Turning Multiple Fixed Axle Trailers

[ABCs]

I am an apple grower and want to build trailers to haul apples (in bins) through my orchard. I want to couple 5 - 10 foot X 40 inch wide trailers (in tandem) and tow them through the orchard. The rear axel on each trailer is fixed and the trailer connects to the trailer in front of it (on a pintle hook) and uses the wheels / axel of the towing trailer as the support for the following trailer to hold its front up.

I don't understand how may turning radius works. I know my tractor turning factor sets one part of the turning radius, but once my tractor makes, say a sharp "U" turn, what do the trailers behind the tractor do. I am told that each tailer will cut the corner of the trailer in front of it, but that doesn't tell me what happens in real life. I don't know what happens if I shorten the axel to axel length between the trailers (guessing that makes a big difference), guessing axel width and wheel sizing don't play a role ... so just axel length .. maybe ... and then what happens in the turn .. need help.

 

[berkeman]

Welcome to the PF.

You need to have a tongue on the front of each trailer to facilitate turns. Otherwise the front corner of one trailer will impact the rear corner of the trailer in front of it. How long of a tongue are you going to use in your design?

Since these fixed-axle trailers will be towed on dirt, I guess we can probably assume the slipping of the tires on the dirt is about equal and opposite in direction during turns?

 

[jack action]

Here some videos to help you see what happens with 2 single-axle «trailers». First, a hay wagon. Look at the first 30 sec of the following video and imagine the tongue/front axle is one trailer and the wagon/rear axle is the second trailer:

​

You can notice that the 2nd «trailer» cuts more the corner for 2 reasons:

1. because it is longer;
2. because it is in 2nd place.

Next, to show an extreme case, here's a maneuver call jackknife tipping. Again, the apparatus can be seen as two single-axle trailers. You can see how tight of a radius can be achieved in certain circumstances:

​

The previous arrangements can be modeled like figure $A$ below:

But note how figure $B$ show an arrangement with 2 trailers of the same length and with the axles having the same spacing as arrangement $A$, but it will behave differently.

Assuming the tractor makes a sharp turn, the pivot point of the first trailer is the center of its axle, whether in figure $A$ or $B$.

With figure $A$, it will be like for the hay wagon example, i.e. the 2nd trailer will cut the corner more than the first trailer. Because when the first trailer pivots, the second hitch doesn't move.

With figure $B$, as the first trailer pivots about its axle, the second trailer pivots in the opposite direction. So as the first trailer is pulled, the second trailer will actually have to pivot back before following the first trailer. This will reduce the actual «cutting the corner» effect, meaning it will follow more closely the path of the first trailer.

You will most likely have a set up similar to figure $B$ in your case. Where the axle will be with respect to the front/rear hitches will make a difference in the trailer's behavior.

 

[Ketch22]

What Jack is suggesting is exactly right. In his example B by adjusting the tongue length and the hitch length you can make the trailers follow the tractor very closely. This is often seen at the fair or a campground where little kids get to ride around in trains made of barrels. These follow even around winding paths in a nice line.
Here is a link to a sort video of a barrel train with the axle arrangement that Jack mentioned. I am sure one can search for plans and interpret from there. Notice in the video how close the last cart is to the path of the "tractor" cart.

 

[Baluncore]

Title; Design of Steering Mechanism and Control of Nonholonomic Trailer Systems.
Authors; Yoshihiko Nakamura. Hideaki Ezaki. Yuegang Tan. Woojin Chung. 2000.

There is a down-loadable copy here.
https://www.semanticscholar.org/pap...zaki/2beb7d8e2bcb282471bfa5f18abb7b933ff4614c

https://en.wikipedia.org/wiki/Nonholonomic_system

 

[jack action]

I didn't know what to look for, but thanks to @Ketch22 , I discovered «barrel trains». Here is the type of video I was looking for, I think the OP will like it:

​

Keep the proportions similar (i.e. where the axle is located between the hitches) and you should get similar results.