Kagama Rear Suspension/Drive shaft induced oscillation

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Stattle said:
Not entirely sure, but thanks for your help. One last thing, how do I cancel or delete my membership to this forum?
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Type "I'm a complete moron.", hit "Enter", click your heels three times, then go back to FB.
 
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On the subject of driveshaft phasing, I read an excellent book by Hillier about this subject as part of my engineering diploma in 99. At this time, the Internet was in it's infancy and was only available using dial up modems. So books were still hugely important.

1000030227.webp

To my astonishment, something similar is still available now. A 625 page overview of motor vehicle technology. Parts 1 & 2 = over 1200 pages! 😎

Cardan joints, Rzeppa CVDs were detailed. As I recall, I had to detail the advantages of Rzeppa over a Cardan joint in an assignment essay.

Perhaps one of the very best detailed explanations in relation to the variation in output velocity (non-uniform rotation) I found in recent times can be found here:


It's an excellent and clear discussion.

This thread may have started off horrifically, but the subject has raised a topic, which to my knowledge, has not been discussed on this forum previously.

This is why we need proper ball drive CVDs for our rig's steering (like the Uber Ball Drive system - but for 1/8th). Our 'CVDs' are merely variants of Cardan joints and are subject to the exact same issues.

There is no reason that I can think of why manufacturers cannot tool up and make these kind of ball drives. In this era, we have the machines, materials and precision required. The only thing missing is the will. 👍

Once people start desiring the concept, a market will surely follow. 🤞
 
I'm going to watch that video and do some research of my own. I don't really know anything about the subject but am always interested in mechanical things like this so thanks for listing a source. I've seen you bring up this topic earlier and it indeed seems like our RC drive shafts could use some improvements. If I have a look over the forums, a lot of problems seem to be originating from the drive shafts. Often they are also the limiting factor to steering angle and other geometry changes.

I used to think that not perfectly constant velocity wouldn't make such a big impact on driving experience/handling. But when I changed my badly notched outdrives for the upgraded ones I was suprised how big of a difference that made. I know that doesn't make them constant velocity, but if that changes the feel so much already, an even more "direct" transmission would make it even better in my mind.
 
Niekname said:
I'm going to watch that video and do some research of my own. I don't really know anything about the subject but am always interested in mechanical things like this so thanks for listing a source. I've seen you bring up this topic earlier and it indeed seems like our RC drive shafts could use some improvements. If I have a look over the forums, a lot of problems seem to be originating from the drive shafts. Often they are also the limiting factor to steering angle and other geometry changes.

I used to think that not perfectly constant velocity wouldn't make such a big impact on driving experience/handling. But when I changed my badly notched outdrives for the upgraded ones I was suprised how big of a difference that made. I know that doesn't make them constant velocity, but if that changes the feel so much already, an even more "direct" transmission would make it even better in my mind.
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The video is excellent. It's mainly oriented around the application in relation to crawlers, but it applies to all rigs.

Just as Razor explained, the CVD's we use as upgrades are smoother than dog bones and less likely to fall out. Always a bonus!

But dogbones can be made very, very burly for high torque applications relatively cheaply, where as 'CVDs' have limitations on the smaller pin inside the joint.

In fairness, my XTR's CVD's (and my XT8, T2E, Savage) have been very good. I had issues initially with some of my 1/10 touring car CVD's, but this was to do with a coating that Yokomo used on theirs (on the 'barrel'). With some work, they operated smoothly and reliably.

cvds.webp


Some people have had issues with Corally clips coming undone and jamming up inside the hubs. Heat shrink is likely the cure, in place of the clips. This is exactly what I did on my touring car drive shafts back around 2003 to hold the pins in. I also filed a flat on the pin, so the grub screws could mate properly.

Note the 'blades' on the dog bone ends, which were from a Corally touring car as it happens!
We need these. It will help with wear in the slots and with backlash/slop.
 
IMO, actual constant velocity is not necessarily a good thing for off-road. It's a tuning option, which is why most 1/8 buggies have the option of universal (more free) or CVA's (more bind).

I could be wrong, but I think this causes the driveshafts to want to straighten under power, which can help the rear end resist squatting. I was talking to Jared Tebo once and he mentioned you want to land jumps on power to cause the driveshafts to want to straighten, and effectively stiffen the suspension and resist bottoming out.
 
razorrc said:
IMO, actual constant velocity is not necessarily a good thing for off-road. It's a tuning option, which is why most 1/8 buggies have the option of universal (more free) or CVA's (more bind).

I could be wrong, but I think this causes the driveshafts to want to straighten under power, which can help the rear end resist squatting. I was talking to Jared Tebo once and he mentioned you want to land jumps on power to cause the driveshafts to want to straighten, and effectively stiffen the suspension and resist bottoming out.
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Given that our 'CVD's' on 1/8th buggies & truggies are not really constant velocity - it's simply just the name they were given - what they really are, are re-buildable universal joints, first introduced by MIP.

The debate about how free they are will always exist, but the truth is universal joints and re-buildable universal joints freeness will depend on a number of variables.

"CVDs are:
1. rebuildable
2. not as compact so maybe more rotating mass
3. sometimes uses a larger inner bearing on the hub to capture the cvd pins. This larger bearing may have more rolling resistance than a smaller one.
4. the location of the drive shaft pivot point can be different, so dogbone plunge and the operating angle of the joint can be different.
5. Both pivot on 2 points and 4 friction points, but the surface area on the pivot points is more 'even' with the u-joint. The CVD pivots on a small pin at 2 points and a larger diameter 'drive shaft coupling' on the other 2 points." Razo125

So, given the function of our CVD's is exactly the same, including the input/output velocities at any given angle, the 'freeness' of one type over the other depends entirely on the engineering quality - tolerances, design, fit, finish as well as the level of servicing by the user and state of wear with either type of joint, as well as the design of the platform it's being fitted to.

Jared's tip of landing 'on power' is very interesting from a driveshaft perspective. It largely depends on what rig you are racing I suppose. If your rig is burly enough to deal with on power landings (like Nitro - as they have a clutch), I suppose it makes sense.

Not sure I'd try it in the Baja though. 😅🙏
 
I had the exact same issue with my Kagama4. Out of the box, the droop with set with alot of suspension travel, which I liked, but when on throttle the rear wobbled horribly. It did it without the tires on with the truck just sitting on the stand, so it's not a wheel balance issue. When the droop was set to have alot of suspension travel, the dog bone was hitting the axle at the hub due to the angle it was entering the hub. As the droop is adjusted to make the arms level or near level, the angle decreases until it doesn't hit the axle material. It happened on the rear and to a lesser degree on the front. It seemed like it was just the way it was designed due to distance the axle comes out from the hub. If you compare to Arrma 6s, their axle at the hub doesn't come out from the hub, so the dogbone goes deeper into the hub because there is no material there for the bone to hit, allowing for more suspension travel if you desired to set the droop as such. That, along with the extra work it would need to change the pinion and work on it in general prompted me to sell it. I was hoping it would fill a monster truckish role, but it is more of a stadium truck/buggy with bigger tires. With the arms needing to be near level to avoid the binding, the ground clearance was less than my 3s car with 2.8 tires, so it just didn't fulfill my need for this rig. Was hoping for a lighter Skeeter. Loved that car, but it felt so heavy, and was also a pain to work on but drove great.
 
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I have the same problem with my Kagama 4. This dude has it as well:
(at 15:08). Are there shorter dog bones that resolve this? Or are we just going to have to live with shorter suspension travel?
 
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The heat shrink over the pin is what I used to do on my Touring Car CVD's on the Yokomo.

Many, many years ago...

cvds.webp
 
frenkel said:
I don’t understand. How is that going to solve dogbones binding in the rear?
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It wont if the pins escaping isn't causing the issue. But the video posted above talks about the escaping pins, which to be honest is a primary issue - no pins - no drive on the front CVD's. Corally have fixed these with new retainers.

Lots of droop and dogbones is never a good idea.

When the car is loaded, the arms wouldn't normally be in the position shown in the video.

Better to use more sensible droop settings until rear DVD's are available at a length that works. Inherently much smoother than dogbones. 👌
 
Horatio said:
It wont if the pins escaping isn't causing the issue. But the video posted above talks about the escaping pins, which to be honest is a primary issue - no pins - no drive on the front CVD's. Corally have fixed these with new retainers.

Lots of droop and dogbones is never a good idea.

When the car is loaded, the arms wouldn't normally be in the position shown in the video.

Better to use more sensible droop settings until rear DVD's are available at a length that works. Inherently much smoother than dogbones. 👌
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Sorry, I meant at 15:08 it demonstrates my problem.
 
frenkel said:
Sorry, I meant at 15:08 it demonstrates my problem.
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Lots of droop and dogbones is never a good idea.

When the car is loaded, the arms wouldn't normally be in the position shown in the video.

Better to use more sensible droop settings until rear DVD's are available at a length that works. Inherently much smoother than dogbones. 👌
 
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