Hummingbird 20kw-ish Mid-Drive Concept Bike

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Chambers   10 W

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Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 20 2020 1:25am

As the title suggests this is a new concept bike I'm developing (name subject to change :lol: ), Still lots of work to go but the current specs are as follows.

- QS138-70H motor concentric to the swing-arm pivot

- Nuc' 24F controller

- Removable battery - 20s21p Samsung 30Q's

- Seat height 940 mm (adjustable)

- Ground clearance 350(ish)

- Monocoque aluminium module housing the Battery, Motor and Controller allowing for multiple
upper sub-frame sections for different geometries etc.

- A few things I've probably forgotten :roll:

Rear suspension hasn't been figured out yet but not too far off - Thoughts welcome.

A few pics below.
P.s Ignore the headlight it's a work in progress :lol:

Geometry 26 inch ASSY.200120-2.jpg
Geometry 26 inch ASSY.200120-2.jpg (188.46 KiB) Viewed 2010 times
Geometry 26 inch TEST 200120-4.jpg
Geometry 26 inch TEST 200120-4.jpg (184.74 KiB) Viewed 2010 times
Geometry 26 inch ASSY.200120-3.jpg
Geometry 26 inch ASSY.200120-3.jpg (234.54 KiB) Viewed 2010 times
Geometry 26 inch TEST 200120-5.jpg
Geometry 26 inch TEST 200120-5.jpg (187.93 KiB) Viewed 2010 times
Geometry 26 inch TEST ASSY REV E.jpg
Geometry 26 inch TEST ASSY REV E.jpg (234.94 KiB) Viewed 1807 times
Geometry 26 inch TEST ASSY REV E annotated.jpg
Geometry 26 inch TEST ASSY REV E annotated.jpg (256.89 KiB) Viewed 1795 times
Last edited by Chambers on Jan 25 2020 2:29am, edited 5 times in total.

Nobreaks   1 µW

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Nobreaks » Jan 20 2020 5:58am

QS138-70H motor concentric to the pivot?
To the rear swing arm pivot?
Like the BMW rear suspension on there enduro bikes early 2000 s then on huskys after they brought them out CTS i think it was called pivot was also the front drive cog? 2013 te449f
Or am i way of

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Chambers   10 W

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 20 2020 6:14am

@Nobreaks

Not 100% familiar with the bikes you mentioned but yes - The swing-arm pivot is concentric with the motor shaft

This avoids the need for a tensioner and allows more room for the batteries

Sur-ron and various others run a concentric jack-shaft, Which does the same thing but is more complicated and takes up more room

Cheers

EDIT: You are correct I just googled the 2009 BMW G-450-X and it has a concentric pivot
Last edited by Chambers on Jan 20 2020 6:24am, edited 1 time in total.

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Chambers   10 W

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 20 2020 6:15am

I edited the original post to be clearer :thumb:

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 20 2020 8:56pm

Question -

What is your preference - linkage driven rear suspension or single pivot?

Do you think linkage is worth the extra time, cost and complexity to design and build?

I'm trying to solve as many problems as I can before I start the build as I'm sure plenty will come up during fabrication.

I'm leaning toward single pivot at the moment simply because it has less parts to worry about but I don't want to regret it later :confused:

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by jpacadd » Jan 20 2020 10:05pm

Cool to go down the creative road, keep it up, good start on the frame.

A few thoughts:

I looked twice maybe missed it somehow, are you figuring on belt drive? If chain you don't need a tensioner.

I was recently thinking about concentric. All even the best mainstream dirtbikes are not concentric drive/pivot, chains work great and concentric would add considerable expense, weight, and compromises I think. Maybe worth it, but I have to figure something so simple KTM/Beta/Japanese big 4 wouldn't all be not concentric.

I'll have to look more why surron does it.
July 2019 first build: 2009 Giant Trance X3 with stock BBSHD 52V
Next build: Just bought used 2009 Giant Trance X4, likely BBSHD also, maybe hotter controller/battery, undecided
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Chambers   10 W

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 20 2020 10:47pm

Yes chain drive with no tensioner - (except at the axle) just haven't bothered to model the chain yet.

In my opinion the big brands dont do concentric pivots with gas bikes because of the added complexity of doing so with a gas engine - This isn't the case with electric.

That's the beauty of clean sheet design.

The new Zero SRF also has a concentric motor.

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by efMX Trials Electric Freeride » Jan 21 2020 12:09am

concentric is done on electric for efficiency.. variable chain tension, chain guides, etc can steal power train efficiency .. (not an issue with petrol bikes).. however, for off-road.. drive sprocket forward location and suspension linkage can be used to increase traction under acceleration by pulling the rear wheel into the terrain..
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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 21 2020 12:12am

@emfx agreed.

Thanks for the input.

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by thoroughbred » Jan 21 2020 3:57pm

Is your choice of battery components forcing you to make it a cube?

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Chambers   10 W

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 21 2020 6:42pm

Hi thoroughbred,

My battery config is on REV F haha.

I guess I could make it any shape but this was the most space efficient.

Down the line a little further I have some ideas using this modular battery, so I wanted to keep the shape simple.

I am however working on rounding out the front bottom corner on the monocoque section - purely for aesthetic reasons.

Cheers

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 21 2020 10:38pm

Added a new pic showing the current revision with a 5-ft-7 person that I got from GrabCad (thanks) for reference.

Also shows the front suspension at full compression.

The bikes weight hasn't been taken into account in this image.

Cheers

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Hillhater » Jan 23 2020 9:02pm

efMX Trials Electric Freeride wrote:
Jan 21 2020 12:09am
..... drive sprocket forward location and suspension linkage can be used to increase traction under acceleration by pulling the rear wheel into the terrain..
Yes, its called “anti squat”.
If the drive pull on the chain is above the pivot center, it will tend to compress the suspension under power.
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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 24 2020 12:52am

Battery layout - 3 groups of 140 cells
3 x 140 group x.jpg
3 x 140 group x.jpg (120.82 KiB) Viewed 1699 times
Hoping to make the cell holders and spacers from cast thermally conductive epoxy - Some tests required!

The top right corner of each group will be removed in the final design for BMS space.

The edges of the spacers and cell holders make contact with the aluminium outer case for heat dissipation.

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 24 2020 1:12am

Geometry 17 inch TEST ASSY REV g.jpg
Geometry 17 inch TEST ASSY REV g.jpg (291.48 KiB) Viewed 1685 times
Quick and dirty 17 inch Supermoto render with a bit of a different swing-arm

Seat bracket still not pictured :lol:

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 25 2020 2:23am

Geometry 17 inch TEST ASSY REV h-4.jpg
Geometry 17 inch TEST ASSY REV h-4.jpg (194.25 KiB) Viewed 1630 times
working on a new embossed design in the battery box

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by John in CR » Jan 25 2020 4:16am

Regarding motor concentric to the pivot, even without considering losses it is not necessarily the same as a jackshaft at the pivot, because you have to option of anchoring the motor to the frame or to the swingarm. This can have significant differences on the suspension. Gassers can only dream of it just like they can only dream of 2wd.

With the motor anchored to the swingarm it will create some anti-squat force during acceleration and anti-dive force during regen braking. The extent to which these forces can be felt will depend on the weight of the rider and bike as well as the height of the swingarm pivot and length of the swingarm. eg Toolman2 referred to the effect as "suspension jacking" that took a bit of getting used to, but he and his bike were quite light.

If you anchor the motor to the frame, then the forces will act more directly on the suspension in ways that are negative in my opinion, and the magnitude of those forces will vary depending on the diameter of the drive sprocket with a concentric to the pivot mounting of the motor.

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Jan 25 2020 6:54am

@John in CR,

Thanks for the input.

I have read that thread you refer to several times where you and many others weigh in on the topic. (I believe this was it?)viewtopic.php?f=28&t=88909

It's because of that thread that I have left myself some room to adjust the motor slightly relative to the pivot point. This is also a good case for using a linkage type suspension to dial in the desired characteristics as mentioned earlier.

Cheers

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Feb 02 2020 6:08am

mid test assy 9-3.jpg
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mid test assy 10.jpg
mid test assy 10.jpg (311.92 KiB) Viewed 1307 times
Bit of an update -

I have been working on more of a 'bicycle' version as above.

This uses an LMX/Big Block style motor with a few mods (details to come later) and has 2 of the 140 cell modules instead of 3 - so 20s14p.

Still with the nuc' 24f.

Also thinking about 'internal' gearing as I want to run a single chain to the rear wheel, This could also eliminate the front bicycle sprocket giving better obstacle avoidance.
This will work by running reduction gears to an IGH mounted under the frame then to a freewheel sprocket on the motor shaft (let me know if that doesn't make sense) :lol: . the trick here will be to get the ratio right so that pedal input is of some use!

The monocoque section has been modified to give a better approach angle, strength and aesthetics.

Cheers

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by John in CR » Feb 02 2020 7:32am

If only the pedal power is going to the IGH, then sure why not. If you run motor power through the IGH then it's sure to be a point of failure and frequent maintenance unless you're talking about sub 1kw power.

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Chambers   10 W

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Feb 02 2020 7:48am

Just the pedal power, the motor is direct to the wheel

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by devo1223 » Feb 05 2020 12:16pm

I'll take one with pedals, but with the QS3000, I could care less about q-factor. Sorry but the square battery is ugly, make it a rectangle/triangle up into the frame even if you lose a few cells. Love the single chain idea, keep up the good work! I'll be following this closely
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Chambers   10 W

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Feb 05 2020 8:50pm

Thanks Devo,

Both versions will have a pedal option - though it will be pretty difficult to pedal the big bike being 215 wide! But with QS3000 you're not going to be pedaling much :lol:

I have toyed with various battery shapes - watch this space

Cheers

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Ohbse » Feb 05 2020 10:27pm

I quite like your supermoto inspired mockup. In some regards I really like the square, but I'm wondering if making it somewhat more fitting of the available space would be an improvement. Conceptually the bolting of variable subframes to the universal monocoque containing the battery, controller and motor is very cool.

Look at your torsional stiffness. Twisting force on the swing arm and the portion that mounts the motor and swing arm is non-trivial and can result in a very poor feel. A simple rectangular section for the swing arm really won't cut it - you'll need to make this a larger triangle, or use very, very strong box section. Simple force analysis in CAD will reveal what a dramatic improvement you can make here.

Similarly the opening for the square battery will really suck structurally. There's a reason the LMX have a bolt on brace to cover the battery! Something similar here would largely solve the issue. Perhaps have an overlapping flange on the battery enclosure itself which is bolted to the frame? *shrug*

Look at having a linkage based rear suspension. This is actually very important for riding dynamics IMO. I've tried a few frames that don't and frankly they blow compared with proper linkage designs. I've got a kinematic model of the surron rear suspension with force/travel graphs and it's clear why it's nicer to ride. It's very tricky to get a single pivot rear suspension to function without a wheel rate that decreases with travel, resulting in having to use very stiff static spring rates or tricky progressively wound springs to ensure it doesn't bottom out. That compromises comfort the 99.9% of the time you're NOT hitting huge jumps or curbs.

Don't use chains. They're loud and shitty. They require maintenance, they spray lube everywhere and wear out. Belt tech is more efficient, long lasting, well proven and relatively readily available now. Concentric pivot is awesome, allows for variable regen to provide the majority of your braking effort. I barely use the physical brakes on my Nucular equipped Surron now.

Keep it up man! I will totally buy a frame

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Chambers   10 W

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Re: Hummingbird 20kw-ish Mid-Drive Concept Bike

Post by Chambers » Feb 06 2020 12:20am

Thanks Ohbse,

I appreciate your input! A few thoughts below.
Look at your torsional stiffness. Twisting force on the swing arm and the portion that mounts the motor and swing arm is non-trivial and can result in a very poor feel. A simple rectangular section for the swing arm really won't cut it - you'll need to make this a larger triangle, or use very, very strong box section. Simple force analysis in CAD will reveal what a dramatic improvement you can make here.
- Agreed - This will most likely be a tubular structure as shown in some of the mock-ups
Similarly the opening for the square battery will really suck structurally. There's a reason the LMX have a bolt on brace to cover the battery! Something similar here would largely solve the issue. Perhaps have an overlapping flange on the battery enclosure itself which is bolted to the frame? *shrug*
I'm trying to design a 'door' for this purpose - I want it to be relatively easy to access so at this stage bolting is a no go.
Look at having a linkage based rear suspension.
agreed with all notes on this one - This is the area I have the most work to do.
Don't use chains. They're loud and shitty. They require maintenance, they spray lube everywhere and wear out. Belt tech is more efficient, long lasting, well proven and relatively readily available now. Concentric pivot is awesome, allows for variable regen to provide the majority of your braking effort. I barely use the physical brakes on my Nucular equipped Surron now.
Keeping my options open here in that both have their use cases
Keep it up man! I will totally buy a frame
Thanks!

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