Center Hub Steer Cargo Bike

Hey everyone!

I’ve spent the past few months designing and fabricating a new, center-steer hub cargo bike. Now that the bike is rolling (and will soon be riding with a new belt), I’d like to share my current progress. I’ll add more to this thread as the bike is finalized and share some of the important learnings I had throughout the project.

First, some quick details/highlights of the bike:

  • Frame Layout: Lots of bends/curves. I wanted to showcase some of the design possibilities of a center steer hub. There’s an upper and lower cargo deck, and the upper cargo deck is very low (no stack height from a headtube/headset).
  • Center-steer hub: Cable-driven, +/- 40° steer angle, Shimano 203mm rotor, axle flat + bolt mounting pattern to handle brake torque.
  • Gas Strut kickstand: Over-centered, furniture feet (huge improvement for stability + durability over my earlier design), sturdy tube stop for lowered/raised positions.
  • Dropped chain stays: Clearance for belt drive w/o frame split.
  • Integrated Lighting: Front/rear lights are encased in CNC housing, bolt directly to the frame, and are controlled by a PCB operated via a button on the stem cap. PCB and battery live in the base/downtube.

Here are some photos I recently took of the bike. I was sent a CDN instead of a CDX belt, and need to wait a few days before I’m up and running again. I’m excited!









31 Likes

SO COOL!! I can’t wait to hear how it rides. Is the steering hub an off-the-shelf product or is that custom?

Also wow, what a flex using an optical table for fixturing :star_struck: that’s rad!

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Thanks, Eva! The center steer hub is my own design. This is the second center steer hub I’ve made; the design goal was to package everything as tightly and elegantly as possible.

Figuring out how to route the steering cables, cram the pulleys inside the hub, integrate the brake rotor, and have the whole assembly easily come apart for servicing was tough. There are definitely some design oversights I’d like to change for the next hub, but nothing that’s a showstopper for the current design. I hope to do a deeper dive in future posts.

Optical tables are awesome. The one pictured above was literally sitting, forgotten and collecting dust, in a back room at my university. I have a smaller table at home that I scored from an industrial liquidator. Cheaper than a Stronghand/Siegmund type welding table and very versatile. I machined my own notcher bearing block and mitered several joints with the tubes in-situ. Using a handheld drill (maxed RPM) with the fine-pitch Rockhard hole saws from Metal Guru make short work of thin wall tubing.

The optical table + 3D printed clamp + cordless notcher combo is pretty amazing for challenging miters. I went through 2x 1kg rolls of ASA to make all of the adapters for my frame, and a significant amount of Markforged Onyx filament as well (I’m fortunate enough to have access to a Mark Two at my school). The Markforged Onyx is no joke, really stiff, tough, and dimensionally accurate with a high HDT perfect for tacking and welding in the fixture. The ASA also worked well with high infill (30-40%) and lots of walls (5-6, with a 0.6mm nozzle).


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Now this is really cool.
Even as someone who’s not very into cargo bikes, I finding it difficult to sufficiently express how rad I think this is. Very well done!

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Impressive!

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:exploding_head:

Amazing work!

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This is wild. Very very cool design and execution! how does it ride? And how is changing a flat?

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This i incredible. I was already impressed with your earlier version, but this hub almost looks - dare I say - production ready? I would buy one!

I am working on a cargo bike design right now, and I am considering a hydraulic steering linkage with a pair of these: McMaster-Carr . I have been trying to figure out how ‘slow’ the system would be, but I may just have to try it. If it works, it could integrate really well with this hub steer concept.

Thanks for sharing! Once you get the belt issue resolved, I want to see a fully loaded picture!

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Thanks! I’m really pleased with how the new hub looks. The hydraulic actuators you linked look awesome. I remember stumbling across a YouTube video of a hydraulically actuated cargo bike steering mechanism.

I’d love to learn from your experience if you go the hydraulic route. It might be worth making a small bench setup first with handlebars/headset to qualitatively/quantitatively test the mechanism. I’m curious how hard it’d be to bleed the system, and how that translates to responsiveness and perceived slop.

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Beautiful!
I am also trying to build a cargo but not as cool as yours!

For the steering I’ll use a classic tube but I have mocked up a way to use miter gears to bring the motion from the back to the front so I could hide the whole system inside the tubing.

I assume the trinket is for the lights?

So awesome.

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I love all the random cargo bike innovation on the web

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Lighting PCB done! It’s really hard to solder small SMD components. Here’s a quick test with the front/rear light blinking. The front lights alternate so one light is always on (hopefully this allows me to see and be seen at night). I’m running the front lights (Cree XP-G2 3-up PCB’s) at a 1% duty cycle and they’re still insanely bright. My average power consumption is about 0.8w, which should give me around 20 hours of runtime with my planned battery.

I also took the bike on its first ride a few days ago (about 28 miles round-trip). Everything feels pretty solid! I’ll have to experiment with the cable tension. When the cables are too tight, there is a lot of drag in the system and the steering feels a little disconcerting - the wheel does not want to “flop”. However, setting the cable tension too loose introduces play into the system. There’s probably a happy medium somewhere I haven’t found yet.

More to come soon!


Test Comp 2

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I do like to see that Trinket M0 put to use!! Good work!

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Really interesting work. I look forward to hearing how the cable steering works for you. I’ve ridden the Frances Smallhaul which uses cable steering, but also saw that R&M had to recall all of their Packster 70 bikes (man, that must have been painful for them) due to cable steering issues. I think it was due to the bikes developing shimmy at speed. Yuba is the other big company that I can think of who shipped a cable steered bike.

In the third photo there are two things that the cable passes over, are those some sort of eccentric to adjust cable slack?

Are there any photos of the left side of the hub?

What do you see as the big advantages of center-steering?

How does one think about trail in this system? Is this like building a zero-offset fork?

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I had the same issue with cable steering. I think it is possible to make it work, but I would reduce the amount of cable housing as much as possible, and make the cable pulleys as large as possible to “increase stiffness”. Although increasing pulley diameter might not be possible with your hub.

I test rode a Yuba Supermarche that felt sorta ok. I imagine you’d have to tighten the cables regularly, and they suggest replacing all the cables and housing once a year.

I noticed that some builders use larger diameter aircraft push/pull cable. Might be worth a look.

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Adding on to what Paul said above, I’m thinking that it might be worth looking into getting some high performance compressionless housing for the cables to increase the stiffness of the system.

In a mechanical disc brake application, it made a huge difference swapping from standard brake housing (as seen in your earlier post) to compressionless housing from Yokozuna. Nokon housing also comes to mind.

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@JMY This is a good idea. I switched to Jagwire’s elite brake link housing and the performance difference with compressionless is significant. It’s uncomfortably expensive, but you can add and remove links and use it seemingly over and over for many cable changes. Much less of a throwaway part. Plus it looks really baller.

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@Alex

Hey Alex - I’m using barrel adjusters mounted to brackets where the front axle attaches to the bike. I’ll add some photos soon of the left side of the hub with the brake mount + rotor.

The biggest motivating factors for me were the novelty of this layout, different frame geometry (no head tube needed), and ability to create a low cargo load floor. Trail is effectively set like a zero offset fork, where the kingpin axle within the hub is inclined around 70°.

@PaulD @JMY @Dave_PMW

Thank you for all of the advice! Paul, you’re exactly right - I can’t make my steering pulleys any larger due to packaging limitations in the front hub. I’ll give compressionless housing a shot - I hadn’t thought of using it and am excited to see/feel the results.

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