Looking for featherweight geared hubmotors, >10kW

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Looking for featherweight geared hubmotors, >10kW

Post by kubark42 » Feb 12 2021 10:02am

I'm looking for the lightest of lightweight geared hubmotor options in the 10-15kW range. My particular application is one where I need high torque (~100Nm) at low RPM (~1300) in a COTS package, and hubmotors really fit the bill.

However, the motors I've found so far seem to be trending around the 15kg (33lbs) mark, which is very heavy compared to direct drive motors. I realize the geartrain adds weight, but when direct drives are exceeding 10kW/kg, I'm hoping there's a hubmotor which does significantly better than 1kW/kg. My cooling potential is excellent, and my steady-state max power is only for 30 seconds, so I could potentially overdrive a smaller motor if it fit the bill (and the geartrain could handle the torque).

Anything out there which people would recommend?
Last edited by kubark42 on Feb 14 2021 12:17pm, edited 1 time in total.

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Re: Looking for featherweight hubmotors, >10kW

Post by Chalo » Feb 12 2021 12:45pm

When comparing the weight of these different systems, remember to include the weight of ratio reduction and motor/jackshaft mountings together with the aero motor. Also be sure to derate power output in consideration of the fact that the motor won't be driving a propeller or generating very much airspeed, so it won't be able to reject as much waste heat.

If you assess these factors honestly, I don't think you'll find the difference in overall power-to-weight to be significant enough to justify the extra noise, wear, maintenance, friction, and complicated installation of an aero motor.
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Re: Looking for featherweight hubmotors, >10kW

Post by amberwolf » Feb 12 2021 8:08pm

kubark42 wrote:
Feb 12 2021 10:02am
I'm looking for the lightest of lightweight hubmotor options in the 10-15kW range. My particular application is one where I need high torque (~100Nm) at low RPM (~1300) in a COTS package, and hubmotors really fit the bill.

However, the motors I've found so far seem to be trending around the 15kg (33lbs) mark, which is very heavy compared to direct drive motors. I realize the geartrain adds weight, but when direct drives are exceeding 10kW/kg, I'm hoping there's a hubmotor which does significantly better than 1kW/kg. My cooling potential is excellent, and my steady-state max power is only for 30 seconds, so I could potentially overdrive a smaller motor if it fit the bill (and the geartrain could handle the torque)
If you provide the exact details of your project, people might be able to help with other suggestions as well. Without that we have to presume it's for some type of wheeled vehicle/etc that the hubmotor is used in the wheel to directly drive the tire to the road/etc surface.


Question: You say you are looking for a hubmotor, but then you say "and the geartrain could handle the torque" referring to overdriving a smaller motor? If you are using a hubmotor (in a wheel), there isn't a geartrain, as it would be feeding the torque directly thru the spokes (if any) into the rim and then the tire.


FWIW, "direct drive" is normally used to refer to a hubmotor that has no planetary gearset to convert motor speed into wheel torque (i.e. has a "direct" connection to the wheel), also called a DD hubmotor. I can't tell for sure, but it appears you are using the term unusually to refer to a "mid drive", i.e. a drive not mounted in the wheel? You may wish to change your terminology, as it might help future information searches. :)


Hopefully you'll reply to this thread instead of abandoning it like you did your previous query.


There are a number of threads discussing "light" motors, if any of them are useful
search.php?keywords=lightest*&terms=all ... mit=Search
THere are others not in that list; not sure which search terms would best find them.

Some other possibly less relevant threads
search.php?keywords=light*+hub*&terms=a ... mit=Search

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Re: Looking for featherweight hubmotors, >10kW

Post by kubark42 » Feb 12 2021 8:56pm

Good questions. I try to avoid too much initial detail so responses don't get bogged down in trying to address readers' perception of my problem.

My application is to swing a propeller, and I'm asking in this subforum because the torque and RPM requirements are similar to motorcycles.

At the time I wrote the original post, I hadn't yet learned that hubmotors come in two variants, one direct-drive and the other geared. I am specifically asking about the geared variant, as it is what's required to get the high efficiencies at high torque/low output RPM. Apologies for the confusion.

I had originally discarded using planetary gears because custom gearing is prohibitively expensive. (Most OTS planetary gearsets are seen in car transmissions, where they wind up being too heavy and impractical for my application.) A planetary gearset is very capable of carrying high torques, though, thanks to its balanced construction. This a balanced load is also a lot easier on the motor bearings. However, 100Nm is an awful lot more than most applications deal with, and the simple plastic gears in a 300W bike motor won't survive.

Regarding mid drives, that's a topic for another thread. I already have a design which uses belts in a very similar way, but if I could find a single monolithic power unit-- i.e. a hub motor-- it would greatly reduce the design complexity.

P.S. I'm drawing a blank with what previous query you're referring to. Perhaps you've confused me with someone else? viewtopic.php?f=30&t=109899 is the only other topic I've started here ever. I didn't sense much interest in having the technical discussion I hoped for, so there wasn't a need to beat a dead horse. I got better traction with the same question at https://www.rcgroups.com/forums/showthr ... rom-a-BLDC.
Last edited by kubark42 on Feb 13 2021 8:28am, edited 2 times in total.

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Re: Looking for featherweight hubmotors, >10kW

Post by amberwolf » Feb 13 2021 1:08am

kubark42 wrote:
Feb 12 2021 8:56pm
My application is to swing a propeller, and I'm asking in this subforum because the torque and RPM requirements are similar to motorcycles.
Ah. What size propeller, at what RPM? (it wont' mean anythign to me, but it will to others here familiar with aircraft of various types, and they may be able to help you more directly knowing the specifics, even potentially giving you a "better way" of doing something, if you're open to that). And what drive mechanism from the motor to the prop?

What voltage system at what expected current?
At the time I wrote the original post, I hadn't yet learned that hubmotors come in two variants, one direct-drive and the other geared. I am specifically asking about the geared variant, as it is what's required to get the high efficiencies at high torque/low output RPM. Apologies for the confusion.
Makes sense. But the best of the geared hubs is meant for about 1kW, maybe 2kW, and some have been pushed a little harder than that for short bursts. Part of that is because of heat dissipation problems (see paragraph after next), and part of that is mechanical limitations.

The best geared hubs I know of are the GMAC, the MAC, and the BMC. The Ezee probably follows after that. Then it's a bit of a jump down to the next level, like the BPM and such. There aren't any I've ever seen made for motorcycle power--the ones I've seen have all been DD hubs, and the best of those I've seen in person are QSMotor, or customized versions of their motors by other companies or individuals.

There aren't any geared hubs I've ever heard of that are likely to do anything near 10KW...unless you perhaps completely replace the planetary assembly in there, including their roller/ramp clutches, with something that's capable of dealing with the massive heat and torque you're going to have to deal with.

A geared hub has three layers, with air gaps between each, and each of those air gaps is an *EXCELLENT* insulator for heat, with the part that really needs to be cooled at the very center of the tootsie pop...er, motor. ;) So it is very easy to cook a geared hub with overheating. You could greatly open up the outer shell (which may mechanically weaken it) to allow airflow onto the middle layer, which is the planetary and clutch and rotor bell with magnets. So those would be a little cooler, depending on the airflow you generate thru it. But the stator is inside that rotor bell, and getting airflow thru that is harder, especially since AFAICR it is counter-rotating to the outer shell, so any holes you have in the bell will be chopping up the airflow thru it and disrupting it, so no nice easy way to help force flow thru there.

It's not impossible...just not easy.

Some people have used various liquids to fill geared hubs to help them cool faster, but this does add drag (whcih increases the power required to spin at any particular RPM, and thus increases the waste heat), and requires better seals on the bearings and motor wiring to prevent leakage than what these come with. I dont' know how mcuh good it would do at the power levels you're after. There is a thread by Justin_LE about Definitive Testing of HEating and Cooling of Hub Motors that has actual testing of various things, not just speculation, so you can check that out, and the http://ebikes.ca/tools/simulator.html can also help you see some limitations of various geared hubs that have been characterized (it's not perfect, but it's very useful as a baseline).


I'll assume that you're going to be using the spoke flange of the hub, or the disc brake mounting holes, to bolt a sprocket to to use a chain or belt to then drive your prop? (because you won't be able to mount a prop directly to the housing of hte motor--I doubt it has the strength for it, and it probably has far too much runout in various places and would shake the prop to pieces).


Theoretically you can spin a small motor really fast to get higher power out of it, then reduce the RPM to torque via an external reduction (maybe your application wouldn't want the reduction,b ut rather keep the speed?)....but motors will have increasing losses (internal heating, wasted power) the faster you spin them beyond their design. I am not sure, but I expect you would have to spin one of these hubs something like 10x or more faster than it's designed for to get the kind of power you want out of it, and even if it managed to mechanically hold together (no promises ;) ) then the heat from the losses could be high enough to damage it (winding insulation, hall sensors if you're using them, magnets, plastic gears if you don't replace them, etc).



I had originally discarded using planetary gears because custom gearing is prohibitively expensive. (Most OTS planetary gearsets are seen in car transmissions, where they wind up being too heavy and impractical for my application.) A planetary gearset is very capable of carrying high torques, though, thanks to its balanced construction. This a balanced load is also a lot easier on the motor bearings. However, 100Nm is an awful lot more than most applications deal with, and the simple plastic gears in a 300W bike motor won't survive.
That's the problem--there aren't any all-metal planetaries in any geared hubmotor I have ever seen, or any of them with a clutch that's all that great. (I think the clutch problem is one reason the GMAC by Grin Tech has no clutch, and thus can't freewheel--the motor is always engaged with the shell, just like a DD hubmotor).

So you'd probably have to have the gears made for you, or choose a motor that has metal gears (of the quality you need) already available (if there is one; some motors have offered the ability to change to one steel gear but leave the others plastic (because they're incredibly loud, and wear the sun gear faster, probably due to poor tooth/etc design, using all three steel gears has only been done by a few DIYers over the years that I can recall, and I think that might actually be in the Cyclone middrive rather than a geared hub).

You might also have to have the sun gear (often, maybe always, part of the axle itself) remade to match the new gears (if you ahve to change their profiles, etc), and the ring gear too (sometimes part of the shell, but usually a separate "track" that slips into the shell).

That ring gear may be another issue if you need a lot of torque. Some geared hubs have had failures where the ring spins inside the shell, having broken loose from whichever method was used to pin it to the shell. I dont' recall which ones.


Without being a mechanical engineer, and without knowing the details of your setup and intent, I would guess that it is going to be "easier" to use an external planetary reduction (that *is* designed for the task you have for it) on a motor that is designed for the power level (and necessary cooling) that you're after. I could be wrong...and to the hacker in me, it would be very interesting to see an ebike geared hubmotor driving a prop on an aircraft with really high power (relative to the design intent of the motor)...but I just think heat buildup and mechanical issues in a geared hubmotor are going to be problems that will take more re-engineering than it will be worth.

P.S. I'm drawing a blank with what previous query you're referring to. Perhaps you've confused me with someone else? viewtopic.php?f=30&t=109899 is the only other topic I've started here ever. I didn't sense much interest in having the technical discussion I hoped for, so there wasn't a need to beat a dead horse. I got better traction with the same question at https://www.rcgroups.com/forums/showthr ... rom-a-BLDC.
Ah. That is the thread.

Many people at least come back to comment on the answers they get, if they have any interest in the help they got; and typically when they dont' come back it means they abandoned the idea and/or the forum, or they just don't care. That's not universal...but it's common. :) FWIW, there are a lot of times someone creates a thread asking a fairly technical question that is going to need a lot of work to answer, and I (or others) will start with a basic reply (often asking or implying questions for the OP to answer) to see if the OP is going to participate in a discussion, before spending all that time and work answering completely, or researching things for them, etc. When the OP doesn't come back, at least that time wasnt' all wasted, taht way. ;) (most of the time, they don't...they may start a new thread about a different idea, or never come back, or evne start a new thread about the same idea because they didn't like the answers they got the first time, etc)).

Most of that has nothing to do with you...sorry. :) Just thought you should know why I had said what I did. (I guess I'm too old to "get" the typical internet behaviors and expect more sociability than the average person has to give. :( )

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Re: Looking for featherweight hubmotors, >10kW

Post by SlowCo » Feb 13 2021 8:06am

kubark42 wrote:
Feb 12 2021 8:56pm
My application is to swing a propeller
Are you sure you want the extra weight and complexity of a geared instead of a direct drive motor?

Most propeller driven EV's (drones, para-motors) use direct drive like these:

https://nl.aliexpress.com/item/32922096 ... 3262iMfOBl (1.63kg motor with 49kg thrust @ 13.2kW)

https://nl.aliexpress.com/item/10050016 ... 3262iMfOBl (2.78kg motor with 70kg thrust @ 19kW)

https://nl.aliexpress.com/item/10050016 ... 3262iMfOBl (4.2kg motor with 91kg thrust @ 21kW)

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Re: Looking for featherweight hubmotors, >10kW

Post by DogDipstick » Feb 13 2021 8:22am

SlowCo wrote:
Feb 13 2021 8:06am
kubark42 wrote:
Feb 12 2021 8:56pm
My application is to swing a propeller
Are you sure you want the extra weight and complexity of a geared instead of a direct drive motor?

Most propeller driven EV's (drones, para-motors) use direct drive like these:

https://nl.aliexpress.com/item/32922096 ... 3262iMfOBl (1.63kg motor with 49kg thrust @ 13.2kW)

https://nl.aliexpress.com/item/10050016 ... 3262iMfOBl (2.78kg motor with 70kg thrust @ 19kW)

https://nl.aliexpress.com/item/10050016 ... 3262iMfOBl (4.2kg motor with 91kg thrust @ 21kW)

Dont leave out collective pitch. Widely used since the dawn of propeller design.
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Re: Looking for featherweight hubmotors, >10kW

Post by JimVonBaden » Feb 13 2021 10:11am

Another concern with the situation, different from small drones, is the loading on the bearings. Even assuming the propeller is perfectly balanced, the prop is going to put an undesigned for load on the bearings as it pulls the shaft forward, not just rotationally.

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Re: Looking for featherweight hubmotors, >10kW

Post by spinningmagnets » Feb 13 2021 10:46am

There is a wide selection of hubmotors that would be up for any task given it. In an aero application where there is significant air-flow, i suspect a large Quan Shun /QS direct drive hubmotor (for small motorcycles) with 15ml of ferro fluid would provide the best weight-to-performance rating.

The V3 variant is heavier due to a cast aluminum stator-core to absorb heat spikes and you would not need that.

I can't imagine any system that would be better. Do not use the factory ratings as a guide, as hubmotors for vehicles don't have the slip of a propellor through the air, and the traction of a tire on pavement from a heavy vehicle can draw very high amps.

Propellors each have an optimum RPM range for maximum efficiency during cruise, and a peak RPM range for takeoff. If you provide these numbers, it could be helpful.

I understand your desire to hold onto some privacy for a new developing product, but there is no secret sauce that google cannot provide to you and also your competitors.

Therefore, you dont have to answer, but...is it for a fixed wing craft with the propellor in a tractor or pusher configuration?

Is it for a vertical lift craft? Is it multi-rotor? Be aware, there are already many garage developers working on manned and unmanned electric craft of all configurations.

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Re: Looking for featherweight geared hubmotors, >10kW

Post by kubark42 » Feb 14 2021 12:52pm

Thanks for the responses, everyone. I feel bad about discussing too much aviation in the motorcycle subforum, but I'm really, really happy to discuss the airplane more over at viewtopic.php?f=38&t=108791! So to keep myself from drifting, I'll just say that I've got a pretty good handle on the design and am just taking a second look at extremely low RPM, high torque motors.

Disappointingly, it sounds like there are unlikely to be any geared solutions at these power levels, based on the points which @amberwolf raises. (I'd consider that a definitive post on the subject.)

P.S. For direct drive motors used in small-scale aviation, Geiger and Rotex are very popular. A little smaller and you can use Neu motors. A little larger and you have Emrax. All are very good, but very, very pricey. And none can get any kind of decent power density at 1000-1500RPM.

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Re: Looking for featherweight geared hubmotors, >10kW

Post by fechter » Feb 14 2021 1:13pm

I wouldn't rule out using multiple motors on the same shaft to get the desired power output.
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Re: Looking for featherweight geared hubmotors, >10kW

Post by kubark42 » Feb 14 2021 1:39pm

fechter wrote:
Feb 14 2021 1:13pm
I wouldn't rule out using multiple motors on the same shaft to get the desired power output.
It's the torque that's the limiting factor. For reasons which I don't fully understand-- could be physical, could be economic-- there are no lightweight, high-efficiency, high-torque, low-power motors on the market. The opposite is easy to find (LMT makes a 2.2kg 95% efficient motor which, at 50,000RPM and 40kW, makes only 7Nm of torque).

The upshot is that the redrive is critical to getting high torque density. From what I learned here, so far no one is making COTS redrives in my power rating.

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Re: Looking for featherweight geared hubmotors, >10kW

Post by amberwolf » Feb 15 2021 12:06am

The problem you're having (torque vs watts vs size vs rpm) has been discussed in some detail around here before, but I couldn't find the threads in a minute's search. If I run across one later I'll link it for you.

Basically, the problem is watts = torque x rpm, and it takes a certain amount of physical windings and magnets to produce a certain amount of torque, more or less, given a certain rotor diameter. And motors are really efficient only in a part of their RPM and torque range--each one with it's own curve.

So if you want more torque, you either make the motor larger diameter (larger moment arm, I think it is called), or you make it more massive with more copper and magnets. Or some compromise between the two.

If you want more torque but you cant' make it big like that, you spin a smaller one really fast instead, and then downconvert that speed into torque externally (losing some of the power in the conversion).

The little I have read and seen of EV-aircraft of all types end up using the latter option. Some of them don't say why, but those that did usually were that the weight and volume of a high-rpm motor plus the reduction unit was less than that of a direct drive system massive enough to do it. And that the fast motors / reductions were tyipcally COTS and DD systems were not. Some that said why did it because their props needed the high RPM anyway, rather than the torque, so they just directly used the motors without reductions.

But I know nearly nothing about how to figure out what an aircraft needs for this kind of thing :oops: so while I can help "keep it real" ;) for some things (I'm good at pattern analysis, deductions, stuff like that, and have a lot of general knowledge tucked away in here somewhere, when I can find it), I am not sure I am qualified to advise which actual systems will do what you want. :/

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Re: Looking for featherweight geared hubmotors, >10kW

Post by Chalo » Feb 17 2021 4:48pm

kubark42 wrote:
Feb 14 2021 12:52pm
And none can get any kind of decent power density at 1000-1500RPM.
That's so very slow for a prop. What gigantic diameter are you working with?
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Re: Looking for featherweight geared hubmotors, >10kW

Post by kubark42 » Feb 17 2021 6:27pm

Chalo wrote:
Feb 17 2021 4:48pm
That's so very slow for a prop. What gigantic diameter are you working with?
1.92m

@amberwolf, the slowest props are the most efficient. Prop dia. is largely limited by ground clearance, so usually you have to compromise on dia so you don't have obnoxiously large landing gear. You get the power by spinning a smaller prop faster.

As you say, P = T*\omega, so when you need big P and can't do big T you gotta do big \omega. I would have preferred a planetary geartrain for packaging purposes, but I'm going to go with my original plan of a sprockets w/Gates belt. Very similar to the bike middrive systems.

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Re: Looking for featherweight geared hubmotors, >10kW

Post by rynhardt » Feb 18 2021 2:35am

This is probably a bit out there, but your requirement for low rpm, high torque reminds me of marine thrusters.
Maybe have a look at rim-drive thruster configurations and see if anything there might be useful..
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Re: Looking for featherweight hubmotors, >10kW

Post by meddesign » Apr 05 2021 9:02pm

spinningmagnets wrote:
Feb 13 2021 10:46am
There is a wide selection of hubmotors that would be up for any task given it. In an aero application where there is significant air-flow, i suspect a large Quan Shun /QS direct drive hubmotor (for small motorcycles) with 15ml of ferro fluid would provide the best weight-to-performance rating.

The V3 variant is heavier due to a cast aluminum stator-core to absorb heat spikes and you would not need that.

I can't imagine any system that would be better. Do not use the factory ratings as a guide, as hubmotors for vehicles don't have the slip of a propellor through the air, and the traction of a tire on pavement from a heavy vehicle can draw very high amps.

Propellors each have an optimum RPM range for maximum efficiency during cruise, and a peak RPM range for takeoff. If you provide these numbers, it could be helpful.

I understand your desire to hold onto some privacy for a new developing product, but there is no secret sauce that google cannot provide to you and also your competitors.

Therefore, you dont have to answer, but...is it for a fixed wing craft with the propellor in a tractor or pusher configuration?

Is it for a vertical lift craft? Is it multi-rotor? Be aware, there are already many garage developers working on manned and unmanned electric craft of all configurations.
I am looking for 6000 rpm 15-20kw for a 32" prop....any suggestion on a DD hub motor? This is for a Ultra-Lite Power launch glider

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Re: Looking for featherweight hubmotors, >10kW

Post by fechter » Apr 05 2021 11:50pm

meddesign wrote:
Apr 05 2021 9:02pm
I am looking for 6000 rpm 15-20kw for a 32" prop....any suggestion on a DD hub motor? This is for a Ultra-Lite Power launch glider
That sounds pretty close to a Sur-ron motor. Not a hub motor, but they have a good track record.
Hb7c639aa20574a128981347b921f6980v.jpg_q50.jpg
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Re: Looking for featherweight geared hubmotors, >10kW

Post by Chalo » Apr 06 2021 12:58am

The problem with trying to substitute traction motors in aero motor applications is that traction motors never see 100% duty cycle, and aero motors are expected to come through in that situation. They usually have better cooling than traction motors, but often no time in which to cool off.
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Re: Looking for featherweight hubmotors, >10kW

Post by meddesign » Apr 06 2021 12:40pm

fechter wrote:
Apr 05 2021 11:50pm
meddesign wrote:
Apr 05 2021 9:02pm
I am looking for 6000 rpm 15-20kw for a 32" prop....any suggestion on a DD hub motor? This is for a Ultra-Lite Power launch glider
That sounds pretty close to a Sur-ron motor. Not a hub motor, but they have a good track record.

:bigthumb: thanks a bunch....

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Re: Looking for featherweight geared hubmotors, >10kW

Post by meddesign » Apr 06 2021 12:43pm

Chalo wrote:
Apr 06 2021 12:58am
The problem with trying to substitute traction motors in aero motor applications is that traction motors never see 100% duty cycle, and aero motors are expected to come through in that situation. They usually have better cooling than traction motors, but often no time in which to cool off.
The powered launch glider could have staged power settings....such as 2 min. 100% 2 min 75% .....etc.....also the DD motor is where the prop attaches and lots of cooling air will be blowing over it......

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Re: Looking for featherweight hubmotors, >10kW

Post by meddesign » Apr 06 2021 2:49pm

fechter wrote:
Apr 05 2021 11:50pm

That sounds pretty close to a Sur-ron motor. Not a hub motor, but they have a good track record.
I could not find specifications ....I send them an e-mail.....do you have the specifications?....

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Re: Looking for featherweight geared hubmotors, >10kW

Post by flippy » Apr 06 2021 4:36pm

please dont forget that motor bearings are designed for axial loads. aka: rotating, not pulling/pushing.

a prop directly attached without thrust bearings will basically pull the rotor out from the stator and kill the bearings en if they do stay together. not something you want to happen in the air, or like...at all.
Lithium beats liquid dinosaurs.

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fechter   100 GW

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Location: California Bay Area, USA

Re: Looking for featherweight hubmotors, >10kW

Post by fechter » Apr 07 2021 11:17am

meddesign wrote:
Apr 06 2021 2:49pm
fechter wrote:
Apr 05 2021 11:50pm

That sounds pretty close to a Sur-ron motor. Not a hub motor, but they have a good track record.
I could not find specifications ....I send them an e-mail.....do you have the specifications?....
Check out this page:
https://www.sur-ron.com/us/power.html

Keep in mind the power rating of an electric motor is largely determined by the controller and heat dissipation. With a lot of air, you can run the motor at a higher power level without overheating. The motor on my Sur-ron is "rated" at 4kW but I can run it at over 10kW for fairly long bursts.
"One test is worth a thousand opinions"

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everythingisawave   100 mW

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Re: Looking for featherweight geared hubmotors, >10kW

Post by everythingisawave » Apr 08 2021 12:49pm

kubark42 wrote:
Feb 14 2021 1:39pm
fechter wrote:
Feb 14 2021 1:13pm
I wouldn't rule out using multiple motors on the same shaft to get the desired power output.
It's the torque that's the limiting factor. For reasons which I don't fully understand-- could be physical, could be economic-- there are no lightweight, high-efficiency, high-torque, low-power motors on the market. The opposite is easy to find (LMT makes a 2.2kg 95% efficient motor which, at 50,000RPM and 40kW, makes only 7Nm of torque).

The upshot is that the redrive is critical to getting high torque density. From what I learned here, so far no one is making COTS redrives in my power rating.
Silly question perhaps, what's a redrive?

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