Setting up dual drivetrain ebike

General Discussion about electric bicycles.
Chromotoast   1 mW

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Re: Setting up dual drivetrain ebike

Post by Chromotoast » May 14 2020 9:26pm

MadRhino wrote:
May 14 2020 11:08am
Gearing must be according to motor RPM. Electric motors can be very fast. Bigger, slower motors don’t require much reduction. They are more silent too.
So all the motors I’m finding require insanely large gear reductions when I plug their Kv values into calculators. I’m looking at this https://hobbyking.com/en_us/turnigy-aer ... motor.html motor specifically. Theoretical speeds of 100+ mph meaning I’d either have to use a 8:1 gear ratio (a sprocket that large would weigh like 30+ pounds) to have good torque. Would a less powerful motor, like a 1000w be better and give me more torque with a gear reduction in the ~2.35ish range if I only care about hitting a max mph of like 25ish?

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Re: Setting up dual drivetrain ebike

Post by Chromotoast » May 14 2020 9:27pm

Electric Earth wrote:
May 14 2020 6:06pm
Chromotoast wrote:
May 14 2020 1:08am
Did some more research and found this video of a guy who built a mid drive. He just takes off the fixed gear, leaves the freewheel on the other side attached to the pedals, and attaches a belt and pulley system to the other side to be powered by the motor. The motor doesn't spin the pedals even though there's no free wheel on the motor shaft or the pulley that he put on. So maybe I don't in fact need a freewheel on the motor chain drive part and can just keep it on the pedal drive?
Ah. I thought you were trying to give it a freewheel to avoid motor drag anytime you're peddling the bike normally. My misunderstanding. If you don't mind the drag then you have no problems. Just throw on a motor and go.

Yours will be easier since you have the fixed gear hub and can just utilize that gear rather than his belt system. That should be a fun project.
Haha I’m definitely more of a chain guy, I just think they sound cooler and I’m far more comfortable with them over belts and pulleys.

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Re: Setting up dual drivetrain ebike

Post by amberwolf » May 14 2020 9:37pm

Chromotoast wrote:
May 14 2020 9:26pm
So all the motors I’m finding require insanely large gear reductions when I plug their Kv values into calculators.
If you look at the various RC motor builds, you'll see many of them use double-reductions, like the recumpence drive, etc., for that reason.


You can instead use a hubmotor in the frame, and have essentially no reduction, if you like (because the hubmotor is already meant for the right speed range). There's a thread called something vaguely like "hubmotor in frame media group" (by spinningmagnets?) with links to examples.

Brushed powerchair motors with rightangle gearboxes, various MY-xxxx in-frame motors brushed and brushless, all sorts of motor options that won't require much in the way of reductions.

But those are all heavy, because power handling of a motor is a function of rpm and size. The slower the motor goes, the bigger it has to be to handle the same power as a much faster motor would.


People generally go with a lightweight small fast motor and huge reduction for a specific reason, which varies with the build, but if you don't have a specific reason to do that, you may want to consider larger motors that don't require such reductions.

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Re: Setting up dual drivetrain ebike

Post by Chromotoast » May 14 2020 9:58pm

amberwolf wrote:
May 14 2020 9:37pm
Chromotoast wrote:
May 14 2020 9:26pm
So all the motors I’m finding require insanely large gear reductions when I plug their Kv values into calculators.
If you look at the various RC motor builds, you'll see many of them use double-reductions, like the recumpence drive, etc., for that reason.


You can instead use a hubmotor in the frame, and have essentially no reduction, if you like (because the hubmotor is already meant for the right speed range). There's a thread called something vaguely like "hubmotor in frame media group" (by spinningmagnets?) with links to examples.

Brushed powerchair motors with rightangle gearboxes, various MY-xxxx in-frame motors brushed and brushless, all sorts of motor options that won't require much in the way of reductions.

But those are all heavy, because power handling of a motor is a function of rpm and size. The slower the motor goes, the bigger it has to be to handle the same power as a much faster motor would.


People generally go with a lightweight small fast motor and huge reduction for a specific reason, which varies with the build, but if you don't have a specific reason to do that, you may want to consider larger motors that don't require such reductions.
At this point I’m committed to the mid drive just out of pure stubbornness to make it work lmao. I’m gonna look into either a two stage reduction or see if I can fab a custom sprocket that isn’t comically heavy.

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MadRhino   100 GW

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Re: Setting up dual drivetrain ebike

Post by MadRhino » May 14 2020 10:42pm

Those Turnigy motors, and similar RC motors, are fast because they are made to spin a propeller. They have no bearings designed for lateral force.

There are many slower motors that will stand lateral force, and won’t require much reduction.
Make it fool-proof, and I will make a better fool.
Current bikes
Street:
Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

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Re: Setting up dual drivetrain ebike

Post by amberwolf » May 14 2020 11:02pm

Chromotoast wrote:
May 14 2020 9:58pm
At this point I’m committed to the mid drive just out of pure stubbornness to make it work lmao.
Everything I described above *is* a middrive, and can drive the left side of the rear wheel (though many of hte versions created here on ES drive the pedal drivetrain, some of them do the left side to give you direct examples).

So you can build it any of the many ways that have already been done, or even mix them up and come up with your own. ;)

But you really will want to read all the existing projects / threads about whatever drive you consider, because you'll find out the things *not* to do.

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Re: Setting up dual drivetrain ebike

Post by Electric Earth » May 15 2020 6:17am

Mid Drive Hub Motor Media Group
viewtopic.php?f=6&t=38553&hilit=media

With modern bafang style mid-drives available, is there any benefit to using a hub motor as a mid-drive rather than one of those?

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Re: Setting up dual drivetrain ebike

Post by john61ct » May 15 2020 7:42am

I think "mid drive" is an overly broad term, basically means "not a hub drive" right?

Those that are universal / easy to mount via the BB seem to be pretty darn limited in power and subject to quickly overheating in a low-rpm high-torque context

And do they all work through the pedal drive train?

The other type I've been considering is the Lightning Rod Big Block line, which requires specially engineered mounting brackets designed for specific frames,

and I believe always bypass the pedal drivetrain.

Then I've seen friction drivetrains, those driving a ring threaded through spokes, and I'm sure many other non-mainstream options

before getting into the wild west world of true DIYers with access to machine shops.

Is there a reference resource that gives a sensible taxonomy , classification vocabulary so these various options can be referred to without having a clarifying discussiin every time?


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Re: Setting up dual drivetrain ebike

Post by Chromotoast » May 15 2020 11:08am

So I found this https://michobby.com/products/maytech-5 ... 3402345536.
It has a 70kv offering which seems low enough to have a single stage reduction, either that or try to design a two stage reduction.

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Re: Setting up dual drivetrain ebike

Post by Chromotoast » May 17 2020 10:55pm

Found this design after deciding on doing a belt drive for the first stage and a sprocket and chain for the final drive. viewtopic.php?t=62190

Just wondering what the best way to connect the pulley to the sprocket would be. Would running a jack shaft in between them work?

https://youtu.be/JMgVEpT4aTU

This also seems to use a jackshaft to transfer power from the primary to final reduction stage. Might switch to all chain and sprocket instead of belt and pulley + chain and sprocket, as it seems to be easier to find parts that are compatible.

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