mid drive hub motor advantages?

[cajunjay]

I have at my disposal 3 different ebike kits one is a 36v 250w hub motor a 36v 500w hub motor and a cyclone knock off kit rated 48v 450w.

The 36v 250w motor is okay as I run it at 48v but is really just for commuting as it hasnt got much power at all, need to pedal on start up to get the bike moving as to not bog down the motor to much, hill climbing is non existent without pedaling obviously.

Now the 36v 500w kit run at 48v isnt really that bad, along with pedaling it can get upto speed pretty quick and i like this setup the most, the cyclone knockoff is the best performance wise but is a bit noisy for my liking as I prefer something more stealthy.

I have seen a decent thread where a guy made a mid drive hub motor running through some freewheeling cranks just wondering if anybody knows the advantages of running a hub motor this way instead of in a wheel? seems very stealthy and might have alot more torque aswell as being able to run through the gears.

This is the thread I saw and it does look pretty easy (for some) to implement a build like this.


viewtopic.php?f=28&t=17070&start=15

[dogman]

Through the gears doesn't get you more power, but it can get you up steeper hills on the power you have. Gearing down means slowing down of course, but it's the way to climb steeper hills.

The question is, do you need it? Most direct drive hubmotors on 48v are quite capable of climbing 7% grades for long distances, or even 10% with lots of pedaling help.

So what are your needs? Towing 3 kids at a time to the top of hills to skate down? then you need the gears.

[DrkAngel]

Proper link to "referenced" post. - Hub motor BB drive
Note: Build required wider BB, for proper clearance of hub motor.

Running through the bottom bracket, could effectively produce a multi-gear ebike.
With a 7 speed 11-34T rear sprocket, a 3:1 torque ratio is available at the "bottom end".
At the "top end" "gearing" could apply additional speed for downhill, tailwind, drafting, crouched etc.

I would highly recommend a chain guard, for any type of mid-drive!
Getting a pant leg caught in the motor chain could be extremely painful-dangerous!

[pdf]

I have one bike that drives through the BB and one hub motor. The hub motor is a 9C 2810. If all you need is a bike to carry yourself and you are similar in weight to me (around 165 lbs), then this set up will sprint up a steep short hill or do around 20 or a little better up a shallow (7-10%) hill for a long time. This is running on an 18FET controller at 72V LiPO. If you want to carry a lot of weight up steep hills, you need to go through the cranks. However, I have been amazed at how well the 2810 does on 72V LiPO. And it was cheap. Top speed of the 2810 is around 28 mph for me.

My crank-driven bike is a StokeMonkey on an Xtracycle conversion. It runs on 36V and can pull a very impressive load up a steep hill (15-20%) with surprisingly little power, but of course, it doesn't do it in a hurry. If you want to run a lot of power through a bottom bracket drive, you will need to be careful of the components and how you shift. With a chain-driven setup, you can put a lot of torque through the system and you can't shift under power with a deraileur setup, same as with pedaling. I have gone through one BB bearing, one chain, and one rear sprocket in around 4000 miles with this bike. The ability to send more torque through the parts was partially the reason, although the components weren't top of the line either.

I'd say that unless you want to pull a big load up a big hill, the appropriate hub motor on 72v LiPO and a decent controller will surprise you. I have a 20% grade that I have to go up every day and when I ride the hub motor, bike, it flies up it. The BB drive bike goes up on much less power, but at about 1/4 the speed. This has nothing to do with the BB drive, but the fact that this bike has low C 36v LiFePO4.

[MadRhino]

A mid drive that is built to use the bicycle gears is a fail waiting to happen. I wouldn't like having to shift through the derailer range either, that is too many gears for the need of a powered bike and too weak for any interesting power to last. The best way to build a mid drive IMO, is to drive the disc side independently from the bicycle drive train. This would need two speed at the most, only one with enough power, and can be made with components that are reliable for the kind of torque that a motor can produce.

The advantages to build a mid drive using a hub motor are obvious, but the design and fabrication required to make it a good ride is such, that one has to really need it to make it worth the trouble and investment.

[John in CR]

A mid drive that is built to use the bicycle gears is a fail waiting to happen. I wouldn't like having to shift through the derailer range either, that is too many gears for the need of a powered bike and too weak for any interesting power to last. The best way to build a mid drive IMO, is to drive the disc side independently from the bicycle drive train. This would need two speed at the most, only one with enough power, and can be made with components that are reliable for the kind of torque that a motor can produce.

The advantages to build a mid drive using a hub motor are obvious, but the design and fabrication required to make it a good ride is such, that one has to really need it to make it worth the trouble and investment.

I don't need it and I'm still building one. 2 reasons:
1. To gear the hubby down slightly for more acceleration
2. To retain all the benefits of a hubbie (silence, durability, etc) while reducing the unsprung weight in that wheel by 70% or so.

[DrkAngel]

Mid-Drive, through the bicycle gears (sprockets)...

A mid drive that is built to use the bicycle gears is a fail waiting to happen.

A typical healthy male is, briefly, capable of outputting 900w+ of power into the bicycle gears. (NASA 1964)
(Probably alternating between 1700w and 100w surges, per pedal stroke?)
A much smoother, continuous, 500w motor input should hold up nicely, ... tho I would recommend reducing throttle during shifts.

If the motor is placed in front of the Bottom Bracket, then there would actually be less stress on the BB!
The torque to the rear wheel would be equally offset by the torque from the front motor, (with equally sized chainrings).

Rear hub bearings will suffer more stress.
Though, compared to the weight of the bike, rider , batteries etc. I would think this to be a minimal factor!

So the "fail waiting to happen" would be the chain, or rear cluster. Both easily replaceable, and cheap ...

I wouldn't like having to shift through the derailer range either, that is too many gears for the need of a powered bike and too weak for any interesting power to last.

You don't have to shift through anything ...
You could pick whatever ratio suits your present needs, and keep it there ...


Even though the "legal" eBike speed is, (USA), a Federally recommended 20mph ... 30mph seems more ... eBikey ...
Personally, I would recommend a, wide spaced, 7 speed 11-34T rear cluster.
Effectively producing a 3:1 torque increase at the bottom end.

30 mph capable eBikes.
(Up to 10 mph) - With a common 500w, (output), motor, that would give you the torque of a 1500w, (output), motor!
Errr ... except at about 30%, of no load speed, the 1500w motor might be, barely, 30% efficient, meaning that the 1500w output motor might require 5000w input to produce the same torque as the 500w, using 600-650w input.
With judicious shifting, this efficiency advantage continues, but at a reducing rate, as speed increases, equalizing somewhere in the mid 20's mph.

So ...
Looks like a nice little toy-project to me!

I planned on doing similar, but using an eZip gear reduction brush motor.
Noisier! ... but cheap and simple!

Note: 30mph from a 500w motor?
Estimated power requirements for propelling a Mountain style bike, with upright seated rider is near 700-750w.
Lowered seat with crouching rider lowers this estimate into the 500w range.

See -Aerodynamic Factors

Wind resistance is the major factor, above 20 mph!
Funny enough ... even the addition of a rounded front basket, makes for a noticeable speed increase!
... I don't believe pink tassels on the handle bar ends help! ... err ... actually, they might.

[MadRhino]

@DrkAngel

All those numbers are fine, but most lack a 0 at the end to make any Ebike interesting to me.
When you start feeding 10 times human power, which I consider only the beginning of interesting performance, a bicycle drive train is not very long to show its limits.

[DrkAngel]

Mid-Drive, through the bicycle gears (sprockets)...

A much smoother, continuous, 500w motor input should hold up nicely, ... tho I would recommend reducing throttle during shifts.

Further thought on the "impact" during "shifts".
This damaging jolt could be effectively eliminated-buffered by the placement of a properly "heavily-sprung" idler sprocket on the tensioned side of the, motor to chainring, chain. (Heavy tensioned sprocket = H)
Of course, there would also have to be a lightly tensioned idler sprocket on the opposing, unloaded chain segment. (Lightly tensioned sprocket = L)
At full throttle, the H sprocket should be at near full bend of the chain, with the L sprocket idling on a near straight chain.
At shift, the H sprocket will briefly allow a straightening of the chain, (L sprocket taking up the slack), effectively spreading the shift impact over a much longer time period - similar to a shock absorber.

(H idler sprocket would require heavier than normal bearings, being under constant heavy load.)

This should increase the survivability of the 7 speed eBike drivetrain an extreme amount!

Sorry if this is not clearly described.
It might need diagrams, or a mock build, to properly get the idea across.

Will re-think explanation, or post pictures.
Just brain-storming at present.

[ddk]

Mid-Drive, through the bicycle gears (sprockets)...

A much smoother, continuous, 500w motor input should hold up nicely, ... tho I would recommend reducing throttle during shifts.

Further thought on the "impact" during "shifts".
This damaging jolt could be effectively eliminated-buffered by the placement of a properly "heavily-sprung" idler sprocket on the tensioned side of the, motor to chainring, chain. (Heavy tensioned sprocket = H)
Of course, there would also have to be a lightly tensioned idler sprocket on the opposing, unloaded chain segment. (Lightly tensioned sprocket = L)
At full throttle, the H sprocket should be at near full bend of the chain, with the L sprocket idling on a near straight chain.
At shift, the H sprocket will briefly allow a straightening of the chain, (L sprocket taking up the slack), effectively spreading the shift impact over a much longer time period - similar to a shock absorber.

(H idler sprocket would require heavier than normal bearings, being under constant heavy load.)

This should increase the survivability of the 7 speed eBike drivetrain an extreme amount!

Sorry if this is not clearly described.
It might need diagrams, or a mock build, to properly get the idea across.

Will re-think explanation, or post pictures.
Just brain-storming at present.

I've done that and will be using the same system on my current project so pictures will be available.
I wasn't entirely happy with the first version, as it was near impossible to change spring tensions, but with the new build I should have that part worked out a little better (hopefully much better)
For the "first build" idler I used two 5/8" axle bearings threaded in loo of a freewheel for the idler sprocket.
Unfortunately In my current location of the world, I lack access to a bearing house or well-equipped machine shops with requisite skilled helpers, limiting my choices
I'm still unsure how I wanna do this one (it will happen when I get to that point )
There are manufactured 'solutions', but they are rather expensive -and I can't remember if they make any of those devices for 410/415 chain

[DrkAngel]

@DrkAngel

All those numbers are fine, but most lack a 0 at the end to make any Ebike interesting to me.
When you start feeding 10 times human power, which I consider only the beginning of interesting performance, a bicycle drive train is not very long to show its limits.

In a way ... I must agree ...

But ... 10 times human power?

I think we are talking about 2 different types of "eBike"!

Maybe we should sub-categorize "eBikes"?
A subject I consider worthy of it's own thread! Continued here > eaBike vs eBike vs eMotorcycle

[DrkAngel]

Mid-Drive, through the bicycle gears (sprockets)...

A much smoother, continuous, 500w motor input should hold up nicely, ... tho I would recommend reducing throttle during shifts.

Further thought on the "impact" during "shifts".
This damaging jolt could be effectively eliminated-buffered by the placement of a properly "heavily-sprung" idler sprocket on the tensioned side of the, motor to chainring, chain. (Heavy tensioned sprocket = H)
Of course, there would also have to be a lightly tensioned idler sprocket on the opposing, unloaded chain segment. (Lightly tensioned sprocket = L)
At full throttle, the H sprocket should be at near full bend of the chain, with the L sprocket idling on a near straight chain.
At shift, the H sprocket will briefly allow a straightening of the chain, (L sprocket taking up the slack), effectively spreading the shift impact over a much longer time period - similar to a shock absorber.

(H idler sprocket would require heavier than normal bearings, being under constant heavy load.)

This should increase the survivability of the 7 speed eBike drivetrain an extreme amount! ...

If the motor runs through the BB, with no shifting on the front chainring, the application of a Heavy idler on top of the chain, slightly rearward of the chainring, should greatly simplify the build of a "shifting shock absorber"!
The "slack side" (L) of the chain is adequately served by the derailleur.

[DrkAngel]

Mid-Drive, through the bicycle gears (sprockets)...

A much smoother, continuous, 500w motor input should hold up nicely, ... tho I would recommend reducing throttle during shifts.

Further thought on the "impact" during "shifts".
This damaging jolt could be effectively eliminated-buffered by the placement of a properly "heavily-sprung" idler sprocket on the tensioned side of the, motor to chainring, chain. (Heavy tensioned sprocket = H)
Of course, there would also have to be a lightly tensioned idler sprocket on the opposing, unloaded chain segment. (Lightly tensioned sprocket = L)
At full throttle, the H sprocket should be at near full bend of the chain, with the L sprocket idling on a near straight chain.
At shift, the H sprocket will briefly allow a straightening of the chain, (L sprocket taking up the slack), effectively spreading the shift impact over a much longer time period - similar to a shock absorber.

(H idler sprocket would require heavier than normal bearings, being under constant heavy load.)

This should increase the survivability of the 7 speed eBike drivetrain an extreme amount! ...

If the motor runs through the BB, with no shifting on the front chainring, the application of a Heavy idler on top of the chain, slightly rearward of the chainring, should greatly simplify the build of a "shifting shock absorber"!
The "slack side" (L) of the chain is adequately served by the derailleur.

I found an idler that might be adequate for the job.
Sprocket Idler 14 tooth 3/8" ID 410H 415H 40 41

Staton Inc.
They also have a large variety of build components!

[thickhead]

What about the possibility of a using an internal rear hub like a Rohloff or nuVinci, and even a Schlumpf high-speed crankset up front? I don't know the power ratings of these devices, but they seem pretty sturdy. And, they can be shifted at any time and would make a very clean chain line.

[ddk]

What about the possibility of a using an internal rear hub like a Rohloff or nuVinci, and even a Schlumpf high-speed crankset up front? I don't know the power ratings of these devices, but they seem pretty sturdy. And, they can be shifted at any time and would make a very clean chain line.

several members have used the NuVnci 191B developer's kit (no longer available)
I apparently bought "the very last one"
(i does that a lot)
If I remember correctly Rassy had some issues with some of the other geared-hubs because they were, well, geared.
Don't know much about the NuVinci 360 except it's of much smaller/lighter construction than the original 191.
The Schlumpf has also been used in more than a few builds by members of this board.

Using the forum "search" function may be of use...
(although that never werks so gud for me)

[d8veh]

I built one with a Bafang QSWXK motor driving a chainwheel on the left side - just to see what sort of power characteristics it had. It pulls up the steepest hills without pedalling, and will do about 20mph on the flat. The only problem I had was the chain jumping on the motor sprocket - probably because it was the wrong size chain.I keep meaning to complete the project. I've bought a rear motor and a free-wheeling Cyclone crank. I you don't want to go too fast and you want to keep to a 250w limit, it would be a good solution because it's light and efficient; however, a bigger geared motor like a BPM or MAC has just as good climbing, better speed (on the flat) and is far simpler although heavier. If you want, you can have a look through this folder, which gives some details:
http://s451.photobucket.com/albums/qq23 ... k%20drive/
....and a video of it working:
http://www.youtube.com/watch?v=qfWSQh8cAzI

[REdiculous]

10x human power isn't that far out there...

If you figure you can output 100w fairly continuously, an ebike that's 10x more powerful is only pushing 1000w.

[spinningmagnets]

A while back there was a discussion about what is the strongest IGH, and there were several links to gasser bikes that used a Nexus 3-speed as a jackshaft. I recall AussieJester mentioned that he broke one of these, but he had the electric motor driving the right-side sprocket as a one-speed.That being said, he was using a lot of power that was applied suddenly (more power than I would use).

I think a Nexus-3 is a great candidate to be a 3-speed jackshaft that drives the left side. If the final chain-drive from the Nexus to the rear axle has a 2:1 ratio, then I believe the torque applied to each IGH gear-tooth will be halved.The Nexus will be spinning twice the RPMs of the rear wheel, but I believe that will be acceptable. "if I ever get around to doing this"...I plan to add some type of snubbing to the throttle to ramp up the power rather than dumping it suddenly.

Daily use for me would find the Nexus used as a 2-speed (starting out in 2nd which is direct-drive, and very strong, 3rd is a 33% overdrive). First gear would be reserved for especially steep hills. If second gear is ratio'd to provide 20-MPH, then first should be around 15-MPH and 3rd would be approximately 26-MPH...48V plus limiting amps with a cycleanalyst to match the data a temp probe provides.

Even with a mid-drive used as a single-speed, changing the gear ratios for a hilly trip is as simple and cheap as a sprocket swap.