Tractor "bouncing" ?

[timbrr]

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. ... Some imbalance of weight coupled with a very small uneven motion that starts it all.

So, no track-tractor system is perfectly balanced to start with, thus uneven motion is inevitable. Uneven motion results in small-scale modification to the surface of the track. Subsequent trips with similar speeds/loads results in similar motions, and further similar modifications to the same parts of the track. As the modifications stack up (or compact down, as the case may be), eventually you get a series of indentations/ripples in the track. Driving over those ripples results in the bouncing. Or something like that?

Sounds like what happens on a particular unsealed road not far from my place`. Lots of cars with similar wheel-bases (and suspension systems) travelling at similar speeds (i.e. the speed limit) end up creating "corrugations" in the road surface, which then vibrates the heck out of similar cars as they pass over it.

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

Any vehicle with a different wheelbase would logically experience something different. Maybe less bouncing, maybe rocking, maybe nothing at all. Hmmm...

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 ;(

Yeah, not much can be done to the tractor itself whilst driving apart from adjusting speed. If flexible tyres are the only type of "suspension" that tractors have, then increasing pressure may make them stiffer, and change the dynamics. Not clear if that would be for the better or worse, though.

Modifying the track... Well, adding dirt and smoothing it out definitely helps. Just -- unfortunately -- not for long. It's not practical to back-blade the track every trip to keep it smooth. I could run with a box blade instead of the counterweight, and scrape regularly on return trips, but given my BB is only about 1/3rd the mass, that would make the tractor more front-heavy and other parts of the operation painful (e.g. harder to dig, smaller bucket loads). Given that the tracks themselves are temporary, spending large amounts of time/resources/money 'improving' them also doesn't make a whole lot of sense.

 

[timbrr]

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.

Why would a lighter tractor bounce less? I was under the impression that ballasting the rear tyres/axle or putting more counterweight on the 3PH were pretty-much guaranteed/universal ways to make a tractor more stable.

 

[k0ua]

Why would a lighter tractor bounce less? I was under the impression that ballasting the rear tyres/axle or putting more counterweight on the 3PH were pretty-much guaranteed/universal ways to make a tractor more stable.

Because your torque arm is much less. You have weight sticking out in front of the tractor with the loader. You have weight sticking out back of the tractor with the ballast. Remove those torque arms, and you will bounce much less if at all. Try it at the exact same ground speed, with a fully loaded loader and the ballast, then try the bare tractor. There will be worlds of difference. Not that it helps anything as the tractor then would be useless for your purpose.

 

[finn1]

Why would a lighter tractor bounce less? I was under the impression that ballasting the rear tyres/axle or putting more counterweight on the 3PH were pretty-much guaranteed/universal ways to make a tractor more stable.

It’s a mass-elastic system. Changing either the mass or the stiffness will change the response of the system.

Many cars have weights bolted to the drivetrain or bodies in strategic points to change the system natural frequency, mostly to improve nvh.

Going up or down with mass changes things, but adding mass is often easiest. A lot of computer modeling is done in designing cars to get the stiffest, lightest structure possible. Fifty years ago, they just added weight to get a smooth ride. Not an efficient method.

Try playing with tire pressure to change the “suspension” stiffness.

My CTL has what is called ride control to address this situation. I typically adjust the speed when driving my tractor on the paved county road to minimize the bouncing. The travel speed is advertised at a little over 14 mph, but I can only control it at about 10 mph with the heavy front snowblower mounted.


An empty bucket instead of the heavy snowblower helps.

It’s physics.

 

[timbrr]

The various "soft ride" loader additions are designed to dampen the loader oscillations and will do so.

Are you saying that the bouncing phenomenon I am experiencing is actually called "loader oscillation"?

At the speeds you are traveling I'm surprised that you are in 4wd

No speedo on the MX5100 HST, so I can't say for sure, but TractorData says that in M gear the tractor will do a maximum of 11.7km/h (7.3mph) at 2700 RPM. Given that I do most loader work at about 1700 RPM that would suggest that even if I put the pedal to the metal I'd be lucky to break 10km/h (6.2mph).

I might have to do a test to get a real number, but 10km/h doesn't strike me as being particularly fast.

one item to be aware of is with the tractor bouncing and loading and unloading the tires is that every cycle will change the loaded radius of your tires which in turn will affect your front - rear tire balance.

I do actually hear accentuated HST/drive-train noise when the bouncing happens. Given that the 5100 has MFWD, and the front and rear are effectively coupled, then it makes sense that a changing radius would impact the balance and cause additional stress/load somewhere in the system.

Would increasing the pressure on the front tyres (from their current 32psi to the maximum 40psi) help resist the deformation, and thus preserve the loaded radius?

Would increasing the pressure on the back tyres make any difference at all?

 

[timbrr]

Because your torque arm is much less. You have weight sticking out in front of the tractor with the loader. You have weight sticking out back of the tractor with the ballast. Remove those torque arms, and you will bounce much less if at all.

That makes sense.

Since adding liquid ballast to tyres, or wheel weights to the rim, results in additional mass that does not "stick out" beyond an axle, does that effectively make the length of those "torque arms" zero (or, at least, minimal)? Would either of those approaches be a valid way to reduce the bouncing?

Or would additional mass (hypothetically) need to be added between the axles to be effective?

 

[cdaigle430]

Has to do with the frequency of the suspension-there is always a slight bounce and as you go further and further the frequency gets worse and worse. Nothing you can do about it because the tires are your only suspension minus the front axle sway. Its designed that way for many reasons.

I wonder if loaded tires or nitro filled tires can help but I doubt it. Key thing is to slow down or get a dump trailer if speed is a huge factor. Maybe smaller tires? Just best to slow down or get a dump trailer. Not worth redesigning something perfect for certain things in order to fix it for something it is not designed for.

 

[CobyRupert]

Tractor "bouncing" ?

I imagine that as the soil gets packed down, even if smooth and no ripples, that when in 4WD any difference where tire size ratio doesn’t perfectly match the 4wd gearing ratio could create a push-then-pull hopping effect as the tractor tries to unbind itself.
Similar to driving in 4WD on pavement.
Especially if the rear tires push more than the front pulls.
Does OP get bounce in 2WD?

...but even in 2WD and no FEL my tractor will hop sometimes at road speed for a variety of reasons:

Tires may have flat spots.
Or rough road initiate bounce, tractor bounces, causing seat to bounce, causing my leg on the throttle to bounce, which causes tractor to bounce again ...and the feedback loop continues...I can eliminate this by eliminating seat and leg component by speeding up (or slowing) with the hand throttle.

 

[mred2]

Did you answer if it was in 4 wheel drive? I think all front wheels turn a little faster than the back.

 

[John Skull]

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