Based on the build described in my previous 'Fire Monitors part 4' blog, the performance of the fire monitors on the lake was less than impressive so I decided to rework the plumbing.

The solenoid valve based solution worked, but the water flow was restricted by the small bore of the valves. Using two valves to divert water from the ESC cooling to the monitors also meant that one or other of the valves was always energised resulting in unnecessary battery drain. To overcome these limitations, a diverter valve was constructed based on a 10mm compression fitting from the local plumbing store. A central rotor was turned on the lathe and then cross drilled to produce a three port valve which is actuated using a small servo. I wasn't sure that this would work without leaking, but with an o-ring fitted on the rotor shaft it seems to be OK. At one extreme of the servo rotation, water is routed from the pickup scoop to cool the ESC and motor. At the other extreme of travel, water is routed from the pickup to the monitor pump. An RC switch connected to the same Rx channel as the valve servo switches the monitor pump on when the valve is routing water to the pump.

The pump was also upgraded. I have tried a variety of pumps sourced on-line, most of which did not have adequate performance. The pump now in use is an aftermarket windscreen washer pump which seems to work OK.

To make it easier to install in the model, a ply chassis was constructed to hold the valve, pump and the RC switch. The chassis also provides a locating box for the LiPo.

Out on the lake this afternoon, I was able to get a few photos of the monitors in operation. The performance is much improved.

The last gadget to be added to complete the Crash Tender refit is the searchlight.

The body is made from a short piece of 15mm copper water pipe. A domed piece of copper soldered to one end closes off the body. The tube is just the right size to take a 1W LED and lens. The front cap was made from a ring of copper cut from a Yorkshire fitting which slides over the body of the light. Two small nuts (8BA) soldered 180 degrees apart on the circumference of the body provide mounting and pivot points. The body is mounted to a U shaped brass bracket which in turn is soldered to a brass tube.

In addition to being able to rotate the searchlight, I wanted the challenge of making it elevate. A mechanism mounted under the wheelhouse roof provides both the rotation and elevation mechanics. A small servo provides the rotation function. Two plastic gears, salvaged from a defunct inkjet printer, couple the servo to the brass searchlight mounting tube. The gear ratio gives the searchlight a rotation of 270 degrees.

To provide the elevation function, a pushrod passes through the centre of the searchlight mounting tube. As this pushrod is moved up and down, it adjusts the elevation of the light via a wire connected to an arm on one of the searchlight pivots. The pushrod is hollow and tapped with an M2 thread. A length of M2 studding threaded into the end of the pushrod is rotated by a small stepper motor. As the motor rotates the studding pushes or pulls on the pushrod, thus elevating the light. A small scratch built electronic module converts the demand from a receiver channel into step commends for the stepper motor. The motor was salvaged from an old floppy disk drive.

The completed assembly was primed and then painted with Tamiya Gunmetal Grey. The LED is driven from an RC switch and constant current source and is quite bright, even in full sunlight.

Graham93