2wd mini bike builds?

General Discussion about large electric scooters and motorcycles and other things with no pedals.
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bigoilbob
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2wd mini bike builds?

Post by bigoilbob » Jun 14, 2017 9:18 am

As a Surplus Center degenerate browser I have been spending time looking at their selection of tiny hydraulic motors/pumps. I have a 750 watt, homebuilt e mini bike with a deep reduction Nuvinci 171 Developer's Kit (i.e. auto trans) and I day dream about making it a 2wd ride. I know that there are tech issues, but I can calc torques/pressures, chain pulls/chain speeds etc. ok, and think I could figure out a theoretical design that could work. But I don't wanna grow the bike just to make it 2wd. Has anyone else either thought or acted on a similar project?
Last edited by bigoilbob on Jun 15, 2017 6:12 pm, edited 1 time in total.

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amberwolf
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Re: 2wd mini bike builds?

Post by amberwolf » Jun 14, 2017 2:39 pm

There has been previous discussion about making bikes with hydraulic motors rather than using a transmission on an electric motor, though I don't know if any of it is useful to you.

Unfortunately the search engine is limited in it's refinement ability, so the only "easy" search that finds a few posts is this
https://endless-sphere.com/forums/searc ... mit=Search
which has some irrelevant and some relevant stuff.



For myself, both my 2WD (one bike and one trike) simply use two hubmotors ATM.

bigoilbob
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Re: 2wd mini bike builds?

Post by bigoilbob » Jun 14, 2017 6:58 pm

Thanks amberwolf. As you said, related posts, but I can't find anyone who has tried what I might. I found a pump/motor combo that has the right rates/radial velocities and pressures, and can handle 150-200# of chain pull, and is "light enough", and only costs an arm without a leg. I also have the mounting points, and my front steering bracket is strong enough to not pull apart while pulling me and the rest of the mini bike out of a stream. Finally, with the Nuvinci 171 keeping me in my motor efficiency "sweet spot" my losses should drop from dreadful to plain old high. I don't need 30 miles of range (10 would be nice), so I might just give her a try.

Thx again, aw....

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neptronix
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Re: 2wd mini bike builds?

Post by neptronix » Jun 14, 2017 7:14 pm

Two geared motors would do swell and be pretty cheap and will be powerful with such small wheels, given the right voltage.

no need for transmissions or reductions.. 5:1 planetary gears and a clutch are inside already.. power to weight ratio is already really good.
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

bigoilbob
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Re: 2wd mini bike builds?

Post by bigoilbob » Jun 14, 2017 8:40 pm

neptronix wrote:Two geared motors would do swell and be pretty cheap and will be powerful with such small wheels, given the right voltage.

no need for transmissions or reductions.. 5:1 planetary gears and a clutch are inside already.. power to weight ratio is already really good.
Respectfully disagree on the need for multiple gear ratios. BLDC motors do have good torque characteristics, but (1) they can be inefficient outside their optimum r/m ranges, and (2) the power/weight ratios of most e mini bikes (including mine) would yield bad off road performance without them. FYI, my drive train has no clutch.

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neptronix
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Re: 2wd mini bike builds?

Post by neptronix » Jun 14, 2017 9:57 pm

Some BLDC motors have very broad torque and efficiency bands. Proper controller tuning can make things better. The thinner the laminations, the more you run them at an ideal load, the better, as well.

A transmission continuously gives you an efficiency hit. If you are climbing ridiculously steep things though, they start to make sense. The kind of terrain you need to conquer will determine whether a fixed gear setup that is slightly oversized to the point where it maintains thermal stasis, or transmission.

That being said, what kind of offroading are you dealing with?
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

bigoilbob
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Re: 2wd mini bike builds?

Post by bigoilbob » Jun 15, 2017 9:54 am

neptronix wrote:Some BLDC motors have very broad torque and efficiency bands. Proper controller tuning can make things better. The thinner the laminations, the more you run them at an ideal load, the better, as well.

A transmission continuously gives you an efficiency hit. If you are climbing ridiculously steep things though, they start to make sense. The kind of terrain you need to conquer will determine whether a fixed gear setup that is slightly oversized to the point where it maintains thermal stasis, or transmission.

That being said, what kind of offroading are you dealing with?
Grades that are marginal for my traction. My build has only 750 watts, and I therefore need the reduction. And I won't be messing with motor construction or hot rodding my controller. I already had the Nuvnci 171 ~3.5/1 reduction trans, and wanted to exploit it, Agree on combined efficiency hits. ~15% trans hit. ~25% motor hit (would be twice as bad without transmission), and assorted jackshaft and chain losses. Now, I want to add a hydraulic motor/pump with weight and more drag! I agree that it sounds silly but my only defense is that I have ridden my current config enough to know how muly it is, and I think the drive train can handle 2wd.

Thx for taking the time to discuss, neptronix,,

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Re: 2wd mini bike builds?

Post by bigoilbob » Jun 29, 2017 7:18 pm

Here is the thread I started for my mini bike, as currently built. This is the machine I'm pondering converting to 2wd...

https://endless-sphere.com/forums/viewt ... 12&t=89188

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