The radar unit is something that deserves to be made as a ‘dynamic’ feature rather than a static fixture and Simon (Skydive130) showed the way forward on this and set the bar quite high too!.
Determined to at least match his efforts I set about making my own. The first consideration was whether to build it around a micro servo modified for continuous rotation, or concoct my own motor and gearbox solution or buy something ready-made. I opted for the latter as it was readily available and quite well engineered (but not inexpensive!)
https://www.mr-rcworld.co.uk/shop/radar-motor-gearbox/
It consists of a small DC motor coupled to a gearbox and controlled by a small circuit board that enables it to be connected to and be powered from the receiver, which means it can be switched on and off using an auxiliary radio channel.
The small PCB also has a variable pot to allow adjustment of the rotational speed.
Fortunately the ‘Furuno’ radar units fitted to the pilot boats are quite common and some very useful specifications and dimensional drawings can be found on the manufacturer’s website which makes life a little bit easier.
The radar unit ‘scanner’ bar was made first by laminating some square styrene bar and some half-round profiles to form the basic shape which was then worked with files and abrasives to the right shape and then some end caps were fitted to this after cutting the bar to length.
I found a useful little splined brass collar on RB Models website which is perfect for the attachment of the scanner bar to the drive shaft with a grub screw fixing. This collar was set into the underside of the scanner on a rectangular fixing plate with a styrene collar to conceal it. Some styrene hex bar was used to simulate the fixing bolt heads.
The main supporting pillar ‘bearing’ was made up from a combination of brass tube, styrene tubes and brass rod with a brass porthole at the base to simulate the roof mounting flange. The 2mm brass rod at the centre of this piece was threaded at the bottom end to mate with a short piece of 3mm brass tube onto which I silver soldered a 2mm brass nut which I reduced down to the diameter of the tube.
This short tube fits over the motor/gearbox output drive shaft and it will allow me to separate the drive shaft from the motor and so very much simplify the final fitting and adjustment. This brass adaptor tube was epoxied over the drive shaft and after a quick test this shaft proved to be a very smooth and free running within the support pillar bearing.
The unit at the top of the pillar is the motor unit on the real thing, and this was made from some obeche square section wood laminated together and the drilled centrally to accept the supporting pillar.
This obeche wood was then formed to approximately the right shape by carving and filing and adding some very thin Plasticard overlays to finish it off.
When I was happy with the shape of this motor housing I sealed and primed the wood and finished it with a coat of white gloss, the scanner bar was also sealed and painted in the same way. This pillar and the motor unit were glued together and I then added a square mounting flange made from some Plasticard sheet and finished with some more simulated bolts. After a final overall coating of gloss white I painted the pillar below the square flange with some silver paint.
I had previously made some waterslide transfers of the Furuno logo and this was applied to the face of the scanner bar and really makes the part look authentic.
I assembled all of these bits together to test and found that a .25mm PTFE ‘shim’ between the top of the drive shaft and scanner bar greatly improved the rotational smoothness. The next thing to do was drill the cabin roof to take the pillar, the lower part of which extends below the mounting flange and passes through the roof to be flush with the underside of the roof panel.
The motor and gearbox unit was slightly modified with a brass tube spacer between the mounting flanges to add strength for the screw fixing and some neoprene ‘pads’ applied to form a resilient interface between the gearbox and the cabin roof so that the unit has a bit of ‘give’ rather than be rigidly fixed.
The 2mm brass central drive shaft was then fitted by screwing this down through the bearing into the threaded gearbox adaptor and the scanner bar fixed to the top of the shaft with the grub screw (not forgetting to add the shim in between). Fortunately I got all of the measurement right so I didn’t need to adjust the length of the drive shaft.
The whole assembly was then given a final bench test using a 1.5v battery to run the motor and it works really well and is also fairly quiet in operation too. Satisfied that all was well the mounting pillar was temporarily set into the hole in the roof and the motor/gear box and output drive shaft centralised in the pillar bearing so that the fixing holes in the gearbox could be marked and drilled. With this in place the scanner bar was fitted and secured with the grub screw and the whole unit tested again to check that there was no additional friction that would affect the rotation.
Happily all was well, and satisfied that it worked as intended and also looked fairly authentic I then removed it all and set it aside ready to be fitted in the final assembly of the cabin.
Cheers Marky👍