RcTek : Information & Resources for the Model Car Racer

The Importance of the Circle to Model Car Handling

This article is part of a section of the RcTek site devoted to radio controlled model car handling. As car handling is an extremely complex subject, it will be quite some time before it is finished.

This article is about circles and their importance in understanding the fundamentals of model car handling.

Circle?

Although it may seem strange that we would devote an entire article to something as basic as a circle, it will serve as a reference for many of the other articles in this model car handling section.

What is a Circle?

A circle is defined in the Oxford English Dictionary as being;

“(The line enclosing) a perfectly round plane figure whose circumference is everywhere equidistant from its centre.”

Whilst this is true, as far as model car handling is concerned a circle has important benefits in acting as a means of converting or transferring motion and forces.

Motion Conversion — The Wheel Example

The easiest example that demonstrates this concept is the wheel, as it is a circle which goes round to enable the car to move forward. If you Play the animation to the right you will notice that the wheel does as you would expect it to, it rotates and moves forward. You may Stop the amination if you so wish.

The red line shows the path of the movement of the rotated wheel and suitably demonstrates the conversion of circular movement into a straight line one.

So What?

The above example using the wheel should be easy to understand concept for all, but if you think of this motion conversion from an opposite point of view, you can see that it can be reversed, i.e. straight line motion can be converted into circular movement.

This is the fundamental concept that we are introducing here and explains how many aspects of model car handling works. Any pivot point forms the centre of a circle and this fact can be used to manipulate movement to create the desired results.

How? & Why?

The animation to the left shows the reverse of the wheel example shown above and when Played shows that rotating the circle moves the grey lever in a horizontal direction (which is marked as A). The distance B is the horizontal distance that the end of the lever that is fixed to the circle has travelled through. This should be straightforward concept to understand, but what the important thing to understand is that this movement has been achieved by the end of the lever travelling through an arc. You may Stop the amination if you so wish.

This movement involves both horizontal and vertical movements at the same time and it is the relationship between these two movements relative to the position around the circumference of the circle that is the important factor.

If you Play the close up view of the above animation on the right, it shows just how the translation of the movement occurs. The important factor that we are trying to make clear is that in the first 45 degrees of the rotation of the circle, the majority of the movement is vertical, and so does not generate a great deal of horizontal movement of the left hand end of the lever. You may Stop the amination if you so wish.

The second 45 degrees of movement, though, is more in a horizontal direction and therefore moves the left hand end of the lever a greater amount than the first 45 degrees does.

The above should clearly explain how such things as the Ackerman Steering Principle works when you consider the relative positions of the steering arms around the circumference of the circle.

There’s More

Another point worth noting is that the relative position of the free end of the lever affects the amount of horizontal movement that rotating the circle generates.

In the animation to the left the free end of the lever is positioned level with the bottom of the circle. When the circle is Rotated the horizontal movement generated at distance A is less than than that of distance B. You can reset the animation to its Starting position if required.

This contrasts with the animation to the right where the free end of the lever is positioned level with the centre of the circle. When the circle is Rotated the horizontal movement generated at distance A is more than than that of distance B. You can reset the animation to its Starting position if required.

Summary

Hopefully this article has made you understand the importance of circles in model car handling and geometry.

There is more that could be said on this subject, but this will be introduced when relevant to a particular aspect of model car handling.

Related Information

Ackerman Steering Principle

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© 2001, 2009 by Darren Burnhill