Faulty drivetrain always breaking

[saulemmetquinn]

I made this as an experiment and i'm having trouble designing a working drivetrain.  The issue is that whenever I start it, either a link falls off, or the cv joints in the steering break. 

Here are some pictures.

Here is an image of the placement of the cv joint on one side of the steering.  I have made an effort to put stabilizers of some sort around it, but nothing has worked so far.

Surprisingly, the floating axle connections do not break.  (Most likely because of the use of the new cv joints)

If you have any solutions, please let me know.

Thanks!

Edited December 15, 2022 by saulemmetquinn

[Jurss]

For this power only new CV joints everywhere.

Something could be done, if You would do power transfer trough gears also trough suspension. It is doable, but could be bulky etc.

[DrJB]

I assume you're driving the two motors in 'parallel' (otherwise the gears would break), to have a higher torque on the drive train. If that is the case, then the down-stream components are certainly not designed to handle that high of a torque/power. There is enough published data about such motors to enable one to do some basic calcs, and that for sure could be a fun/rewarding activity. However here, I would do a brute force approach: if you run the drive-train with a single motor, do you still have the same issue? Depending on the answer, we can tell whether the components are under-sized, on something wrong with the kinematics ... my 0.02

On a different note, it looks like you're using suspended pendular axes for an 'all-terrain' vehicle ... that and the dirt on the tires tell me you might be pushing the parts to their limit.

Edited December 15, 2022 by DrJB

[allanp]

This tends to happen mostly when the CV joints are carrying high loads at their maximum angle. So I would first try limiting the steering angle. I think you can also replace the frictionless pins in the steering with friction pins. It'll still work but it will remove the sloppyness and hold the hubs in place a bit more tightly. I don't own a BuWizz (yet) but is there an option to ramp up the speed over, say 500 - 1500 milliseconds, instead of having instant 100% power? Another thing you could try (if you don't mind a little "cheating") is to make small circular paper shims, like paper washers, to add onto the red 2M axle behind the CV joint to push it outwards just a little further into the wheel hub.

These are only small changes but you are really pushing the limits of those tiny CV joints. Unfortunately I also see some wear in the male and female parts of the CV joint from lots of use and lots of popping out, so those copies might have to be relegated to purely manual models and replaced with new. Those new ones will also wear fairly quickly, due to being undersized for their task (the newer, bigger ones are much better as you've seen), unless you apply some lubrication. 

Perhaps another solution is to redesign the wheel mounts so that they can use the newer larger CV joints, the downside of that is you will have wheels mounted to axles (which will slide off) instead of the usual 3 pin mounting.

[2GodBDGlory]

One thing that may or may not help is that it looks like you've got your CV joints going directly out of an axle extender, which (I think?) then goes into another extender, and isn't really braced anywhere in between. I'd try putting some kind of connector or beam right next to the CV joint with an axle going through it, to take out some of the wobble in the axle.

[gyenesvi]

I think this gearing would result in way too much speed and hence pressure / wear on the components. As far as I see you don't even use a differential in there? What kind of a car will this be? A fast one? By the looks of it, it is more like a rock crawler. Even if you put the drive from 2 Buwizz motors through a new heavy duty differential (12/28) and then into a planetary hub (1/5.4) then you get a fairly decent speed for such a car, and then your components won't be eaten up (if you lubricate them). With this gearing, everything would wear quite fast I think. If you want something a bit faster though, I'd recommend first trying with planetary hubs and an old differential (20/28). That combo has still decent speed and lot of torque.

I'd do Buwizz motors to regular hubs without down-gearing only in one condition: when it goes straight to the wheel, but independently for each wheel (no coupling of two motors), and when the angel of CV joints is low and the suspension does not move too much, like in sportscars. But even then it might wear out fast.

[saulemmetquinn]

On 12/15/2022 at 12:48 AM, Jurss said:

For this power only new CV joints everywhere.

Something could be done, if You would do power transfer trough gears also trough suspension. It is doable, but could be bulky etc.

 

On 12/15/2022 at 1:57 AM, DrJB said:

I assume you're driving the two motors in 'parallel' (otherwise the gears would break), to have a higher torque on the drive train. If that is the case, then the down-stream components are certainly not designed to handle that high of a torque/power. There is enough published data about such motors to enable one to do some basic calcs, and that for sure could be a fun/rewarding activity. However here, I would do a brute force approach: if you run the drive-train with a single motor, do you still have the same issue? Depending on the answer, we can tell whether the components are under-sized, on something wrong with the kinematics ... my 0.02

On a different note, it looks like you're using suspended pendular axes for an 'all-terrain' vehicle ... that and the dirt on the tires tell me you might be pushing the parts to their limit.

 

On 12/15/2022 at 2:40 AM, allanp said:

This tends to happen mostly when the CV joints are carrying high loads at their maximum angle. So I would first try limiting the steering angle. I think you can also replace the frictionless pins in the steering with friction pins. It'll still work but it will remove the sloppyness and hold the hubs in place a bit more tightly. I don't own a BuWizz (yet) but is there an option to ramp up the speed over, say 500 - 1500 milliseconds, instead of having instant 100% power? Another thing you could try (if you don't mind a little "cheating") is to make small circular paper shims, like paper washers, to add onto the red 2M axle behind the CV joint to push it outwards just a little further into the wheel hub.

These are only small changes but you are really pushing the limits of those tiny CV joints. Unfortunately I also see some wear in the male and female parts of the CV joint from lots of use and lots of popping out, so those copies might have to be relegated to purely manual models and replaced with new. Those new ones will also wear fairly quickly, due to being undersized for their task (the newer, bigger ones are much better as you've seen), unless you apply some lubrication. 

Perhaps another solution is to redesign the wheel mounts so that they can use the newer larger CV joints, the downside of that is you will have wheels mounted to axles (which will slide off) instead of the usual 3 pin mounting.

 

On 12/15/2022 at 8:58 AM, 2GodBDGlory said:

One thing that may or may not help is that it looks like you've got your CV joints going directly out of an axle extender, which (I think?) then goes into another extender, and isn't really braced anywhere in between. I'd try putting some kind of connector or beam right next to the CV joint with an axle going through it, to take out some of the wobble in the axle.

 

On 12/15/2022 at 9:37 AM, gyenesvi said:

I think this gearing would result in way too much speed and hence pressure / wear on the components. As far as I see you don't even use a differential in there? What kind of a car will this be? A fast one? By the looks of it, it is more like a rock crawler. Even if you put the drive from 2 Buwizz motors through a new heavy duty differential (12/28) and then into a planetary hub (1/5.4) then you get a fairly decent speed for such a car, and then your components won't be eaten up (if you lubricate them). With this gearing, everything would wear quite fast I think. If you want something a bit faster though, I'd recommend first trying with planetary hubs and an old differential (20/28). That combo has still decent speed and lot of torque.

I'd do Buwizz motors to regular hubs without down-gearing only in one condition: when it goes straight to the wheel, but independently for each wheel (no coupling of two motors), and when the angel of CV joints is low and the suspension does not move too much, like in sportscars. But even then it might wear out fast.

To all who responded, thank you! 

It seems that the prevalent issue is the amount of power and stress on these parts.  I will try to implement the new cv's in the model at some point and redo the steering or gear down the drive train entirely.  The goal with this model was to combine a rock crawler with a trophy truck, and I expected these types of issues.