Geared Front Hub Motor Used As A Mid-Drive In Frame Triangle

[Santa'sLittleHelper]

Hello all. Pretty new to E-bikes here, but have played around with a BaFang 350W/37V mid-drive equipped hardtail eMTB for the last six months. I now ride a full suspension (FS) carbon MTB with the typical curved down tube near the bottom bracket (BB), that has a small triangle space below the rear shock that sits horizontal below the top tube. The only thing I miss about the eMTB is the climbing assistance it provided. Otherwise I like the feel of the FS MTB as is.

An ideal electric assist setup for me would be something like a geared front hub motor that free wheels, mounted in the small triangle space below the rear shock and above the BB, that is activated by a torque/cadence sensor and/or on-off boost push button throttle when climbing.

Limiting factors for my idea require the 100mm front fork motor selected to be only 5” maximum total diameter (or can have the spoke mounting lip cut off on a lathe to meet that diameter) with the wiring coming out of the motor itself, not the axle (so the axle can be cut down for a thin nut, keeping the overall width to a minimum) and has a disc brake mount. Power output must be California legal, so 350W-750W/37v-48V minimum-maximum. My initial thought for power to the crank is to mount a sprocket to the disc brake mount that goes to a right square crank arm mounted on the left side of the BB with a sprocket. This will also allow further geared reduction as needed.

Has anyone installed a geared front hub motor that freewheels within a bikes frame triangle? If so, please provide a link (I could not find such an application using the search engine).

Are there any geared front hub motors that meet the requirements stated? (Power, diameter, wiring, disc, etc...)

Do you see any problems with this approach? (I can't be the first one to think of this, so why don't I see them out there?)

Any chance there are rear hub single speed motors out there that are “narrow” like the typical 100mm front fork mount motor? (That would make the motor to crank chain setup easier)

Thank you for your thoughts and experience.

 

[ScooterMan101]

Since I have thought about this myself, and have not done it because the lack of examples. ( just a few , but none doing a light weight one like I want to do )

Here a couple of thoughts I have had,

1) It is hard to find a light weight front hub motor with the wires coming out of the side, there are one or a couple, but the axle wire motors are much more prolific.
So
What you can do is to take a front hub motor, with axle wires and cut down the axle most of the way, leave enough for a nut and one or two washers for the mounting plate you are going to have to design and make for your particular bike.
Now make a L shaped, better yet a U shaped , piece of metal / or from Delrin , to protect the wires from rubbing on your legs.

2) Get a small 350 watt motor . ( They are 350 watt when on 36 volts, but I run mine at 450-500 watts, indicated on the Display , on 48 volts
I have the Q100c CST on the Rear, However a front Q100 would work the same. )

3) Make the parts of the Clamp/Mounting Plate mostly out of Delrin, at least the part that goes around the frame .
( I would like to see an example or two of someone doing this with Fiberglass/Carbon Weave , Composite .)

Here is a couple of Link's

https://bmsbattery.com/41-36v Shipping on a motor is apx $ 55-$ 60 to the U.S.

http://www.ebikes.ca/shop/conversion-kits/geared/front-mini-geared-kit-advanced-pas.html Shipping Costs from Vancouver to U.S. are better.

An ideal electric assist setup for me would be something like a geared front hub motor that free wheels, mounted in the small triangle space below the rear shock and above the BB, that is activated by a torque/cadence sensor and/or on-off boost push button throttle when climbing.

Limiting factors for my idea require the 100mm front fork motor selected to be only 5” maximum total diameter (or can have the spoke mounting lip cut off on a lathe to meet that diameter) with the wiring coming out of the motor itself, not the axle (so the axle can be cut down for a thin nut, keeping the overall width to a minimum) and has a disc brake mount. Power output must be California legal, so 350W-750W/37v-48V minimum-maximum. My initial thought for power to the crank is to mount a sprocket to the disc brake mount that goes to a right square crank arm mounted on the left side of the BB with a sprocket. This will also allow further geared reduction as needed.



Are there any geared front hub motors that meet the requirements stated? (Power, diameter, wiring, disc, etc...)

 

[Santa'sLittleHelper]

Thanks for those. I'll go take a closer look through those links. Many of what I did find in the past was high powered direct drive motors placed under the bottom tube, but my initial peek saw a few in the triangle with what looked like a production frame mount and might be geared front hub motors (?).

some builds
https://endless-sphere.com/forums/viewtopic.php?f=6&t=38553

forum area with more info
https://endless-sphere.com/forums/viewforum.php?f=28

Will try to get back wiht more info later; gotta head to work.

 

[Santa'sLittleHelper]

That ebikes.ca link looks interesting. Didn't see a diameter for the front mini geared kit motor, but will spend some more time there looking around. A complete kit that can be adapted would be great and the motor pictured has the wiring coming out of the motor, not the axle like I need.

This is all the space I have to work with. The circle is 5” in diameter and the two arrows are in-frame water bottle mounting points that can be attached to for support.

I was thinking of using this Micarta composite material for the initial design. It is about 3/16” thick, light weight, very rigid and easy to cut. I think it is material commonly used for large circuit boards and electric panels.

Keep the info coming!

Since I have thought about this myself, and have not done it because the lack of examples. ( just a few , but none doing a light weight one like I want to do )

Here a couple of thoughts I have had,

1) It is hard to find a light weight front hub motor with the wires coming out of the side, there are one or a couple, but the axle wire motors are much more prolific.
So
What you can do is to take a front hub motor, with axle wires and cut down the axle most of the way, leave enough for a nut and one or two washers for the mounting plate you are going to have to design and make for your particular bike.
Now make a L shaped, better yet a U shaped , piece of metal / or from Delrin , to protect the wires from rubbing on your legs.

2) Get a small 350 watt motor . ( They are 350 watt when on 36 volts, but I run mine at 450-500 watts, indicated on the Display , on 48 volts
I have the Q100c CST on the Rear, However a front Q100 would work the same. )

3) Make the parts of the Clamp/Mounting Plate mostly out of Delrin, at least the part that goes around the frame .
( I would like to see an example or two of someone doing this with Fiberglass/Carbon Weave , Composite .)

Here is a couple of Link's

https://bmsbattery.com/41-36v Shipping on a motor is apx $ 55-$ 60 to the U.S.

http://www.ebikes.ca/shop/conversion-kits/geared/front-mini-geared-kit-advanced-pas.html Shipping Costs from Vancouver to U.S. are better.

 

[amberwolf]

In general, this kind of thing has actually been done a lot, though most of the stuff actually posted is big DD motors simply because they're often skinnier than geared hubs and can be made to fit easier in the triangle.

I have a project to hang a tiny geared hub (tongxin) under my Nishiki's chainstays to drive the chain by pulling it thru the cranks, but I haven't ever even gotten the design finished, mostly because it's gotten hard for me to ride regular types of bikes (it's much easier for me to do lower-to-the-ground semi-recumbent types, so that's what my main bike and trike are, linked in my sig).

I also have a plan to work a geared hub into the drivetrain of the trike, too, but I dunno if I'll ever get around to that, as it also requires adding a peerless differential (whcih I'd have to build from scrap) to get power to both rear wheels to make it useful. But I've thougth about it a lot, though I haven't got much up about it in the trike thread.

that is activated by a torque/cadence sensor and/or on-off boost push button throttle when climbing.

With all the crank torque sensors I've seen, you'll have to not run the motor thru the cranks, or the sensor will detect the motor torque and apply more power. You may be able to run it thru the pedal drive chain by having it pull just behind teh cranks, perhaps via a jackshaft (since the motor will be in the triangle), but this means you need keep up with pedalling so it doesn't push the chain off the crank chainrings. If it's torque-sensing and shuts off quickly when you stop pedallling, that wn't be a problem.

A cadence sensor could be used even if you drive thru the cranks, but you need to put a freewheel on the cranks such that the motor can't drive them, or else anything that triggers the motor could cause the cranks to start spinning and then the system won't stop until you turn it off or engage an ebrake to cut off motor.

Limiting factors for my idea require the 100mm front fork motor selected to be only 5” maximum total diameter (or can have the spoke mounting lip cut off on a lathe to meet that diameter) with the wiring coming out of the motor itself, not the axle

That last is going to eliminate all of the ones I know of--but you can easily pull the wires back into the motor while it's opened up, then cut the axles, and then push the wires back thru.

My initial thought for power to the crank is to mount a sprocket to the disc brake mount that goes to a right square crank arm mounted on the left side of the BB with a sprocket.

To use the disc mount to drive the cranks...you'd have to do it that way, because you can't flip the motor over and reverse rotate it to drive the right side, because of the internal freewheel/clutch.

If you have to use a motor without disc mounts for some reason, then attaching the sprocket to the motor may present difficulties. If there are open spaces inside between the clutch and the side cover, you can use bolts thru the side cover to secure one to it; this lets you use any size sprocket or chainring that you wish, as long as you have or can make an adapter to secure it to the cover. (like cutting the spider off an old triple ring crank, and using the smallest ring bolt holes to mount it to the cover, and either of the larger two to hold the actual chainring).

If there isnt' any space for bolts, you may ahve to use a large-tooth-count chainring and bolt it to the spoke flange, via a spacer ring that lets it line up with the crank chainring.

You could also use a belt, if you can put a belt sprocket on the chainring spider.

Another option is to do it crossbreak-style. Look up member Crossbreak's geared hub middrive, where he modified the motor so the axle itself spins, and the hub casing is stationary. This gives a lot more options on output methods.

Any chance there are rear hub single speed motors out there that are “narrow” like the typical 100mm front fork mount motor?

The motors themselves are often (but not always) exactly the same, other than having the threading for the freewheel sticking out, and a longer axle. Cassette (CST) types aren't, as they have stuff sticking out for the built-in freewheeling mechanism and bearings. You might still be able to hack that stuff off since you aren't using it to drive anything anyway.

On one of the old Fusin front geared hubs I have, it's sort of both a front and a rear, though the axle is too short to use as a rear on a typical bike, but it has partial threads for a freewheel on it's side cover (you can see where it was machined down so it would fit as a front, at the factory).

 

[Santa'sLittleHelper]

In general, this kind of thing has actually been done a lot, though most of the stuff actually posted is big DD motors simply because they're often skinnier than geared hubs and can be made to fit easier in the triangle.

I found one done from way back in 2012 in the link provided that actaully used a right drive crank arm on the left side. My simplistic existing parts idea might just be where all this started to take advantage of leveraging the gears on the bike.

With all the crank torque sensors I've seen, you'll have to not run the motor thru the cranks, or the sensor will detect the motor torque and apply more power.

Excellent point I did not think of! Don't want to even consider a jackshaft or other elaborate systems that add weight and complexity; big fan of the KISS method here. That concern eliminates the BB torque sensors for me.

A cadence sensor could be used even if you drive thru the cranks, but you need to put a freewheel on the cranks such that the motor can't drive them, or else anything that triggers the motor could cause the cranks to start spinning and then the system won't stop until you turn it off or engage an ebrake to cut off motor.

Another good point. The BaFang BBS## mid-drives use a rear wheel spoke sensor and don't have this problem due to their freewheel crank system and adjustable shutoff time period when the pedals stop. Do they also have a pedal sensor that overides the rear wheel sensor? I am beginning to have more appreciation for the simple bolt-on BaFang mid-drive systems complexity and its' simplicity of installation and function.

My initial thought for this possible build was a simple throttle only assist when climbing. I think I will stick with that thought to "Keep It Simple Stupid" and spend my time on how to mount and gear a unit cleanly.

To use the disc mount to drive the cranks...you'd have to do it that way, because you can't flip the motor over and reverse rotate it to drive the right side, because of the internal freewheel/clutch.

I hadn't thought of that. Do you know if the freewheel/clutch uses simple pawls? And if so, couldn't they be removed and flipped over to function in the new rotation direction?

Another option is to do it crossbreak-style. Look up member Crossbreak's geared hub middrive, where he modified the motor so the axle itself spins, and the hub casing is stationary. This gives a lot more options on output methods.

This brings up a question I had. Are the motors heaviest parts attached to the axle or the spoke mounting ring portion of the motors?

One of the big advantages of using a geared front hub motor in this way is to take advantage of the freewheel function already in the hub. It'd be best to have the rider spinning the lightest portion of the motor while it is off and freewheeling.

Another question for those that have ridden this design. How much drag does the geared front hub put on the crank when pedaling with the motor off?

One thing I don't like about every E-bike I have ridden is the drag (and/or weight) that has to be pulled by the rider when the motors are off. Claims that they "freewheel" without drag are not true IMHO. "I" can feel it on every E-bike, but it is difficult to tell how much is drag/friction and how much is just the excessive weight of the bike itself. Even the BaFang mid-drive becomes virtually unridable IMHO after running it 40 miles and the battery dies. If felt like I was fighting against magnetic resistance when pdealing and wasn't even worth riding that way.

I'm hoping this design eliminates that and it is one of the big reasons I'm considering it. If this design has a crazy amount drag/friction, then this whole exercise is moot for me, as I will be pedaling my FS MTB with the power off all the time. Experienced real world thoughts on this are greatly appreciated.

On one of the old Fusin front geared hubs I have, it's sort of both a front and a rear, though the axle is too short to use as a rear on a typical bike, but it has partial threads for a freewheel on it's side cover (you can see where it was machined down so it would fit as a front, at the factory).

This generated another question. Are there any "geared" electric motors out there that spin the axle that are non-bike designed motors? If so, then that may be worth looking into as freewheel axle spockets are readily available and they can be installed on the right side. The rider would only be spinning that little sprocket on the axle when the motor is off. In addition, they may be available in smaller sizes and narrower widths (?).

As usual further thought generates more questions...

 

[d8veh]

Here's mine. I built it before crank-drive kits like Bafang and GNG were available:

 

[Santa'sLittleHelper]

Here's mine. I built it before crank-drive kits like Bafang and GNG were available:

Hi d8veh. I spotted your ride in The Mid Drive Hub Motor Media Group section. Is that a "geared freewheel" front hub motor mounted in that triangle? What can you say about the riding experience when the power is turned off? Please tell me about your ride. What do you like/dislike about it? You built my idea over 4 years ago. Nice!

 

[d8veh]

I only did it as an experiment to test efficiency and climbing power. It has a free-wheel in the motor, but not a freewheeling crank, so the pedals go round with the motor, which is a bit weird at first. The motor doesn't turn when you pedal it though. If I did it again, I'd use a front Q100 or Q128 because they have easily reversible clutches, which means you can flip them round to get a motor with a narrow axle and you can fix a sprocket on the right side disk mounting holes. Then you can use a normal free-wheeling crank from Cyclone.

I made a freewheel sprocket fixing by cutting a steel BMX hub in half, though it didn't need to be a freewheel because there's one in the motor. O could have just used a sprocket and a spacer from a cassette, drilled with 6 holes:

 

[Santa'sLittleHelper]

If I did it again, I'd use a front Q100 or Q128 because they have easily reversible clutches, which means you can flip them round to get a motor with a narrow axle and you can fix a sprocket on the right side disk mounting holes. Then you can use a normal free-wheeling crank from Cyclone.

Good to know! I originally had my eye on the Q100H 350W/36V, but the wiring out the axle wasn't ideal.

I'm not familiar with the Cyclone free-wheeling crank, so I will go check that out and put it in my mental tool box.

Have you or anyone else had experience with this 250W/24V or 350W/24V geared motor that is designed to mount near the rear axle on the left side? Does anyone know if it is brushless?

The geared motor itself nor the 9T spocket free-wheels, but it looks like the 16T rear sprocket that comes with the kit might. I appears to be easily adaptable for use as a mid-drive with the drive already on the right side of the motor and a free-wheeling crank. Don't know its' diamentions, weight or if it can handle 36V-48V and more watts. It does look nice and small in the pictures.

Here are the stated specifications for the 250W/24V kit:

Specifications:
1.24 Volt DC Operation
2.Permanent Magnet DC Motor
3.No Load RPM: 3850
4.No Load Current: <2.2 Amps
5.Rated Wattage: 250W (0.33 Horsepower)
6.Rated Load RPM: 3300
7.Torque (NM): 0.80
8.Rated Current: 13.4 Amps
9.Efficiency: 78%
10.Reduction Ratio: 9.78:1
11.Direct Drive (No Free Spooling)
12.Suitable for Forward and Reverse Operations
13.Base Mount Model
14.9 Tooth Sprocket for 1/2" x 1/8" Pitch Chain
Package included :
1、Brakes Lever ( DUAL ) X 1
2、24V Twist Throttle X 1
3、24V 250W Controller X 1
4、24V 250W Motor X 1
5、Lights ( with Horn button / Key / Power indicator ) X 1
6、38 chain / bearings / 16 Tooth sprocket / Other Parts X 1

 

[d8veh]

There was a guy on the Pedelecs forum that made a nice crank-drive bike out of the similar, but better 450w motor. He just made a simpe brachet out of scaffold clamps to hold it to the frame downtube. It drove a normal Cyclone free-wheeling crank IIRC.

https://www.aliexpress.com/store/product/450W-UPGRADE-ELECTRIC-BICYCLE-BRUSH-MOTOR-LED-LENS-ELECTRIC-BIKE-HEADLIGHT-THROTTLE-WITH-KEY-SWITCH-BRAKE/632724_32680836340.html

 

[Santa'sLittleHelper]

There was a guy on the Pedelecs forum that made a nice crank-drive bike out of the similar, but better 450w motor. He just made a simpe brachet out of scaffold clamps to hold it to the frame downtube. It drove a normal Cyclone free-wheeling crank IIRC.

https://www.aliexpress.com/store/product/450W-UPGRADE-ELECTRIC-BICYCLE-BRUSH-MOTOR-LED-LENS-ELECTRIC-BIKE-HEADLIGHT-THROTTLE-WITH-KEY-SWITCH-BRAKE/632724_32680836340.html

Thanks again. That one looks like a beter choice than the one above. Don't see a weight listed and that is always important. It does say it has brushes in the motor. Not sure that is desirable (?). Briefly looked at the Pedelec Forum (UK?) and didn't see it. Do you have a link?

d8veh - How does your hub motor mid-drive feel pedaling with the motor turned off? Do you know what it feels like to pedal with a geared front hub motor connected to the crank by chain? I'm guessing the least resistance method would be the Cyclone freewheel crank as you only have to pull the freewheel bearing and not the chain and motor housing of the hub itself.

My end goal is a MTB that pedals normally, but has an added 500W-1000W "peak" boost when climbing only. Any thoughts on the best lightest weight method to achieve this? Simple 3kg motor and mounting brackets with throttle that has little to no drag on pedaling when not under power is my thought (plus small battery on bike or in a fanny pack). The BaFang is out because they don't pedal well when not under power IMHO and they won't fit with proper ground clearence on most model MTB frames; certainly not on mine.

 

[d8veh]

GNG make a whole range of mid-drive kits. This one is quite good. You can always make your own brackets if you want to mount the motor inboard, and if you have the right shaped frame, you can fit it inboard with the standard brackets. The primary chain is just normal bicycle chain so you can get a longer one if you need it. I fitted the first version of that kit about 4 years ago:

 

[Santa'sLittleHelper]

That's a pretty clean setup. Does it come with a free-wheel sprocket at the crank or does the motor free-wheel?

How does it feel to pedal without power?
(This is very important to me, because i want to ride my FS MTB without power all the time and only add assist when climbing)

GNG make a whole range of mid-drive kits. This one is quite good. You can always make your own brackets if you want to mount the motor inboard, and if you have the right shaped frame, you can fit it inboard with the standard brackets. The primary chain is just normal bicycle chain so you can get a longer one if you need it. I fitted the first version of that kit about 4 years ago:

 

[d8veh]

Yes it comes with everything - freewheeling crank and free-wheeling motor. You just need to add a battery.

 

[Santa'sLittleHelper]

How does it feel pedaling when not under power?

This is the MOST important thing for adding any kind of power assist to my main FS MTB. For some reason no one seems to want to comment on this. I know the BBS## motors are awful in this regard (first hand experience). Those motors are great when the power is on though; best thing since sliced bread. Not everyone wants an electric moped. i have two bikes and they will be setup differently. Some of us want a normal MTB with just a little assist when climbing to take the age or tired legs edge off. Lol... Not that I'm old, but I'm getting there.

I would love to hear everyones comments on what each of their systems feel like when pedaling without power.

d8veh - You seem to have vast experience with different systems. What does this one feel like? Is there any particular setup that is the least noticable in this regard?

 

[d8veh]

It's completely free. When you pedal, the primary chain and motor drive sprocket turn, which is similar to back-pedalling a normal bike.

 

[Santa'sLittleHelper]

It's completely free. When you pedal, the primary chain and motor drive sprocket turn, which is similar to back-pedalling a normal bike.

That sounds good to me! I assume you are refering to having a free-wheel crank AND free-wheel gear on the motor, right?

I see GNG makes a makes a complete 450W-48V kit with that setup:

http://www.gngebike.com/450wbrushed.htm

 

[Santa'sLittleHelper]

It's completely free. When you pedal, the primary chain and motor drive sprocket turn, which is similar to back-pedalling a normal bike.

d8veh - When a hub motor is setup as a mid-drive with a single freewheel sprocket on the motor (pedalling without power turns both the motor and drive chain), what does it feel like to backpedal? (Which would spin the motor and of course only done with the power off.)

This is by far the simplest and easiest setup just using a standard dual or triple front chainring on the right side with one ring to the mid-drive freewheel sprocket.

 

[d8veh]

It's completely free. When you pedal, the primary chain and motor drive sprocket turn, which is similar to back-pedalling a normal bike.

d8veh - When a hub motor is setup as a mid-drive with a single freewheel sprocket on the motor (pedalling without power turns both the motor and drive chain), what does it feel like to backpedal? (Which would spin the motor and of course only done with the power off.)

This is by far the simplest and easiest setup just using a standard dual or triple front chainring on the right side with one ring to the mid-drive freewheel sprocket.

If you use the Cyclone freewheeling crank, only the pedals turn when you back-pedal. Not even the chainwheels turn.

To use a Cyclone crank, the motor has to be a rear one to have the sprocket on the right side. That means that it'll be a bit wider. The only front motors that you can use are the Q-series because they have reversible clutches and can be run backwards. You bolt a sprocket to the disc holes.

 

[Santa'sLittleHelper]

It's completely free. When you pedal, the primary chain and motor drive sprocket turn, which is similar to back-pedalling a normal bike.

d8veh - When a hub motor is setup as a mid-drive with a single freewheel sprocket on the motor (pedalling without power turns both the motor and drive chain), what does it feel like to backpedal? (Which would spin the motor and of course only done with the power off.)

This is by far the simplest and easiest setup just using a standard dual or triple front chainring on the right side with one ring to the mid-drive freewheel sprocket.

If you use the Cyclone freewheeling crank, only the pedals turn when you back-pedal. Not even the chainwheels turn.

To use a Cyclone crank, the motor has to be a rear one to have the sprocket on the right side. That means that it'll be a bit wider. The only front motors that you can use are the Q-series because they have reversible clutches and can be run backwards. You bolt a sprocket to the disc holes.

I understand that 2 freewheels (crank and motor) resolves all issues, but because you have experience with so many different types of applications I was hoping you could tell me what it "feels like" to backpedal on a system with only a freewheel at the motor.

Although not a hub motor, the small light geared MY1018 brush motor (similar to pictured above) can run both ways too. That is the setup I'm leaning towards for strickly climb assist only.