Yuba Mundo BBS02/Nuvinci (3400 mile update)

Here are some pics of my latest ride. As my kids are getting bigger, I was finding it difficult to make that final hill to school. With BBS02 and the Nuvinci Developer kit, all I need to do is pedal and brake. I can go as slow as I want up a hill, yet it is also scary how fast this thing can go.




I am using a 20t sprocket and have set the Nuvinci cadence to 80 RPM. The Nuvinci controller and 48-12volt dc-dc converter are hidden under the top deck.




For the battery case, I used a super heavy duty electrical enclosure box ground down to shape. A 14s 20 ah Li pack fits perfectly in the space between the chain and pedals.


After a little over 2200 miles, the the Nuvinci 171 has been retired. The hub still worked but sounded like it had gravel in it. Also, spare parts for the obsolete developer's kit were hard to come by.

Over the past couple weeks, I converted the drive train to an 8-speed derailleur system. On the front is a 37 or 38 t chainring mounted to the 104 bcd adapter.



Since this is a Yuba Mundo, the rear dropouts are 14mm and horizontal. As a result, motor chain power pulls the right side of the wheel forward. Even using aggressive washers did not help at all. Finally, I pinned the axle into the dropout using a metal plate and 2 bolts.



The bike definitely performs better than before in terms of acceleration and top speed. I am using throttle control but not PAS in order to decrease dead time between gear changes. The brake cutout button is too slow, and the throttle control circuit (ala Kepler) does not seem to work on my setup.

Overall, the bike is much lighter now and more responsive. I like it.

That looks very nice. I have a yuba with a 5404 and 24s of lifepo4 on the rear rack.

Been considering doing something similar. I really hate the wasted space on my bike where you have your battery.

Does it seem to take off pretty good or is that more limited by changing gears ?

Something I do like on my ride is ability to get up to speed pretty quick which is about 30 mph.

Another question - who did you get to build up the rear wheel with the nuvinci or you do that yourself ?

Thanks for sharing.

Thanks. Make sure you get a battery that fits though.

I have set the start current to 22% on pedal assist. This bike gets up to 30 mph in no time and smoothly by using the Nuvinci CVT.

Sweet cargo bike!

It's a very stealth and clean build.

Is that a horn on the front fork?

Yes, 48V forklift horn. Comes in handy with preoccupied drivers.

snowranger said:

Yes, 48V forklift horn. Comes in handy with preoccupied drivers.

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That's a great idea. I have a 12V horn, but it taxes the DC-DC converter. 48V horn would be sweet. I'll have to check that out. I subscribed to this thread, looking forward to anything else you got up your sleeve

Make sure it is not a frame-grounded horn. I made that mistake with some 12 V Fiamm horns I was going to use in series.

The lights at the front are around $20 and come with an 8.4 volt li battery, but they seem to work fine with the 12 V converter. I am using the 8.4 volt in case I run down the main battery and still need light.

What a luverly bike! Much admiration for such a practical setup.

Thanks. I cannot believe how much better a Mid-drive Nuvinci developer combo is for San Francisco hills than my BMC hub motor. The Nuvinci is automatically always in the right gear ratio, so the strain on the motor is minimized. With 150 lbs of kids on board, there is no worry about going too slow and stalling / burning out the motor. On the other hand, the top speed is even higher than the old motor.

I wish I had a way to measure power use and speed overlaid on a map. If anyone is in the SF area and wants to take a test ride, let me know.

Snowranger, how does the Nuvinci deal with the torque output from the motor. I was watching some videos of how the Nuvinci works and it doesn´t look like here´s much contact area for transferring the torque to the wheel so I was wondering if the balls in the CVT could "slip" at high torque.

velovelo said:

Snowranger, how does the Nuvinci deal with the torque output from the motor. I was watching some videos of how the Nuvinci works and it doesn´t look like here´s much contact area for transferring the torque to the wheel so I was wounding if the balls in the CVT could "slip" at high torque.

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From the User Manual:
…bicycle and light electric…

• Maximum Sustained (pulse-free) Input Torque: 65 NM (48 lb-ft)
• Maximum Instantaneous (spike) Input Torque: 130 NM (96 lb-ft)
• Maximum Sustained Input Power: 5 kW (7hp)
• Maximum Input Speed: 1000 RPM
• Maximum Output Speed: 1000 RPM

Followed by:
Operation at these torque and power conditions is not recommended for extended durations, and durability is heavily dependent on duty cycle. Use discretion and contact Fallbrook Technologies Customer Support for production application needs or customized configurations.

I saw that the Bafang at 700W produces 120nM of torque so it should be ok but as you say, I'm not sure if I'd want that kind of stress on the hub.

You guys got me all concerned about the torque limitations. Yesterday, I was riding on assist 9 up a big hill. After coming down, I noticed that the hub would immediately go to a high shift position at 18 mph (Safe Mode?).

I hooked up hyperterminal this morning on the way to work and found that there was no speed signal being generated. Turns out that the disc brake rotor had worn down the sensor insulation and was shorting the circuit. Then I remembered I had replaced the brake pad the other day, and must have moved the sensor wire.

Moving the wire away from the disc resolved the problem. BTW with this rig, my shimano hydraulic pads are only lasting 450 miles. The Nuvinci is sill going strong.

snowranger said:

Thanks. I cannot believe how much better a Mid-drive Nuvinci developer combo is for San Francisco hills than my BMC hub motor. The Nuvinci is automatically always in the right gear ratio, so the strain on the motor is minimized. With 150 lbs of kids on board, there is no worry about going too slow and stalling / burning out the motor. On the other hand, the top speed is even higher than the old motor.

I wish I had a way to measure power use and speed overlaid on a map. If anyone is in the SF area and wants to take a test ride, let me know.

Click to expand...

Good review!

This is interesting. Thanks for sharing. I have a Yuba mundo and need to make it electric.

Didn't you lose the 400 lb carrying capacity at the rear wheel when you changed out the hub? I'm trying to keep that and hence my quest to determine whether to go with a mid drive like the Bafang or the 500w Ezee.

Any thoughts?

How often are you going to be hauling 400 lbs? My Xtracycle free radical was rated at around 200 lbs, and that was with a bolt-on long-tail that flexed like crazy and 36H wheels.

You have done a great build...the mundo is a great platform.

Can you provide more details on you build, for instance, your battery and battery box. Also, where did you get the rear seat cushions for the rear deck?


http://endless-sphere.com/forums/viewtopic.php?f=6&t=42509

Thanks for the input. I think I'd like to keep the weight rating for the rear. Two kids, a full grocery shop and I'm betting I'd be over 200. Plus, it's nice to give friends the occassional ride.

Both bbs02 and nuvinci are still playing well together. Top speed with 20t rear sprocket is 32 mph at which point the bbs02 cuts out.

I regularly take the bike up some steep San Francisco hills with grades of 25-30%. The motor never gets hot. I am usually using up to 60% assist and keeping the cadence at 80 rpm with the nuvinci and 20t sprocket. This is probably good for reliability.

that really is steep. that is like 1st gear for a car and really even hard to walk up.

It looks steeper than it really is. A black diamond run is around 30 degrees. The below translate to about 17 degrees max.

The Steepest Streets in the City, Purportedly
1. (tie) Filbert between Leavenworth and Hyde (31.5% grade)
1. (tie) 22nd between Church and Vicksburg (31.5% grade)
3. Jones between Union and Filbert (29% grade)
4. Duboce between Buena Vista and Alpine (27.9% grade)
5. Jones between Green and Union (26% grade)
6. Webster between Vallejo and Broadway (26% grade)
7. Duboce between Alpine and Divisadero (25% grade)
8. Jones between Pine and California (24.8 grade)
9. Fillmore between Vallejo and Broadway (24% grade)
Source: San Francisco Bureau Of Engineering.

Really like++ the design of a Yuba Mundo cargo bike with the BBS02. Put it my Imaginarium portfolio of design ideas which I use in presentations of what's possible.

Nice build. Very well integrated. I'm glad to hear the NuVinci can handle some work.

I think the bbs02 can go faster than 32 mph on my setup. I am specifying a 16 inch wheel in the controller but actually using 26" wheels. All my readings are in metric although they are really in mph. This gets me maximum speed of 33-33.

I know that the wheel size could be specified even smaller to go faster, but then that would mess up my odometer. Are there any other ways to increase the speed limit?

Hi Snowranger et al,

I'm also considering electrifying our Mundo as the kids are not getting lighter... and the school run is getting longer. We have some big hills here in south Wales, and I have been told that mid-drive is the way forward. I think I am going to mis the purity of the bike as it is at the moment, but it is a price I'll have to pay. Here in the EU, we are limited to 250W, so my feeling is that hub motors + hills + cargo is not a good solution.

At the moment I have 24 gears, including 22->34 lowest gear... a huge range that I use daily. I'm trying to find solutions that keep a reasonable gear range so that, should battery power fail, I can still get up some of the steeper hills and home. What gear range do you have, and, when the battery power is gone, is it "enough"?

I have been considering a Rohloff 14-gear hub with the BBS02, although do wonder if it will handle the torque ok.

Fraser.