Flux mid-drive

Alrighty, so the flux's bread and butter is going to be hub motors but I'd love to build a sweet mid drive
So, non-hub aficionados, sway me to the dark side

My requirements are:

A: Neat. I want as much of it contained inside the frame if possible. Maybe the motor half or 3/4 hanging out the bottom ? Ideally don't want to see any of the reduction gear externally. This is a steel frame so can easily be cut and welded to. Something like Thud's sweet 2 speed drive could be excellent. Thoughts Thud ?

B: As quiet as possible. You can't argue with the power:weight benefits of RC screamers but I've grown rather attached to the complete silence you get from a hub and sinewave controller. Big block style motor ? Transmag ? Something else ?

C: Equal or better performance to a cro motor or similar running 10kw bursts. Or if the size and weight can be kept to a minimum maybe I'd be happy with around 5kw (I think that would be the minimum). This rules out running through the bikes gears. A bigger/more powerful motor direct driving straight to a large rear sprocket would probably be ideal from a simplicity point of view but I'm open to suggestions on some sort of combo that will yield quiet results (internal chain reduction, external belts, etc)

Here's what we've got to work with:
The frame is 120mm wide at the side covers, other rough dimensions as below. Obviously I'd have to eat into the battery space but that's OK. A larger motor half protruding with no reduction shenanigans inside the frame would be preferable though to maximise battery space.








Maybe something like this as a finished look ?

Yoho J,
I was looking at this when the pm came in lol. I'll throw some quick thoughts on the bike & what i could do for it...
If your looking for off road perfeormance, the current 2 speed would be useless imho. (Not nearly enough reduction)

The reduction unit designed for Gregs DH is unproven...& ultimatly limited in power input because the high reduction gets the final stage chain to its stress limits...needs to be feild tested for durability & aplicability....ideally it was to drive the BB & run thru the bikes drive lines....the only realistic way to handle chain growth asscociated with long travel suspension again imho. I plan to put it on my full sus 29r & see if it works at all. Someday, Day job is taking all my time....

That said, i can't see what the chain line on that frame looks like. & since the bb is on the swing arm, it limits the bb drive option dramaticly. I have one of Justins phase runner controllers here looking to build a silent rc system.

I could tell you how easy it would be to hang a motor under the the bike & rig up some chain rollers...but that would kinda suck.
I have taken a vow to elliminate giant reduction pulleys hanging out in in the wind, & time bomb motor set ups.

Any way to summerize, not much but I do look foward to seeing what you decide on & implement.

Hey Thud,
Sounds like I needn't have bothered paging you!

Thanks for the input.
I'm looking forward to seeing what you can do with the phase runner, perhaps I should wait and see what you come up with, then shameless copy it I see we're on the same page about banishing the giant reduction pulleys.


Sounds like this requires more thought...

I think any design that uses a jackshaft through the swing arm pivot is the way to go. Trying to deal with chain growth through the travel is a huge design challenge. With a fixed rear sprocket and heavy duty chain it seems like a good chain tangle at speed could rip the bike apart or catch a body part.

I started my downhill bike project with the same basic goals in mind and 2 years later i still have a transmag motor on the shelf and a mile of 219 chain. I've mocked up more idler and tensioner locations than I care to admit. It just gets too complex with lots of parts to make and tons of points of failure. So I'm with Thud in the "rollers would suck" camp.

What about mounting a med sized motor (transmag, bigblock etc.) to the swingarm just in front of the tire? Or use the walls of a fabricated hollow swingarm as the side plates of Thuds 2 stage reduction! That would be light, powerful, compact, and have no chain growth during suspension travel. Keeps your drive hidden in the arm and all your battery space in the frame.

Or perhaps put the motor in the frame and belt drive to a planetary gearbox mouted on the swingarm. Im picturing the gearbox right in front of the bottom bracket again eliminating the chain growth in the final drive.

Good luck. I also look forward to seeing how this works out.

Spring loaded chain tensioners work great if made well. This eliminates chain growth.

Mounting a hub in the frame like this is a great option IMO. Hyena is wonderfully familiar with hub systems and this setup allows for a higher RPM from the motor, thus granting more power per pound, and moves the weight to a MUCH better chassis location for phenominal handling. I say "Well Done!"

Not sure why the general disdain for large reduction pulleys all of a sudden. I am moving in the oposite direction. Large pulleys provide deeper reduction in one stage, thus maximizing motor RPM and efficiency at the same time. I actually like the way they look.....

Oh, well, to each his own......

Matt

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Tench's beautiful build directly comes to mind. I bet you have seen it.
Drives through the chainline, but the layout is similar to your idea.

https://endless-sphere.com/forums/viewtopic.php?t=37489

Fully agree with near to silent solution. I'm not an engineer nor anything around it so can't contribute much. But I did use Bafang Mid Drive offroad - it worked very well and it was very quiet. The fact that everything is inside and there is no secondary chains, sprockets ect ect makes it so neat and clean. A bit underpowered yes.
But could a bigger version of something like Bafang with Adaptto Mini could be a solution? Or is 750W the limit this type of solution can take?

Still wondering if we can't get a LR kit onto the swinger somehow...

How about one of the Revolt RV160 narrow, with a low KV and a single chain to the rear wheel. You won't get max power out of it, but still get a lot of power in a light setup.

Any More Developments on a this middrive frame ?
I'm definitely interested in using a RV-160Pro Short, 10 --> 15kw continuos at 5KG

I've shelved the alpha idea for the moment and am going to try on the beta instead. With the concentric BB it should be easier to pull off. The frames aren't ready yet but when I have one to play with I'll post some updates

I think you should make a design similar to pic below. Could work with the beta to be something similar?

That's essentially the same as a flux beta, but purpose built for a mid drive

Is it just an optical illusion or is that bottom bracket really far behind the middle of the seat? What frame is that? Custom?

Thanks Hyena

That Frame is an LMX-81 by LMXbikes (https://www.facebook.com/LMXbikes) and Biktrix (http://www.biktrix.com/).
It is still in its infancy (i.e prototype phase)... https://www.youtube.com/watch?v=A80rL95_Npc
I really do like the look of the 81 !!!

Hmm would also be keen on using a "Big Block" too if a RV-160 is too cost prohibitive..

Hyena said:

I've shelved the alpha idea for the moment and am going to try on the beta instead. With the concentric BB it should be easier to pull off. The frames aren't ready yet but when I have one to play with I'll post some updates

Click to expand...

that could be a benefit, but im afraid we will loose the ability to pedal. or do you know of a crankset that can be used or modified for that?
i wonder how many freewheels in total it must have than..

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Have you bought the Flux frame already, or is the frame choice still an option?

spinningmagnets said:

Have you bought the Flux frame already, or is the frame choice still an option?

Click to expand...

He sells the frames so if one is purchased he can just add it to inventory I presume.

Jay, if this is not the case and you won't have one to tinker with, feel free to use my Flux Beta as a test mule (I still want my Alpha as soon as it is ready though!). I don't NEED the beta as soon so you can take the time to sort out a mid-drive for it. I am building up the Beta for my wife so I can explain that the delay is for "improvements." I don't think she is fooled by the "this is for you" talk though.

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This I need to follow!.

Any updates on how this frame project is going ?
I'm getting super keen