Gen in the bus, hitch installed - but I've got a stupid Question

kyle4501 · April 13, 2010, 10:23:24 AM

Sorry, I don't like the look of that hitch. Like Brian said, it is extending the load too far away from the support.
The deflection increases exponentially with the cube of the distance from the support, but the stress increases linearly.

One of my concerns is that the ball will not stay tight. The flange isn't supported front to rear & that is the direction of pushing & pulling. This will result in it working loose. I've had properly supported balls work loose. Is there a support sleeve welded inside the tube? If not, the tube walls will bend under load & the ball will become loose.
I'm not a fan of welding trailer balls on either.

Then there is the vertical loading. In ANY ball coupled hitch, there will be 2 kinds of vertical loading, one is from expected loading & is easy to plan for, the other is a result of the unexpected which is much more difficult to plan for.

Many assume there is minimal to no vertical loading if you are towing a car 4 down, however this assumption can be very wrong. If the rear raises during a hard stop, the tow bar is no longer horizontal. If the toad is pushing, this angle will get worse as the toad's front end drops. This angle will create a vertical load on the hitch.

For example - assume a tow bar is 3 feet long (ball to toad's bumper pivot) & the coach rises 6" & the car dives 6" (a height difference of 12").
If the toad is pushing 2500# in the horizontal plane, the resultant is ~884# in the vertical plane.

If the height difference is 16", the same 2500# push will result in a 1240# vertical lift on the hitch.
(These are only example numbers to show how a little angle can go a long way to increase the actual tongue load. The force of the push can exceed the actual weight of the toad due to momentum.)

I never thought too much about this until I was riding beside Dad's coach & saw how much the tow bar moved when he hit the brakes hard - AND, he has a functioning brake buddy in the toad applying the brakes.

Another way to look at it, in theory, with a long enough lever, you can lift that end of the bus by yourself (of course this assumes favorable levers & fulcrums

).

tnichol · April 13, 2010, 10:38:23 AM

Quote from: kyle4501 on April 13, 2010, 10:23:24 AM
Sorry, I don't like the look of that hitch. Like Brian said, it is extending the load too far away from the support.
The deflection increases exponentially with the cube of the distance from the support, but the stress increases linearly.

Thanks sincerely to all of you who responded. I value your suggestions - and the time and thoughtfullness of your answers.

The trailer I was planning to use is really light - I just reach down and pick it up and attach it to the hitch on my truck, never use the jack - even when I've got the bike on it. I guess because its so light that I didn't give the design of the hitch the consideration it deserved.

I'm going to go back to the drawing board on this after I get a few of the more pressing issues resolved - and before I try to pull anything with it.

Thanks again.

Tim

kyle4501 · April 13, 2010, 10:52:49 AM

Tim,
It takes a hell of a man to accept the criticisms of their work & not take offense at any of it.
You are setting a fine example for others.

I wish you well with your new design.
Having a trailer come loose is a sure way to ruin someones day.

desi arnaz · April 13, 2010, 10:54:59 AM

in all fairness i will say you did a wonderful job on the generator! what will you be using for insulation? also you might want to put her on a joey bed for better access. it looks like a real tight fit as it is...

gumpy · April 13, 2010, 10:56:07 AM

Quote from: tnichol on April 13, 2010, 10:38:23 AM

I'm going to go back to the drawing board on this after I get a few of the more pressing issues resolved - and before I try to pull anything with it.

That's a very sound decision.

Do a search on this board. There are plenty of hitch threads with good photos and info.

Here'a a link the hitch I put on my MC9. It's been on there almost 10 years, and not problems.
http://www.gumpydog.com/Bus/MC9_WIP/Towing_Hitch/towing_hitch.htm

I'm going to try to update the thread with some photos of a similar hitch I put on a friend's MC9, also.

craig

grantgoold · April 13, 2010, 12:18:12 PM

I will try and post some pictures of my hitch set up (similar to many others). Took a 10,000 lb rated hitch and "fabricated or customized it to work with the structures already on the 9.

I am impressed that you quickly realize the people on this board on only really interested in your safety and those around you and not attacking your credibility.

This is the kind of person that will much appreciated here!

Grant

Tom Y · April 13, 2010, 06:50:20 PM

I sent a pic of my hitch on my 5C. Tried to post here but file to large. Not sure about that, I take all my pics on the same setting, and some will post. Hope the pic helps. Tom Y

grantgoold · April 13, 2010, 07:07:04 PM

As promised here are some pictures of my hitch. As you can see, I used the examples provided by gumpy!

Hope it works out!

grantgoold · April 13, 2010, 07:08:53 PM

Another picture!

grantgoold · April 13, 2010, 07:09:33 PM

One more!

philiptompkjns · April 13, 2010, 08:00:06 PM

Quote from: kyle4501 on April 13, 2010, 10:52:49 AM
Tim,
It takes a hell of a man to accept the criticisms of their work & not take offense at any of it.
You are setting a fine example for others.
I wish you well with your new design.
Having a trailer come loose is a sure way to ruin someones day.

well put Kyle... I know I would have had the "let me try it" attitude.