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 :)

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This entry was posted on Thursday, October 8th, 2009 at 1:15 am and is filed under Development. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

 
 

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