This is a quick-release hitch for use with the Burley Travoy bike trailer. It can be put on and taken off a bike quickly, and with the appropriate clamp, as described below, it can be used with bike share bikes, like the Chicago Divvy bikes. If you intend to make one for a bike having a smaller diameter seat post, then you'd have to source another clamp, or use something to make up the difference in diameter (like some old inner tube rubber, wrapped around the seat post).
Step 1: Gather Your Parts
1. Truss clamp sized for seat tube. I used a Milos Cell 102 clamp for 32mm (1-1/4") tube. Found some on eBay for about $14 each. They came with a wingnut on the non-hinged end of the clamp, which I removed.
2. M6 size lifting eye bolt - 316 stainless, marine grade. Found some on eBay for about $1.25. The length wasn't specified in the listing, but it turns out that the threaded part is 1cm long, which is the perfect length. It fully threads into the nut, but doesn't stick out into the clamp face, so it won't scratch the seat post.
3. M6 size stainless nylon lock nut. I got a bag full at the local hardware store. I think they came out to about $0.20 each
4. Wire lock latch pin. Also called a hitch pin or wire lock pin. 1/4" diameter pin, 2" long. About $2 each.
Step 2: Assemble and Roll
Assembly is pretty self-evident. Have a look at the main picture.
Put the lock nut in the slot inside the clamp body, then screw the eye bolt into it. The slot of the clamp prevents the nut from turning, so you just grab on to the eye bolt and turn. This part of the assembly stays put. The latch pin can be done and undone to attach to the Travoy.
The clamp doesn't need to be tightened down onto the seat post very hard. Finger tight with the wing nut is sufficient. I found that for the Divvy bikes in Chicago, it's easiest to use this sequence:
1. Fit clamp around the seat post loosely, with the eye bolt facing the rear of the bike.
2. Place the hitch part from the Travoy on top of the eye bolt, then put the latch pin through both, starting from the top. Pull the wire part of the latch over the pin to secure it. This will take place on the bottom of the assembly, under the eye bolt.
3. Now slide the clamp up the seatpost, to just under the seat, and tighten. Depending on how tall you are, you might not take it all the way up under the seat, but I think for anyone under 6 feet tall, you'll probably bring it up all the way.
4. Ride on!
I like to keep the clamp attached to the Travoy when out and about. For one thing, it's hard to undo the latch pin when it's on the bike and up under the seat. For another, undoing the clamp every time (rather than the latch pin) ensures that it won't be left on a bike share bike accidentally.
I've found that the clamp and bolt arrangement is very sturdy. In the attached picture, we had Travoys loaded up with my inflatable kayaks and accessories, probably close to 40 or 45 pounds. Since the weight limit for a Travoy is 60 pounds, I feel pretty confident that this hitch will handle any load that the Travoy can handle. When we got to the Chicago River, we dropped off the Divvy bikes, folded down the Travoys into their bags, and loaded them on the front decks of the kayaks. It worked perfectly for a one-way paddle trip down the river, and allowed us to hook them up to other Divvys at the destination, for a ride home.
When I get a chance, I think I'll put some tape over the inside parts of the clamp, in order to be very gentle on the Divvy seat post and prevent any potential scratches. Something like gaffer tape should do just fine.