A few questions about e-bike motors

Hi, I've never built a EV but I have experience with electronics/robotics etc. Been researching for a few months and I have a few questions. looking to build ~3kw e-bicycle.

1. why would one use hub motors for bicycles/motorcycles? They seem 10 times heavier with same performance of 'normal' brushless outrunners. Is it only due to simplicity of them not requiring gearing/chains etc? I'm suspecting the weight comes with the amount of wire required to create such a low KV motor?

2. I see orders of magnitude price differences between motors of seemingly similar performances, like,

https://alienpowersystem.com/shop/brushless-motors/aps-6384s-sensored-outrunner-brushless-motor-130kv-4000w/
and
http://www.astroflight.com/3220

how come? (maybe the alien power rating isn't continuous but peak? still, they do have way cheaper higher rated motors as well..)

3. speed controllers. I often see really big speed controllers for e-bikes, while e-skate controllers seem super light with same performances.. how come?
would something like focbox be ok for an e-bike? http://www.enertionboards.com/FOCBOX-speed-controller.html

thank you!

My thoughts on the first question

If your just road riding hub motors make good sense whereas for trail riding geared mid drive motors are pretty much needed. Some choose hub motors for their ease of installation and lack of maintenance while others choose a mid drive with gears for hills and off road trail type riding etc.

Motors (boosters) work best when they switch poles while powered. Full power at 0 RPM = 0 efficiency.

Efficiency isn't linear to speed, more like logarithmic to speed. Depends on the motor design.

No matter what booster you choose it comes with advantages and disadvantages. Efficiency, simplicity, gearing options, packaging, noise, rider application, a dozen other things, pick any 3 and at least 1 of the 3 items will be compromised. With any system.

Hubs are pretty darn easy. Biggest problem for me was when the hub didn't quite fit and there was some spreading to do on the old XGames Moto bike. The old Currie kit with the wheel that hung the motor off was similarly easy. Think of trying to line up the motor with the rear sprocket, the chain tensioner, etc. Nonissues for the hub. Can't compare performance as I've had only 1000w and higher hubs and nothing so powerful in chain drive.

As for those price differences, there's more involved than the performance. You can't assume the same wattage will be the same price. Not much more to say, except you have to know that maybe a Unite can't be worth as much as anything you posted because it's just low tech, etc. I don't thing there's a whole lot to discuss on that one.

Controllers for skate boards. Let's just remember than if you go back 6-8 years people here were hot and heavy with those little RC controllers, some of them would never try it again. I assume there's been some improvement in the controllers but mostly the boarders don't have much choice, they need small. So they deal with it. Sometimes I'm curious at the boards not having the fires that the bikers did, but I haven't seen an explanation.

I guess I'm in the minority but I don't see any advantages to hubs except they are easier to ride since the motor doesn't depend on shifting.

I have both a rear 750W hub bike and a BBS mid-drive bike and the mid-drive bike is much easier to install and work on for me. The mechanical installation of the BBS literally took a few minutes (pop-out old BB, slide motor in, shim properly, tighten locknut, beer). The hub is more of a pain to install for me. Because the BBS has an integrated controller wiring was easier although this is where the lion's share of time went on the BBS install. Rear wheel mechanical maintenance on the hub bike is a pain - I hate tire changes. I've come up with a system to hoist the heavy hub motor wheel into place so it's better but still unpleasant. Mechanical maintenance on the BBS bike is the same as the bike prior to motor installation.

The mid-drive bike is way more fun to ride for me. It will climb any steepness I have the gumption to attempt. Likewise it goes faster than I am comfortable going and I don't even know the top speed. It took time to refine the BBS controller parameters and get the gearing perfect but even on the maiden flight it was very clear the hub bike would collect dust and refining was a pleasant chore. Initially it chewed up driveline components and range was less than the hub-bike but after the tuning and learning how to ride properly that's all swapped now. Exceedingly happy with the BBS bike - the only thing I'm wanting on it is to fix the PAS/throttle issue and I expect I'll resolve that in the next week or two =]

The hub bike is what I loan to friends because like I mentioned it's just plain easier to ride - in particular for people that don't do a lot of riding and so don't have shifting down to an autonomous task. It just plain sucks on slopes. Speed is limited to about 25mph by the battery voltage (52V batt).


YMMV...

Nice to hear the BBS middrive was a easy to install encouraging for others and good to hear as I will likely switch over to a BBS at some point.

I know some frames don't give up to the BBS easy... but for those that do it's a breeze. I've been hand's on with three BBSHD installs and they all went fairly easily. One we had to get a spacer for the non-drive side but that was the worst of it.


This is my BBSHD fattie:

Hello, lesh. Whether you are reading about RC motors and controller, or hubmotors...don't believe the advertised power levels. One issue with RC motors is that...in their designed uses, they accelerate fast under a light load. Using them on an ebike can easily burn out the expensive ESC

Hubmotors remain relevant because they are the most affordable motor to install in an ebike. Direct Drive hubmotors (DD) are also the best choice if you plan to boost the power levels in the future, due to their tolerance for high heat.

Here are some benefits and drawbacks

DD hubmotor benefits:
Affordable
with a sinewave controller, a DD hubmotor can be near silent
Can take high temporary peak power without any stress on bicycle drivetrain (chain, sprockets, etc)

Drawbacks:
Not stealthy (if you need that), if the hubmotor is large
For high power at low RPMs, hubmotors will be heavy
High amps require high-current cells, or...a very large battery pack (can be heavy, expensive, hard to fit)
At high speed, a heavy hubmotor is unsprung weight that hurts suspension handling on bumps

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Benefits of mid drive:
Running the motor through the gears means it can climb hills well by downshifting, no overheating
A smaller motor can have a wider range of speed and torque, visually stealthy
Potentially more efficient to get more miles from a smaller battery pack
Can provide a wide range of performance on a lower-amp pack, possibly more affordable/fittable battery

Drawbacks of mid drive:
More expensive
Puts high wear on chains and sprockets, frequent replacement.

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Benefits of an RC drive:
Super lightweight, tiny controllers (ESC's)

Drawbacks of RC drive:
Loud
Needs high reduction, can be complex with belts and chains
Expensive ESC's can suffer from inductive loads, cannot take the same abuse as ebike controllers
No "plug and play" RC ebike kits available

eCue said:

My thoughts on the first question

If your just road riding hub motors make good sense whereas for trail riding geared mid drive motors are pretty much needed. Some choose hub motors for their ease of installation and lack of maintenance while others choose a mid drive with gears for hills and off road trail type riding etc.

Click to expand...

You can use a hub motor for offroad, you just need a much stronger rear suspension to keep the unsprung mass under control. More specifically, you need a stronger spring to control the higher momentum of the larger mass.

So for a heavy enduro like ebike with a person (combined ~250-300lbs), and a QS205 50H V3 hub motor (~32lbs), you'd want a spring between 650lbs and 800lbs. They don't really make 800lbs springs for bicycles though, mostly just for small dirt bikes. DNM makes small dirt bike suspension though, so that's an option if you want an 800lbs spring with appropriate shock. Largest I've seen for bicycles is 650lbs from known manfs, and 700lbs from no-names.

That is good info Thanks its something to seriously consider when building. I was thinking about slow speed performance or more so lack of with Hub motors.as trail riding is often slow n steep.

As it is Im using a tiny 48v 350w geared front hub motor that can't take the heat/ Amps on slow speed hills at all.
I do need a better motor and battery so will be upgrading at some point

I imagine you could trail ride with a DD just fine if your selective but maybe Im under estimating them , it sounds like it. How do you find the large DD hub motors with slower speed on trails and hills heat wise with the amp load ?