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Building a strong flexible bicycle trailer coupler.by weblar on June 20, 2009

Table of Contents

Building a strong flexible bicycle trailer coupler. .......................................................................................

Intro: Building a strong flexible bicycle trailer coupler. ................................................................................

Step 1: Determining or building an attachment point on your bicycle frame. ...............................................................

Step 2: Building swivel attachment. .............................................................................................

Step 3: Attach trailer swivel to bicycle trailer. ......................................................................................

Step 4: Attach trailer to coupler. ................................................................................................

Related Instructables ........................................................................................................

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Comments ................................................................................................................

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Author:weblar

Intelligent tinkerer who would rather design and build exactly what I want rather than purchase something designed for the masses.

Intro: 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 dowside 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 thensuggested 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 th

investment in a second swivel caster mounted on a f ixed frame at a 90 degree angle to the first swivel caster, you could very easily attain flexibility in all 3 planes ofmotion: (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 sito 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 thebicycle, 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 othis 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" fromside 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 availafrom 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 galvaniconstruction 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 asthe 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 wheeas 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 wa 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 pininserted through the caster on the right side of the accompanying photo). This is also a hardware store item and should cost less than $4.

Image Notes1. By straddling the connected trailer with the caster wheel frame, and using thecaster wheel cut to fill the remaining gap of the caster frame, you can make a

hitch point that doesn't pivot.2. By attaching the caster wheel to the bike (red) so that the caster frame canstill rotate around the wheel, the caster can turn around the wheel and swing upand down on the caster swivel. The caster swivel on the trailer tongue(black)allows the trailer to swivel on its vertical plane.

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Image Notes1. After cutting the caster wheel, I drilled and bolted it to a fixed piece of 3/4" X3/4" steel that was in turn clamped to the bike frame and extends slightly past thback wheel, allowing the trailer to turn a full 180 degrees behind the bike. Thecaster frame is attached to the cut caster wheel with a removable hitch pin(replacing the caster wheel bolt) to facilitate easy removal of the bike trailer.

Image Notes1. This picture shows the inside of the Simpson right angle connector and thenylon-insert lock nuts on the ends of the bolts holding the 2 casters to theoutside faces of the right angle connector.

Image Notes1. This caster, attached immediately to the bike trailer, can still rotate (and thusallow the bicycle trailer to "twist", but by using the caster frame to straddle thetrailer tongue and the cut caster wheel to fill the remaining gap between the axlebolt and the trailer tongue, the caster "axle" will no longer allow turning.2. This caster wheel was drilled and bolted to the bicycle frame extension andthe caster frame attached over the wheel, and allows the caster to turnhorizontally, and the caster swivel still allows the trailer to "bend" up and down.

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Image Notes1. Caster wheels can be cut and dril led to use either as fixed "blocks" to attachthe caster swivel (shown) or as pivot points that allow the trailer coupler to turn.

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 bikhave 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 abl

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 3/43/4" 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 alongthe 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 thebicycle 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 withDremel 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 thenattached 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.

Image Notes

1. After cutting the caster wheel, I drilled and bolted it to a fixed piece of 3/4" X 3/4" steel that was in turn clamped to the bike frame and extends slightly past theback wheel, allowing the trailer to turn a full 180 degrees behind the bike. The caster frame is attached to the cut caster wheel with a removable hitch pin (replacingthe caster wheel bolt) to facilitate easy removal of the bike trailer.

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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 r ightangle 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

Image Notes1. This picture shows the inside of the Simpson right angle connector and thenylon-insert lock nuts on the ends of the bolts holding the 2 casters to theoutside faces of the right angle connector.

Image Notes1. This caster, attached immediately to the bike trailer, can still rotate (and thusallow the bicycle trailer to "twist", but by using the caster frame to straddle thetrailer tongue and the cut caster wheel to fill the remaining gap between the axlebolt and the trailer tongue, the caster "axle" will no longer allow turning.2. This caster wheel was drilled and bolted to the bicycle frame extension and thcaster frame attached over the wheel, and allows the caster to turn horizontally,and the caster swivel still allows the trailer to "bend" up and down.

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 trailerconstructed 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 therotational 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 thtrailer 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 thcaster 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 Ifilled 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 salso 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 twheel in the diameter of the bolt, but then use a larger drill bit to countersink the bolt head into the wheel).

Image Notes1. Caster wheels can be cut and dril led to use either as fixed "blocks" to attach the caster swivel (shown) or as pivot points that allow the trailer coupler to turn.

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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 mbicycle 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 thframe, 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 wiLiquid 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 boltthrough 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 nI 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 i ts enusing 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 thisboard. 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 attachedimmediately underneath the lid.

Image Notes1. The 5 gallon bucket is NOT part of the trailer, but is here for photographicpurposes ONLY.

2. The trailer coupler remains attached to the trailer when it is detached from thebicycle.3. Two eye screws provide attachment points for bungee cords that can be usedto attach additional items to the top of the plastic tub.

Image Notes1. Two short pieces of 1" X 3" dimension lumber (one at each end of the plastictub) provide attachment points to attach the plastic tub to the trailer frame. The

plastic tub is attached by 1/4" carriage bolts through these short pieces of boardto conduit clamps that attach the plastic tub to the trailer frame.2. This piece of 1" X 3" dimension lumber reinforces the lid of the plastic tub,allowing me to use the top of the plastic tub for addtional storage.

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Image Notes1. Detail of attachment point for 1" X 3" board that reinforces the lid of the plastictub, showing short wood screw that initially attached this board and the two eyescrews that will provide anchor points for bungee cords that can be used toattach items to the top of the plastic tub.

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Comments

29 comments Add Comment

plasticorange says: Mar 13, 2012. 3:53 PM REP

do you have a photo of the attachment to the bike? you mentioned you have 3 separate axes ---- I assume the 3rd axis is at the attachment to the bicycle?

Thanks!

billy508 says: Aug 24, 2011. 7:20 PM REP

Good job. Your idea offers a effective solution to a difficult problem. Simple,Cheap, and effective. I like it Thanks.

MuggsinSD says: May 24, 2011. 2:57 PM REP

Weblar, I'd love pictures of how you attached this to your bicycle. I looked at your other posts and didn't see one and am not happy with most of the otherones I've seen. I love this design, and can only imagine how cool your attachment point is!! !

Salvage Steve says: Apr 15, 2011. 11:11 AM REP

VERY SLICK!

spark master says: Apr 3, 2011. 7:05 AM REP

elegant,

off the shelf parts

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KWHCoaster says: Feb 18, 2011. 9:03 AM REP

Great idea to use what appears to be a folding golf cart for the trailer chassis & wheels. I haven't golfed in 15+ years and I have a folding golf cart in mystorage locker that now can be re-purposed!

weblar says: Feb 18, 2011. 11:03 AM REP

Good deal. Folding golf carts are relatively sturdy and are well-suited to make undercarriages for bicycle trailers.

BillBiker says: Jan 22, 2011. 9:39 AM REP

This is the 2nd I have came across by you weblar! Indeed yet another awesome 'able. I'm currently working on a project having to do with a bike trailer. Imay use part of this in my project. Thanks

weblar says: Jan 23, 2011. 6:54 PM REP

I hope that you can make use of anything I post here on Instructables. This is a great website and I start many of my projects here, looking to see whatothers have invented rather than simply buying something off the shelf.

BillBiker says: Jan 24, 2011. 5:22 AM REP

Yes definitely and my other half likes the idea I do not have to go buy "new stuff" lol. This site is invaluable!!!

yel3an_ha says: Dec 4, 2010. 7:28 AM REP

U Could've Done It With 1 Wheel Only!!

felmont says: Mar 7, 2010. 3:51 PM REP

I love the design!!!Question - before I embark on building this hitch, I'm a bit sceptical about the amount of load that will be put on the the "swivel" part!Since the whole trailer will be pulled on the pivot, it will be pulling "through" one of the swivels (the swivel on the second caster, which provides the rotationmovement)...Is the ball bearing mechanism and plates holding it together really strong enough to hold out over long distances and time? Seems like it might just bend agive out!! Which inclines me to use the D-bolt and eye-bolt hitch instead.See my progress so far for pics of both of my hitch ideas (second one is inspired from this page!)www.flickr.com/photos/48007949@N03/sets/72157623536962194/ 

weblar says: Aug 30, 2010. 2:02 PM REP

I do understand your concern; and perhaps my experience is reflective of the quality of the casters I bought; but I have had no separation problems at abetween the ball bearing mechanism plates. I guess if you stop and think about it for a second (and I must admit, I haven't done this until now), the casis designed for use, not just to hold its "load" off the floor and swivel when pushed, but also to withstand a fair degree of lateral force when the load ispushed around the floor. Therefore, the ball bearing mechanism/plates assembly would have to be reasonably strong to withstand those same lateralforces. In any event, I have not had any problems in actual use with separation or failure of the caster ball bearing mechanism.

weblar says: Mar 9, 2010. 8:22 PM REP

With some regularity, I pull loads with this trailer, probably up to 75-80 pounds at a time, on the chat-covered Katy Trail State Park here in centralMissouri (US). In spite of the moderately rough surface and the amount of use, I have had no problems whatsoever with this coupler or the platesholding it together. Ido occasionally lubricate (with spray lube) the ball bearings and pivot joints in the two casters to ensure free motion.

I can grasp either side of the right angle building connector and cannot bend or open the angle any further - and I am a relatively strong individual. I hano real concerns with the strength or durability of this trailer coupler; and in light of the length of my recumbentbicycle and the narrow trail where Ioftenride,do really appreciate the wide range of motion that this coupler design allows.

bo88y says: Aug 29, 2010. 4:13 PM REP

These casters are designed for eccentric loading-- when used in the usual way, the caster axle is offset from the swivel axis, and these casters loolike they're rated in the 200 lb. range. And while towing subjects the bearings to more jerks and shocks, I doubt you're getting anywhere close to therated load on the bearings. The weak link, I think, is the attachment of the caster to the red square tubing, but even that seems strong enough.

bikerusl says: Jun 25, 2010. 12:13 AM REPAt this point you might as well go for something purpose built that will be cheaper and less work:http://www.midwestcontrol.com/catdisplay_short.php?pg=119 Use 12mm or 0.5" for heavy duty trailers (>300lbs) and you could use smaller like M10 for amore average 200lb trailer. The only problem with midwest is you have to buy bulk.

Center for Appropriate Transport Eugene has these kind of hitches http://hpm.catoregon.org Also if you are in Vancouver, BC I just boult 15 of them and Idon't need that many so I could sell a few to anyone interested at cost - or I am going to make a kit like HPM CAT has which has some pre-made parts (lesDIY) bicyclefamily.ca

weblar says: Jun 27, 2010. 2:27 PM REP

Of course the problem is that you have to buy bulk........ The purpose of this website is to assist people to build what it is they need for themselveswithout relying on the market to "purpose build" what commercial interests decide they can sell to you for a profit. My purpose in offering my ideas andpublishing these plans is to allow others who don't want to buy this item in bulk to build a perfectly acceptable alternative at a greatly reduced price. I paless than US $25 for the parts constituting this coupler and got a much more satisfactory result than the products for which my local bicycle shop chargtwice as much.

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joshfromga says: May 1, 2010. 9:49 PM REP

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 rotationfor 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-below. anyways its just an ideayou can play with and see if it meets your needs.

weblar says: May 13, 2010. 6:31 PM REP

That's an interesting twist (no pun intended) on using casters for a bike t railer coupler. I'm not sure that you're addingan 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 yourbicycle where you intend to attach the trailer coupler, the design you propose couldallow some different attachment options.

joshfromga says: May 22, 2010. 5:48 AM REP

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.

godspiral says: Oct 2, 2009. 6:28 PM REP

a big improvement would seem to be able to get rid of the wheel and dril the caster axel directly through the red bar. Stress is amplified the further the pivopoint from the caster bearing, and its not obvious the caster will stay bolted.

weblar says: Oct 2, 2009. 6:52 PM REP

Though I (think I) understand your concerns, I've given the trailer coupler design plenty of use under load since I built i t and it seems to be holding upquite well, with no bolt failures (can't really see how its going to come unbolted with 2-1/4" bolts with lock nuts holding them in place). Moving the caste

axle slightly away from the red attachment bar allows a greater range of motion, though I agree that you shouldn't move that pivot point any further awafrom the attachment bar than is necessary to allow that full range of movement.

Tinworm says: Sep 30, 2009. 1:48 PM REP

very clever indeed! :)

depotdevoid says: Jun 23, 2009. 11:50 AM REP

Nice idea! I like the final product, and wish I still had my bike trailer to try it on!

weblar says: Jun 23, 2009. 1:45 PM REP

It seems to work very well for me, and it sure was simple to put together from readily available parts.

lieuwe says: Jun 23, 2009. 5:46 AM REP

heh, the commercial bike trailer i have just uses a spring-thingy with a rope as backup for when the spring fails...

weblar says: Jun 23, 2009. 8:42 AM REP

Yeah, I saw semi-flexible plastic sorts of couplers that the bike trailer makers offer - like that plastic won't eventually fatigue and crack over time. Swivecasters have ball bearings in the swivel joint and sleeve bearings through the wheels - they are better engineered than the junk that the bike trailermakers offer to connect their overpriced trailers to your very expensive bike. Its very easy (and in fact, less expensive) to make a trailer coupler yoursethat will get the job done better than what they'll sell you for much more.

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rimar2000 says: Jun 22, 2009. 5:53 AM REP

Very good idea.

weblar says: Jun 22, 2009. 9:05 AM REP

Thanks. This is why I like this website - you can read other peoples' good ideas and then build upon them.