Off road trailer factor of safety 1

[tjmartin]

Hello all,

I work for a small manufacturing company (~40 people) and I have been tasked with designing an off road trailer for use with UTV's.

I have a base design that is manufacturable for what we want to do but I can't find any concrete numbers for what I should use as a factor of safety for trailers.

I've seen as low as 1.5 and all the way up to 5.

Or if anyone knows any standards that would be associated with trailer design.


Thank you in advance.

 

[dhengr]

Tjmartin:
Is this a trailer for hauling UTV’s on the public highways, or is it a trailer to be used for misc. work behind, pulled by, the UTV, out in the sticks or field? These two situations imply different degrees of safety to the general public as opposed to the safety of one operator and a helper in the field, and they should probably have different FoS too. The Consumer Product Safety Commission actually has something to say about the UTV (Utility Task Vehicle) itself, doesn’t it, ROPS (Rollover Protection Systems) and such like? While the same stds. may not apply to a trailer, they may at least give you some direction. Are there any manufacturer’s associations which set some stds. for this type of equipment?

Obviously, you have to design this trailer so that it can be built and sold at a competitive price. But, you should also keep in mind that many users don’t know the difference btwn. a 500# load of soil, loaded with a hand shovel, and a 3000# bolder, and they will drop it into the bed. What sort of loads is this going to be designed for, and how much load? What about stability of the trailer under load, and will it tip the UTV over if it tips? You might have several different Factors of Safety (FoS), one against material yield under loading, with some dynamic factor on the loads; another for things like stability under load or on a side hill. Are there any existing products, which you are competing against? Can you start dissecting one of these to get a handle on strength, capacity, material sizes and thicknesses, FoS, etc? What are the suspension components and the running gear, their cap’y. and life expectancies? If I had to pick a FoS, I’d guess 1.7 to 2, against yield or buckling, for the various components. Then, nice clean detailing to make it easy to build and service, and smart economical material selection should come into play.

 

[racookpe1978]

Biggest problem you have is is not a "factor of safety" but the "redneck-from-hell" idiodicity overloading the thing (assuming field and woods use off-highway) and the "I know its overloaded but I don't have anything to use" just plain bad judgment/bad decisions.

Assume a load (300 lbs, 600 lbs, 900 lbs whatever) and state that load in your handbook (User Guide, Instructions, Printed Warning on the trailer "IN BIG LETTERS") Then frankly, design for double that load and impact forces (as recommended above) but expect those limits to be regularly exceeded.

You cannot ever make this thing strong enough to avoid overloading by idiots. Pick a load, pick a FS that will make it economic to build and sell, and state the design limit. Sell more trailers to those who break them. Equally, consider the "two level" sales: An "economy" trailer and the "Woodsman" or "Professional" . A user who wants a more durable product will choose to pay more (thicker frame, heavier tube steel, larger welds, thicker axle, better bearings, extra side angles to brace the tow hitch bar, etc. )

We see that design all the time in tools. Cheap grade. Average grade. Professional grade.

 

[CooperJerWI]

I would also recommend looking at MIL-STD 810 rev G for the vibration levels of off road transportation. This will give you an idea of the accelerations the load on the trailer may have. The spec can be found on everyspec.com. I have noted down that "unimproved roads" and "unprepared terrain" have a vertical acceleration of 2.24 g rms, transverse (side to side) acceleration of 1.48 g rms, and a longitudinal (front to back) acceleration of 1.90 g rms. In addition to the MIL-STD take a look at ISTA (ISTA.org) for off road transportation information. They may have recommendations for loads to design to.

 

[ameyerrenke]

UTV cant tow a whole lot... tow ratings of 1400#. Not hard to design a trailer to handle that. Being offroad, you should be more concerned about what its going to be run into than what it can carry. Just keep the center of gravity low so that it won't want to flip, use 10ga steel as the minimum material thickness on the entire trailer, and make the bed only big enough to hold 1000# of soil (9 cuft). If you rate the trailer for 1500 gross weight use an axle rated for 3000#.

 

[tjmartin]

Thanks for the replies everyone. A little more information about the trailer:

-It is for a company that sells customized UTV's to the military.
-It is to be made of all aluminum construction,
-Weigh under 400lbs,
-minimum ground clearance to be the same of the UTV
-uses independent torsion suspension axles (max capacity of 2000 lbs combines trailer and payload weight)

Most of the design is complete, I am tasked with improving and verifying the strength of this trailer.

I will take a look at those Military standards, with all the searching I've done online I'm surprised that didn't pop up.

 

[Timelord]

There are a lot of various mil specs for all kind and sizes of vehicle trailers. Check here:

http://www.nssn.org/search/AdvancedSearch.aspx

I searched the word "trailer" in the document titles and limited the search to DoD approved standards and got 299 records. See if any of these specs fit your application.

Timelord

 

[MikeHalloran]

This would be a good time to find out exactly what your salesperson promised your customer.

E.g., dig out the contract and related (e)mail documents and look through them for references to standards and other requirements.

Expect to be shocked.




Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

>>>Most of the design is complete, I am tasked with improving and verifying the strength of this trailer.<<<

Actually, it smells like your boss has already been yelled at because the product weighs too much and carries too little, and/or a prototype already failed a test that has been a requirement since the project began, and/or the prototype does not look anything like what the customer wanted.

Dig, politely but persistently, until you understand the actual customer requirements.







Mike Halloran
Pembroke Pines, FL, USA