eRacingPro Rzeppa Joint True CVD
(Driveshafts / Axles / Swing Shafts)

Frustrated by the design and durability of the typical metal "dog-bones" that always slip out of socket? Feeling that the full potential of your truck has been limited by the "Universal Joint"'s pulsing output? Heard / discuss about all the great features of what a true Constant Velocity Drive (CVD) can offer but the sad part is it is only available in real cars? Well, not anymore! In eRacingPro, we have once again pioneer another real car luxury item into the RC World. Introducing our latest break-through: the Rzeppa Joint True CVD

What is CVD?

Without getting into all the complex scientific theories behind... this is how your truck accelerates in slow motion:
And for those scientific minds who are eager to learn the nuts and bolts behind, here is a YouTube video from Buick's Know-how Series explaining the advantages of the Rzeppa Constant Velocity Drive in the first 5 minutes
Buick - Drive Axles & Constant Velocity Joints (1988) Video will open in a new window Using the mobile app? Copy this link into your browser:

If we look at Wikipedia, it said: Constant-velocity joints allow a drive shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. They are mainly used in front wheel drive and many modern Rear wheel drive cars with independent rear suspension etc.

In simple terms, it means when CVDs are running at an angle, its output rate is at a constant which will provide stability & preserves velocity. Unlike universal joints, it will not generate oscillating variable output which causes vibration and noise and reduces the life of the axle.

Our True CVD utilizes the concept from Rzeppa joints. It consist of 5 metal ball that are guided on a CNC machined grooved ball joint. This creates 10 point of contacts on each joint and increases the durability of the joint dramatically! This revolutionary frictionless design will survive higher torque and handle higher RPM. Each shaft is build with two half shafts which are connected to each other with a 6 splines configuration. It allows up to 15mm of shaft length extension to accommodate toe-in, camber and extreme arm angles.

Exploded View

Feature

Rzeppa Ball Joint guided with 5 metal ball
Frictionless operation, Smooth Power Transfer, Zero Binding
Provide Stability and Preserves Velocity
Zero Vibration, Zero Noise
Built with 2 Sliding Halfshafts to achieve Variable-length
20mm Slider to accommodate Toe-in, Camber and Extreme Arm Angles
Each Joint has 10 Points of Contact to Maximize Durability
Slider has 6 splines to secure shaft in place
Able to tolerate excessive torque
6mm Shaft Diameter - Strengthen to handle serious abuse
Extra protection against crashes
Replacement for the original plastic fragile axles
Provides better support for the upper and lower arms
Increase stability in sharp corners
Better Steering
Light Weighted: 96g per shaft
Length (compressed): 181mm
Polished, Chromium Plated for a shiny finishing
Computer Numerical Control (CNC) machined
Rebuildable (Rebuild Kit available in our store)

What is so special about your True CVD? Why should I use it?

Typically, this is what is available in the market today:

Universal Joints (aka Cardan Joint)

Dog bones

Feature Comparison Table

True CVD Universal Joint Dog Bone Constant Velocity Output Yes Depends Yes Vibration Zero Yes Angular Velocity Yes Awearing out Point of contacts 10 4 2 Torque Tolerance High Medium Low Angled Operation Frictionless Notchy Will wear out Drive Cup Half Shaft Yes Yes No Free Play (Wear & Tear) Zero On U-Joints A lot, due to dents on Drive Cup Variable Length 20mm 15mm 5mm Durability Excellent Above Average Below Average

Below are a list of shortfalls Of the Universal Joint and Dog bones.

Universal Joint Disadvantages

Universal Joints are also known Cardan Joints. It consist of a pair of hinges oriented at 90 degrees to each other, connected by a cross shaft. Although it is more durable than dog bones, there is one major short fall this design is suffering. Due to the Equation of Motion (more info on Wikipedia), when power is transmitted at an angle from input to output, even when the input is rotating at a constant speed, the output will rotate at a variable speed (with magnitude depending on the operating angle), causing vibration and wear. Below is the Output RPM at various input angles:

At 0 degrees indicated by the green line, the input is 2400RPM and Output is 2400RPM. This is the ideal value and what we expect from CVD.
At 15 degrees, the RPM fluctuates between 2320 to 2480 RPM two times on each revolution, That is, two accelerations and two decelerations. This translate to an average of 80 light pulses per second.
As the Operation Angle increase to 20, 30, 40 degrees, the RPM will fluctuate between 2250 - 2550, 2080 - 2770, and 1840 - 3130 respectively. The larger the angle, the stronger the pulses and the faster the shaft will wear out.

Unfortunately, RC Monster Trucks are always operated at an angle of at least 15 - 20 degrees, and more extreme when doing jumps and tricks. This will put a real beating in the drive shafts. Below is an illustration of the typical Drive shaft Operation Angle:

Even with the Double Cardan Joint which can cancel out the angular velocity when the input and output shafts are parallel and act as a CVD, the intermediate shafts will still suffer the sinusoidal component, which contributes to vibration and stresses.

Dog Bones Disadvantages

Although dog bones are CVD by default, the design suffers a major problem. And that is, it only has two pins going a 5mm drive cup. Given the high torque in today's RC trucks, it does not take long at all to dent the drive cup until one day, your shaft just falls out.

This is what the drive cup of a dog bone look like after a few runs. That dented drive cup will create a lot of play, it will cause vibration, noises, and slow down your vehicle. The worst thing is, because it is loose, further operation will cause the cup to be even more dented, and more vibration will result, which makes a bigger dent and the vicious cycle continues.

Not convinced? Here is a short explanation from one of the popular RC forum by member Kkant:
https://www.rcgroups.com/forums/showthread.php?t=695076

A word of explanation on the difference between CV joints and universal joints, and the pros and cons and uses of each. On R/C cars, dogbones are CV joints. That means "constant velocity". The input and output shaft rotate at exactly the same speed, no matter what the angle. That's the plus side. The bad part is that they involve a pin sliding against a flat surface. The sliding increases friction. Plus the flat surface can get dented, as we all know, which screws up the joint. This is what causes the clicking noise in a worn-out CV joint in a real car. A universal joint is different from a CV joint. The MIP "CVD" joints (and most of the other "ball and socket" joints in the R/C world that are labeled as "CV") are actually universal joints. The usual shape of a universal joint is two forks pronged together with a gimbal in the middle, but if you examine the MIP-style joint closely, you'll see that it is mechanically equivalent to a u-joint, not a CV joint. The good part of a universal joint is that it is more durable and has less friction--no sliding parts, just a couple pins rotating in bushings. The bad news is that the shafts don't rotate at the same speed, when they are at an angle. If the input shaft rotates at a constant velocity, the output shaft's speed varies like a sine wave. The bigger the angle you put on a universal joint, the bigger the "pulses" on the output speed. That translates to vibration which wears out parts and slows you down. But there is a way to get around this problem: if you have 2 universal joints connected together, where the 2 end shafts are in parallel and the middle shaft is at an angle, then the end shafts rotate at the same speed (because the pulses in the middle shaft get converted back to a constant speed at the output shaft). The key is that the end shafts need to be *exactly parallel*, so that the angle between the input shaft and the middle shaft is exactly opposite to the angle between the middle shaft and the output shaft. Many real RWD cars use universal joints on the driveshaft: this is why it's so important to check the angle of your rear axle when you replace your leaf springs. So what does this mean. Well, to start with, you never want to get a shaft that has a U-joint at one end and a dogbone at the other. That includes a MIP-style "CVD" at one end with a dogbone (real CV) at the other. That's about the worst thing you can do, since you are guaranteed that the output will be pulsed. Real CV joints (i.e. dogbones) at both ends work for any situation. But CV joints are more fragile and have more friction, so you want to use a pair of universal joints instead when you can (you should only use them in pairs, for the reason described above). When can you use a pair of u-joints or MIP-style "CVD"s? The best place is in center driveshafts, because the input/output stays parallel. You don't want u-joints (or MIPs) on the front wheels because these need to be steered and the input/output is never going to be parallel. However, you can use u-joints on the rear wheels if you have very little camber and toe-in.
Last edited by kkant; Sep 27, 2007 at 11:26 PM