Building a Strong Flexible Bicycle Trailer Coupler.

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Introduction: Building a Strong Flexible Bicycle Trailer Coupler.

This Instructable will demonstrate how to build a coupler that can be used with a variety of bicycle trailers that will turn and rotate in all possible directions: up and down, side to side, and rotate to allow the trailer to "tip" from side to side during travel.

I had seen a previous Instructable that relied on a single swivel caster to allow the bike trailer to turn from side to side and move up and down vertically, but then suggested a "pipe and sleeve" sort of coupler to allow trailer rotation (tilt). Although that proposed Instructable would work as suggested, it seemed to me that, with the investment in a second swivel caster mounted on a fixed frame at a 90 degree angle to the first swivel caster, you could very easily attain flexibility in all 3 planes of motion: (1) allowing horizontal turning side to side; (2) allowing the trailer tongue to move vertically up and down; and (3) allowing the trailer to "rotate" - to "tip" from side to side.

The proposed plan allows this movement in the following ways: (1) one caster wheel is trimmed flush on one side to allow it to be bolted horizontally to a point on the bicycle, and then the caster wheel frame is again reattached to the wheel, allowing the caster to turn horizontally on the bicycle mounting point; (2) the caster swivel on this first caster also allows the trailer tongue to move up and down vertically; and (3) the caster swivel on the second caster allows the trailer tongue to "rotate/tip" from side to side during travel independent of the vertical angle of the bicycle.

The parts you will need for this plan are simple:

(1) Two swivel casters of sufficient size - I used 2" swivel casters that are available at local hardware or home improvement stores for about $4 apiece.

(2) A frame to attach these casters at right angles to each other. I purchased a heavy duty right angle galvanized construction connector (i.e., Simpson), readily available from local lumber yards or construction supply stores, also for less than $4.

(3) Sufficient short bolts and locking nuts to attach the caster to this frame. I used eight 1/2" long 1/4" bolts and nylon-insert lock nuts to bolt the casters to the galvanized construction connector.

(4) Appropriate hardware to attach the coupler both to your bicycle and to the trailer frame. I fabricated an extended mount on my bicycle (see step 2) that is shown as the red square tubing in the picture illustrating this step. The trailer tongue is the black section of square tubing also shown in the same picture. I used the caster wheels as described in the following steps to attach the trailer coupler to both the mounting point on the bicycle and to the bicycle trailer.

(5) Though purely optional, I wanted to be able to quickly attach and detach the bicycle trailer from the bike; and therefore replaced one of the two caster wheel bolts with a similar diameter and length locking hitch pin that slips through the caster wheel bolt holes and the caster wheel bushing (see ring on top of this locking hitch pin inserted through the caster on the right side of the accompanying photo). This is also a hardware store item and should cost less than $4.

Step 1: Determining or Building an Attachment Point on Your Bicycle Frame.

Although many bike trailers attach to the left rear hub of the bicycle, this attachment point prohibits the trailer from turning a full 180 degrees around the rear of the bike. I have a long wheelbase recumbent bicycle that already is difficult to turn in a tight radius - I did not want a trailer coupler that was not fully flexible and would not be able to allow my bicycle trailer to turn freely behind the bicycle.

In order to move the pivot point between the bicycle and the trailer to a point where it would allow the trailer to turn from side to side as far as possible, I attached a 3/4" X 3/4" length of square channel steel tubing that fastens behind the main chainwheel of the bicycle, and is firmly clamped with several coaster brake frame clamps along the left chainstay to the left rear dropout (hub), and then extends past the rear dropout past the rear tire of the bike. I painted this piece of tubing the same color as the bicycle and it remains on the bike at all times.

At the very end of this piece of added tubing, before it was installed, I drilled and attached one of the two caster wheels. This caster wheel was cut flat on one side with a Dremel tool cutting wheel to facilitate its attachment to the tubing, and was drilled though vertically to allow it to be bolted to the tubing. The caster wheel frame is then attached over the caster wheel and turns around the caster wheel (much in the manner it was originally designed) and allows the trailer to turn left and right freely.

Step 2: Building Swivel Attachment.

The swivel attachment itself is very simple. It consists of two 2" swivel casters that are bolted with half inch long 1/4" bolts and lock nuts to the outside faces of a right angle Simpson construction connector. You will have to drill holes in the appropriate spots in the right angle connector to match the holes in the corners of the casters.

Step 3: Attach Trailer Swivel to Bicycle Trailer.

Now you need to attach the coupler to your trailer. Here you are going to have to be "inventive" and consider the design and geometry of your trailer tongue. My trailer, constructed from the frame of a push-pull golf cart, consisted of 3/4" X 3/4" square tubing (similar to the attachment point I fabricated for my bicycle). I needed the rotational ability of the second coupler in order that the trailer could turn on its "third plane" - to be able to rotate (tip) from side to side - but decided that I didn't want the trailer to be able to turn left to right from a second joint in the coupler.

So when I attached this second caster to the handle of my bike trailer, I used the wheel frame of the caster wheel to straddle the tongue of my bicycle trailer, cutting the caster wheel with a Dremel tool cutoff wheel to fill the gap between the width of the trailer tongue and the bolt hole in the caster frame for the caster wheel. Although I filled this gap tightly with the cut caster wheel and it was probably sufficiently "friction fit", I did not want to take a chance with the wheel slipping off the trailer tongue so I also drilled this second caster wheel and bolted it to the trailer tongue (you can see the bolt hole in some of the pictures of the caster wheels - I drilled a hole through the wheel in the diameter of the bolt, but then use a larger drill bit to countersink the bolt head into the wheel).

Step 4: Attach Trailer to Coupler.

Of course, the appearance of the trailer as attached to your bicycle will vary, depending on the design of your bicycle trailer. The first two pictures depict the frame of my bicycle trailer attached to the attachment point of my recumbent bicycle, using the simple and very strong bicycle trailer coupler explained in this Instructable.

To that frame, I added a large plastic tub with a locking latch lid to shelter what I am carrying in my bike trailer from the elements. In order to attach the plastic tub to the frame, I used two short sections of 1" X 3" dimension lumber that fit into the bottom of the plastic tub perpendicular to the trailer frame, attached the boards in place with Liquid Nails glue and through the bottom of the plastic tub with short wood screws, and then attached the plastic tub to the frame using 3/4" conduit clamps that bolt through through those short pieces of wood, the bottom of the plastic tub and the "ears" of the conduit clamps using 1/4" X 1 1/4" carriage bolts and nylon-insert lock nuts. I used two short pieces of board in the bottom of the plastic tub and two conduit clamps to create two attachment points for the plastic tub.

I also reinforced the lid of the plastic tub using a piece of 1" x 3" dimension lumber that spans the top of the plastic tub under its lid. I glued this board in place at its ends using the Liquid Nails and a short wood screw at each end, but also used 4 small eye screws that go through the side walls of the plastic tub and into the ends of this board. These eye screws will provide anchor points for bungee cords if I were to strap items to the lid of the trailer that is reinforced by the extra 1" X 3" board attached immediately underneath the lid.

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I'm thinking this can be done with a singular coaster wheel. I'll be updating with an image shortly

The blue shaft being the lead to the trailer. A U bolt goes around the groved rubber wheel of the coaster and the legs of the U bolt up and through the trailer lead. The coaster is then U bolted onto the bike sit stem. This is a simpler 2 pivot U joint junction, backed up with industrial duties of a simple coaster. Hope this helps. I bought a used Adams bike trailer recently that is missing a stem junction, your posting spiked my interest and my picture below will be a good method of accomplishing what I need at this point.
Thanks for the help

imageedit_18_8880993351.jpg

That version is only appropriate for single-wheeled trailers, because they can lean with the bike. A trailer that can't lean with the bike needs a freely rotating roll axis in the hitch (unless you plan to ride only in a perfectly straight line).

this is a great idea, I am at present building a trailer to take my terrier around places where you can't get in a car, I have started a blog called a handy hoarders blog, my first project was a Bicycle sidecar, the coupling I did worked great, allowing the bike to roll without the wheel leaving the ground. I almost had it finished but realised that I would be to far out in the road and the green rights of way aren't wide enough so I turned to making a trailer. I am using a similar idea to this , with castor wheels but not with the wheels in. The square hollow bar I am using fits perfectly where the wheel belonged. To strengthen it and avoid the screws pinching it when I tighten them I have put wood down each end. I have not yet fitted it, when I do I will do a dummy run with just the metal chasses which is an old climbing frame. Do you think I will be better off doing it the way you have for strength?

hmm... i like your design. it looks effective, but i saw something on the road a few months ago that was a bit simpler and gave an additional axis of rotation for the trailor. it was an older fellow who took 2 large casters, took the wheels off, and ran a single axle through both of them. it looked like the quick mock-up below. anyways its just an ideayou can play with and see if it meets your needs.

casters.JPG

That's an interesting twist (no pun intended) on using casters for a bike trailer coupler.  I'm not sure that you're adding an additional axis of rotation, because my design also turns/swivels/rotates on 3 separate axes.  However, depending on the design of your trailer tongue and/or the point on your bicycle where you intend to attach the trailer coupler, the design you propose could allow some different attachment options.

yeah, the older fellow who built it had it attached to the cargo rack over his rear wheel.  he offered to sell the whole setup (minus the bike of course) for 80 dollars. didn't have the cash at the time though. 

This is a clever way to build a 3-axis gimbal-ish thing out of existing parts. It's also the weirdest trailer hitch I've seen so far (though I haven't looked at many yet). Anyway, I don't see how it achieves the stated goal of 180° range of motion in yaw. It looks like the red tube would hit either the black tube or the caster mounting plate before that.

Rode my old Varsity to the thrift store last year and found that same golf bag cart being sold for $1.00; bungee corded it to the rear rack and brought it home. While the bungee wasn't ever going to be my permanent arrangement (love yours!), it worked in a pinch, only getting messed-up one time and that was when a couple of cars crowded me while trying to figure out "what the...???"
Your use of casters, ?