Trailer Hitch and 3D printed accessories for S40

egervaswatson

New Member
I wanted the S40 for touring, and for me part of that was always going to be towing a trailer. I have two trailers--the Topeak Journey and the Bob Yak. My ideal trailer hitch was going to be one that could work with both trailers and would be very sturdy, without modifying or putting large amounts of torque on any part of the frame.

To prevent a lot of torque on any braze-ons, I wanted two points of attachment, one of them preferably being the rear axle. I designed and 3D printed several iterations of a tab that would span the quick-release and the fender bosses on the rear fork. Once I had a shape that fit perfectly, I sent the CAD model to my brother, who CNC machined it out of aluminum, resulting in the following parts:

ga2tolgy.jpeg

Since these were machined by CNC, where I wanted to tap threads I was able to spec the holes to the exact tap drill diameter.

The stock rear skewer for the S40 is too short to accommodate an extra 3/8" of stock. I bought a standard "rear" skewer, but this was, in turn, too long. I used an M5 die to thread the skewer further up its length.
BKQaFwOc.jpeg
Now I could clamp the hitch mounts to the rear fork, but there was still a lot of excess length on the skewer. Normally, cutting a threaded rod absolutely destroys the threads, making it very hard to use the bolt from then on. To prevent this, I threaded my die onto the skewer, cut and chamfered the excess off, then threaded the die back off to clean up the threads.
v_4fX0E3.jpeg
On a hitch mount design for a previous bike, I simply drilled out holes for the M5 bolts, but this resulted in a small amount of slop. This time, I decided to thread the holes to eliminate any slop whatsoever. Of course, if the threads on the hitch didn't line up with the threads on the bike, I'd be in trouble--so I clamped the hitch mount in place (with thin nylon spacers to protect the paint), carefully threaded my tap into the fender boss, then proceeded to cut the threads into the hitch mount.
ep-b22IT.jpeg
No room between the dropouts for a tap wrench, but that's why God invented visegrips.

I threaded in the M5 machine screws,found that they fit perfectly, and tapped the holes for the actual hitch bolts. This served to eliminate slop and let me use a single nylock on the back side in a jam nut configuration to ensure zero risk of loosening up.

7d62D4s-.jpeg

With all the metal components working perfectly, all that remained was to 3D print the actual hitch bushings. Designing them to accommodate both trailers resulted in an interesting vase-like design, but one that works flawlessly.
oAJh17Hl.jpeg
Bare Hitch.
IrqEgIkb.jpeg
With Topeak Journey.
-DWr9loz.jpeg
With Bob Yak.

For additional cargo capacity, I also wanted a rear rack. The stock rack for the S40 is fine, but I really wanted something that would accommodate my Topeak shopping basket for grocery runs. I therefore decided to use a Topeak seatpost rack. The problem, of course, is that the S40 doesn't have anything that really resembles a seatpost.

I replaced the bolt that holds the headrest in place with a much longer one so that I could use that as the top anchor point for my "seatpost". Of course, seatposts aren't usually straight up and down, and racks designed to clamp to them take this into account. I therefore 3D printed 2 70° shims that would clamp my stock between them, holding it at a precise angle.
2 - EQCTQAB.jpg
One point of attachment on a piece of 1/16" aluminum wasn't going to cut it, so I added two struts supporting it against the braze-ons near the top of the seat stays.
3 - iw0nkTL.jpg
 
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egervaswatson

New Member
3D printed objects tend to be abysmal in tensile strength but quite reasonable in compression, so they're great for making shims and bushings. To attach the rack, I've shimmed out the ¾" square tubing to a 30mm cylinder.
4 - 0kbDka2.jpg
Given that this still isn't as sturdy as a standard seatpost, I thought it prudent to support the rack with some addittional struts leading to the braze-ons further down the seatstays. To make the struts, I simply crushed the ends of some ½" round tubing in my vise and drilled out holes for the bolts.
6 - 5nyv26R.jpg

3D printing presents unique opportunites for a custom cockpit layout. The things I wanted were:
  • A phone mount for navigation/communications/audiobooks
  • A ham radio handset for rural communications
  • A USB port to recharge my phone/taillight/anything else
  • An 8.4v regulator for my headlight and ham radio
  • A voltage meter to monitor battery usage
Here was my solution:
9 - vovW0zQ.jpg

The phone and radio mount to a single 3D printed receptacle that spans the handlebar bracket, attaching on either side with a combination of double-sided mounting tape and zip ties. The USB converter/voltage meter is on a bracket mounted by a similar method under the boom and is easily removed for use away from the bike. The voltage regulator mounts just ahead of that. All of the connections are xt-30s injected with dielectric grease to prevent corrosion. The battery mounts behind the seat, and I can use any combination of lithium ion and lithium polymer batteries from 12-24 volts. The battery I built for this is an ~8 amp hour 12v lithium ion battery with built-in cell balancing that can accommodate other batteries in parallel and charge off of a small solar panel. The battery will run my light for about 8 hours on a charge.
1 - uBwnOPv.jpg
And here's the full thing (pre trailer-hitches)!

Additional mods include:
  • A 3D-printed pump mount secured to the bottle bosses behind the seat
  • A touring toolkit mounted opposite the pump
  • capacity for 2 Nalgene bottles with camelbak-style hoses for easy access, mounted behind the head.
 

benphyr

Guru-me-not
@egervaswatson Wow! I guess no one ever says can’t to you! Welcome to the Cruzbike Tribe! Quite the intro posts! I can’t seem to find enough exclamation points for this post.‼️
 
Oh yeah? What components? I'd love to see them!
Lots of stuff. I'm the Lab Supervisor in charge of Fabrication including the 3D printers at or local University.
Here's a few. I've designed and printed handle bar and bar end mirror mounts, light mounts, Frnt derailleur mount shims, also some brackets, mounts and vent ducts for my Hot Rod. 3D printers are really nice tools to have and long as you understand the limitations.
 

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Suz

Well-Known Member
I wanted the S40 for touring, and for me part of that was always going to be towing a trailer. I have two trailers--the Topeak Journey and the Bob Yak. My ideal trailer hitch was going to be one that could work with both trailers and would be very sturdy, without modifying or putting large amounts of torque on any part of the frame.

To prevent a lot of torque on any braze-ons, I wanted two points of attachment, one of them preferably being the rear axle. I designed and 3D printed several iterations of a tab that would span the quick-release and the fender bosses on the rear fork. Once I had a shape that fit perfectly, I sent the CAD model to my brother, who CNC machined it out of aluminum, resulting in the following parts:

View attachment 8087

Since these were machined by CNC, where I wanted to tap threads I was able to spec the holes to the exact tap drill diameter.

The stock rear skewer for the S40 is too short to accommodate an extra 3/8" of stock. I bought a standard "rear" skewer, but this was, in turn, too long. I used an M5 die to thread the skewer further up its length.
View attachment 8084
Now I could clamp the hitch mounts to the rear fork, but there was still a lot of excess length on the skewer. Normally, cutting a threaded rod absolutely destroys the threads, making it very hard to use the bolt from then on. To prevent this, I threaded my die onto the skewer, cut and chamfered the excess off, then threaded the die back off to clean up the threads.
View attachment 8090
On a hitch mount design for a previous bike, I simply drilled out holes for the M5 bolts, but this resulted in a small amount of slop. This time, I decided to thread the holes to eliminate any slop whatsoever. Of course, if the threads on the hitch didn't line up with the threads on the bike, I'd be in trouble--so I clamped the hitch mount in place (with thin nylon spacers to protect the paint), carefully threaded my tap into the fender boss, then proceeded to cut the threads into the hitch mount.
View attachment 8086
No room between the dropouts for a tap wrench, but that's why God invented visegrips.

I threaded in the M5 machine screws,found that they fit perfectly, and tapped the holes for the actual hitch bolts. This served to eliminate slop and let me use a single nylock on the back side in a jam nut configuration to ensure zero risk of loosening up.

View attachment 8083

With all the metal components working perfectly, all that remained was to 3D print the actual hitch bushings. Designing them to accommodate both trailers resulted in an interesting vase-like design, but one that works flawlessly.
View attachment 8089
Bare Hitch.
View attachment 8088
With Topeak Journey.
View attachment 8085
With Bob Yak.

For additional cargo capacity, I also wanted a rear rack. The stock rack for the S40 is fine, but I really wanted something that would accommodate my Topeak shopping basket for grocery runs. I therefore decided to use a Topeak seatpost rack. The problem, of course, is that the S40 doesn't have anything that really resembles a seatpost.

I replaced the bolt that holds the headrest in place with a much longer one so that I could use that as the top anchor point for my "seatpost". Of course, seatposts aren't usually straight up and down, and racks designed to clamp to them take this into account. I therefore 3D printed 2 70° shims that would clamp my stock between them, holding it at a precise angle.
View attachment 8091
One point of attachment on a piece of 1/16" aluminum wasn't going to cut it, so I added two struts supporting it against the braze-ons near the top of the seat stays.
View attachment 8092

Oh my goodness! Would you sell a set of the trailer hitch pieces? I thought it would be easier hooking my kids bike trailer to my S40 but I’ve already chipped paint and had to jerry rig the connection because of the lip area you carved out. This is fantastic!!!!

Kudos and welcome.
 

egervaswatson

New Member
Oh my goodness! Would you sell a set of the trailer hitch pieces? I thought it would be easier hooking my kids bike trailer to my S40 but I’ve already chipped paint and had to jerry rig the connection because of the lip area you carved out. This is fantastic!!!!

Kudos and welcome.

The hitch pieces are pretty specific to this type of trailer--most kid haulers I've seen use a pretty different mounting system that would put different stresses on the frame. Additionally, the only way I got them is because my brother turned them out between batches at work--fine occasionally, not something the bosses want him to do too often.

I'd love to send you some if I had the means, but sadly I don't.
 
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