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Car turning path drawing.
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* March 21, 2020, 03:04:22 AM
Has anyone any idea if I can draw the turning path for a vehicle in DesignCAD (V.20).
I'm redesigning the car parking area at my home. It's for 2 cars and a van. The turning circle, wheelbase and so on are available from the manufacturers.
There's an online program called Autoturn but it's a bit pricey for just this one job, besides I've been using DesignCAD for years.


« Last Edit: March 21, 2020, 03:11:56 AM by Flatron »


* March 21, 2020, 04:22:25 AM
I use the attached turning templates which I think I originally downloaded from the NZ building regulations website.
I certainly wouldn't bother to try to plot a turning radius for a specific model of car (consider that you may change your car in the future!)
If however you do want to there is no reason why you can't do it in DesignCad, but you do need to understand the principles of vehicle dynamics to do that. (I've actually designed vehicle suspensions for my own amusement using DCad)
The fundamental error on your design is that the centre of rotation aligns with the rear axle of the car, not the front axle (unless your car has 4-wheel steering, (like a Mitsubishi/Dodge 3000) Remember too that each of the front wheels turns on a different radius, the result being that the rear of the car tracks on a tighter radius than the front, You need to account for the vehicle overhang too.


March 21, 2020, 06:32:44 AM
Here is a drawing that I used to determine turn circle stats and ideal ackerman for our ERA GT.


March 21, 2020, 08:36:49 AM
To design space requirements for a car, it seems to me one would have to draw a rectangle the size of the car, and swing this rectangle around a radius point, while tracking where the outside corners have travelled to take into account where the rear of the car will be when the front reaches the edge of the space, then turning the rectangle while backing up is a bit more difficult because the radius is taken at the front wheel outside edge I believe.

Also, people don't usually turn the wheel full lock to lock while standing still at the furthest point

User since Pro-design

* March 21, 2020, 10:28:43 AM
Wow, thanks.

That's all useful stuff.

Updated drawing attached. It seems to work when rotating about centre.




* March 21, 2020, 11:32:22 AM

You and Rob S are correct, as long as the center of your radius is on the centerline of the rear axle.
Having given up calculus years ago, I tend to solve these problems with finite element analysis.
See attached model created for a 30deg steering angle using the N and M  macros.
This model appears to be accurate to 1/2 inch, as that is the distance from the center of the constructed radius to the rear axle.


ps Had some spare time today, waiting out Covid 19.
« Last Edit: March 21, 2020, 12:31:55 PM by bdeck »


* March 21, 2020, 12:02:22 PM
Calculus.....a reminder those dark days at school...along with Chaucer!

I'm not sure what the N and M macros are but I think I've done something similar in a more basic way. It gives me a good starting point for the car parking here.


I expect there will be a lot of similar projects planned during these Covid-19 times.


* March 22, 2020, 01:09:18 PM
I'm not sure what the N and M macros are but I think I've done something similar in a more basic way.

Hi Ron,

The N, M, and S macros may be downloaded in a single zip file here:

The M and N macros perform a Move or Duplication (with rotation) in a single operation with 2 (or 4) mouse clicks, and without requiring the user to set discrete handles.

S is an improved select macro that allows very quick unshifted multiple selections, and also replaces DC's convoluted XOR logic with simple OR when selecting overlapping regions.

I expect there will be a lot of similar projects planned during these Covid-19 times.

Alternative Array Macro Attached

Yes. With some extra time on my hands, I found my old N macro could serve as a prototype for a new "Alternative Array" macro that can be used to create sequential copy arrays like the one in the finite element analysis above. The bulk of the array can be created by entering the number of copies desired and then setting 4 points. (It will also create a simple linear array from 2 set points)

The new macro restores what I "remember" to be the last bit of functionality that was removed from the old N command when DC moved to the Windows platform some 26 years ago.

I've had use for this macro on multiple occasions over the years, but it was always faster to do multiple copies with the N macro, than to code a new tool.

Stay Well,

« Last Edit: March 22, 2020, 10:17:28 PM by bdeck »