I see 2 major issues with this project, the pump and the steel selection.
The Vickers vane pumps as used for power steering come with a built in flow control and pressure relief valve. Somewhere between 1200-1800 rpm, they typically deliver full flow, and the flow rate does not change from that point with more speed due to the flow control. Precision lifting or lowering at low engine rpm ain't happening. With a 1:1 pulley ratio, engine idle will result in about 5 gpm flow unless the pump has been modified from the more normal 2 gpm unit as found in a GM car in which case, 7.5 gpm won't happen until 4100 rpm.
If it is a modified car power steering pump, it might actually be satisfactory. The flow rates across the board will work, but now your choce is slow tractor speed, or overcontrolling the hydraulics due to excessive flow and small cylinders. Neither is acceptable.
Quarter inch wall tube is heavy, and the weight of a typical loader is balanced on the front axle. Along with the normal weight of the tractor that normally lands on the front axle, and the weight of the loader (and bucket) that all lands on the axle, comes the payload in the bucket, and something in the order of 60-65% of the payload weight that come from the countering weight at the rear of the tractor to keep the whole thing in balance. That is 300 lb of tractor, 300 lb of loader, 300 lb of payload, and 200 lb of counterweight, or 1100 lb of load on the front tires and spindles. Narrow tires tend to make ruts and get difficult to steer with that kind of load.
One eightth wall seems to work well for most GT loaders for the arms and posts. Use 3/16" plate for any gussets required.
It's all about triangles and the sine of certain angles. For a triangle formed by the post, the cylinder, and the arm, use the pin holes for the apexes of the triangle. Fill in the blanks of this triangle calculator and hit Compute. Multiply the Sine of the angle formed by the cylinder and the arm by the calculated force of the cylinder to find the effective force available.
From this point, you can continue to break down the loader dimensions into triangles and continue the calculations, or do it the easy (although slightly less accurate) way by using ratios. Place a long scrap of lumber on the ground under the arm and drop a plumb bob from the post to arm pin, the cylinder to arm pin, the bucket to arm pin, the center of the bucket, and the cutting edge of the bucket. The ratio between the post and cylinder pin length and the post to any of the other points will give you the multiplier for calculating the lift force from the effective cylinder force at each of the other points. eg. If the post to cylinder pin length is 20" and the post to bucket center is 60", the ratio is 3:1 or 1/3 of the effective cylinder force is available for lifting payload.
-This is a theoretical calculation and does not take into consideration the weight of the loader and its individual parts which will downgrade the calculated payload capability.
- All dimensions and forces change as the arms are raised. Typically, calculations are done at zero lift, c.50% lift, and 100% lift heights.
Loaders require ballasting and counterweight. The added weight allows a marked increase in torque application at the rear wheels which puts a strain on the frame to axle connection. A subframe that directs this torque from the axle directly to the post's crossmember is highly recommended.
For additional suggestions, check out this thread.
Edited by TUDOR, August 08, 2015 - 11:52 PM.