![]() Other things that could cause discrepancy, which you should consider. ![]() * Ignoring Fx (it is quite possible that the highest tie-rod loads are from Fx, although you don't get much steering wheel torque)- matrix method would use Fx as long as you input it aha (Matrix method would acurrately use an off-horizontal plane moment arm at 90deg) * Using caster as a distance on the horizontal ground plane, when in reality, the moment arm must be 90deg to the steering axis. Theres a number of simplifications that could be made when doing the steering axis method, which would lower the accuracy of that method below the Matrix method, which does not make these assumptions. You could get the same results with calculating moments about the steering axis, although it would depend on how you do it. Also having clearance, so that the drive shaft can move along its spline will prevent axial force like you said. It should have constant velocity (CV) joints on both ends, which act as pin connections, making the driveshaft a two-force member, that can't transmit radial loads at either end. If there is, something is wrong with you driveshafts that should be fixed. This is the same thing.ĭriveshaft should not transmit radial or axial force. If I had a beam under both bending and tension, then remove the bending, the side that was under compression due to bending actually sees higher stress after tension is removed, but overall there's less stress in the beam. In general loads will go down, but there might be one or two links where that doesn't hold true. Having said that, there's a lot going on for the links- they are still reacting forces in Fx, Fy, Fz, Mx, and Mz. The driveshaft should reduce the overall load on the suspension links. It's just easier to visualize if you calculate the moments about point 2 in the simplified image, or about the axle like I suggested. The contact patch and the reaction in the Fx direction by the suspension arms together create the torque in My. However, if you take the moments about point 1, it will appear that Force 1 is not creating a moment- but what's happening is F1 and F2 together create the moment. If you look at the rectangle on the right of this image-, you'll agree that both Force 1, and Force 2 are creating a moment. The thing here is because in the examples, the moments are all taken about the origin, because Fx has a height of 0, its moment arm to the origin is 0, and you get My=0. The difference between inboard and outboard brakes is if we include additionally an equal and opposite torque as well.Īt 11:30, it can appear that there isn't any My created because the "y" position of the matrix is equal to 0. We apply an Fx at the contact patch, and calculate the moment it creates as (r x Fx) (11:30 in the video). The torque applied at the contact patch from braking (Fx) is included in both scenarios. The torque will be transferred to the rest of the vehicle through the driveshaft, instead of the suspension arms reacting this torque, which should usually result in much lower forces on the lower suspension arms. Because force is transferred through the 7th, unaccounted for link (the driveshaft), we must correct that. However, with inboard brakes, the braking torque is transferred through the driveshafts to the inboard brake. In this case, all the braking torque to be reacted to the rest of the car through the suspension links (which is what happens in real life). No torque through the driveshafts means they can safely be ignored, which the base analysis does by default. With normal outboard brakes, there is no torque going through the driveshaft. If there's torque going through the driveshaft, then we have to correct for this. The base analysis of the 6圆 matrix ignores any torque that is transferred through the driveshaft (it's assuming there's only 6 links, ignoring the 7th). The driveshaft can only transfer a torque- nothing else. The 6 suspension forces plus the 7th which is the drive shaft. So there's really 7 links transferring forces from the wheel assembly to the rest of the car in the rear. Issue with one of the dates? Please contact the moderators. Unofficial discussion forum for Formula SAE and Formula Student engineering competitions, part of the SAE International Collegiate Design Series.Ĭontribute to the FSwiki: 2023 North & South American Events
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