Professional Motorsport Data Analysis: Force Measurement
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Force Measurement
05.44
| 00:00 | - Fundamentally, force and displacement are directly related to each other in that for a given load case and material, the amount that a component deflects is known for a given applied force. |
| 00:12 | This deflection could be in tension, compression, torsion, bending or sheer. |
| 00:18 | Force is often something we're interested in in data acquisition and the way we're calculating it is ultimately by measuring the displacement of some component and back calculating the force from that displacement. |
| 00:30 | Whether we're talking about measuring the displacement of metallic or composite components, in human terms these displacements are tiny. |
| 00:38 | That means we need a very sensitive method of measuring these displacements accurately. |
| 00:43 | In motorsport applications, the way we generally do this is by using what's known as a strain gauge. |
| 00:49 | A strain gauge is a small electrical device that's permanently bonded to a component. |
| 00:54 | It measures the amount of deflection over the area it's bonded to and we can then calculate the amount of deflection experienced by the strain gauge by measuring the electrical resistance across different parts. |
| 01:07 | The parts of the strain gauge that change with resistance are known as the bridges and the number and layer of the bridges depends on the type of strain gauge. |
| 01:15 | The changes in electrical resistance are very small and cannot be directly measured by a datalogger. |
| 01:22 | The strain gauge is connected to what we call a strain gauge amplifier which senses the small changes in resistance, processes it and converts it to an output signal suitable for the logger. |
| 01:34 | The output is usually either an analog 0-5 volt signal or directly over CAN. |
| 01:40 | The amplifier is generally mounted in close proximity to the strain gauge to prevent the sensitive signal being corrupted by electrical interference between the gauge and the amplifier. |
| 01:52 | Strain gauges are implemented throughout a car, either by attaching to components of interest or alternatively by load cells. |
| 02:00 | Let's look at strain gauges first, these are applied directly to elements of the car and that's generally done by a specialist. |
| 02:07 | The load cases and magnitudes must be well known in advance. |
| 02:11 | As this affects what type of strain gauges should be used, where they should be mounted, how many are required and what the appropriate orientations are. |
| 02:20 | Strain gauges are permanently attached to a component and the only way to remove them is by destroying them. |
| 02:27 | Once the strain gauges are installed, they are calibrated against known loads and the expected real world load cases. |
| 02:34 | Together with their amplifiers. |
| 02:36 | This gives the user a known force to voltage output. |
| 02:39 | Suspension wishbones, damper eyelets, suspension push or pull rods, torsion bars and mounts for aerodynamic elements, are just some of the most common cases in which you'd tend to find a strain gauge. |
| 02:52 | As the displacements we're measuring are so small, thermal expansion of components also needs to be accounted for within the measurement. |
| 02:59 | For this reason, strain gauges often have temperature sensing built into them which can be then corrected for inside the amplifier. |
| 03:07 | Load cells on the other hand are simply pre manufactured components with strain gauges built into them for convenience. |
| 03:14 | This means that load cells are not necessarily always an actual functioning part of the car, they can be an extra component and they're generally purchased for specific load cases and force ranges. |
| 03:26 | Once common place we'll find load cells in racing is within the flat patch scales we use when setting up and corner weighting your car. |
| 03:33 | These are either in the form of small cantilevered beams or compression type load cells built into each scale pad. |
| 03:41 | Other applications include strain gauge gear knobs to sense the force and direction of the gear change and spring platform load cells to directly measure the reaction force of each coil spring individually. |
| 03:54 | By using load cells and strain gauges on individual components, we're able to know with a higher degree of accuracy, the amount of load each individual element of a system is subject to. |
| 04:06 | For example, in the suspension this allows us to understand the contribution of force each element is providing between the springs or torsion bars, anti roll bars and third elements. |
| 04:17 | This allows us to properly validate against simulation and understand the forces to help finely tune the suspension and aerodynamics. |
| 04:25 | As well as ensuring everything is behaving as intended. |
| 04:28 | In the case of aerodynamics, to properly understand the amount of downforce being generated, there's no substitute for using strain gauges. |
| 04:36 | While we can get some useful data from using suspension potentiometers to measure displacement, there are so many assumptions involved that it can be very difficult to measure small changes in aerodynamic configuration, even more so when the suspension deflecttions are small because of a necessarily stiff suspension setup. |
| 04:55 | When measuring the forces in certain elements directly, it's possible to measure the aerodynamic impact, of quite subtle aerodynamic changes. |
| 05:03 | For example, it's possible to measure the change in downforce from the tyre pressures changing throughout a stint or the rubber building up inside the brake cooling ducts. |
| 05:12 | Wireless communication techniques are also improving constantly, and these days, it's now possible to get direct torque measurements of rotating components such as tail shafts and axles, this is obviously a great tool to have if you're interested in monitoring powertrain performance in real time. |
| 05:30 | In reality the amount of things we can instrument with load cells and strain gauges is almost limitless. |
| 05:37 | The limiting factor is really only budget and regulations. |
