Diameter / Roller Lenath Ratio  To achieve a certain static load rating, the bearing diameter increases if the needle length decreases. As  considerable axial deflection between inner ring and outer ring was expected, a design with short needle  lengths was chosen combined with a bearing diameter as large as possible to still have high load  capability even if axial deflection occurs by spreading the load to a higher number of needles. Using  shorter needles reduces also the impact of edge pressing.  Needle Roller Diameter  Investigations on the needle roller diameter were performed. It turned out that, computing the static load of  needle bearings with different needle roller diameters while keeping the outer race diameter constant and  also keeping the needle length constant, the load capability increased with decreasing needle roller  diameter:  However, the static load capability is not the only parameter to be taken into account. The friction moment  of the bearings increases with the number of rolling elements. As this effect can not be numerically  evaluated for needle bearings we relied on experience from previous needle bearings. The ratio between  roller diameter and roller length increases with higher roller diameters leading to less friction caused by  misaligned tilted rollers.  Bearina Outer Rina Thickness  To distribute tensioning loads, lateral loads, and torsional loads of the gimbal on a high number of bearing  needle rollers, the stiffness of the load-transferring elements, which are the bearing housing and the rings,  should be as high as possible. A comparison of different thickness ratios between bearing outer ring  thickness and housing thickness within the envelope constraints has been performed. The inner diameter  of the bearing outer ring and the outer diameter of the bearing housing (formed by the yoke) have been  assumed as fixed.  The comparison showed that the smaller the bearing ring thickness, the more stiffness is gained. The  higher Young’s modulus of the bearing steel Cronidur 30 (208000 N/mm2) compared to the Young’s  modulus of the housing of Ti-GA14V-ELI (1 10000 N/mm2) has less effect on ihe stiffness than a thicker  rectangular section of the yoke of Ti-6AI-4V-ELI. No shear force transmission was assumed between the  bearing and the housing in this comparison. Following this, the bearing outer ring thickness has to be as  small as possible.  The lower limit for the bearing ring thickness is a manufacturing issue. The ring thickness must stay above  2 mm according to the bearing supplier.  Bearina Inner Rina Thickness  The bearing inner ring js supported stiffly by the gimbal cross, which is made of lnconel 718 (Young’s  modulus 205000 N/mm ). Therefore, load transfer is not a driver for the inner ring thickness. The design  driver for the bearing inner ring thickness was integration issues. The gimbal cross insertion process  requires a relatively small shaft diameter.  Bearina Sizinq  The bearing pre-dimensioning was done keeping in mind above considerations and using standard  formulas fo;full-complement roller bearings. The final bearing calculation (including Hertzian pressures in  the roller needles) was then done using the results of the FEM calculation.  A coefficient of static load f, of 0.7 was assumed as the application exhibits small angular oscillations and  shock loads. The largest bearing that fits in the room given and having the necessary static load capacity  was selected.  Bearina Rina Desian  The bearing inner side is not covered by the gimbal, so borders were designed to prevent intrusion of  contamination. Shoulders on the outer and on the inner rings limit the travel during the axial insertion  process. Figure 2 shows the gimbal bearing design:  271