Instructables

Building a strong flexible bicycle trailer coupler.

Bike Trailer from left.jpg
Bike Trailer from right.jpg
Coupler detail bike end swivel.jpg
Coupler detail inner.jpg
Coupler detail outer.jpg
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.
 
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andrea biffi2 months ago

could you remove the wheel and use the original pivot to joint the square tube?

3366carlos1 year ago
nice.
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!
billy5082 years ago
Good job. Your idea offers a effective solution to a difficult problem. Simple,Cheap, and effective. I like it Thanks.
MuggsinSD3 years ago
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 other ones I've seen. I love this design, and can only imagine how cool your attachment point is!!!
VERY SLICK!
elegant,

off the shelf parts
KWHCoaster3 years ago
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 my storage locker that now can be re-purposed!
weblar (author)  KWHCoaster3 years ago
Good deal. Folding golf carts are relatively sturdy and are well-suited to make undercarriages for bicycle trailers.
BillBiker3 years ago
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. I may use part of this in my project. Thanks
weblar (author)  BillBiker3 years ago
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 what others have invented rather than simply buying something off the shelf.
Yes definitely and my other half likes the idea I do not have to go buy "new stuff" lol. This site is invaluable!!!
yel3an_ha3 years ago
U Could've Done It With 1 Wheel Only!!
felmont4 years ago
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 rotational movement)...
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 and give 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 (author)  felmont3 years ago
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 all between 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 caster is 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 is pushed around the floor. Therefore, the ball bearing mechanism/plates assembly would have to be reasonably strong to withstand those same lateral forces. In any event, I have not had any problems in actual use with separation or failure of the caster ball bearing mechanism.
weblar (author)  felmont4 years ago
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 central Missouri (US).  In spite of the moderately rough surface and the amount of use, I have had no problems whatsoever with this coupler or the plates holding it together.  I do 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 have no real concerns with the strength or durability of this trailer coupler; and in light of the length of my recumbent bicycle and the narrow trail where I often ride, do really appreciate the wide range of motion that this coupler design allows.
bo88y weblar3 years ago
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 look like 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 the rated 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.
bikerusl4 years ago
At 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 a more 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 I don'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 (less DIY) bicyclefamily.ca
weblar (author)  bikerusl4 years ago
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 themselves without 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 and publishing 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 paid less 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 charges twice as much.
joshfromga4 years ago
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
weblar (author)  joshfromga4 years ago
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. 
godspiral4 years ago
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 pivot point from the caster bearing, and its not obvious the caster will stay bolted.
weblar (author)  godspiral4 years ago
Though I (think I) understand your concerns, I've given the trailer coupler design plenty of use under load since I built it and it seems to be holding up quite 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 caster 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 away from the attachment bar than is necessary to allow that full range of movement.
Tinworm4 years ago
very clever indeed! :)
depotdevoid5 years ago
Nice idea! I like the final product, and wish I still had my bike trailer to try it on!
weblar (author)  depotdevoid5 years ago
It seems to work very well for me, and it sure was simple to put together from readily available parts.
lieuwe5 years ago
heh, the commercial bike trailer i have just uses a spring-thingy with a rope as backup for when the spring fails...
weblar (author)  lieuwe5 years ago
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. Swivel casters have ball bearings in the swivel joint and sleeve bearings through the wheels - they are better engineered than the junk that the bike trailer makers offer to connect their overpriced trailers to your very expensive bike. Its very easy (and in fact, less expensive) to make a trailer coupler yourself that will get the job done better than what they'll sell you for much more.
rimar20005 years ago
Very good idea.
weblar (author)  rimar20005 years ago
Thanks. This is why I like this website - you can read other peoples' good ideas and then build upon them.