a (modified) Generic ET build

[cpucampin]

I have really taken to Mike's Generic ET design. I like the idea of a standie for changing, lavatory, shower, dinette, king-size bed, and an outside galley. At 12'L x 6'6"W x 7'H (approx) and probably under 2,000 pounds loaded for camp, it seems perfect. Here is my current conceptual "sketch-up".



My first area of concern as I get closer to build day is the frame. I have studied the "Aussie Rules," consulted Andrew's formula and poured through the forums. Here is what I have come up with for a custom built frame for this trailer.

Frame, Tongue and A-Frame members: 2x3 .125 box steel
Crossmembers: 2x2 .25 angle (??? not sure of thickness or if I need any internal crossmemebrs at all if I do a full torsion axle)
Spacer for drop floor: 2X2 tube steel (??? not sure of thickness)

Axle is about 4' 6" from back of the 12' frame.
Tongue length is 5'. This would allow 3' of clearance even with tongue box. (??? I think this is correct application of the rules)
Tongue is welded at 1st and 2nd crossmember
Planning on Dexter or Flex-ride full torsion axle
Tire size is undecided (look and ride height will determine)



I am planning a drop floor in the front that will run the full width of the trailer. I am not sure how to best accomplish the 2" spacer I am looking for to drop the tongue under the floor. I figure I should use 2x2 but I am not sure what thickness and if I shoudl run a full length piece like I show in the front, or just short pieces where the welds are needed like I show in the back. I want strength but don't want to tow any extra steel.



Does anyone see any issues with this plan for a frame? Am I over/under building anything? Are there any obvious things I am forgetting to consider? Am I planning any blunders?

What road clearance do I want to maintain at the front of the trailer under the drop floor? I am currently at 7". Is that too low? Can anyone direct me to some links on approx ride heights using Dexter or Flex-ride axles and different size tires?

Looking for any and all input.

-Ken

[Cliffmeister2000]

Does anyone see any issues with this plan for a frame? Am I over/under building anything? Are there any obvious things I am forgetting to consider? Am I planning any blunders?

-Ken

Hello, Ken,

I'm no mechanical engineer, but it seems to me that there is potential for a tremendous amount of stress to be placed on the joints where the two main sections for the frame come together. Of course, the tear itself will become a huge torsion box and help distribute the load. If it were me, I'd probably extend the siderails up to the angled tongue supports to spread the flex pressure.



The design itself looks very interesting! I look forward to watching the build.

[mikeschn]

I recognize certain features of that frame. I'd sure like to get Andrew's opinion on the frame.

The rest of it looks very familar. I think you'll like the arrangement.

Mike...

[angib]

I think that frame design should work, but I'm a bit worried about how much load is concentrated in the ends of that second cross-member. I'd be very tempted to continue the wide side rails back a bit to fit in a second connection, as shown below:





I think the central tongue member is a bit pointless as the side ones will be doing all the work. However you need a central one to put the hitch on and if it runs back to the first cross member, it might as well go back to the second cross member.



For the spacer tubes, I think 2x2x0.125 would be fine, but with the ends sniped at 45 deg. Fitting each spacer so that it lines up with the tube above would be a good method. Note that the side spacers are rather long (14" at the top, 10" at the bottom) because of the shallow angle the side tongue members are at.

(Sorry to draw solid 'tubes' - too much trouble to hollow out the insides!)

I think you need to draw out the whole side view, with tow vehicle hitch as I suspect the low ground clearance all the way from the hitch back to the second cross member will never get out of road dips at the curb (kerb? - I forget which is UK and which is US!).

And a 54" axle spacing on a 144" frame is a long way back for a getting-larger-than-tiny trailer - that's going to give a high hitch weight - do you have a really big truck to tow it with?

Andrew

[mikeschn]

Now that's some good feedback. Thanks Andrew!

Mike...

[cpucampin]

I'm gonna do this in two posts so Mike first...

Mike,

Thank you for making this wonderful sight. It is a great little spot on the web with a great feel. That is a tribute to you, your admins, and this community. Bravo.

Thanks for the input and advice; and yes, my trailer should look very familar. I studied your album, design and build threads for hours and hours, working out the specs. I am in love with the design. I like the idea of a shower in the tear and when I heard you were abandoning one in yours I began to wonder if it was because of the limit on the drop floor due to the frame width. I decided to play with a custom frame that carried the drop floor the entire width of the tear. Your idea for the spacer and the tongue supporting the drop floor is great.

I have about a million questions for you on your design so far, but let me hit my top 5. Do you have any idea of what you weight is going to be? I am estimating mine at about 1400 empty, but I am having trouble finding good weight estimators for different building components. What is your clearance under the drop floor? What size tires did you end up with? What is the length breakdrown for your Generic (galley, bed, front)? Mine right now is at 2' galley (20" counter depth), 6'8" bed, 3'4" front for a total frame length of 12'. How did you attach the roof spars to the A/C shroud/hood?

Once again, thanks for your input and the updates on your build. This design finally got me to bite the bullet.

-Ken

[cpucampin]

Andrew,

Thank you for your advice. I had not even thought about the load on the second cross member, I was so concerned about the load on the tongue welds. Thank you to you and cliff. I will modify my design to work in your ideas.

As far as the tongue length is concerned, I would like to make it no longer than 36" (my tow vehicle is a tacoma 6' wide). The reason it got so long was I am using the tongue under the drop floor to provide support for the floor. As a result I brought the memers all the way to the outside of the frame, but the angle got pretty wide with a short tongue. I thought I was supposed to keep that angle at between 40 and 50 degrees on an a-frame. The middle member is to support the floor, a tongue box and the hitch. Is there a better setup for a tongue under a drop floor like this? Can I make the middle member any lighter and still accomplish this? I will work up the frame with a 36" tongue and post a pic showing the angles. I must admit that figuring the tongue out has been the most challenging part of this frame design.

As for tongue height, that was one of my main concerns, but I have only lowered the tongue by 2" (the height of the spacer). That shouldn't cause a problem for the hitch should it?

Thanks for the advice. Modified design coming...

-Ken

[angib]

I thought I was supposed to keep that angle at between 40 and 50 degrees on an a-frame.

If you want to use a standard A-frame coupler, then the A-frame angle must be exactly 50 degrees. If you are using a straight tongue coupler, then you can make the angled tongue members any angle you want.

Using the centre tongue member as a way of supporting the dropped floor is pretty wasteful and adds unnecessary weight, so you could simplify to a regular 50 deg A-frame like this:





I've shown a 42" tongue length as the ET body sticks forward of the frame so this only gives about 36" of 'exposed' tongue.

Two 3"x2"x1/8" tongue members would give you a weight limit of about 2600lb on the Aussie rules. From looking at other trailers it would seem that you can safely exceed those rules by a factor of two - the rules are designed for (abused) utility trailers - so that's plenty of strength without the third tongue member.

Supporting the drop floor can be done just with some wood - it's only 28" 'wide' (ie, front to back) so even 3/4" ply on its own would be enough.

Andrew