You can put a filtration system in place before the diverter and this does help prevent them getting clogged with moss and other debris from the roof but, they are then essentially filtering everything that comes off the roof and the filter will need emptying/cleaning often.

My preference is to have the filtration system after the diverter as it makes more sense. This means the filters are much less likely to become full with debris because the diverter will just pass the water and debris straight through when the tank is full. The filtration system no longer has to filter all the rainwater coming off of the roof. In the winter months, the water in the tank is not really used and it can remain full for a long time.

This approach also means that I can control the diverter much more intelligently based on when it last rained, last stopped raining, or based on other factors, to ensure that an initial heavy rainfall after many months of dry weather is not collected and will therefore not be passed through the filtration system.

The main housing is a semi-circular design, with two mounting holes in the rear face. The water comes in via a top lid, vertically above the main exit hole at the bottom. This ensures there is minimal restriction of water when the diverter is not in operation (i.e. off). There are two bottom exit holes 64mm in diameter and their centres are 76mm apart.

To simplify the 3D printing of the main enclosure, the bottom pipe connectors are separate parts that will be glued in place. These fit through the two bottom 64mm exit holes and down into the two exit pipes.

The diverter 'blade' rotates around a 5mm driveshaft and can be moved underneath the main inlet pipe. It has a sloping face, to divert the water over to the other side of the enclosure and down through the second outlet hole, which leads to the filtration system and onwards to the rainwater storage tank.

I'm using a reversible, high torque, worm geared motor that rotates at 3RPM at 12V. This equates to about 5 seconds to rotate the 'blade' the required 90°.

The control interface is a simple 3-wire connection. A common ground wire is used with two power lines. Power is applied to the 'Open' line one to turn the diverter on and applied to 'Close' line to turn it off. Two end-stop switches detect the fully on and fully off states and cut power to the motor and the relay, so that power is only used by the motor when the diverter is moving. When active, the relay basically reverses the polarity of the power to the motor and makes it run in the opposite direction.

These micro-switches are used to detect the travel end points. They are just 20mm × 10mm.

The first thing I did was to 3D print the pipe connector, to ensure it fits my standard 68mm pipe. This then allowed me to size the enclosure correctly. Note that this is printed with a brim, to improve adhesion to the build plate.

The pipe connector cleaned up. It has a 2mm wall thickness.

The motor arrived and is nice and compact, yet powerful. Testing with a 12V supply shows it to be very quiet and just the right speed of rotation for this application.

Attached to the motor spindle below the motor but inside the 'lid' is the 'needle'. This closes the micro-switches to detect each end point. This is my 3D design and this will be 3D printed to test the mechanical elements of the diverter before the whole thing is 3D printed.

The motor spindle is attached to the diverter using this aluminium coupler.

My contextual smart home already has a connected optical rain sensor, which is very accurate and reliable. It knows if it is currently raining, when it last started and stopped raining and how long it has rained for in each of the last 31 days. This means it can log daily rainfall and monthly rainfall.