Joint Chief

What’s the difference between a CV joint and a universal joint?

In the full-scale world, a constant-velocity (CV) joint is truly homokinetic— no matter what angle the joint is bent at, shaft speed is constant. That’s a huge advantage over a universal joint (also known as a “Cardan joint”), which causes shaft speed to fluctuate as the joint is deflected. Further, true CV joints can operate at higher angles of deflection without binding. But here’s the thing: RC cars don’t have true CV joints. What we call “Cv-style” joints all spring from MIP’S original CVD (constant-velocity drive), which is a variety of universal joint. While the design does not offer true “constant velocity,” it does offer advantages of traditional U-joints. A biggie is easy rebuildability. Depending on brand and construction, U-joints must be pried open or have a pin pressed out to remove or install the “cross,” while CV joints simply come apart by removing a setscrew. Or if the design uses a bearing to capture the CV’S crosspin, no tools are required for disassembly—just slip the joint out of the bearing. CV joints are also stronger than many universal joints because they have a continuous “bell” rather than yokes with tabs that can flex or break, causing the joint to fail. Traditional universal joints and Cv-style joints serve equally well in RC, with no significant difference in performance when operating properly. The CV joint’s main advantages are durability and rebuildability.

Here's a Cv-style joint and a traditional universal joint. They look very different, but you can see that each pivots on two intersecting axis.

This stylized illustration of a true constant-velocity joint as used in full-size vehicles shows the sliding-ball mechanism essential to the design, which must be well lubricated and kept free of contamination. It’s not practical for RC use, assuming...