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4/16-speed RC combinable transmission for Control+

April 29th, 2020 Leave a comment Go to comments

More advanced version of my combinable transmission design, featuring 4 speeds that can be shifted while driving and using a Control+ or Boost motor for shifting. Instructions available.

Having designed a robust 3-speed transmission that could be shifted instantly using a PF Servo motor, and combined into a single 9-speed transmission, I went one step further and packed 4 speeds into a unit of the same size, getting rid of the PF Servo and changing speeds using a Control+ or a Boost motor, or a mechanical stepper.

The building instructions are available here: http://sariel.pl/downloads/

This transmission design is shifted by rotating the shifter axle every 90 degrees. It’s a loopable sequential transmission, meaning that it shifts from 1st to 2nd, 3rd, 4th and back to 1st again. It can shift instantly without stopping and the key to shifting is making sure that the shifter axle only rotates by 90 degrees. This can be achieved in two ways: by simply attaching any Control+ or the external Boost motor and programming it to act as a stepper in a way shown in the instructions and in the video below, or by using any motor equipped with a mechanical stepper such as this one. The first approach keeps the transmission small and simple but requires checking the shifting motor’s output’s position when turning on the Powered Up or Control+ hub the motor is connected to. That’s because the Powered Up app reads the initial position of the motor’s output upon starting and uses it for rotating it 90 degrees. So if you start with a misaligned axle (meaning not set at 0, 90, 180 or 270 degrees), the misalignment will continue and that may lead up to locking up the entire transmission. The mechanical stepper approach doesn’t have this problem, but it makes the transmission much larger and more complicated.

Just like with the 3/9-speed version, this design offers the following key advantages:

  • shifting while driving instantly, to any speed, without any need to stop or to check or observe the transmission, with 100% precision and without jamming
  • gear ratios ranging from 9:1 to 1.6:1
  • input and output aligned end-to-end, rotating in the same direction; you can easily turn the transmission around to swap input for output and get ratios that gear up instead of down (from 1:1.6 to 1:5)
  • input and output are centered in the transmission unit for easy integration into a chassis, and the PF Servo can be attached to either side
  • the whole unit is relatively compact (5x7x10 studs not including motors and side beams), heavily reinforced and conveniently shaped like a cuboid
  • can be easily built into a studless or studfull structure
  • designed so that you can easily combine two units into a single 16-speed transmission producing gear ratios from 81:1 to 2.77:1





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