Physics .. "Active" tractor weights .. Shifting the C/G ZTR ??

[tmajor]

If the weights are of equal mass and if the only force acting on them is gravity, they will just sit wherever they happen to be when you install them.

Did you ever see a balance scale or teeter-totter work?

 

[zzvyb6]

My F935 already has a manual version of this via the deck lift hydraulics. Now you need a fool/lawyer proof pendulum or gyro sensor to automatically adjust it. That takes care of the incline/decline situation. For roll weight transfer, you would need a suspension with adjustable spring lengths so you can push down on one side and lift the other. The Active Corvette I worked on was equipped with this.

Mr. Bose (as in Bose audio products was trying to sell suspension units for cars based on their speaker cone mechanisms (only on steroids). It actually worked, but the cost and the technology was very hard to move to production. And, he wouldn't open up the computer program so we could see how it was working (skyhook, reference model, or Rube Goldberg). When people sue you because their machinery did something unexpected, its not a good idea to claim that "its a secret".

Now remind ourself that this is for a lawnmower, not the Space Shuttle, so any costs more that $19.99 will be hard to sell to an average customer.

 

[tmajor]

Now remind ourself that this is for a lawnmower, not the Space Shuttle, so any costs more that $19.99 will be hard to sell to an average customer.

Like I said, I'm not intending to market this fine product. Just trying to get some input and thoughts.

 

[cttractor]

I tend to disagree. There is an external force .. "gravity", which will be applied to both.

BeezFun is correct in his assessment. Take the drawing you made and just tilt it more and more "downhill" and you'll see that the uphill weight will lie horizontally in the tube while the downhill weight will be pulled down by gravity. And if you consider the tubes to be frictionless, or lubricated, the downhill weight is going to pull the uphill weight horizontally. That is going to allow the downhill weight to drop lower and move the center of gravity even more to the downhill side risking a tip-over. This is why I mentioned this being a tricky application and why you would likely want a dynamic system that automatically moved the weights to counteract the tilt as the angle of your mower shifts back and forth.

Groundcover's suggestion of moving oil between two tanks is such a dynamic system. Of course, things get complicated when you start to need a bi-directional pump and a control system to monitor and make changes dynamically as the mower pitch changes. It's somewhat akin to the active or adaptive suspension systems in many new vehicles these days.

 

[tmajor]

Do we have any pilots on here, who are familiar with figuring weight and balance .. arm and moment? It is possible, that the uphill weight contribution could be heavier than the downhill one. The reason being, the "arm" gets longer. Like one person on a teeter-totter sliding further toward the fulcrum, while at the same time the other person slides further away from the fulcrum.

 

[cttractor]

Do we have any pilots on here, who are familiar with figuring weight and balance .. arm and moment? It is possible, that the uphill weight contribution could be heavier than the downhill one. The reason being, the "arm" gets longer. Like one person on a sliding board sliding further toward the fulcrum, while at the same time the other person slides further away from the fulcrum.

Yes, I'm a Private pilot. If you're planning on changing the arm lengths dynamically, that will have an affect on the system and give you more control. But there are several points that have to be met:

• - The system would likely require an automatic control system; and
• - The angle between the two weights will also have to be dynamic and controlled so the uphill weight can't go horizontal in the tube, because if it does, that actually raises the center of gravity on the uphill side -- precisely what you don't want -- you want it lower.

 

[tmajor]

The diagram I created, was with a 15 degree incline. So for the upper side tube to go horizontal, the tractor would have be on an incline of 75 degrees.
Edit: That's not quite right, because the tube has a built in angle of ?? 15 degrees. So, maybe the tractor would have to be on a 60 degree incline (which you shouldn't be on in the first place).

As a test example, if the weights were 15 pounds and the lower 12 inch arm decreased by 4 inches, the moment would be 120 inch/pounds, while at the same time the upper arm would increase from 12 by 4 inches, the moment would be 240 inch/pounds. (which doesn't factor in the angle) With the tractor level, there would be 180 inch pounds on both sides, at balance.

 

[cttractor]

The diagram I created, was with a 15 degree incline. So for the upper side tube to go horizontal, the tractor would have be on an incline of 75 degrees.
Edit: That's not quite right, because the tube has a built in angle of ?? 15 degrees. So, maybe the tractor would have to be on a 60 degree incline (which you shouldn't be on in the first place).

As a test example, if the weights were 15 pounds and the lower 12 inch arm decreased by 4 inches, the moment would be 120 inch/pounds, while at the same time the upper arm would increase from 12 by 4 inches, the moment would be 240 inch/pounds. (which doesn't factor in the angle) With the tractor level, there would be 180 inch pounds on both sides, at balance.

I never presume to scale dimensions or angles off of a drawing unless I know it truly is to scale, so thank you for providing the angles that you're proposing for the weights. I do agree with you that a 60 degree bank is one I wouldn't even want to take up or down with a dozer, let alone sideways on a mower. That said, I still think you're going to need an external, active control mechanism of some sort. That could be hydraulic as has already been mentioned, some mechanical affair, or what have you. If the weights don't move because they're fixed or because of friction in the tubes, the downhill weight will be lower and that will amplify the center of gravity on the downhill side -- that's the opposite of what we all want. If they do move, they will likely do so unpredictably or will slide to the downhill side again.

An active system can shift the weight to put it where you want it as the mower's angle changes. It can do so reliably as you go up, down, turn, etc. A human manually controlling it would likely forget or adjust too late on at least some directional changes -- an automatic system wouldn't unless it failed.

 

[cttractor]

TMajor; because you're sticking with your view, I keep feeling either you, us other posters, or both are missing something or talking past each other on your design. Unfortunately, I haven't figured out what that is yet.

Unrelated question: before retiring, did you do much glass-cockpit work? And do you still need an FCC General Class (old class 1 or 2) license to work on avionic transmitters? I have one and did some of that work when I got out of college, but haven't touched it in decades and am just curious.

 

[tmajor]

We should have a better feel for things, shortly, as I am working on the mock-up. Of course, the "real test" will be on the mower, should the mock-up prove the potential. We'll see.