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Under $50 DIY 3-axis coupler


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jscherb

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#1
If you take your trailer off-road, you may find that an ordinary ball-type coupler doesn't provide enough flexibility of movement for some terrain obstacle situations.  A "three-axis" coupler can greatly improve off-road tracking in such situations.  

Here's a Dinoot trailer in a driveway test with a 3-axis:

[Image: 3AxisTwist1.jpg]

There are a number of companies offering 3-axis couplers commercially, but the one under test above is a DIY-design that you can build for less than $50.  Here's a few photos:

[Image: 3AxisCoupled.jpg]

[Image: 3AxisFinal1.jpg]

[Image: 3AxisFinal2.jpg]

In the next few posts I'll describe how this coupler can be constructed.  Tools required will be a drill and bits, a method for cutting metal (angle grinder with cutting disc, band saw, or even a hand hacksaw), and a welder. A drill press with a hole saw is very helpful for making a notch in one of the tube parts.

Most of the materials required for this coupler can be found at Tractor Supply, in the tractor attachment linkage parts section.  This drawing lists the parts and shows generally how they are used.

[Image: TSCCoupler12.jpg]

I'll cover most of the construction steps in the following posts.

First I'll cover the main shaft, which provides the longitudinal axis of rotation.

I ground the hex points off the 1" bolt which will form the main shaft so the head of the bolt would be small enough to fit in the 2" square tube and rotate freely. I also ground the ball a bit so it will fit nicely on the end of the square tube.

[Image: MainShaftStep1.jpg]

This next photo shows the bolt inserted in the ball as it will go into the square tube:

[Image: MainShaftStep2.jpg]

A sleeve is slipped over the bolt, this will be welded in place to secure the bolt in the ball and allow the bolt to rotate inside the ball. This sleeve is full length in this photo, it will be cut in half and the other half will be used around the bolt through the ball mount.

[Image: MainShaftStep3.jpg]

And in this photo, the ball is in place in the end of the tube, it will get welded in that position. Also, before final assembly, a hole will be drilled and tapped in the ball to accept a grease fitting.

[Image: MainShaftStep4.jpg]

Next I'll make the t-fitting for the end of the shaft, this provides the vertical axis of movement.

I started by notching a sleeve with a hole saw in the drill press.

[Image: TFitting1.jpg]

The notched part will mate with this sleeve:

[Image: TFitting2.jpg]

Once welded, this will form a very strong 't':

[Image: TFitting3.jpg]

And here's how the whole thing goes together.

[Image: TFitting4.jpg]

2 axes of movement down, 1 to go.

Note that at this point in the project I'm using a t-pin, but later in the project I've switched to a more standard receiver hitch pin.  Either works fine but in the end I decided the standard pin would be more handy.

The third axis of rotation is around the base.

I started by cutting the main base out of a piece of 2 1/2" square tubing.

[Image: Base1.jpg]

[Image: Base2.jpg]

Here's how the parts will go together:

[Image: Base3.jpg]

Here's the base assembled to the ball mount:

[Image: Base4.jpg]

The sleeve goes inside the hole in the base and the shaft collar; the shaft collar will be welded to the base and that will form a roughly 5/8" high bearing surface around the sleeve.

Here are some shots of the complete assembled (but not yet welded) coupler.

[Image: CouplerAssembled1.jpg]

[Image: CouplerAssembled2.jpg]

[Image: CouplerAssembled3.jpg]

I spent about 90 minutes making all of the parts in the posts above.  Might take a little longer if you don't have a drill press or a metal-cutting band saw, but all of these parts can be made with a hacksaw and an angle grinder if necessary.

While I was building this, I got the following great suggestion from my friend JD:

Quote:Jeff, a minor tweak came to mind.  I'm assuming that the hitch pin connection will be the primary hook/unhook point.  That means that forces on the tongue will have to be carried and controlled buy the operator while trying to get the pin inserted. If you weld in just less than half of a thick, suitably-sized washer on the inside of each side of the coupler base, you would form a drop-in "shelf" to help support the tongue during hook up.

It's a great idea, so here's the implementation:

[Image: BaseCradle3.jpg]

You can't see the washers too well in this shot, but it does show the bushing that will make up the 't' being cradled by the welded-on washers... and it definitely will it a lot easier to hitch up - just drop the t into the cradle and then the hitch pin slides right in.

And JD also had this suggestion:

Quote:On an other note,  Is there a thicker-walled 5/8" ID bushing available that would allow the use of a standard 2" receiver pin for locking purposes?

In the standard collection of tractor hitch parts, there isn't a bushing meeting those specs.  However, a Category 1 to 0 Top Link bushing is 5/8" ID and 3/4" OD, so it could slip inside the bushing I'm already using.  It's a little shorter at 1 5/8" (the larger bushing is 1 15/18 long) but it can be used.  

[Image: TSleeve1.jpg]

Or, probably a proper size of thicker wall DOM tubing tubing could be found instead of using the bushing inside a bushing solution.  

But since I've already made the parts for the coupler, I've retrofited them with this new bushing inside my "t".   I cut pieces from two bushings to make up the full length of the outer bushing, and I secured them in place inside the outer bushing with a couple of plug welds.

And since I had already drilled the base to accept the 3/4" hitch pin, I also welded short pieces of the new smaller bushings into the 3/4" holes to reduce them to fit the 5/8" pin rather than make a new base with smaller holes.

I haven't done the main welding of the parts yet, but here's a shot showing the bushing in place inside the top of the t:

[Image: TSleeve2.jpg]

[Image: TSleeve3.jpg]

Here's a few shots of the coupler with the "JD mods" implemented, almost ready for final welding.  I still have to drill and tap the hole for the grease fitting, and drill the hitch pin hole in the 2" tubing, but other than that it's ready for welding.

[Image: CouplerAssembled11.jpg]

[Image: CouplerAssembled10.jpg]

[Image: CouplerAssembled12.jpg]

After welding... here are some photos of the completed 3-Axis coupler in primer.

First a close-up, in this photo you can see the two grease fittings, one is near the tongue of the trailer and lubes the longitudinal axis (twist), and the other is at the ball mount and lubes the left-right axis.  I didn't put a grease fitting on the up-down axis (the t-coupler), because that's how it's coupled/uncoupled and it would be easy to manually grease (or not) as you please.

[Image: 3AxisCloseUp.jpg]

[Image: 3AxisCoupled.jpg]

For comparison, the ball coupler:

[Image: BallCoupler.jpg]

Here are two shots showing how easy it is to couple due to the "cradle" JD suggested - in this first photo you can see the cradle inside the base which will hole the t-coupler:

[Image: 3AxisCoupling1.jpg]

All you do is set the t-coupler into the cradle, then you can easily slip the hitch pin in place without having to hold the tongue of the trailer in position.

[Image: 3AxisCoupling2.jpg]

To do a strength test on the coupler, I chained the trailer end of the 3-Axis to the jack and lifted the back tires of the Retro Wrangler off the ground.  The Retro weighs a bit more than a standard Wrangler, so this is probably about a 2000 pound lift, which is 4x the weight of the my unloaded trailer (6x the weight of a base model Dinoot with no accessories), and almost 3 times the weight of the my trailer with the tent platform and tent.  I'm confident the coupler can handle much more weight than this, but I don't have a safe way here to test with any more.

[Image: 3AxisTest1.jpg]

[Image: 3AxisTest2.jpg]

Even though my Dinoot has a receiver in the tongue and I can easily switch between the ball and the 3-axis couplers, I never use the ball type anymore.  I find the 3-axis to be extremely easy to couple/uncouple using the standard hitch pin, and it's also much quieter than the ball type.  For less than $50, it's a great improvement, both pn and off road.

Scott

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#2
Thanks for the post, $50 multi-axis coupler sounds like a pretty good deal and looks like a fun project to make.
Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping

Wagoneer

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#3
That's awesome, this is why I love forums like this, so many good ideas.

I don't think my trailer is worthy of a multi-axis coupler but when I upgrade to a more off-road worthy rig I'm definitely going to try this out!

Scott

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#4
Depending on where you go, they can be very helpful. Normally I don't need one, although I do carry a spare coupler just in case.
Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping

jscherb

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#5
The following question came up about this design on another site, and I thought it might be useful to answer it here.

Quote: I viewed the build site and like the idea but have a concern about what size trailer is used to pull with this hitch. All the torque and pull is all relying on the T welded fitting (fish mouth cut pipe welded to another pipe)??

If you use something like an ER70S6 MIG weld wire, a weld with that wire with proper penetration will have 70,000 pounds per square inch of tensile strength. The length of the weld with a fish-mouthed joint as shown in the plans will be about 3.5", more or less. Let's say you do a 1/4" wide weld bead with proper penetration, times 3.5" equals 0.875 square inches of weld. At 70,000 pounds per square inch, that's 70,000 * 0.875 = 61,250 lbs. of tensile strength. Obviously this is dependent on the skills of the welder, but I believe that provides an adequate margin of safety for a 2,000-lb. (or so) off-road trailer to be towed by a Jeep.

In addition, the bolt that forms the longitudinal axis of rotation butts up against the crosswise tube of the "T" and is welded to it before the base of the "t" gets slid up to the crosswise tube and welded, so the joint is double welded.

It's plenty strong enough.

Old Desert Rat

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#6
At first glance, it appears that the t-fitting could be replaced by a solid block of metal with two holes drilled (and one blind tapped). That would remove the concern about the weld. You might have to radius the "rear" surface of the block for clearance, but I'm too tired right now to figure that out.
It ain't the miles, it's all those lumps, bumps, and contusions on the highway of life Undecided

jscherb

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#7
I'm planning to build a second one of these couplers, so I created a detailed shopping list for my trip to Tractor Supply:

[Image: TSCCouplerPartsList.jpg]

Also, here's a slightly updated design drawing:

[Image: TSCCoupler12-3_zpsc5b3b759.jpg]

Scott

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#8
Thanks for adding the shopping list.
Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping

rickid57

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#9
(01-30-2013, 02:21 PM) jscherb Wrote: I'm planning to build a second one of these couplers, so I created a detailed shopping list for my trip to Tractor Supply:

[Image: TSCCouplerPartsList.jpg]

Also, here's a slightly updated design drawing:

[Image: TSCCoupler12-2.jpg]


Ive made 2 of these and they are perfect. the hardest part of the whole deal was getting the 1" bolts after searching every hardware supplier no one wanted to sell singles. I found this place in Texas and they will send single bolt orders FMW Fasteners. I think I could build a complete welded assembly in under an 1 1/2 hour. I had a blast making them and now everyones asking me to build them one. I tell them to check out your story and look at all the great ideas you have done. Thank you for sharring such a cost savings fun project

jscherb

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#10
(02-03-2013, 10:00 AM) rickid57 Wrote: Ive made 2 of these and they are perfect. the hardest part of the whole deal was getting the 1" bolts after searching every hardware supplier no one wanted to sell singles. I found this place in Texas and they will send single bolt orders FMW Fasteners. I think I could build a complete welded assembly in under an 1 1/2 hour. I had a blast making them and now everyones asking me to build them one. I tell them to check out your story and look at all the great ideas you have done. Thank you for sharring such a cost savings fun project

Thanks!

Let's see some photos of the ones you've built!

No Tractor Supply stores near you? They sell the 1" bolts individually, at least here in NY state.
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