Custom high power full suspension aluminum cargo bike

haulincolin

100 W
Joined
Apr 28, 2013
Messages
103
Location
Seattle, WA
I've been riding my existing cargo bike/tandem for years now, upgrading it piece by piece, and I'm ready for the next iteration, starting from the ground up.

Here's my current feature/part list
  • Custom 6061 aluminum frame machined and welded by me, heat treated at another local shop.
  • Mid-tail length rear end with integrated racks and bags--longer than a standard rear end, but shorter than an Xtracycle/Big Dummy.
  • Front flatbed cargo area in the style of a Bilenky or Omnium with linkage steering to a smaller front wheel under the cargo area.
  • Motorcycle style swing arm.
  • Aftermarket Honda Ruckus fork legs and disc brakes.
  • QS 273 17" x 3.5" 50H V4 cast rear wheel.
  • QS 14" x 2.5" cast front wheel.
  • ASI BAC 8000 controller.
  • Surplus electric car battery pack.
  • Pinion 18 speed gearbox.
I realize I'm really pushing the limits of what one could even consider a bicycle here, but I still like to pedal and I still like the ability to use bicycle infrastructure (I always ride slow and pedal when doing so). This is basically my dream vehicle for running errands across town while navigating horrible Seattle traffic.

Here's my long-winded explanation of how I came to these design features.

My current cargo bike is a tandem where the stoker sits recumbent in front and the captain in back (see https://endless-sphere.com/forums/viewtopic.php?f=6&t=64928). It's great, but I want to switch to rear wheel drive, and a slightly shorter wheelbase for greater maneuverability. It's neat to have the stoker position pedaling a generator, but it feels crappy to pedal, and contributes very little to charging the battery, so I'm ready to ditch it and the dedicated front seat for a flatbed cargo area. I can still carry someone there, or sitting on the rear rack.

I'm always chasing higher power setups just for fun and excitement so it's time to upgrade from QS 205 to 273, switching to a cast wheel while I'm at it, so no more chance of spoke issues. I still want to be able to pedal over a wide range of speeds, and such a big motor will only take a single speed freewheel (in fact the cast 273 doesn't take a freewheel at all--I will have to modify the side plate), so it's time to upgrade to the Pinion 18 speed internally geared bottom bracket, which has an even greater range than the Rohloff on my current bike.

I've learned that potholes and speedbumps become a much greater hazard with a 200+ lb vehicle than goes 50+ mph, so it's time to upgrade to full suspension. A motorcycle-style swingarm will support the QS 273, and aftermarket Ruckus fork legs will support a front wheel. The Ruckus comes with a 130/90-10 front tire, but I think I can stuff a 90/90-14 in there with a little tighter fender clearance, and possibly a custom arched crown. I'm pretty sure I don't want to even think about using a bicycle fork to support a 200+ lb vehicle that can easily carry three people.

Same with the disc brakes--my Tektro Dorados are nice brakes for sure, but they already feel underpowered for my existing bike. It's time to switch to scooter/motorcycle brakes.

Fabricating the frame out of aluminum is a bit risky since it means having to get the whole thing re-heat treated if it breaks and requires rewelding, but it means all of the machining leading up to welding is easier, plus I love welding aluminum. I think a large cargo bike is the perfect application to utilize aluminum's advantages because I have ample space to use very large diameter tubes.

I currently have a BAC 8000 controller on my cargo bike, and it's the best high power controller I know of, so I'll probably stick with that. I'm also using 18s of Chevy Volt cells from a 2015 vehicle. It has served me well, but I'm considering other options. Leaf cells are tempting because their modular nature would make it easier to arrange them on the frame, I could max out the voltage on my controller by upping my series to 20s or 22s, and I could get a greater range with the 64 ah cells. However, I've heard that they tend to have saggy voltage under heavy load. My Chevy Volt pack at 50ah and supposedly rated for something like 8c sags quite a bit now that I've put it through several years of heavy use and I actually have a controller that can draw 400+ amps. I wouldn't want to downgrade to a battery with worse performance. Would love some advice from people with experience with Leaf cells, or other options here.
 
haulincolin said:
[...]so it's time to upgrade to the Pinion 18 speed internally geared bottom bracket, which has an even greater range than the Rohloff on my current bike.

Is that the same Rohloff hub I remember, that you bought secondhand with a racing MTB attached?

I really like the idea of the Pinion gearbox. I'm not terribly confident that it's a good idea for my combination of high rider weight and long cranks. And I hate the fact that the bike frame must be Pinion only forever.

I'm pretty sure I don't want to even think about using a bicycle fork to support a 200+ lb vehicle that can easily carry three people.
Well, typical two- and three-passenger pedicabs use non-suspension mild steel trike clamp "chopper" forks, and they do okay. They're not going very fast. My thinking is that long travel triple clamp MTB forks would be even better, if their travel were shortened to a streetwise amount.

Same with the disc brakes--my Tektro Dorados are nice brakes for sure, but they already feel underpowered for my existing bike. It's time to switch to scooter/motorcycle brakes.

Using motorcycle brakes generally means motorcycle hubs (therefore spokes, therefore rims, therefore tires), forks... you can easily get into a heavyweight death spiral, where you need more and more power to do what you could do with pedals alone if you hadn't added all the dead weight and chunky rubber.

For our 6 passenger electric assist pedicabs (which can easily exceed 2000 pounds in action), we use dual front and dual rear discs-- BB7 or Tektro Auriga with 8" rotors. Granted, we have engineered them for 15mph. But it's a lot of weight, on 29" wheels, and the brakes work well. The wheels are motorcycle-strong while weighing less than a moto rim by itself. Or hub. Or tire. https://precisionpedicab.com/?product=super-duty-rear-pedicab-wheels-29

As for batteries, my current pack is one I built from Panasonic 25Ah cells that came from I think a Ford hybrid car. They're rated for many times as much current as I ask of them, so they don't really sag at all-- the voltage droops a tiny bit under load, but it's the voltage drop across the resistance in the cables. I'm very happy with them, even though their energy density isn't as high as the 18650 pack I used before.

I like my cargo bike well enough now, but I have another one in the pipeline-- longtail instead of front loader this time, with full sized wheels for better ride quality and efficiency.
 
Chalo said:
Is that the same Rohloff hub I remember, that you bought secondhand with a racing MTB attached?

Yes, the very same one! It's really old, and it now has periodic skipping in 6 of the speeds, but I've been too cheap to send it back to Cycle Monkey / Rohloff for a rebuild.

I really like the idea of the Pinion gearbox. I'm not terribly confident that it's a good idea for my combination of high rider weight and long cranks. And I hate the fact that the bike frame must be Pinion only forever.

Yes, that's definitely a drawback, along with every other modern mid-drive production frame. Maybe someday there will be a market for bottom bracket shell adapters to repurpose older Bosch bikes to human power only.

Well, typical two- and three-passenger pedicabs use non-suspension mild steel trike clamp "chopper" forks, and they do okay. They're not going very fast. My thinking is that long travel triple clamp MTB forks would be even better, if their travel were shortened to a streetwise amount.

I see what you mean, and I think it's the combination of weight and speed that worries me. Plus I'm not sure how I'd find/modify a MTB suspension for to work with a smallish wheel and several hundred pound load.

Using motorcycle brakes generally means motorcycle hubs (therefore spokes, therefore rims, therefore tires), forks... you can easily get into a heavyweight death spiral, where you need more and more power to do what you could do with pedals alone if you hadn't added all the dead weight and chunky rubber.

For our 6 passenger electric assist pedicabs (which can easily exceed 2000 pounds in action), we use dual front and dual rear discs-- BB7 or Tektro Auriga with 8" rotors. Granted, we have engineered them for 15mph. But it's a lot of weight, on 29" wheels, and the brakes work well. The wheels are motorcycle-strong while weighing less than a moto rim by itself. Or hub. Or tire. https://precisionpedicab.com/?product=super-duty-rear-pedicab-wheels-29

I'm already down the motorcycle weight rabbit hole with the cast QS 273, and I'm fine with it since it means never breaking spokes, and rarely getting flat tires. Dual rotors is a good idea that I hadn't considered yet. So you have 4 or 6 total rotors on a three wheel pedicab? How quickly do you go through brake pads? I still like the idea of thicker rotors and larger pads to soak up all the heat of stopping a vehicle with 500+ lb GVW from 50+ mph.

My current cargo bike weighs over 200 lbs and my hope is that my new smaller aluminum frame with some more thoughtful design and engineering will lessen my weight by close to the same amount I'm adding with the larger wheel and suspension, ending up still less than 250 lbs total. If I really have to, I can still pedal around without using the motor, but I move pretty slow. When in use, the motor more than makes up for the extra weight of the entire electric system and associated parts.

I like my cargo bike well enough now, but I have another one in the pipeline-- longtail instead of front loader this time, with full sized wheels for better ride quality and efficiency.

I look forward to seeing this!
 
haulincolin said:
Chalo said:
Is that the same Rohloff hub I remember, that you bought secondhand with a racing MTB attached?

Yes, the very same one! It's really old, and it now has periodic skipping in 6 of the speeds, but I've been too cheap to send it back to Cycle Monkey / Rohloff for a rebuild.

Aaron Goss's shop is a Rohloff service center, last I heard.

Plus I'm not sure how I'd find/modify a MTB suspension for to work with a smallish wheel and several hundred pound load.

When you cut a spring in half, you reduce its travel by half but you double its spring rate. To me, that means you cut down the springs, put spacers on the top out sides, and get a shorter, stiffer, stronger fork with increased spring rate.

Dual rotors is a good idea that I hadn't considered yet. So you have 4 or 6 total rotors on a three wheel pedicab?

4 rotors and calipers per trike. It would probably be even better to have 4 rotors on the rear axle, but the levers can only be split up so many ways.

How quickly do you go through brake pads?
I don't really know. It hasn't been a complaint or a functional issue. We use sintered metal pads. I expect we'll learn more as the new trikes accumulate a bigger mileage base.
 
Chalo said:
Aaron Goss's shop is a Rohloff service center, last I heard.

Aaron can do cleaning and oil changes, and replace shell components, but cannot service the guts. As far as I know, even Cycle Monkey sends them back to Germany for internal repairs. I'm not even sure they'd be willing to work on mine since we drilled the flanges for a 48 spoke wheel.

When you cut a spring in half, you reduce its travel by half but you double its spring rate. To me, that means you cut down the springs, put spacers on the top out sides, and get a shorter, stiffer, stronger fork with increased spring rate.

This is an interesting idea. I will look into it more. Thanks!
 
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