Two Design questions...

[Rezarf <><]

Here is the final decision, mostly inspired from a relook at Kurt's trailer and Wildyotes trailer...

A single 2.5" structural square tube with .25" wall. This will eliminate a bunch of fab work and geometry at the front end. It will also be the easiest to get really really square. There won't be more than 120lbs on the tongue at its HEAVIEST, so all the extra steel just isn't needed.

This also allows me to use a ball coupler on road, and then unpin and install a lunette ring for light trail work. I have a ball/pintle combo. In addition, the ability to do a 90 degree jackknife is possible with this setup.

The drawbar will be fully welded through the front and second crossmembers.

I will "gusset" the draw arm with 2" HREW tubing with .125" wall bent up on a bender, and the basket will sit on top of it. Clear is mud? The draw bar will be welded at each intersection of the crossmembers.

What do you think?

Thanks!

Drew

 

[Rezarf <><]

Whoops, forgot to attach...

 

[ntsqd]

Highly suggest spending the $30 on the second of the two books I linked. Then you'll know whether or not that is enough. Dimension is always better than wall thickness, but at some point it doesn't fit. That's where the techniques in that book come in handy.

 

[Rezarf <><]

Does the book get into this aspect? Could you look through it and give me your opinion based on the data? I have failed to find that book at a few different stores now.

Thanks!

Drew

 

[ntsqd]

I've never found it in a store either. I ordered my copy from Northern Tool though I have found it on Amazon too.

There is enough info needed that it would be difficult to try to work it thru on a forum. Would be better to work it thru & then show the results for check-off & suggestions.

 

[cruiseroutfit]

Good idea on the tongue re-design... my first rendition of the trail trailer (circa 2000) had a standard tongue, similar to your option 2. I didn't actually have a complete welded joint, I notched the frame, heated it at the bend and then bent the two sides in, then welded the joint. Strong enough if done properly. This was actually just away to get it mobile. At the time I was still running the FJ55 rear axle that was bolted underneath it

It was several years later that I removed the old tounge and added one long enough to jacknife without damage. SOOOO crucial IMHO... mandatory in a trailer that is intended to be used in anything tougher than a 3 rated trail as I see it. I have encountered numerous times that I needed to be able to really back it up "tight".

I've been extremely happy with my tounge length, it tows nice, does great "tracking" offroad (I went with a slightly narrower axle for this reason). I have ~3500 miles on mine... all either on the trail, or enroute to the trail, no failures yet (crossing fingers :sombrero: )



As for the "engineering" behind the different tounge designs... I can't say I have put alot of thought into it, but all of the options you have presented could easily work with proper material selection and construction. While I respect what a book might have to say in relation to building a trailer, they are not likely taking many aspects into consideration (such as clearance, the jackknife factor, etc).

 

[ntsqd]

All the book does is make sure that the design can support the load w/o failure and that it will tow properly on the hiway. It does this in layman's terms, enough so that I used the book to help me understand Statics when I was taking that class. The book did a much better job of getting the ideas across than the class text & w/o burying it in Engineer-Speak.

The off road considerations are not considered or even mentioned, but those goals really aren't at odds with the goals of the book.

 

[cruiseroutfit]

All the book does is make sure that the design can support the load w/o failure and that it will tow properly on the hiway. It does this in layman's terms, enough so that I used the book to help me understand Statics when I was taking that class. The book did a much better job of getting the ideas across than the class text & w/o burying it in Engineer-Speak.

The off road considerations are not considered or even mentioned, but those goals really aren't at odds with the goals of the book.

Sounds like a good book, don't get me wrong... I'm just saying that either of his designs could be fabricated (engineered) to hold the intended loads with a SF included. When it comes to a trailer, I am less worried about statics and more so worried about dynamics Engineer speak it is

 

[ntsqd]

I don't disagree that they could as I've seen some that worked, but those that failed in one way or another are more common. The author, an P.E.- M.E. with trailer design history, specifically warns against that type of layout. Mostly, as I recall, from a concern about dynamic loadings - both vertical & horizontal. Obviously if the bending strength of the structure at that point is high enough, then there's no problem.

When I worked the Shear-Moment diagram for CSUC's HEV APU trailer frame (of the basic design type in question) the front edge of the box/platform was a surprising hot spot. Since that is the only time I've done that exercise for that type of application, I do not know whether it is the exception rather than the rule. Seemed more conservative to assume that it's the rule.

Crudely put, Dynamics are nothing more that Statics multiplied by acceleration(s). A Statics study, with appropriate Factors of Safety and suitably adjusted loads & given that it will likely be over-built anyway, I believe is sufficient for this application.

 

[cruiseroutfit]

I don't disagree that they could as I've seen some that worked, but those that failed in one way or another are more common.

How many have you seen fail in this manner? I known of a dozen+ homebuilt trailers that get used off-road... I have seen zero frame failures... and most are using the simlple single beam tongue design with adequate fabrication techniques.

The author, an P.E.- M.E. with trailer design history, specifically warns against that type of layout. Mostly, as I recall, from a concern about dynamic loadings - both vertical & horizontal. Obviously if the bending strength of the structure at that point is high enough, then there's no problem.

Well, I still can't comment on the contents of the book nor the validity of the authors assertions. But I am willing to bet he was assuming trailers designed to carry heavy cargo, such as automobiles, construction debris, tractors, boats, etc.... The average off-road trailer has a maximum load capacity of ~500lbs give or take, versus 7k+ for a standard trailer. I stand by my assertions (both as a trailer owner and an Engineer) that either design would be fine for the loads a off-road trailer will encounter... simply put.

When I worked the Shear-Moment diagram for CSUC's HEV APU trailer frame (of the basic design type in question) the front edge of the box/platform was a surprising hot spot. Since that is the only time I've done that exercise for that type of application, I do not know whether it is the exception rather than the rule. Seemed more conservative to assume that it's the rule.

I am not even going to waste my time doing a SMD, if I was even remotely worried about the construction of the trailer I would model it in an FEA software and test it... but that is a waste of time IMHO.

Crudely put, Dynamics are nothing more that Statics multiplied by acceleration(s). A Statics study, with appropriate Factors of Safety and suitably adjusted loads & given that it will likely be over-built anyway, I believe is sufficient for this application.

No need to school me on the differences, I spent 5 years playing with them But I would never discount statics over the use of dynamics in such an application. The loads experience by different components can be mulitplied over and over when you consider an off-road trailer bouncing down the road or falling down a 3' ledge.

Disclaimer: Trailer frames are NOT the area of engineering I studied by any means... while I spent considerable time with chassis construction, suspension, FEA, etc... I havn't done anything with trailer loading past some dynamics problems several years back. So take my opinion with a grain of salt

 

[ntsqd]

I really haven't been keeping count. I'd guess somewhere btwn 1/2 dozen & 1 dozen that I've personally seen plus those photo documented floating around the net, plus those used as examples in the book. Note that these are trailers in general, not OR specific. Usually they some basterdized contraption made from what ever that was laying around.

The adequate fab techniques statement is the crux of the situation. It has been my observation that good fabricator can build things that work & live w/o the benefit of an Engineering degree. The TrailBlazer in my driveway is a prime example of this. The guy who built the frame under it did so with only what he learned working in the oil patch. It has 2 or 3 full penninsula runs plus a several weeks long trip into the Copper Canyon region under it's belt. The only detectable damage of any sort is the rock chipped paint, & the cracked tub perimeter aluminum frame - which he had nothing to do with.

I think FEA is a fine tool if properly defined. Too easy to GIGO for the casual user. The more involved the model & loading, the easier this is. Since I don't use it everyday I personally would be hesitant to solely use it's results as validation of my design.
A Shear-Moment Diagram is something nearly anyone can do with a little guidence, and it gives a simple graphical idea of where the frame needs more or less strength. The book does an admirable job in that guidence, or I found it to be so for me. I encouraged consulting it b/c absent the fab experience to make those judgement calls it offers the builder a tool to justify or negate what ever design decisions he/she has made. It is certainly not the only way to do things.

It has been a while since I read thru this book, but while most of the examples do tend toward your assumption, the stated intent is that a successful design can be had for any loading.

I wasn't stating the difference btwn Statics & Dynamics for your benefit as I was quite sure you more than knew the difference.

 

[Bob_Sheaves]

Sidebar Info

Just a sidebar....


FEA usually means Finite Element Analysis to the uninitiated, but to those that use it every day it also means:

F*&kedup Every Analysis :sombrero:

Seriously though, it is nice to be able to read a board with people on both sides of a discussion that know what they are talking about. For me, I'd like to interject a third opinion, that is to say, IF you are going to design a trailer (or complete vehicle) for the absolute balance of weight and load carrying capacity (such as used in military trailers) FEA, as well as Dynamic analysis are required, simply because it is a dang sight cheaper to cut, weld, and break electrons than it is any other material, IF you have the tools and understand their use and limitations. Having someone analyse you design is not too big a deal-I know several companies (including my own) that make a living out of doing just this. The cost for some is too high....until they get into an accident and a sharp lawyer finds out that a "homebuilt" is involved. The cost for a pro to analyse your design is peanuts compared to the costs of liability.

Best regards,

Bob Sheaves
CEO
catNET Incorporated
http://www.catnetsolutions.com

 

[Rezarf <><]

Man, I leave for a day and I come back to an engineer pissing contest! That was awesome!:bowdown:

Seriously though, Kurt, I highly value your imput, you use and built your trailer on a similar basis that I plan on using mine. Extended multiday trips in the Utah/Colorado area.

That said, saftey to me and others is my first and paramount concern. But the fact is this will be a light trailer, around 1200# complete and full of all fluids and gear, including the trailer.

I have a friend at Agco, that I might ask to run the FEA on, but he usually laughs at how I like to overbuild stuff and tells me, "what are you thinking, you don't need to run ______ thickness! You can get by just fine using this ______ thickness." I almost always over build my junk, but weight is an issue here. That said, he isn't familar with the flex that can occur when trying to get up the first switchback on Elephant hill with a trailer in tow... well actually he does, we have hit that trail together. Anyhow, equations and the real world don't always play fair with one another.

Kurt, what deminsions are you running on your trailer tongue? It looks beefy.

If I run with a single draw arm, I can always retro fit side supports like an A design if I start to show signs of torsional flex in the main tube. But it will only be free standing for 24" overall, it is hard to think that I could have a failure in that amout of space.

Thanks guys, I appreciate your opinions... even if I don't speak your language, I am a humble Industrial Designer...

Drew

 

[Grim Reaper]

This thread has my interest as well. I have a little enclosed trailer I picked up and yesterday was the first real road time I have seen with it. I proably had about 300-400lb of cargo (including a Deep cycle battery agains the front wall to run my fridge) with it mostly loaded in front of the axle.



The way the draw bar is attached made the trailer bounce excessively when it bucked. If you hit its correct harmonic with the bumps, weight and speed it was VERY annoying. It was right at about 55mph it was giving me motion sickness. 70 It was smooth and 45 it was tolerable.

I had planned on changed the hitch at some point but after yesterday it is more of a priority. The trailer has a VERY short hitch. Great for drafting the tow on the hwy and minimizing wind drag but it is an absolute pain in the back side to back up.

The problem is the current design. The hitch is welded to the front frame rail (2x2), then to a C Channel floor support about 12 -14 inches back and then to a piece of 2x2 angle iron that is just in front of the forward spring mount. Just too much flex in the Angle iron and C channel so it acts like a big torsion spring. Weight on the ply wood floor adding to the effect.

I think a A Frame where it directs the load back into the main side rails will be the best way to fix the problem with the least amount of weight added. Then make an extendable Tongue much like in the trailer ntsqd showed to fix the backing up maneuvering problems I am having. Replace the Angle Iron with 2x2 or 2.2.5 (to accommodated the 2x2 extension) to remove the flex and triangulate the center tongue bar that will have the extension.


possibly move the axle forward ( I may build an air ride set up like AT has) to offset some of the tounge weight when I mount a battery, propane tanks and possibly a water tank on tounge.

Any thoughts on this?

 

[Mike S]

A thought on tongue length

When I designed my trailer, I included a length adjustable tongue with a swiveling HD pintle lunette. The main beam is supported at the sides by frame extensions that hold a Delta aluminum tongue box (this carries batteries, charger, water pump, and dual tool trays). The frame and tongue are built of 1/4" wall 2" ID square steel tubing. The lunette is attached to the end of a 5 foot tube of 2" OD 1/4" wall square tubing that slides into the main beam, and is held in place by a 1/2" pin through the main beam of the frame.

This set up has a couple of advandtages - at least one of which I did not think of when designing the trailer.

1. The trailer may be towed close up to the 'Cruiser on the highway, and extended out so that on a trail in a jackknife manouver the trailer body and frame do not contact the body or bumper of the 'Cruiser.

2. The tongue may be removed for security - and locked in the trailer.

3. When the tongue is removed, the trailer is nearly 2' shorter, so stowing it in the garage or driveway takes less space.

4. By simply drilling additional pin holes the length is infinitely variable up to about 55"

5. It is easily replaced and another tongue (with a drop hitch, ball coupler. etc.) may be installed in seconds.

We thought about this quite a bit before we started building, and I think we did a good job. I would love to have the susension of a Chaser, but I built mine before that was designed and tested.

I tried to balance the loaded weight by putting two fuel cans in front of the axle, and two to the rear of the axle. The 38 gallon water tank is between the frame rails, below the bed, and to the rear of the axle. Batteries and tool tray are in the tongue box. Spare is mounted ahead of the tounge box. I estimate the loaded weight at 1200 to 1500 lbs., and the tongue weight at about 150 ls.

Mike S