TURN.LSP Question

[skibuf23]

I hope you all don't mind a new thread, I know there might be a few others floating around but I had a quick question about the TURN.LSP application.

I stumbled upon it the other day and first off, I would just like to say what a great piece of free software. My company doesn't have any turn simulating software and to be frank we wouldn't use it enough to justify the expense of purchasing.

But on to the question... I read in the instructions that if the front-left-tire poly-line starts as an arc, align the vehicle block so that it is tangent to said arc. Can you start the block rotated within the steering angle range of the vehicle in question? What I am trying to simulate is a vehicle starting a turn from a standstill with a turned wheel (I've been assuming 30*). The results I've been getting appear to be reasonable, and a test video I saw on youtube showed the application performing this function. If this is not correct is there a method of evaluating this situation? Any input is much appreciated!

Thanks in advance!

 

[IRstuff]

I don't think the program cares whether you're stopped or not; it's a geometrical calculation, is it not?

http://www.hawsedc.com/gnu/turntheo.php

TTFN
faq731-376

 

[CarlB]

I believe the program always assumes the vehicle's front axle is aligned with the path and and no initial turn angle, so block is not rotated. If you want to simulate an already-rotated vehicle, extend the polyline beyond the start point, a distance/radius as necessary so the vehicle is rotated when it reaches the "start".

 

[skibuf23]

Thanks for the reply IRstuff. I might have worded the question poorly. I am more interested in the relative orientation of the initial wheel path to the vehicle block @ the start of my analysis. The program directions state to have the block tangent to the wheel path which to me indicates that the front wheels are parallel with the back wheels (or in-line). I want to start with the front wheels turned say 30*. I think I agree with you and that it shouldn't matter...???

 

[skibuf23]

Read your reply right after I posted the above CarlB. Okay that changes things, could prove that my analysis is not accurate after all.

 

[IRstuff]

If you look at the diagram in the cited site, the "line" is from hubcap to hubcap.

The wheels are always tangent to their own turning circle, so the intersections of the perpendiculars of the tangents is the center of the turn.

TTFN
faq731-376

 

[skibuf23]

I agree with IRstuff. The axle is not aligned with the path unless your going straight. Instead "the line between back and front wheel always tangent to the inner circle being made by the back wheel" The procedure I've been using is to create the front left wheel path (my outside wheel) greater than or equal to the AASHTO minimum radius. After the remaining wheel paths are generated I check the inside minimum radius and steering angle throughout the turn. As long as it checks out I think the turn is realistic.

If it isn't obvious I'm modeling a vehicle cranking the wheel and attempting to turn because of some tight sight conditions.

I appreciate the input. The more discussion the merrier!

 

[DeleteAccount]

skibuf23,

If you are trying to simulate a vehicle starting a turn from a standstill with a turned steering wheel, then the starting portion of the polyline needs to be an arc. The vehicle block should be tangent to the arc. You'll see a little circle in the center of the left front tire of the block. The center of the little circle is the point of tangency and this point needs to be on the starting endpoint of the arc. If you were to draw a radial line from the center of the arc to the starting endpoint of the arc, the radial line would be perpendicular to the side of the vehicle block.

It is important to understand that it is the manually drawn polyline representing the path of the front left wheel which determines the vehicle path. The routine always tracks along the polyline path. The path steers the vehicle, not the other way around. You don't want to rotate the vehicle block in order to affect the modeling. It is the path which determines when the vehicle turns and at how sharp an angle. It's not unlike the electric toy race cars sets many of us had as children; there was a slot in the track and the car had a stem-like structure protruding from its underside which went down into the slot in the track. The car had to follow the path of the slot. Same thing here. Turn.lsp tracks along the manually drawn polyline path. That's why it's imperative to draw your path properly. The routine will track along any path you create whether it's properly drawn or not. If you draw a really tiny radius in your path that is smaller than the minimum radius as listed by AASHTO, the routine will still track along it. You could draw a 1' radius and the routine will track along it and generate a model. The point is, as I've already said, Turn.lsp tracks along the manually drawn polyline path, and the path steers the vehicle, not the other way around. Don't attempt to affect the outcome by rotating the vehicle block. Understand that the routine does not know what the minimum turn radius for vehicles are. This is why you don't want to rotate your vehicle block. It has no check for this and draws whatever it must in order to track along the path you draw while remaining within its own constraints. The block needs to be tangent for controlled and correct modelling.

As you already mentioned, Tom Haws created a "test" video and posted it on youtube here:

http://www.youtube.com/watch?v=DmHMUyquoSI&feature=youtu.be

Keep in mind, however, that this is just a "test" video he posted in response to a user who was having trouble understanding how to use the software. The video was created in order to demonstrate the routine in action. He wasn't concerned with generating a path conforming to any constraints such as AASHTO's minimum turn radii.

As CarlB has already noted. "If you want to simulate an already-rotated vehicle, extend the polyline beyond the start point, a distance/radius as necessary so the vehicle is rotated when it reaches the "start"." I would add to that, that you can always go back and trim out lines you don't want and delete instances of vehicle plots that are before your desired start point.

Kevin

 

[dik]

Catch the file...

 

[dik]

The attached is a more descriptive file... I used this approach for designing the underground loading dock for a large project in Regina about 30 years ago... and transferred the method to CAD.

Dik

 

[skibuf23]

Kevin,

Thanks for the response! I understand the idea that your path defines how the vehicle tracks. I also know to check if the output is indeed feasible using AASHTO's minimum radii for the outside wheel (as well as some other vehicle characteristics). There is still one thing that puzzles me and its not that I doubt your explanation, but rather that the final link hasn't clicked for me yet.

Perhaps you can check my thought process here.

If I hypothetically create an "ideal" turn path. A U-turn that has a long straight approach, a large radius turn, and a long straight departure. I then run TURN.lsp with a plethora of plots to choose from. Each vehicle block generated is perpendicular to a radial line drawn from the center of the manually drawn turn path to the inside edge of the vehicle block. Now I will choose a convenient block from the generated turn, one that is smack dab in the middle of the U-turn, and delete all other blocks. I can then trim each track line generated behind there respective wheels and rotate this configuration to the geometry of my roadway at my starting point.

Because I only care about my original manually drawn track line I will delete the others. I am now left with a manually drawn turning path that starts as an arc and although the outside of my vehicle block is not tangent to my arc (at the front left wheel), the inside of my block is perpendicular to a radial line drawn from the center of the turn. as it was when I first grabbed it.

Is this an accurate way to simulate a turn initiated with a rotated steering wheel?

Again appreciate the input!

P.S. Dik, thanks for the cad file, haven't played around with them yet but intend to give those a shot tonight.

 

[DeleteAccount]

skibuf23,

There are essentially two ways to run Turn.lsp.

1) If you are starting your path as a straight line, your vehicle block needs to be parallel with the straight line with the little circle at the center of the left front wheel of the vehicle block sitting on the endpoint.

2) If you are starting your path on a curve, your vehicle block needs to be tangent to the arc with the little circle as the point of tangency and this point needs to be on the starting endpoint of the arc. As already described, if you were to draw a radial line from the center of the arc to the starting endpoint of the arc, the radial line would be perpendicular to the side of the vehicle block.

I realize that you are likely already clear on these two points so let me elaborate a little more. Assuming you are using a vehicle with a truck, hitch and trailer, both of the above scenarios use a vehicle block which is perfectly straight; there is no angle between the truck and trailer. The truck and trailer fall in a perfectly straight line. It sounds like you are interested in modeling a vehicle which is already part of the way into a curve and so want to show your starting position with the truck already rotated at an angle relative to the trailer. The software doesn't allow for this however you can still do it using CarlB's suggestion. Based on your description of what you are trying to accomplish, I think that what you are describing is exactly the same thing CarlB was suggesting. I have used this method myself. So if indeed you want to show a truck with a trailer starting part way through a curve, as opposed to the beginning of the curve, where the truck and trailer are at angle to one another due to being in the process of turning, the method you are describing is what you would need to do. Keep in mind however, that the instances of vehicle plots shown along your path are not blocks, but polylines representing the location of the truck at various points along the path. There is only one block; it is a block with attributes and is the block you place at the starting point of your path. Turn.lsp uses it along with the front left tire path to generate the model.

So what you need to do is start your path beyond and before where you need it to begin, and as you said, delete all vehicle plots that are before your desired starting point and trim the track lines behind your starting point. This is all that needs to be done and is what CarlB was suggesting. To quote CarlB "If you want to simulate an already-rotated vehicle, extend the polyline beyond the start point, a distance/radius as necessary so the vehicle is rotated when it reaches the "start". " That's pretty much it. Nothing complicated. Don't over-think it.

I don't understand what you mean by "rotate this configuration to the geometry of my roadway at my starting point". There is nothing to rotate. You draw your path meandering through your site and generate the model. This is not the same as using templates. Templates are inserted into drawings and rotated to your road geometry to see if vehicles can make it through or not. Templates are old-school and this software has nothing to do with templates. You don't generate a model and insert it and rotate it into your road geometry. This would be assuming that you are simply creating templates with the software and putting them where you need them. That's not what you are doing. You simply draw the path through the entire site, or through whatever part of your site you are checking. What I typically do is copy my site plan drawing to another file with a file name with the word "turn" in it, then I draw my path through the site and generate the model. The end result is a site plan drawing showing a truck driving through it with all of the paths of the wheels, hitch path, and locations of the truck along the path. I've drawn very complex paths through very tight sites with lots of turns this way. However, it is next to impossible to get it right the first time around. You create a path, run the routine and see what you get. It usually takes several attempts to get it right and you have to tweak your path until you get what you want. In tweaking the path, you may have to change the turn radius, although making certain it's greater than or equal to AASHTO's minimum turn radius for the vehicle in question. You may also have to tweak the location of straight portions of the path. You have to play with it. But don't generate a path and rotate it into road geometry. Generate the path within the road geometry and tweak it until right. The end result is that you will be able to see whether the vehicle will fit through your site or not and you'll have a nice exhibit demonstrating that the vehicle can either make it through the site or not.

If you go to the talk page on the WIKI, I've made several posts explaining other aspects of the software and how it functions, including wheel locations, etc. You don't need to read any of those posts. All you really need to Model Imperial Unit AASHTO Vehicles are the blocks and PDF instruction at the WIKI. I created the blocks and PDF instructions, by the way. However, I'm not one of the developers, I just contributed the blocks and PDF instructions. There were a lot of questions on the talk page by users who couldn't figure out how to create vehicle blocks or use the software properly. I have to admit, I found it a little confusing initially, but studied the code and played with the software A LOT in order to make certain that I could generate models that were as accurate as possible using the parameters as defined in the software code. I've used this routine for a few years now and think it's a great free alternative to the expensive software programs available for purchase.

I think I've run my mouth long enough! Anyway, good luck!

Kevin

 

[DeleteAccount]

skibuf23,

To simplify and clarify, I thought I'd make one last brief post.

To model a vehicle at the beginning of a curve, assuming the vehicle was traveling in a straight line before entering the curve, use method 2) as described in the above post. Also, if you are starting from a dead stop, and the truck is in a straight line with the trailer, and the steering wheel is rotated because you are going to start a turn from a dead stop, again, use method 2).

To model a vehicle where you want to show the point of beginning on a curve where the truck is already part of the way around the curve, meaning that the truck and trailer are at an angle to each other because it has already traveled part of the way through the curve, use the method suggested by CarlB.

These are the only possible two scenarios so pick the one you need for your purposes.

 

[skibuf23]

Kevin,

http://www.eng-tips.com/viewthread.cfm?qid=332373

I think I understand what you are describing. To be honest, I don't think you are fully understanding what I am trying to model. No fault of yours of course, I probably am not doing a great job at describing it. I appreciate the help though and at this point my colleagues and I are comfortable with a path we generated. We were actually able to change the layout of the site a bit, which opened up things a lot.

I read the wiki page when we first downloaded TURN.lsp it was extremely helpful.

Thanks again for the thorough explanation, I am sure it will help others as well!

 

[DeleteAccount]

Hey skibuf,

Sorry I wasn't able to help more but I'm glad you guys were able to come up with something that suits your needs. The internet is great for sharing ideas but sometimes there's just no substitute for sitting down right next to somebody, looking at the screen together and working through ideas. Anyway, good luck and best wishes!

Kevin