Posts Tagged ‘R/C’


Water Rocket Car MkX – Launch Day

The Easter break allowed a chance to actually do some work on the water rocket car and to upgrade the car to test some stability ideas we have been working on. These include

– outrigger rear wheels
– rear wheels rear of the nozzle
– larger rear wing
– bottle alignment guides

All of these design changes added a bit of weight to the car but we wanted to test for stability rather than just increase distance. What we were after was a straighter launch

We also had a small update to the launcher with the addition of a 20L container to hold 20L of water to hold the launcher down and reduce recoil. It also doubles as a good water supply for rocket fuel :)

Here is the video of the launch day

The longest distance recorded was 87m but that was uphill so over 100m on the flat isnt too much trouble even with the extra weight. We were happy with the results of the stability upgrades with the last 120psi run going straight up the middle of the road.

We will do some more work on this model before we build the next one, there are a few more things to test yet. Hopefully the next update wont take soo long

Posted by on April 12th, 2010 Comments Off

Water Rocket Car MkX – Hydrostatic Mishaps

Its always a good idea to hydrostatic test a new setup before a launch day. Considering we hadnt launched these bottles for a few months, it was an especially a good idea to test them first.

The bottles were filled totally with water and pressurized .. no leaks ….  good .. right up to 120psi then … the last bottle ruptured. This was a rip across the middle of the bottle. Pic below

Ruptured Bottle - ripped

Whilst this was not totally unexpected, it was a bit disappointing but easily repaired after a trip to the supermarket for another 2.25L bottle. Also some of the water went into the electronics section so it was left in the sun to dry while we went to the shops.

The new bottle was cleaned and connected into the rocket car and a 40psi air test to check for leaks around the bottle cap. No leaks so the bottles were filled with water to hydrostatic test again.

Again no leaks up to 120psi .. then .. the last bottle (the brand new one) ruptured …

New bottle ruptured

This time spilling about 3L of water directly into the electronic bay .. hmmm .. not good :(
A close look at the ruptured bottle showed it let go right at the thick end of the bottle. Click pic for higher resolution photo

New Bottle ruptured - close up

This is the thickest part of the bottle, so it was either a manufacturing flaw in the bottle or it pressed up against something to make a weak point and ruptured there.

It could have been either that caused the rupture, but when looking closer at the setup, its possible the new bottle alignment guides we installed could have caused this. The way they were setup meant that when the bottles expanded under pressure all three could only moved towards the front of the car. So its possible that all three expanded causing the bottle that ruptured to press agaisnt the back of the servo and possibly cause a pressure spot.

We repositioned and realigned the bottle guides to allow the bottles to expand in both directions and slid all three bottles back in the chassis about another 10mm. This should now allow the bottles to expand without hitting the servo.

Another downside of dumping 3L + of water into the electronics section is that the r/c wouldn’t  work. The electronics bay was pulled apart and dried and all connections checked with a multimeter. It appeared the on/off switch enclosure was still very wet and was shorting, so it was replaced. Another was soldered in and remounted. It is more convenient to access now.

New on/off switch

By the time the electronics was put back together and an unpowered test of the steering done, it was too late to do another hydrostatic test. We will do one tomorrow and hopefully get to do a launch.

Posted by on April 11th, 2010 2 Comments

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

Water Rocket Car R/C Development

The last week or so we have been working on a R/C (remote control) addition to our water rocket car. There is much to learn it seems in the R/C world and we have been on a steep learning curve this last week. We assembled all the pieces we needed to get it working – these are

– Transmitter – Ours is a Futaba T2PH 29Mhz AM 2 channel radio transmitter (built in antenna)
– Receiver – A Futaba R122JE – 2 channel 29Mhz receiver with built in antenna
– A battery pack with a R/C connector
– A servo – we used initially a 46g servo which has 3.4kg/cm of torque

futaba transmitter

futaba transmitter

servos receiver and battery pack

servos receiver and battery pack

Initially we just did some testing of the R/C gear and this is really not too difficult to get working, 12 x AA batteries and some wires and we were in business, both servos were responding to commands from the transmitter.

In the research we did, there doesn’t seem to be a lot of talk about the range of these transmitters, so we tested what range we could get out of it. We did some testing by having one person hold the servo / receiver and battery pack and the other hold the transmitter and keep walking then every 10 steps or so turn the transmitter steering to see if the servo’s reacted. My other trusty assistant was keen to help out and would yell back “STILL WORKING” each time the steering was turned on the transmitter. We managed to walk 170m away up a hill and over the other side and it was still working, we didnt have line of sight and there was 2 large trees in the way and it was still working. We are not sure really how far it will go because we stopped the test there as I couldn’t hear the replies any more not that it wasn’t still working. So we are happy that the range of this transmitter will be fine for our present needs.

The steering was custom made – based around a simple 1 steering arm design connected to the servo. The steering arm is made of metal (steel) and can probably be replaced with something lighter like aluminum or carbon fibre but will do for the moment.The steering arm is connected to the servo via a single rod which has ball joints at each end. This allows the rod to stay horizontal throughout the servo’s circular movement

Steering Arm

Steering Arm

Each wheel connects to a wheel hub which pivots on a single connection to the body of the car. The steering arm is connected to the hub with a bolt and nut which is fitted loosely to allow movement. The nut is glued to the bolt so it doesn’t fall off and detach the steering arm

Wheel hub and steering arm attachment

Wheel hub and steering arm attachment

Here is the steering with everything attached. A second level was temporarily installed to hold the receiver and battery pack just for testing

R/C Steering Setup

R/C Steering Setup

Here is a video of the steering working on the bench. This was also our first attempt at a wide screen video … :)

We did some rolling tests of the water rocket car and had some success with it steering when it was rolling. The conclusion was that the servo is just not quite strong enough for our application. We have been doing some research and have a stronger servo in mind which has torque of 12.4kg/cm which should do the trick. Once this is ordered and fitted we will do some more trials and work up to full pressure tests ….

Posted by on September 30th, 2009 2 Comments