Author Topic: Trailer turn path approximation  (Read 282 times)

miki

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Trailer turn path approximation
« on: August 15, 2020, 09:31:46 AM »
Hello all,
First thanks for great software! I have discovered it only recently, while searching for vehicle turning material, but it has a lot of other great features...


I am trying to develop vehicle turning solution (similar to what you have), which should work also in real-time (like driving a car). It doesn't need all the options that you have, just driving at low speed with predefined vehicle dimensions.
I have handled driving single vehicle (and single vehicle with trailer (without dolly)).
Problem arises when we have this "transition" period, when rotation points are different. For example, starting from straight line and then turning.

After exploring internet and reviewing dozens of documents i have found online, it was made clear to me that this topic is quite complex. What i need at least is approximation, but all these papers describe mostly theory part, with formulas for n-trailer systems, which need to be solved for specific cases - and this requires a lot of mechanical engineering knowledge (and i am software engineer, thus this is out of my scope).

In short:
What i am hoping is pointing me in good direction, maybe some materials with formulas (or explanation) on how to approximate trailer moving path (in "transition" period - centre of rotation points are different) in truck-trailer system (1 trailer at least, 2 trailers would be the best!). Approach that i have used is to move a vehicle 10cm or less, in which steering is constant (with speed, if it is important), and to calculate new positions.

Thanks,
Miki

Lars

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Re: Trailer turn path approximation
« Reply #1 on: August 15, 2020, 03:45:04 PM »
Hi,

Using a line as steering path is probably easier than follow user mouse input. In my software I move the truck 0,2 meter along the path and then apply the trucks endpoint as the second elements startpoint and so fort. For visualization only I turn the wheels based on path tangent and Ackerman steering theories.

Using "free" hand movements would require construction of geometries based on user input behind the scene or huge knowledge in math. That's why I used the simple approach (follow a path)

/Lars

miki

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Re: Trailer turn path approximation
« Reply #2 on: August 15, 2020, 09:04:33 PM »
Thank you for your answer.
Actually, i am not following the mouse, but have steering wheel in user interface, so user changes only angle of steer (but, to be honest, mouse following was one of the starting ideas).

My question is exactly related to calculation of rear endpoint of the trailer_1. Startpoint of trailer (which is also attach point to the truck) is moving with the truck according to Ackerman, but since center rotation points (for truck and for trailer) are different, same formula can't be used for trailer endpoint.

And just today i have found document with something which should help, you can see in the image "trailer steer.jpg".
Exactly my question: front point of trailer is moved along circular path, and arrow shows new position of the trailer endpoint.
Is this acceptable approach? Can it be also applied to to trailer number 2 (except startpoint of trailer 2 is moving along line)?

Lars

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Re: Trailer turn path approximation
« Reply #3 on: August 16, 2020, 09:54:22 AM »
Yes, that image is probably from same document I found "Journal of forest engineering, A method for determinering offtracking of multiple unit vehicle combinations".
The incremental distance (ds) should be no more than 0,30 m.

Move truck startpoint distance (ds) in any direction, calculate endpoint. Use endpoint movement as path for next part of your vehicle. Using this approach you can add as many element you want to your truck.

miki

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Re: Trailer turn path approximation
« Reply #4 on: August 16, 2020, 08:16:32 PM »
Yes, it is from that very document.

Move truck startpoint distance (ds) in any direction, calculate endpoint. Use endpoint movement as path for next part of your vehicle. Using this approach you can add as many element you want to your truck.
That is exactly answer i've hoped for, it fits completely to my design. Thank you for your help!