Hub mid-drive dual motor combos

[hillslayer@]

I built two of these now, first one was a fat bike that had a 500 watt geared hub, swapped the controller to 26 amps and added a BBSHD. This setup goes about 10 mph faster uphill than a BBSHD alone and the mid-drive is probably doing most the work. I also have a hardtail mountain bike that has a BBSO2 I added a CSC 1500 watt DD hub, this really rips uphill with the hub doing the majority of the work. These are all on 48 volts separate batteries for each motor. Haven't range tested the Bbso2 and DD hub combo yet but it is like at least 5 mph faster than the BBSHD combo expect worse range also .
Update: For those interested in doing this I would go with a direct drive hub if you can live with the extra weight the geared hub on my fat bike quits helping at around 25 MPH my BBSO2 1500 Watt direct drive hub will cruise at 40 mph running a 46t chainring pretty good for 48 volts. You can push both motors hard up steep hills without stressing either one.

 

[bengxe]

I tried this when I thought I needed the redundancy, a BBS02 driving a dd hub. The hub was doing the majority of the work back then, and it's making a lot more power now. The BBS02's biggest strength is its light weight, so in this case it's just an expensive way to add 12-1300 watts. I still use both motors, but they're more enjoyable on separate bikes.

 

[Chalo]

Y'all gonna break your rear hub side covers fooling around that way.

Two hub motors on the same bike is a fun arrangement. There's not a strong case for using two hubs over using the same amount of power into a bigger rear hub, though. (I built mine because I already owned everything I needed to do it.) Mid drive should be by itself or not at all.

 

[hillslayer@]

I tried this when I thought I needed the redundancy, a BBS02 driving a dd hub. The hub was doing the majority of the work back then, and it's making a lot more power now. The BBS02's biggest strength is its light weight, so in this case it's just an expensive way to add 12-1300 watts. I still use both motors, but they're more enjoyable on separate bikes.

The hub lacks torque if you slow down or the hill steepens up it heats up and slows down the BBSO2 keeps it in its sweet spot and this bike is way less expensive than something else that can climb steep hills at speed.

 

[hillslayer@]

Y'all gonna break your rear hub side covers fooling around that way.

Two hub motors on the same bike is a fun arrangement. There's not a strong case for using two hubs over using the same amount of power into a bigger rear hub, though. (I built mine because I already owned everything I needed to do it.) Mid drive should be by itself or not at all.

Not the first to do this, don't see the broken side covers being common. The only example of this I could find was from 2008 when a couple hubs broke there side covers, looks more like a manufacturer defect than anything. If you are worried about this just don't use the last 3 cogs on the freewheel because it's more a leverage thing than a twisting force that would cause this

 

[Lectriceye]

When you have both motors operating at the same time, do you have any conflicts? I assume you are using PAS on the mid and throttle on the hub? i have a geared hub, would it operate any different than a DD?

 

[Chalo]

Not the first to do this, don't see the broken side covers being common.

Many have done it without motor help, only pedals. It's asking for trouble to work the freewheel thread with superhuman power.

 

[hillslayer@]

Geared hub freewheels when not powered. My reason for building this was being able to do 25 MPH plus up any hill . If you don't need that mid-drive only is probably all you really need.

 

[hillslayer@]

Many have done it without motor help, only pedals. It's asking for trouble to work the freewheel thread with superhuman power.

Links

 

[Lectriceye]

Links

My problem is that after 50 years of competive riding I turned 82 years old and the hills got a lot bigger and too much for me to handle with out a crutch. I can do the distance and pedal all the way, but those long hils I would be stopping for a breather every mile or so and the enjoyment would be lost, lol. I am more worried about putting a 2kw controller on it and burning out the motor than I am about tearing the wall of the motor out. I thought about putting the mid on my mountain bike but I don't think it would handle the stress either. Sooooo, I am still researching. Usually I learn best by doing.

 

[Lectriceye]

Not the first to do this, don't see the broken side covers being common.

I think if I were to blow the motor or tear the walls out of the motor, I would just get rid of the motor and wheel and put in an analog wheel.

 

[neptronix]

My problem is that after 50 years of competive riding I turned 82 years old and the hills got a lot bigger and too much for me to handle with out a crutch. I can do the distance and pedal all the way, but those long hils I would be stopping for a breather every mile or so and the enjoyment would be lost, lol. I am more worried about putting a 2kw controller on it and burning out the motor than I am about tearing the wall of the motor out. I thought about putting the mid on my mountain bike but I don't think it would handle the stress either. Sooooo, I am still researching. Usually I learn best by doing.

Here's a thought if you're still on the fence; dual shengyi sx2's:

Motor Simulator - Tools



The two motors will come out to 12lbs and scale like a billy goat..
..buy one with regen to help on the way down, and the other one freewheeled..

vs..

bbs02 @ 8lbs + 27mm 9C ( smallish DD ) @ 12lbs = 20lbs total

..the only problem with geared motors is that off road can give the gears a real beating, but if you have a full suspension bike with some air let out of the tires, they might survive.. & if one motor were to go, at least you have another

 

[bengxe]

Many have done it without motor help, only pedals. It's asking for trouble to work the freewheel thread with superhuman power.

I shared this concern before I tried it, but my freewheel came off my DD hub like it was new after a few hundred miles of BBS02 abuse. My guess is this is more based on rider weight than motor power.

 

[bengxe]

When you have both motors operating at the same time, do you have any conflicts? I assume you are using PAS on the mid and throttle on the hub?

I mostly used 2 thumb throttles next to each other. The BBS02 needs to be in a gear that matches the free speed of the hub, otherwise it will either take load away from the hub motor or just not contribute anything.

 

[Lectriceye]

I mostly used 2 thumb throttles next to each other. The BBS02 needs to be in a gear that matches the free speed of the hub, otherwise it will either take load away from the hub motor or just not contribute anything.

I am familiar with sunchronizing twin engines on an airplane, you can hear and feel the difference when they are not synchcronized. More modern airplanes have circuitry to auto synchronize them. I suppose that is too much to ask for on a relatively inexpensive little ebike. If they haven't already, I suppose someone will come up with an inexpensive microprocessor to syncronize the rpm's of the 2 motors.

 

[Chalo]

Links

Popping and grinding coming from rear wheel

A few months ago I started hearing a popping and grinding sound coming from around my rear wheel. This was only when I put a decent amount of pressure on the pedals. The sounds got louder and louder over time. I originally thought it was the bottom bracket. I took it to a bike shop and they...

endless-sphere.com

I shared this concern before I tried it, but my freewheel came off my DD hub like it was new after a few hundred miles of BBS02 abuse. My guess is this is more based on rider weight than motor power.

I'm not talking about stuck freewheels-- I'm talking about the threaded aluminum freewheel boss on the side cover being uprooted and broken out of the side cover by means of cyclical stress from chain tension.

Riders who use rear hub motors and who pedal hard (especially when using the more outboard sprockets on the freewheel) have demonstrated the ability to break the freewheel mounting off of the side cover with pedal power alone. Putting greater than human motor power through the same interface increases this risk.

 

[neptronix]

^-- yeah that's the main reason i wouldn't do a mid drive connected to a hub; it would be better to have a low powered front gear hub to help..

 

[bengxe]

I am familiar with sunchronizing twin engines on an airplane, you can hear and feel the difference when they are not synchcronized. More modern airplanes have circuitry to auto synchronize them. I suppose that is too much to ask for on a relatively inexpensive little ebike. If they haven't already, I suppose someone will come up with an inexpensive microprocessor to syncronize the rpm's of the 2 motors.

They don't really have to be synchronized so much as just not fighting each other (in series vs parallel airplane engines). They auto-synchronize because they're both driving the same wheel. You don't want the chain spinning without actually engaging the freewheel, and you don't want the BBS02 to draw a lot more watts than your hub, but your freewheel/ cassette probably already has a gear that will accomplish that. This is all modeled in the motor simulator, the compare/ add option makes it easy to match the speeds before you combine them.
I still think swapping your geared hub for a DD would get you more overall power per dollar, but the dual drive can make sense with a geared hub.

 

[bengxe]

I'm not talking about stuck freewheels-- I'm talking about the threaded aluminum freewheel boss on the side cover being uprooted and broken out of the side cover by means of cyclical stress from chain tension.

Riders who use rear hub motors and who pedal hard (especially when using the more outboard sprockets on the freewheel) have demonstrated the ability to break the freewheel mounting off of the side cover with pedal power alone. Putting greater than human motor power through the same interface increases this risk.

Again, I think this only an issue for heavier riders with larger wheel diameters. I ran a 25A BBS02 almost entirely through the small end of a 7 speed freewheel with no issues in about 500 miles, but I weigh 130lbs. Good point about the outboard sprockets, if I had to do it again I'd probably pick the right size single freewheel and forgo the shifter/ derailleur.

 

[hillslayer@]

I mostly used 2 thumb throttles next to each other. The BBS02 needs to be in a gear that matches the free speed of the hub, otherwise it will either take load away from the hub motor or just not contribute anything.

So what hub did you use and what was your BBSO2 geared at. I'm finding with a 38t chainring it has to be a really steep hill before I need to shift out of the 14t cog. I have room to run a 42t chainring will maybe give it a try. I pretty much only pedal on steeper hills the 1500 watt hub pulls faster than the BBSO2 top speed.

 

[Lectriceye]

My hub is a Bafang G62 equivelent, 1000w geared. I don't have a mid drive installed yet, but I am planning to purchase the Bafang BBSHD soon and install it. My freewheel has 7 cogs 14/28. The hub alone is good for about 28mph on level ground, and about 12 mph on a 8% slope for 200 yards or so, beyound that my controller starts to overheat.

 

[Lectriceye]

I anticipate the BBSHD will solve the hill limitation.

 

[hillslayer@]

My hub is a Bafang G62 equivelent, 1000w geared. I don't have a mid drive installed yet, but I am planning to purchase the Bafang BBSHD soon and install it. My freewheel has 7 cogs 14/28. The hub alone is good for about 28mph on level ground, and about 12 mph on a 8% slope for 200 yards or so, beyound that my controller starts to overheat.

You will be able to go 25 mph up the same hill without stressing either motor

 

[bengxe]

So what hub did you use and what was your BBSO2 geared at. I'm finding with a 38t chainring it has to be a really steep hill before I need to shift out of the 14t cog. I have room to run a 42t chainring will maybe give it a try. I pretty much only pedal on steeper hills the 1500 watt hub pulls faster than the BBSO2 top speed.

It's a 24" ebikeling 9c clone, and the BBS02 had a 52t 104 BCD ring on an adapter with an 11-28 freewheel. Swapping to 72v let the hub make more power than I ever got out of both motors on 48v.

 

[hillslayer@]

Anything bigger than 42t is going to hit my chainstay I am on 29 inch tires so probably don't need to go that big . 35 mph seems fast enough for me if I get urge to start cruising at 40 mph plus I will just go 72 volt and take the mid drive off.