’s sake to install a launch rail prior to our next launch day.  We looked at the different options available and decided on a launch rail and launch lugs for the wrockets.

On the positive side this launch rail configuration will

• ensure the wrocket can site vertical on the launcher if we get gusts of wind prior to launch
• ensure we get vertical off the pad
• with redundant lugs on the wrocket ensure we still get off the pad vertical even with multiple lug failures

On the negative side

• this configuration will cause extra drag on one side of the wrocket due to the lugs. How this effects flight we will have to see on our next launch day

We decided to go with a curtain rod as it was practically perfect for our needs and also came with the lugs already supplied (normally used to hang the curtains). here are some pics

I had seen these in a local shop and they were about $30 which was a bit steep so I kept looking. Luckily this week is a council cleanup here so everyone puts out their old junk to be picked up and thrown out. I spotted exactly what I needed when driving home one day not 500m from my place. I turned around and picked up 2 x 1.8m rails with lugs attached …. recycling at its finest .. perfect ! As a bonus I found that these actually had another sleeve inside them which allows it to extend up to 2.8m which is more than enough.

The rail is attached to a solid “L” bracket with cable ties (temporary but strong enough to test with) vertically and this is then attached to the base with 2 screws with wing nuts. This allows it to be removed for transport then quickly reattached. At the moment as we are using the 1.25L as our standard bottles the fixed rail location is fine.

To get it to fit we had to move the support pole off centre a little. Here is a pic showing the rails full height on the launcher

Lugs
Next step was to modify the existing curtail rail lugs to fit on the wrocket. These were just cut and filed. Below the original curtain lug is on the right, the middle and left are ones that have been cut and ready to stick onto the wrocket.

These were stuck onto the wrocket body modules with PL Premium (this stuff is brilliant) and left to dry for 24hrs.

The other bottles had one (1) lug each and the dummy nosecone has 1 as well. The parachute modules dont have one to reduce the chance of an elastic band getting caught up on one.

Ready to Fly
Here are H2 and (the new) H3 wrockets with their lugs glued on and aligned. H3 has the bigger Removable Fin Assembly as it will soon have another pressure bottle added.

Here is H3 on the launcher with the lugs in the rail

Initial Testing
The initial test were done with 30psi (no water) just to make sure the bottle would come off the launcher properly.

The launch rail worked perfectly with no hangups. This was tested a few times with perfect results. Next test will be the launch day with H2 & H3 in action.