Using a hub motor as a mid drive?

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BCBeaver   1 mW

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Using a hub motor as a mid drive?

Post by BCBeaver » Jun 13 2018 3:35pm

I'm in the conceptual design phase of building a recumbent bike. Typically these thing have chain lines that are 5-6' long so usually need an idler pulley. So I got thinking, why not 2 chains? Why not make the idler a hub motor? Why not make it a 2 speed hub motor? Why not put a mid derailleur on the bike? This thing could have a front, mid, rear derailleur with a 2 speed in the middle, it could have more gears than a highway tractor. 3 in front x 10 in the middle x 2 x 10 in the rear = 600speed. My next thought was, "Just because you can doesn't mean you should." I figure if I have a rear derailleur I can gear it to be fast on the flats/downhill and be able to climb like a goat. If I use 3 chain rings up front I'll be able to actually add some useful power to the system.

I've a got a Xiongda 2 speed motor so that is likely what I'll be using, it's only rated at 450 watts (but will pull 700 easily) so it would get good range. For the hub motor idler system I think I could mount a chainring to the hub with 18 little screws through the spoke holes and use that to turn the rear chain and power the driver gear from the front as a normal hub would be. I'll need to mount the hub using the axle though a saddle mounted to the frame probably under the seat.

Any suggestions, knowledge to impart or experience to share would be appreciated.
Last edited by BCBeaver on Jun 13 2018 9:30pm, edited 1 time in total.

dustNbone   10 kW

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Re: Using a hub motor as a mid drive?

Post by dustNbone » Jun 13 2018 4:00pm

You should be able to mount a chain ring to the disc brake mount on the hub motor shell. Might be easier than getting it attached to the spoke holes.

BCBeaver   1 mW

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Re: Using a hub motor as a mid drive?

Post by BCBeaver » Jun 13 2018 5:27pm

I thought about that but then it's on the wrong side, if I want any gearing on the rear hub that option is out. That, and the motor I have doesn't have a disc mount.

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amberwolf   100 GW

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Re: Using a hub motor as a mid drive?

Post by amberwolf » Jun 14 2018 1:53am

There's some threads about hubmotors as midrives that may give you some ideas.

This thread probably has the most in one place
viewtopic.php?f=6&t=38553

This list has some relevant ones (many are not, but you can tell by title generally):
search.php?keywords=hub*+mid*+drive*&te ... mit=Search

There's probably other stuff not found in that list (I know there is another recent thread about this I don't see there).

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teklektik   10 GW

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Re: Using a hub motor as a mid drive?

Post by teklektik » Jun 14 2018 4:43pm

From A 'Sun Trip 2018' trike:
midMotor.jpg
midMotor.jpg (242.65 KiB) Viewed 524 times
32560891_738901706233551_6193132434679136256_o_1024.jpg
32560891_738901706233551_6193132434679136256_o_1024.jpg (245.11 KiB) Viewed 459 times
Last edited by teklektik on Jun 15 2018 1:35pm, edited 1 time in total.
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Hillhater   100 GW

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Re: Using a hub motor as a mid drive?

Post by Hillhater » Jun 14 2018 8:49pm

BCBeaver wrote:
Jun 13 2018 3:35pm
......This thing could have a front, mid, rear derailleur with a 2 speed in the middle, it could have more gears than a highway tractor. 3 in front x 10 in the middle x 2 x 10 in the rear = 600speed. My next thought was, "Just because you can doesn't mean you should." ?....

Any suggestions, knowledge to impart or experience to share would be appreciated.
As im sure you realise, many of those ratios would be duplicated..even triplicated.. so really you are just adding complexity, weight and maintenance issues.
Even a "simple" 21/27 speed bike gearset has many intermediate gear combinations that are effectively redundant .
And once you add power assist, the need for multiple ratios reduces dramatically.
Consider that most modern electric drive vehicles only have one ratio !
So figure what max and min ratios you need, add how many more you feel useful inbetween , and keep it as simple as possible.
This forum owes its existence to Justin of ebikes.ca

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dogman dan   100 GW

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Re: Using a hub motor as a mid drive?

Post by dogman dan » Jun 15 2018 8:40am

Now that a pretty reliable mid drive kit is available, I see less reason to make your own mid drive from hub motors.

Unless, you want to run 2000w through it. 8) Hard on the chain though, so that idea would work best as a left side drive, geared for your particular needs.

The other reason to diy would be for the pure fun of the fabrication work.

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Re: Using a hub motor as a mid drive?

Post by Triketech » Jun 17 2018 10:56am

That's something I've been entertaining a while myself for a stealth e-trike. With an array of torque sensing BB's, motors & FOC drivers out there it makes sense to try on a recumbent.

Trikes offer some unique challenges to optimize configuration. Keeping the added drive/battery mass low with proper balance front-rear while hiding a silent drive & battery takes a different approach than the typical tube frame. Some collapse-ability makes it easier to transport, so I've been looking at a final belt drive to the rear wheel which allows easy removal along with a folding trailing arm, and a fold-back boom.

I use SolidWorks for the design tool. Despite being semi-retired, I've been taking on consulting design work and have about 6 months left on a project so its not going to happen this year. At least I can watch the work of others. In the mean time I'll keep riding the beast.

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markz   100 GW

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Re: Using a hub motor as a mid drive?

Post by markz » Jun 17 2018 1:57pm

The only reason to do a hub motor mid drive would be to use a direct drive to reduce the noise produced by the gears inside the motor, my Cyclone 4000W was noisy and it climbed everything. I am back to riding a direct drive rear wheel. I only was riding the C4KW for 6 months or so. I still have it, but it needs the female BB threaded piece that goes into the bb.

BCBeaver   1 mW

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Re: Using a hub motor as a mid drive?

Post by BCBeaver » Jun 18 2018 1:47am

I realize a 600 speed would quadruplicate many ratios. I'll probably go 3 at the cranks, 2 speed hub motor in the middle ( because I have one waiting to be used) and 8 on the rear (because I have a nice sram xo 8 sp shifter). Im going to fabricate the entire bike so im doing mostly fo fun.

I electrified a giant stiletto with custom built mid mount. I electrified a giant simple 3 with a Bafang bbshd. I prefer the custom fab jobs to off the shelf and bolt it on kits like the Bafang.

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dogman dan   100 GW

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Re: Using a hub motor as a mid drive?

Post by dogman dan » Jun 18 2018 7:18am

There you go, for the fun of it. 8)

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