How does an RV speed reducer work? | Structure and function simply explained | Transmission ratio

In this video we take a closer look at the function and structure of a so-called RV speed reducer. This type of gearbox is used in robotics, for example, to move heavy loads with great precision. The RV gearbox is essentially a combination of a cycloid gear and a planetary gear.
The crankshaft of the cycloid drive does not necessarily have to drive the cycloid disks at the center, but can be off-center. The rotation of the crankshaft still drives the cycloid disks around the pins. The only difference from a central drive is that as the cycloid disks rotate, the axis of rotation of the crankshaft also moves on a circular path. Ultimately, it is this circular motion of the crankshaft that is used for the output in an RV gearbox.
The crankshaft is driven by a simple spur gear mechanism. While the output gear can rotate with the crankshaft in this way, the axis of rotation of the input gear remains fixed. Since the axis of rotation of the output gear rotates around the input gear, it is essentially a planetary gear with a centrally located sun gear and a planet gear rotating around the sun gear.
In principle, the RV gearbox is complete. It consists of two gear stages. The first stage is the planetary gearbox, which is used to drive the crankshaft. The second stage is the cycloid gearbox, which provides the circular motion of the axis of rotation of the crankshaft. So note: The planetary drive produces the rotational motion of the crankshaft around its center of gravity, and the cycloid drive produces the circular motion of the center of gravity.
The transmission ratio results from the number of pins, the number of teeth on the cycloidal disk and the number of teeth on the planet gear and the sun gear.
The main advantage is the low backlash, which makes the RV ideal for applications requiring high positioning accuracy, such as robotics. The precise design also ensures high repeatability in motion sequences.
Another advantage is the high transmission ratio combined with a compact design. RV gearboxes are also characterised by their high load capacity. They are very robust and can carry heavy loads, making them particularly suitable for heavy industrial applications. The continuous contact surface of the cycloidal disks ensures smooth operation, reducing vibration and noise. Their robust design and even load distribution also result in a relatively long service life.
Despite these advantages, there are also some disadvantages. For example, the complex design and precise manufacturing of the cycloidal discs and needle bearings make production relatively expensive. In addition, maintenance costs can be higher, especially if special replacement parts are required.
RV gearboxes also require regular lubrication and maintenance to ensure optimum performance and durability. At very high speeds, efficiency can decrease and wear can increase. These gearboxes are generally more efficient at lower speeds.
00:00 Structure and Function of a Cycloid Gear
01:14 Eccentric drive (2nd gear stage, output stage)
02:11 Planetary gear stage (1st gear stage, input stage)
03:52 Transmission ratio of the cycloid stage
05:08 Transmission ratio of the planetary gear stage
06:22 Overall transmission ratio of the RV gearbox
07:23 Advantages and disadvantages

[@zerenzhong]

Thanks for your great job! I am extremely glad that my comments are fulfilled with such wonderful video clip. It is so helpful to my further work!

[@tec-science]

I'm glad you asked, otherwise I wouldn't have looked into this wonderful operating principle.

[@puntabachata]

Great explaination for such an amazing concept.

[@tec-science]

Thank you very much!