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| Maximising Torsional Stiffness |
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| awemawson:
The "end with rungs" is actually not rungs at all but one solid hydraulic tank structure made from very heavy steel plate (it is also used to mount the pivots for the arm - so I'm pretty certain that end will not twist. The pair of stiles projecting towards the tractor axle is where the problem will probably arise if at all, and as I don't know how long they originally were, I'm working to make them the absolute minimum length that will fit. A wooden mock up is in construction to ensure clearances are ok. These stiles are 100 mm box section with a 6 mm wall so pretty stiff and are spaced with about 30" between them. The problem is that I need clear space between them, as a large hydraulic pump directly mounts onto the PTO output shaft - it's all rather tight ! The other modification I'm working on is to give this pumps hydraulic pipes some form of quick release coupling, so that it can be mounted first, then the tractor reversed onto the flail, rather than having to maneuver the heavy pump onto the shaft at arms length between the stiles. However there is considerable flow which mustn't be restricted - the motor that the pump drives on the flail head develops 24 horse power ! |
| vtsteam:
4" x 1/4" square tube is stiff. I think triangular gusset plates at the end, displaced in from the corner a bit, and lapped over the tubes would help in avoiding fatigue at those particular tube joints. If you have the clearance for it, I mean. |
| mattinker:
How about some photos so that we can really understand what's going on. Regards, Matthew |
| Lew_Merrick_PE:
The angle of twist resulting from a given torque applied to an element is: Theta = (Tau * Length)/(PolarMomentofInertia * ShearModulus) Theta is the angle of twist in Radians. Tau is the torque in appropriate units as used in the Length, PolarMomentofInertia, and ShearModulus. The Length should be obvious. PolarMomentofIntertia is the area polar moment of inertia of the element (which can be a compound assemblage). ShearModulus is a value inherent to the material of the element. Thus, to limit twist, you want to minimize torque, minimize length, maximize the Area Polar Moment Inertia, and/or use a material with a greater Shear Modulus. These are the variables you have to play with in minimizing twist. |
| vintageandclassicrepairs:
Hi Andrew, Would it be possible to add a further section centerally but below the two parallel arms ( to avoid PTO etc) This (say similar material to the parallel arms) would be held in place by angled members welded to the parallel arms forming a triangulated cradle below the mounting arms to the tractor the welded in pieces would be alternatively at right angles and 45degrees to the main arms forming a cradle of triangles ? OK difficult to picture ?? imagine 3 vertical members of a radio or power mast forming a V shape The bottom member of the cradle would just serve to carry the triangulation from one arm to the other Hope my ramblings make sense?? John |
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