Dual concentric rotary encoder with switch

During the summer there has not been much progress on the 737 throttle quadrant, but instead I’ve been improving my X-Plane 11 setup and taken some ‘flying lessons’ in the default X-Plane 11 Cessna with help of the great video tutorials of Jason Vriends.

While struggling a bit with the Garmin GNS530 on-screen rotary switches I realized that implementing this GPS as hardware would be a nice ‘test vehicle’ for the future work on the 737 cockpit panels. And having the GPS in hardware will make flying with the Cessna more fun.

As the GPS panel can be undocked to a separate window a small VGA panel can be used for the screen and hardware switches and rotary encoders can be connected as inputs via a single 40 wire flatcable to an OpenCockpits Mastercard.

Speaking of the rotary encoders: in the past I found some affordable concentric rotary encoders on Aliexpress, but for most cockpit functions and also in the Garmin GPS they require an extra push switch and besides I haven’t been able to find suitable knobs for the short internal axis of the Aliexpress encoders.
At leobodnar.com ELMA 37 concentric rotary encoders with integrated push switch and matching knobs can be bought, but they’re expensive and quite a number of them are required for a complete 737 cockpit.

So I decided to try a different solution: build them myself by combining two cheap rotary encoders with integrated switch and some DIY gears and aluminum profiles and tubes and axis.

The design was made in Sketchup. In the 3D warehouse I found a complete 3D model of a rotary encoder and the other parts I created myself or copied parts of other 3D warehouse models. In Inkscape I experimented with gear sizes to match the distance between the two rotary encoder axes in my design. The 2D design of the gears was saved in plain SVG format and imported via SVG import in Sketchup as a template for the 3D ones.

Sketchup was used to determine the position of the holes in the aluminum 15x15mm 2mm thick U profile and the profile design was exported via DXF to Estlcam to create the CNC tool paths.
In a 18mm MDF panel I created slots for a long 15x15x15 U profile (to cut it into 26mm long parts) and a 26mm long slot for fixing the profile during milling of the holes.

For the 4 mm (brass, Karwei DIY shop) and 6 mm (aluminium tube, Karwei DIY shop) axes I milled pockets in the same 18mm MDF plate for stable fixation so that I could flatten one end to a D-shape.
The D-shape end of the internal 4mm shaft is connected to the 6mm rotary encoder D-shaft via 2 plexiglass 5mm thick disks that are glued together with superglue.

The gears are also CNC milled in 5mm plexiglass.
To mount the whole construction to the frontpanel I found 10mm diameter threaded tubes that are used to hang ceiling lamps.

They’re so long that one tube can be cut in two for two concentric rotary encoders, but 3 nuts are required per dual encoder pair.
The inner diameter of the 10mm tubes is 6.8mm, so a bit too large for the 6mm outer axis. While laminating paper I got the idea to wrap a piece of laminating plastic around the 6mm axis for less backlash. This worked quite well.
A 30 x 30 aluminium L profile is milled to connect the 15×15 U profile with the 10mm threaded tube. Also for this pockets were milled in two 18mm MDF panels for easy fixation during CNC milling.
The two rotary encoders are placed as close as possible to each other. Because of this, the pins at one side of the outer axis encoder almost touch the axis of the other encoder. But as the switch of the outer axis encoder is not used this encoder is mounted with the unused pins towards the other encoder.

Finally I want to create a small PCB to join the common ground of both encoders and switch and to connect all encoder pins to a 5-pin header.

The designs for CNC milling can be downloaded here..


3 thoughts on “Dual concentric rotary encoder with switch

  1. Nice work Theo. Ik wil ze ook maken. Ik wilde het met mijn 3d printer proberen. Ik denk dat ik de tandwielen en het huis kan 3dprinten ineen geheel. Ik ga het proberen de komende maand. Ik heb geen CNC frees. Verder heb ik nog wel een vraag aan jou over de fotos die je voor je panels gebruikt. Wil ik ook proberen alleen kan ik geen foto met een goede resolutie vinden. Heb jij een idee hoe ik er aan kan komen of een link voor mij? Groet Robert


    1. Hallo Robert, interessant: hou me op de hoogte. Voor de panels laad ik screenshot foto’s uit de simulator in Inkscape en teken ze dan over zodat ik een vector tekening krijg. Omdat ik meestal niet de originele schakelaars etc heb moeten ze sowieso meestal wat aangepast worden. Misschien kan ik dat ook nog wel een keer in een video laten zien.


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