I have become involved in aspects of forklift operation. One of the big things they tech is The Stability Triangle.
The general idea is that you must keep the center of gravity (mass) within the triangle, or the forklift will tip over. I get the concept, but I am concerned with the use of the triangle. I am not sure why it is not a rectangle. All the forklifts I have seen have the rear wheels spread almost the same as the fronts and have those wheels pivot just inboard the wheels (e.g. not a straight axle attached at the center, which the triangle seems to imply).
These images obviously imply the load and center of mass are above the roll center of the truck, which I think is on the floor anyway since I don't think any of these have any actual suspension.
It should be noted that most all forklifts are heavily counter weighted toward the rear (to counteract any load), but that is already accounted for in the center of gravity. They also steer from the rear (not relevant here from what I can see)
Am I missing something?
BTW, using the triangle for vertical loads is of course very relivant:
Here is an image of a typical forklift, for those who are unfamiliar. As can be seen by the wheel openings alone, the rear wheels pivot pretty close to the rear of the wheels:
Looks like some forklifts (maybe all?) have the rear axle mounted on trunnion bearings which result in the axle providing zero roll stiffness (until it hits whatever bumpstops). 3-wheelers use a similar triangle thing to visualize stability.
It's been a while, but I believe the reason is that the rear tires should only support the weight of the forklift, not the load.
Both of the forklifts I use at work (they are both fairly small) have a single rear wheel mounted in the center.
Like this:
Oapfu said:
Looks like some forklifts (maybe all?) have the rear axle mounted on trunnion bearings which result in the axle providing zero roll stiffness (until it hits whatever bumpstops). 3-wheelers use a similar triangle thing to visualize stability.
This. From a load bearing perspective they're only supported in three places hence the triangle.
OK, interesting. I will have to take a closer look then.
Strange design choice. I am not sure what the advantage of that design is. It doesn't even seem that strong.
In reply to aircooled :
AFAIK, the advantage is manouverability. A three-wheeled forklift with rear steering can turn around in a space equal to its length. Good for fitting down narrow aisles between pallet racks. Narrower aisles means more racks/more stuff for a given amount of space, which saves the business money on warehouse/lot space, so once again it comes down to economics.
In reply to aircooled :
I think it’s the whole 3 points establish a plane concept. If they weren’t trunion mounted like shown in the pick then only 3 wheels would touch the ground (because there is no compliance built in) so without that as the floors moved because they aren’t level they would keep swapping wheels touching the ground. Same deal as most tractors with the pivoting front axle.
aircooled said:
I have become involved in aspects of forklift operation. One of the big things they tech is The Stability Triangle.
The general idea is that you must keep the center of gravity (mass) within the triangle, or the forklift will tip over. I get the concept, but I am concerned with the use of the triangle. I am not sure why it is not a rectangle.
...
I am not a forklift operator, but I'm always game for discussing drivers ed concepts.
Emphasis added to quoted excerpt — it does not say the CoG has to be centered within the triangle. When this is a triangle, the load is relatively stable from side-to-side (L-R) even when the green checks are touching the left or right bounds of the triangle.
If this were instead a rectangle between the four wheels, and the green CoG checks were touching either the L or R bounds, the load is like a full glass of water perched on the edge of a dining table, and turning away from that side while in motion would send the load +vehicle over the edge.
