View Full Version : Slip angles w multiple vbox's - imu's
07-02-2012, 08:40 PM
I have a rather long veh that I did some testing on. I put 1 vbox with antenna and 3axis imu over the rear axle and a second v box w attenna and 3axis imu over the cg of the veh. The data is sync'd with a brake trigger input.
So with all that is there a way to set up something to calculate or look at slip angles?
What kind of formula am I looking for to do the calculations?
22-03-2012, 12:06 AM
This is something which is relevant to my interests as well.
The prospect of using multiple Vboxes on multiple combination vehicles to measure off tracking.
Or repurposing a multi-antenna vbox for the same purpose.
The issue with the latter is the prospect of having to run antenna cable for 50 or more metres, including across multiple points of articulation. Hence you can understand the appeal of multiple stand-alone vboxes.
27-03-2012, 10:58 AM
With your current setup there is a way to calculate a slip angle using the Body Angle Data channel creator in VBOX Tools. If GPS Long acc and GPS Lat acc are logged in the file (with data from an IMU03 or YAW03), this creator can calculate slip, pitch and roll data. The slip will then obviously be for that given point of the vehicle.
You could try and process your files captured already, however there is chance they may not process as there must be a lead in the file where the vehicle is travelling completely straight and a set of parameters are true for so many samples for the calculator to calculate accurate results. These parameters are:
-0.5 < yaw <0.5
-0.1 < smoothed lat acc < 0.1
...I am checking with the software programmer to discover the number of samples required!
Bear in mind also that this method to calculate these angles is good for steady state tests only, so if you have a high dynamic test, then you will not get accurate results during the transitions.
........If this method is not suitable for your application, then there are ways you can calculate a slip angle, but this will involve you getting your hands dirty and a little clever with your calculations.
To calculate a slip angle you need a vehicle body angle channel to compare it to. To calculate a vehicle body heading angle you need to create a bearing calculation by comparing the two longitudinal and latitudinal antenna positions. Further information on how to calculate this can be found online - here is an example (http://www.movable-type.co.uk/scripts/latlong.html)
You can then calculate an individual slip at both antenna points by subtracting the vehicle body heading angle from the antenna heading.
The way I know to achieve this would be to open the .vbo file from one of your VBOX's in Excel, in a space delimited format. You will then have to add the longitude, latitude and heading data from the other .vbo file in to additional columns of the original Excel file (ensuring they are time synchronised). In further additional columns you would perform your calculations.
Note that for each channel you add, you will have to add an extra corresponding name line under the header file, as a .vbo file will not open if the number of channels in the header file does not match the number of data columns. Also avoid using the same names as current channels as this will cause problems.
When you complete the Excel file, you must save it out in a standard MS-DOS .txt format, and after which change the file extension from .txt to .vbo so that it can be opened back up in VBOX Tools.
If this is something you wish to do, but dont feel comfortable in doing (or are unable to accomplish) there may be an opportunity for one of our software developers to create you an application, however this would be chargeable.
Whilst this is a bunch of info, I hope it helps.
If you find it easier you can reply to me (Sam) over email, at email@example.com
27-03-2012, 11:15 AM
With regards to your comment adamtruckeng, the below calculations may not be relevant (if you are using only two VBOX's) due to your comment about the antennas passing multiple points of articulation.
As a result, the reference vehicle body heading calculation could be unrepresentative.
It may help us advise you further if you describe your vehicle and application in a little more depth in an email to firstname.lastname@example.org?
If you could cover the exact data you are wishing to gain in as much detail as possible, and touch upon what accuracies you require, either I, or one of our technical sales advisors could help further.
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