Recommendations for a 72V DD Hub motor in 20" wheel for 45mph (72km/h)

[Residents evil]

I can recommend QS159.8, it's a relatively small direct drive hub, designed for 175mm and capable of 72V, with a posted max torque of 90Nm. It's about 11.5 rpm/v give or take, I'm actually running it in an underpowered setup with 48v battery and very limited current, nevertheless during my build before setting up a speed limit I was able to get a loaded speed of 30mph. So I presume it will def beat your minimum speed req with a 72v pack. It has a fairly good description and tech drawings on QS websites. I am running it with some spacers in a 190mm dropout, but based on the drawings you should be able to fit it in 175. Overall it's comparable to grins all axle fat in weight, but is wider and smaller diameter, which makes lacing easier in a smaller wheel.

Quite a useful advise you just gave me by specifying you're running at 48v and it still hits 30mph. My current battery is a 48V one and I might, with enough luck, fish out a controller from my pile of parts that is still alive and can run that motor while I wait for my 72V system to arrive and to configure it. You're running it on a 20x4 (22" effective size) too? The weight is similar to previous suggestions too. As usual, I just worry about cooling, the 1000W rated is less convincing than some other motors that are higher rated. Appreciate the suggestion : )

 

[Apartunis]

It's definitely a dumb and impractical decision, makes my options much slimmer. It's just the fact that I love the frame I have and couldn't find anything similar that could take bigger rims.

You can use 24 x 2.5" rims and tires, and you might be able to use 24 x 3" or 26 x 2" as long as they fit in the fenders or under the seat stay bridge and fork crown. That won't help you with motor selection, but it would help the bike go fast and handle much better.

 

[neptronix]

Ferrofluid is my go-to cooling mod, think I'll skip the dissipation fins and just go easy on the motor instead. One of the reasons to have a higher top speed is to also be able to reduce a bit from full throttle and ride below top speed to thus ease the load and heat buildup in the motor. 35mph would already be an upgrade from my regular 28mph, I was just dreaming of doing 40mph continuous regardless of battery level (Assuming 5mph is lost for low charge in the battery), hence the 45 mph target.

oh, in a 22 inch wheel, leafbike should be able to do 40mph for pretty good stretches of time. If you had a controller that's capable of phase advance/flux weakening to push higher speeds temporarily, you could boost the motor's natural speed further for short periods of time.

That's what i did on my leafbike build. I had an old school controller with a 3 speed switch:
speed 1: ~25mph max, ie legal mode
speed 2: 39mph max
speed 3: 47mph max ( ~20% phase advance )

Today i would use flux weakening on a VESC and set the flux weakening range to the last 10% of the throttle since it's difficult to find a controller these days that has a 3 speed switch. Then, you just need to push the throttle to max and "the VTEC kicks in"

Don't think the 2lbs will be a deal breaker, I'll lose weight instead haha (Yes I know, rotational mass makes a lot of difference for battery life and whatnot). Will take a look at all those motors properly hopefully this weekend and try to decide. Thanks for the suggestions : )

Rear motor weight makes a bike weird to handle if you have to carry it since the rear is so much heavier than the front. This also makes for problems balancing the bike against a wall etc. Changing a flat tire also becomes harder.

So i always buy the lightest motor i can get away with for the targeted speed personally.

 

[neptronix]

Quite a useful advise you just gave me by specifying you're running at 48v and it still hits 30mph. My current battery is a 48V one and I might, with enough luck, fish out a controller from my pile of parts that is still alive and can run that motor while I wait for my 72V system to arrive and to configure it. You're running it on a 20x4 (22" effective size) too? The weight is similar to previous suggestions too. As usual, I just worry about cooling, the 1000W rated is less convincing than some other motors that are higher rated. Appreciate the suggestion : )

QS motors are very conservatively rated but also tend to be very heavy. That extra weight brings extra thermal mass and resilience against overheating.

Good choice if power to weight ratio doesn't matter.

 

[Alex12345]

Quite a useful advise you just gave me by specifying you're running at 48v and it still hits 30mph. My current battery is a 48V one and I might, with enough luck, fish out a controller from my pile of parts that is still alive and can run that motor while I wait for my 72V system to arrive and to configure it. You're running it on a 20x4 (22" effective size) too? The weight is similar to previous suggestions too. As usual, I just worry about cooling, the 1000W rated is less convincing than some other motors that are higher rated. Appreciate the suggestion : )

While my frame is nominally for 20in fat, I actually have a very unorthodox setup, something along the lines of what Apartunis just mentioned in post #27. So my effective is 23.6, which would mean you get maybe like 2 mph less than me if yours is exactly 22. However, until neptronix said it, I forgot you can use flux weakening, I don't have it enabled, but it would probably benefit your build a lot, with any motor really.

I reread the thread and am somewhat confused about your 200mm dropout reference. I thought most DD motors are actually too narrow, like 150mm dropout, so need spacers to accommodate 175, let alone 190. Price, weight, and 190mm dropout support is why I personally went with QS159.8, even though it has a too high kv for my use. But this may be a completely different choice reasoning for you with 175mm dropout and high thermal load requirements, I somehow suspect more motors out there should be compatible.

In any case I just dug up my config saves, here are the parameters of my particular QS159.8 as assessed by a phaserunner:

Kv: 11.13rpm/v
Ls: 149uH
Rs: 54mOhms

Maybe you can input this into grins motor performance calculator along with your weight, battery, etc, and see for yourself if it's a good fit for you build or not.

 

[Residents evil]

Today i would use flux weakening on a VESC and set the flux weakening range to the last 10% of the throttle since it's difficult to find a controller these days that has a 3 speed switch. Then, you just need to push the throttle to max and "the VTEC kicks in"


Rear motor weight makes a bike weird to handle if you have to carry it since the rear is so much heavier than the front. This also makes for problems balancing the bike against a wall etc. Changing a flat tire also becomes harder.

Bold #1: I was wondering how I'd be able to configure the VESC for something like that. The ebike Spintend ADC addon indicates the possibility of 3 speeds selection, will that be a plug and play sort of system in a one-config VESC? Or should I program 2 or 3 configs into the VESC (Is this even possible? I believe not but haven't looked into it yet) and select them in the VESC directly?

I do wish to have at least 2 speeds, one for inner city usage where I'd like to have more granularity on throttle input to be more predictable at lower speeds, and a fully unrestricted one for the long stretches of my commute, so getting the VESC to do such is still a concern of mine.

Bold #2: Not a problem for me. It's a fat bike, it's heavy as it is and I leave it on the kickstand. As for flats, I don't intend to have them (lol) but if I do, I wont be solving them wherever they happen. I'll take it to the nearest bike shop (if available) or just roll it to one of my jobs where I got a nice bike lift where I can work on. Had one flat and that's when I learned why it's so useful to have the Walk mode in the bike, I would've been dead dragging it 5 miles from the flat to the job to swap that damn tire...

 

[Residents evil]

While my frame is nominally for 20in fat, I actually have a very unorthodox setup, something along the lines of what Apartunis just mentioned in post #27. So my effective is 23.6, which would mean you get maybe like 2 mph less than me if yours is exactly 22. However, until neptronix said it, I forgot you can use flux weakening, I don't have it enabled, but it would probably benefit your build a lot, with any motor really.

I reread the thread and am somewhat confused about your 200mm dropout reference. I thought most DD motors are actually too narrow, like 150mm dropout, so need spacers to accommodate 175, let alone 190. Price, weight, and 190mm dropout support is why I personally went with QS159.8, even though it has a too high kv for my use. But this may be a completely different choice reasoning for you with 175mm dropout and high thermal load requirements, I somehow suspect more motors out there should be compatible.

In any case I just dug up my config saves, here are the parameters of my particular QS159.8 as assessed by a phaserunner:

Kv: 11.13rpm/v
Ls: 149uH
Rs: 54mOhms

Maybe you can input this into grins motor performance calculator along with your weight, battery, etc, and see for yourself if it's a good fit for you build or not.

I went to QS website and majority of the motors state they need a rear fork with 200mm width. I did find one just now saying 150mm. Could be because I was looking in the E-Motorcycle motors section of the website, instead of Electric Bike section. I'm not very bright sometimes...

Thanks for your parameters, but I still need to do my studies to use that information properly. The VESC programming doesn't scare me, but trusting my knowledge to buy the correct motor does, a lot, so I'll use all the suggested motors here to simulate and learn what each parameter does on a motor's output. Maybe then I'll buy something proper. Then again, all suggestions seem to be able to achieve my goals, so if it's not the absolute perfect pick, I can't be mad, only proud that I actually did it in the first place instead of chickening out