3-speed gearboxes 3 speed RC transmissions by Iliya Cerjak

3-speed gearbox, build it yourself transmission for use in radio controlled cars, trucks & other vehicles.

3 speed gearbox for Radio controlled vehicles
RC Transmission logo

3D CAD data and/or 2D production drawings available on request.

Go here for more downloads.

3 speed gearbox RC transmission CT3

CT3 1 channel controlled

2/3, 1/1, 3/2 gear ratio


CT3 – 3 Speed gearbox




This universal 3-speed gearbox can be used in RC cars, trucks, tanks and other vehicle.  Gives your vehicle 3 gearings selectable by remote. Either put an extra low gearing into your all-terrain vehicle, or put an overdrive in your racing car. Configurable as a 3-speed gearbox for your car or truck, or as a 2 speed with reverse. The CT3 Can be used in combination with the CT1 and CT2.



Technical details


A fork operated by a servo moves one gear with pins on each side, coupled to the input shaft into 3 positions.  In the middle position the (steel) gear is engaged to the middle gear on the output shaft. When moved to either side, this middle gear is disengaged, and the pins engage holes in the other (idling) gears on the input shaft, engaging different gear combinations. See the animation of the moving shift fork below for a graphical explanation.


Needed materials: aluminum bar 50x8mm, Aluminum sheet 4mm, brass round 10 & 40mm, Perspex sheet 4mm and miscellaneous fasteners. (Check out the parts list below). All gears are stock size, available for example at Sterling Instruments , RS components, Conrad or any other small drive components supplier, so are all the bearings and shafts.


Above a CT1 & CT3 build by a customer.

His review; ‘Thank for the plans they are working out great…

My name is Chris and I am a Machinist for about 22 years now.

This project has been one of the most favorite ones I have ever made….


(Click on picture to see larger image)


Animation of the moving shift fork.                                        Exploded view and assembly.  



Outer dimensions of the assembly.




The drawing set consists out of; One assembly drawing, with detailed comprehensive exploded views and cross sections. A detailed parts list, manufacturing notes, and all drawings with the parts’ dimensions, manufacturing instructions and details.

 3D CAD data and/or 2D production drawings available on request.

Go here for more downloads.


(Click on picture to see larger image)


CT3 Main assembly drawing & parts list.






The next pictures show the real thing. On the first picture a top view of the CT3 completely assembled. The second shows the CT3 in parts. Don’t mind the very low quality of the parts, I made most of them myself with very little patience.


(Click on picture to see larger image)

CT3            CT3_exploded_perspective

CT3 top view.                                                       CT3 in parts.

Test stand


Having finally build my CT1 and CT3 I had to put them through their paces. The test stand consists out of a 25cc 2-stroke Mitsubishi engine driving a CT1 through a CT3. The engine is mounted on rubber damping mounts onto a wooden base plate. The CT’s stand on aluminum poles, flexible couplings connect the drive shafts. I put all parts together, drowned the CT’s in WD40 and started the engine. Et voila, everything worked as planned. In the video you see the clutches being frantically operated and the gearbox shifting through its 3 gears. To determine the output torque I clamped a vice on one of the output shafts; it was possible to tilt the whole vise turning the input shaft by hand and applying only a small force on the clutch.


(Click on picture to see larger image or video)

CT1_CT3_combo            CT1_CT3_teststand

The CT1&3                                                           The test rig





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