Tractor "bouncing" ?

[timbrr]

Howdy folks. I'm trying to research and understand an issue I'm having with my Kubota MX5100 HST, but don't seem to be using the right search terms.

This is the first tractor I've owned, and I've only clocked up ~220 hours so far. Most of that has been spent in 4WD mode digging and moving dirt -- mainly (what was formerly beach) sand. As I have become more proficient I have been transporting larger and larger amounts in the (4-in-1) bucket. I have a 500kg counterweight on the 3-point hitch. All tyres are industrial R4s. Fronts are inflated to 32psi (with max rated at 45), whilst rears are inflated to 15psi (with max rated at 20).

When I transit from A-B over lightly-vegetated -- but otherwise well-compacted -- sandy soil, the initial few runs will be as expected. The tractor will react to roughness in the underlying terrain in a predictable fashion. Sometimes, however, I end up going over the same A-B track several times, dozens of times, even hundreds of times. In short order my tractor experiences what I can only really describe as "bouncing".

It feels like the whole tractor just starts bouncing up and down. The "severity" of the bouncing increases over time/distance as I traverse the A-B track. In mild cases this is merely annoying. In severe cases the bouncing is so extreme that the springs on my seat are unable to compensate, and I experience a spine-jarring jolt as the seat grounds out. Not fun.

Going forward results in more bouncing than going backward. Full buckets result in more bouncing than partially-full buckets. That said, I have experienced bouncing even going backward with an empty bucket (neither as frequently or severely, but it still happens). Bouncing is usually worse the faster I go, but neither consistently so, nor within a fixed speed range. Sometimes going 'fast' actually prevents bouncing. Going really slowly (~5km/h or less) reliably prevents bouncing, but given the distances I need to travel, such low speeds are undesirable. The gears are in 'M' during transits.

Natural ground deteriorates pretty quickly when subjected to loader operations. It gets dusty/powdery quite quickly. Back-dragging the track with the loader bucket will visibly smooth out the track, but bouncing resumes almost immediately (within 1-3 transits). Dumping and spreading sand over the path helps for a while longer.

Searching the forums for "bounce" or "bouncing" returns zero results.

Can anyone suggest keywords that describe the phenomenon that I am experience which will help me research the matter further?

Cheers!

 

[dodge man]

Is the bouncing front to back, or just straight up and down. When I don’t have any or enough weight on the back the tractor will rock front to back pretty bad. I’d try playing with tire pressure. My initial reaction is your front tire pressure is to high but I’m not sure. It might just be normal also, tractors don’t have a suspension so about all you can do is slow down.

 

[k0ua]

You may or may not have noticed that tractors have no suspension components. NONE. When traversing rough terrain, you may have noticed this "bouncing " phenomenon. The solution to this is to slow the he77 down. Especially in the rough parts and especially when heavily loaded. Low and slow for safety, and in your case comfort too.

 

[Ford850]

I've noticed when hauling heavy bucket loads over the same path, the bouncing gets worse. I've figured it out, at least for me. First, the 'path' I choose gradually gets smoothed out, flattening the many small bumps and rough ground. That leaves a smooth path but accentuates the slightly larger humps and whoopty-doos. Second, once I get that smooth path I gradually travel at a higher speed compared to the first few trips over it, since the many small bumps are gone and I feel safe. If I can drive the path in mid range, 3rd gear, then I should be able to bump up to mid 4th and save some time, right? Third, I find myself loading larger and larger buckets full after the first couple trips. If 'full' worked, then 'fuller' must be better since it will save me trips, right?
Add those three things and by trip 10 I'm nearly ejected off my seat in some spots before my brain kicks in and I slow down and reduce my loads. My suggestion... Slow down and enjoy the ride.

 

[k0ua]

If you insist on operating at the ground speed that causes you discomfort, you can check on increasing the stiffness of your suspension seat's adjustment, or you can lose some weight. Not on the tractor or the load but your weight. I don't know if you are skinny or fat, but a fat man is going to bottom out a seat's suspension travel a lot faster than a skinny man. I know this firsthand, being in the "fatboy" category. An alternative is to replace the OEM seat with an air ride suspension seat. They are sold by several aftermarket vendors, and can be more comfortable than the OEM seat in these conditions. Or you can save the money and reduce your ground speed.

 

[timbrr]

Is the bouncing front to back, or just straight up and down. When I don’t have any or enough weight on the back the tractor will rock front to back pretty bad. I’d try playing with tire pressure.

I'm not sure what front-to-back bouncing would even feel like. Rocking? If that's the case, then no, the tractor doesn't rock froward and backward. Just up and down.

I've entertained the thought that I might not have a big enough counterweight on the 3PH, but given that I even bounce with an empty bucket, I'm not sure that line of reasoning is getting to the heart of the "problem".

 

[k0ua]

Slow down and enjoy the ride.

Best advice of the day..

 

[finn1]

Any object has what, in engineering terms, is called a mass-elastic system and a resultany natural frequency that it “vibrates” at. The mass elastic system can be mathematically modeled given the stiffness, mass and spring rates of the components and assemblies, and enough computational powers. Wheelbase is one of the factors too.

What’s happening is that your machine is compacting the earth, causing “ripples” that excite the natural frequency of your tires, and vehicle mass.

You can change the response by speeding up, slowing down, or changing the air pressure or stiffness of your tires so you aren’t exciting the tractor at the natural frequency of its Nass elastic system.

Cars sometimes, in the past, had what was referred to in technical circles as “California freeway hop”. The story goes that the expansion joints in California freeway pavement were spaced slightly different than most other typical highways. That longer spacing set up many cars structures and suspensions to go into resonance when crossing the expansion joints at the speed limit, resulting in an uncomfortable ride.

Designing cars to a higher mass-elastic stiffness keeps the resonance to a minimum.

This phenomenon was part of the Mechanical Engineering curriculum fifty years ago when I was a student.

 

[Jchonline]

I expect this is due to small indentations created in the dirt/sand as you repeatedly travel over the same path. Sand is very impressionable as you know. The bouncing is accentuated because you have an unbalanced load (not unsafely unbalanced) but from a physics perspective you have more weight out front than out back.

I have also operated a Mini-EX and until I got used to the controls it would rock really bad when I tried to go forward with by actuating both tracks. Same idea. Some imbalance of weight coupled with a very small uneven motion that starts it all.

Oh try it in another vehicle on the same path to see if you notice. Like a car or truck.

Other than slowing down, no way I can think of to fix. Balance the load and slow down to minimize it. Find better dirt that doesnt keep reforming ;(

 

[k0ua]

Now we could get all "technical" on you, and talk about unsprung weight and torque arms, and you could perform your own experiment by taking off the loader and removing the ballast on the 3 point hitch and traversing the same exact ground at the same exact ground speed and you will notice that the bare tractor has much less "bouncing" with those items removed. But none of this offers you the practical solution of traversing the same exact ground at a lower ground speed does. Yeah you can try to adjust the OEM seat or even buy that air ride seat, neither of which will reduce the bouncing, but might prevent the spine jarring bottoming out experience, but the root problem remains. You are simply going too fast for the terrain.